- Email: [email protected]
3. Scientific space mission news
3.
SCIENTIFIC SPACE MISSION NEWS
3.1.
Ulysses, launched 6 October 1990, Out of Ecliptic Interplanetary Medium Mission
[From ESA 19991
Information
Note,
As grains of this particular size travel towards the Sun, they are repelled constantly by the sunlight. This causes them to lose speed until eventually they come to a halt at a distance of four times the Earth-Sun distance. At distances closer than twice the Earth-Sun distance, the findings are unreliable because interstellar and solar system dust are more difficult to tell apart.
17 December
The discovery says something about the optical properties of the banished dust grains. So Landgraf and his colleagues decided to consult tables that list the strength of radiation pressure needed to deflect same-sized grains of different types of material. The best match, they found, was with a mixture of silicates detected in interstellar clouds elsewhere in the Milky Way, suggesting that we are moving through an identical cloud. “We were very excited when we found that the composition fits” commented Landgraf. The notion that we are travelling through an interstellar cloud is not new, as Ulysses had discovered previously that a cloud of gas was moving through the solar system. By 1995, Ulysses had detected enough galactic dust grains to see that they were travelling through the solar system in the same direction as the gas, suggesting that the cloud consists of dust as well as gas.
The force of sunlight is keeping part of our solar system dust free at least free from a particular type of dust. Markus Landgraf, now working at ESA’s operations centre ESOC in Germany together with his international team, made this discovery after poring over data collected by the dust detector on board the Uysses spacecraft. In a paper in Science, they show how their findings lend support to the view that our solar system is moving through a cloud of dust and gas that is made of the same stuff as interstellar clouds observed elsewhere in our galaxy. Landgraf and his colleagues made the discovery when looking at the mass distribution of dust particles collected by the detector between February 1992 and April 1996 as Uysses swept along its solar polar orbit. They were interested in interstellar dust, which can be distinguished from dust originating in the solar system by its speed and direction of travel.
The composition of dust grains in distant interstellar clouds can be measured with telescopes from the way in which light is absorbed and scattered by the clouds. However, dust grains in our local interstellar cloud are too sparse and close to us for such measurements.
Interstellar dust travels very fast, and can be found outside the ecliptic, whereas solar system dust tends to travel more slowly in the plane of the planets’ orbits. “When I got the print out on my desk, it was obvious immediately that there was something unusual about the mass distribution. It was a big surprise” said Landgraf. Interstellar dust grains of a particular size not too big and not too small were missing from the volume of space between two and four times the distance of the Earth from the Sun. After eliminating all other possible explanations, the team concluded that the pressure of sunlight was keeping the dust grains out of this region. The particles were just the right size for sunlight to have this effect. “If the particles are very small, light doesn’t see them because they are smaller than the wavelength of light. If they are very big, they absorb and reflect light, but the light doesn’t push them away because they’re too heavy. The particles being pushed away are large enough to absorb and reflect light, but they don’t have enough inertia to stay still” explained Landgraf.
The findings of the team at ESOC show that there are indirect ways and means of deducing their composition. “The evidence is stacking up for our own local interstellar dust and gas cloud, though the origin of this cloud just isn’t known. We don’t know the whole history of these grains, which is why they are so intriguing. They could have originated in supernovae explosions, or they could be the outflow of old stars which give out star dust when they get old, much like a candle produces soot when it becomes too cold” speculated Landgraf.
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3.2.
Hubble S ace Telesco e, launched 2 B April 1990, As Pronomical Telescope
Ed Weiler, NASA Associate Administrator for Space Science. “I think there is no better proof than these pictures that NASA’s capability to send humans into space to work on Hubble has had a vital role in space science and [in] the renaissance in astronomv we’re now seeing.”
(a) Hubble placed into Safe Hold [From NASA News, 15 November 19991 NASA’s Hubble Space Telescope (HST) was placed into a safe hold on 13 November 1999 when gyroscope #l ceased operation. With only two operational gyros remaining, the science programme was suspended until the completion of Servicing Mission 3A, in December 1999. This gyro situation was not expected to impact the servicing mission due at the end of 1999. In fact, anticipation that another gyro could fail was the primary reason that the HST managers scheduled an early repair mission and split the third servicing mission activities into two flights: Servicing Mission-3A (Decemand Servicing Mission-3B ber 1999) (mid-2001).
“After a two-month hiatus, it is a tremendous boost to all of astronomy to see Hubble back in action. NASA has restored the observatory to a condition that was better than it was even before the fourth gyroscope failed” said Steven Beckwith, director of the Space Telescope Science Institute, the Hubble science operations centre in Baltimore, MD. To verify the telescope’s refurbishment, astronomers resumed operations by aiming it at two scientifically intriguing and photogenic celestial targets. One object is an intricate structure of shells and streamers of gas around a dying Sun-like star 5000 light-years away. Designated NGC 2392, it is dubbed the ‘Eskimo’ Nebula because, as seen through ground-based telescopes, it resembles a face inside a furry parka. In Hubble’s sharp view, the ‘furry’ features resemble giant comets all pointing away from the central star, like the spokes of a wheel.
The telescope was not at risk as the safehold mode had been thoroughly tested and used twice since Hubble’s launch in 1990. This protective safe mode allows ground control of the telescope, though with only two gyros working, Hubble cannot be aimed with the precision necessary for scientific observations of the sky. Consequently, the aperture door was closed to protect the optics, and the spacecraft was aligned to the Sun to ensure adequate power was received by the solar panels.
“The clumps that form the comet heads all seem to be located at a similar distance from the star. This fact will be important in developing a theory of why the clumps formed in the first place,” said planetary nebula expert J. Patrick Harrington of the University of Maryland, College Park, MD. “Of all the planetary nebulae imaged by the Hubble Space Telescope, this new image is unsurpassed in subtle beauty.” (see 1 .l, page 4).
Engineers are investigating the cause of the gyro loss. (The gyro was returned to ground after the servicing mission). Additional information on the servicing mission and on Hubble is available at: http:Nhubble.gsfc.nasa.gov/ (b) HubMe Recommissioned [From NASA News, 24 January
A second target is a massive cluster of galaxies called Abell 2218, which acts like a giant zoom lens in space. The gravitational field of the cluster magnifies the light of more distant galaxies far behind it, providing a deep probe of the very distant universe. The cluster was imaged in full colour, providing a spectacular and unique new view of the early universe.
20001
NASA’s Hubble Space Telescope is back in business, as has been made dramatically evident in stunning new pictures of remote galaxies and a colourful dying star. The images were taken between 10 and 13 January 2000, as part of the activities to recommission the Earth-orbiting telescope. The pictures are a culmination of the successful Space Shuttle servicing mission (STS-103) in December 1999, which restored NASA’s premier optical space observatory to its full capability with a crystal-clear view, and beefed it up with new electronics and critically needed replacement gyroscopes. “Thanks to the great work by the astronauts, Hubble is better than new” said Dr
“For the first time, we can view the internal colour structure of some very distant galaxies. This gives us new insight into details of what young galaxies are like,” said Professor Richard Ellis at the California Institute of Technology, Pasadena, CA, and a co-investigator on the original (black-and-white) Hubble image of Abell 2218 taken in 1994. The colour of a distant source is preserved by gravitational lensing. By matching images of the same
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ture, but this new evidence certainly makes the argument for the presence of an ocean far more persuasive.” It appears that the ocean lies beneath the surface somewhere in the outer 60 miles (about 100 km), the approximate thickness of the ice/water layer. Kivelson explained that ‘Jupiter’s magnetic field at Europa’s position changes direction every 5% hours. This changing magnetic field can drive electrical currents in a conductor, such as an ocean. Those currents produce a field similar to Earth’s magnetic field, but with its magnetic north pole - the location toward which a compass on Europa would point - near Europa’s equator and constantly moving. In fact, it is actually reversing direction entirely every 5% hours. On previous Europa flybys, Galileo identified a magnetic north pole, but did not determine whether its position changes with time. “We wondered ‘was it possible that the north pole did not move?“’ Kivelson said.
colour, families of multiple images produced by the lensing process can be identified. An unusual red feature in the field particularly fascinates Andrew Fruchter, leader of the team that took the early-release observations. “This extraordinary object has colours which indicate it is one of two things, either a rare, extremely cool dwarf star in our own galaxy, or one of the most distant objects ever viewed by Hubble lensed into visibility by the mass of the cluster” said Fruchter. Further observations will be needed to confirm the identity of this unusual object. Spacecraft operators report that all the new equipment installed on the telescope in December is working perfectly, including the new computer, solid state recorder, and fine guidance sensor. In particular, the new gyroscopes are allowing Hubble to point reliably with exquisite precision at celestial objects. Two key science instruments, the Wide Field and Planetary Camera 2 and the Space Telescope Imaging Spectrograph, are now being used for routine science observations to probe everything from planets to black holes and far flung galaxies.
The new evidence was gathered during a flyby specially planned so that the observed position of Europa’s north pole would make it clear whether or not it moves. In fact, the most recent data showed that its position had moved, thus providing key evidence for the existence of an ocean. It is not likely that the electric currents on Europa flow through solid surface ice as ice is not a good carrier of currents. However, Kivelson pointed out that “melted ice containing salts, like the sea water found on Earth, is a fairly good conductor. There is no other likely current-carrying material near Europa’s surface. Currents could flow in partially melted ice beneath Europa’s surface, but that makes little sense, since Europa is hotter toward its interior, so it’s more likely the ice would melt completely. In addition, as you get deeper toward the interior, the strength of the current-generated magnetic field at the surface would decrease”.
The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc. for NASA, under contract with NASA’s Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and ESA. Images are available on the Internet at: http://oposite.stsci.edu/pubinfo/latest.html and http://oposite.stsci.edu/ pubinfo/pictures.html.
3.3.
Galileo, launched 18 October 1989, Jupiter Probe
[From NASA News, 10 January
20001 These latest findings are consistent with previous Galileo images and data showing a tortured surface seemingly formed when Europa’s surface ice broke and was reconfigured while floating on an underlying sea. Further theoretical work is under way to analyse the fluid layer and its properties. “It will be interesting to see whether this same type of phenomenon occurs at Jupiter’s moon Ganymede” Kivelson said. Galileo is tentatively scheduled to fly by Ganymede twice this year.
When NASA’s Galileo spacecraft swooped past Jupiter’s moon Europa, it picked up powerful new evidence that a liquid ocean lies beneath Europa’s icy crust. As the spacecraft flew 218 miles (351 km) above Europa on 3 January, its magnetic field was recorded by the magnetometer which observed directional changes in the field consistent with the presence of a shell of electrically conducting material, such as a salty, liquid ocean. “1 think these findings tell us that there is indeed a layer of liquid water beneath Europa’s surface” said Dr Margaret Kivelson, principal investigator for the Galileo magnetometer (at the University of California, Los Angeles). “I’m cautious by na-
Additional information Galileo are available at http://galileo.jpl.nasa.gov.
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and pictures taken by
The Galileo mission is managed for NASA’s Office of Space Science, Washington, D.C. by JPL, a division of the California institute of Technology, Pasadena, CA.
3.4.
SOHO (Solar and Heliospheric Observatory), launch 2 December 1995, Solar and Heliospheric mission
[From NASA News, 8 February 20001 In just four years of operation, the Solar and Heliospheric Observatory (SOHO) spacecraft has found 102 comets, making it by far the most successful comet-hunter in history. Calculations have shown that the latest comets discovered with SOHO are previously unknown with the 102nd comet observed by Dr Douglas Biesecker (SM&A, Vienna, VA and NASA’s Goddard Space Flight Center, Greenbelt, MD), a member of the SOHO team personally responsible for 45 of the discoveries. A cooperative project between ESA and NASA, SOHO has revolutionized solar science. It also has revealed an amazing number of ‘suicidal’ comets plunging into the solar atmosphere. Like nearly all of SOHO’s comet discoveries, the latest comet showed up in images from and Spectrometric Large Angle the Coronagraph (LASCO) instrument. This is a set of coronagraphs that view the space around the Sun out to 12.5 million miles, while blotting out the bright solar disk with masks. LASCO watches out for ejections of electrically charged gas from the Sun that threaten to disturb the Earth’s space environment. As an unexpected bonus, it also proved ideal for recording objects falling into the Sun. Still pictures and movies from LASCO are freely available on the Internet, and even amateur astronomers have used them to discover comets.
“SOHO is seeing fragments from the gradual breakup of a great comet, perhaps the one that the Greek astronomer Ephorus saw in 372 BC” said Dr Brian Marsden of the Center for Astrophysics in Cambridge, MA. “Ephorus reported that the comet split in two. This fits with my calculation that two comets on similar orbits revisited the Sun around AD 1100. They split again and again, producing the sungrazer family, all still coming from the same direction. The sungrazers’ ancestor must have been enormous by cometary standards.” “The rate at which we’ve discovered comets with LASCO is beyond anything we ever expected” said Bieseeker. “We’ve increased the number of known sungrazing comets by a factor of four. This implies that there could be as many as 20 000 fragments”. Life is perilous for a sungrazer. The mixture of ice and dust that makes up a comet’s nucleus is heated like the proverbial snowball in hell, and it can only survive its visit to the Sun if it is quite large. What is more, the strong tidal effect of the Sun’s gravity can tear the looselyglued cometary nucleus apart. The disruption that created the many SOHO sungrazers was similar to the fate of Comet Shoemaker-Levy 9, which went too close to Jupiter and broke up into many pieces that eventually fell into the planet in 1994. The history of splitting gives clues to the strength of comets, which will be of practical importance if ever a comet seemed likely to hit the Earth. Also, the fragments seen as SOHO comets reveal the internal composition of comets, freshly exposed as it were, in contrast to the much-altered surfaces of objects such as Halley’s comet that have visited the Sun many times. The count of SOHO’s comet discoveries would be one fewer without a late bonus from SOHO’s Solar Wind Anisotropies (SWAN) instrument, which looks away from the Sun to survey atomic hydrogen in the solar system. In December 1999, the International Astronomical Union retrospectively credited SOHO with finding Comet 1997 K2 (SOHO # 93) in SWAN full-sky images from May to July 1997. It remained outside the orbit of the Earth even at its closest approach to the Sun, and thus did not vaporize entirely.
Ten comets discovered by SOHO, including the ones identified as SOHO # 100, 101 and 102, passed the Sun at a safe distance from Earth. However, the rest of the SOHO comets vaporized in the solar atmosphere. Near misses are well known. One hundred years ago, Heinrich Kreutz in Kiel, Germany, realized that several comets seen buzzing the Sun seemed to have a common origin, because they came from the same direction among the stars. These comets are now called the Kreutz sungrazers, and the 92 vanishing SOHO comets belong to that class.
More information and images are on the Internet at: http://sungrazer.nascom.nasa.gov/soholOO and at http://pao.gsfc.nasa.gov/gsfc/ spacesci/sunearth/sunearth.htm#soho
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3.5.
FUSE (Far Ultraviolet S ectroscopic Explorer), launc I: ed 24 June 1999
[From NASA News, 12 January
the 62 guest investigators from around the world selected by NASA for the first year of operations. We are continuing to tune the instrument” Moos added. “In the spring, we expect to begin a comprehensive study of the abundance of deuterium, a fossil atom left over from the Big Bang. As our team becomes more practised, we need less time to optimize the instrument, and the amount of time we can spend on scientific observations will go up. This means higher scientific productivity.” FUSE is able to detect interstellar gas and determine its composition, velocity and distance by viewing bright celestial objects further away. The intervening gas selectively absorbs the light from these objects in a unique pattern of colours, depending on the composition of the gas. The spectrograph on FUSE separates the light into its component colours, the resulting patterns identifying the gas - like optical fingerprints. When the patterns shift to different colours, velocity and distance measurements can be inferred.
20001
The extended halo of half-million-degree gas that surrounds the Milky Way was generated by thousands of exploding stars, or supernovae, as our galaxy evolved, according to new observations by NASA’s Far Ultraviolet Spectroscopic Explorer (FUSE) spacecraft. The spacecraft has nearly completed its shakedown phase, and its first results are already providing a wealth of new information about the material that becomes stars, planets and ourselves. The hot gas halo which surrounds our galaxy extends about 5000 to 10 000 light years above and below the galactic plane and thins with distance (one light year is almost six trillion miles). “The hot gas halo has been known for some time, but we weren’t sure how it got there or stayed hot” said FUSE co-investigator Dr Blair Savage of the University of Wisconsin in Madison. “The new FUSE observations reveal an extensive amount of oxygen VI (oxygen atoms that have had five of their eight surrounding electrons stripped away) in the halo. Some scientists thought that ultraviolet radiation from hot stars could produce the halo, but the only way to make the observed amount of oxygen VI is through collision with the blast waves from exploding stars, called supernovae.”
The 1400 kg spacecraft carries a 2.4 m focal length telescope with a primary mirror made of four separated segments; two of these are coated with silicon carbide (to reflect radiation at wavelengths between 90 and 110 nm) and the other two with aluminum and lithium fluoride (to reflect 100 - 119 nm radiation). The focused beams then fall onto four separate (correspondingly coated) Rowland gratings that disperse the spectrum into four separate photon - counting microchannel flat- plate detectors. A separate star tracking Fine Error Sensor (FES) facilitates location of the source and a pointing stability within 0.5 arcseconds for large integration times. While there have been other far UV satellites such as Copernicus and HST, the investigative thrust on the FUSE data will be intergalactic clouds and interstellar clouds which may well carry the signature of pristine (Big Bang) deuterium ions that have escaped being consumed in stellar cores. The deuterium/hydrogen ratios so obtained may approximate to the status of the universe minutes after the Big Bang.
“Stars destined to explode don’t live long, compared to stars like our Sun, so star explosions are actually a record of star formation” said Dr George Sonneborn, FUSE project scientist at NASA’s Goddard Space Flight Center, Greenbelt, MD. “By comparing supernova-generated halos among galaxies, we may be able to compare their star formation histories.” “FUSE measures the pulse of the lifeblood of our galaxy, the thin gas between stars” said Dr Warren Moos, FUSE principal investigator at Johns Hopkins University in Baltimore. “This interstellar gas courses through our veins, because dense clouds of it collapsed to form new stars and planets, including our solar system.”
The FUSE spectrograph is at least 100 times more powerful than previous instruments and should help reveal a large number of new atomic and molecular features in interstellar gas.
“The FUSE observatory is now open for business” Moos said. “After an extended onorbit checkout and debugging period, common for complex space observatories, we are now performing observations on a routine basis for members of the principal investigator team and
New images related to this investigation, and more information about FUSE, can be found on the Internet at: http:/fuse.pha.jhu. edul
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3.6.
Chandra, launched 22 July 1999, X-ray Astronomy Observatory
black hole, and the evidence that the explosion from the gas near the black hole is pushing the hot gas around”. Indeed, combined radio and X-ray observations suggest that a vast bubble of high energy particles is pushing the hot gas aside, creating the Hydra-like loops of hot gas. Similar processes are likely to be at work in other galaxy clusters, and in newly forming galaxies that are collapsing from a cloud of gas. By using images from Char&a and other telescopes, astronomers may eventually conquer a ‘monstrous’ problem of cosmic significance.
(a) The Heart of the Hydra A Galaxy Cluster [From NASA News 9 December
19991
NASA’s Chandra X-ray Observatory image of the Hydra A galaxy cluster has revealed a possible solution to a Herculean puzzle about the fate of the largest objects in the universe. For years astronomers have been searching unsuccessfully for large quantities of matter they believed must be flowing into the central regions of galaxy clusters. The Char&a image of Hydra A displays long snake-like strands of 35 million degree gas extending away from the centre of the cluster. These structures show that the inflow of cooling gas is deflected by magnetic fields produced by explosions from a central black hole.
The Observatory Smithsonian/Harvard centre in Cambridge (b) Chandra background
is operated by a joint team working at a control MA.
resolves
the universe’s
[From NASA News, 13 January
X-ray
20001
While taking a giant leap toward solving one of the greatest mysteries of astronomy the nature and source of the X-ray background, NASA’s Char-&a X-ray Observatory may also have revealed the most distant objects ever seen in the universe and discovered two new, but puzzling, types of cosmic objects.
The X-ray image also reveals a bright wedge of hot multimillion-degree gas pushing into the heart of the cluster. Like the legendary Hercules, who had to contend with the multiple heads of the monstrous Hydra, astrophysicists now know they must deal with the effects of magnetic fields, star formation, rotation and black holes if they are to understand what is happening in the inner regions of the galaxy cluster. As the largest gravitationally bound objects in the universe, galaxy clusters provide crucial clues for understanding the origin and fate of the universe. Each large cluster such as Hydra A contains hundreds of galaxies and enough gaseous material to make a thousand more galaxies. One intriguing question has been the ultimate fate of this colossal gas reservoir. Early X-ray observations indicated that the gas in the inner regions of Hydra A should be cooling and slowly settling into the centre of the cluster to form new galaxies or hundreds of trillions of dim stars. As astronomers began searching for this cool matter, they were puzzled to find that the new galaxies and stars were not detected in sufficient numbers. The Chart&a results on Hydra A, which is 840 million light years from Earth, may point to a resolution of this problem. The inflow of cooling gas may be deflected by magnetic fields, and even pushed back into the cluster by explosions from the vicinity of a supermassive black hole at the core of the central galaxy.
Char&a has resolved most of the X-ray background, a pervasive glow of X-rays throughout the universe, which was first discovered in the early days of space exploration. Until the arrival of Chandra, it has not been possible to discern the origin of the hard, or high-energy, X-ray background, because no telescope had the necessary resolution. Commenting on the findings with Chart&a, Dr Alan Bunner, Director of NASA’s Structure and Evolution of the Universe science theme said “This is a major discovery. Since it was first observed 37 years ago, understanding the source of the X-ray background has been a holy grail of X-ray astronomy. Now, it is within reach”. The results of the observations with Chandra were presented, by Dr Richard Mushotzky of NASA’s Goddard Space Flight Center, Greenbelt, MD, Dr Lennox Cowie and Dr Amy Barger at the University of Hawaii, Honolulu and Dr Keith Arnaud of the University of Maryland, College Park, at the 195th national meeting of the American Astronomical Society in Atlanta, GA and have been submitted for publication in Nature. “We are all very excited by this finding” said Mushotzky. “The resolution of most of the hard X-ray background during the first few months of the Char&a mission is
“In Hydra, you can see the whole cycle” said Brian McNamara of the Harvard-Smithsonian Center for Astrophysics. “You have the hot gas cloud, the disk of material feeding the
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a tribute to the power of this observatory and bodes extremely well for its scientific future”. The Chandra team looked at a small section of the sky, a circle about one-fifth the size of a full moon, and resolved about 80% of the X-ray glow in this region into specific light sources. Stretched across the entire sky, this adds up to approximately 70 million sources, most of which are galaxies. One-third of the sources are galaxies the cores of which shine bright in X-rays, yet do not shine in visible light. There may be tens of millions of these ‘veiled galactic nuclei’ in the universe. Each of these galaxies quite possibly harbours a massive black hole at its core that produces X-rays as gas is pulled toward it at nearly the speed of light. A second new class of objects, comprising approximately one-third of the sources, is to be ‘ultra-faint galaxies’. assumed Mushotzky said that these sources might emit little or no optical light, either because the dust around the galaxy blocks the light totally or because the optical light is eventually absorbed during its long journey across the universe. In the latter scenario, Mushotzky commented that these sources may be well over 14 billion light years away and, thus, the earliest (most distant) objects ever identified. Resolution of the X-ray background relied on a 27.7-hour Chandra observation using the Advanced CCD Imaging Spectrometer in early December 1999, and also utilized data from the Japan-US Advanced Satellite for Cosmology and Astrophysics. For further information on Chandra, including images, see http://chandra.nasa.gov
3.7.
XMM (X-ray Multi-Mirror Mission), launched 10 December 1999, X-ray Observatory
(a) XMM-Newton
launch from Kourou on Ariane 504 on 10 December 1999, XMM was delivered into its final operational orbit in the following week. The telescope doors on the X-ray Mirror Modules and on the Optical Monitor telescope were opened on 17/l 8 December. The Radiation Monitor was activated on 19 December and the spacecraft was put into a quiet mode over the Christmas and New Year period. The mission’s scientific data are being received, processed and dispatched to astronomers by the XMWVewton Science Operations Centre in Villafranca. Operations with the spacecraft were restarted on 4 January when, as part of the commissioning phase, all the science payloads were switched on one after the other for initial verification. After a series of engineering exposures, between 19 and 24 January, several views of two different extragalactic regions of the universe were taken. These featured a variety of extended and Xray point sources, and were chosen to demonstrate the full functioning of the observatory. This initial series of short and long duration exposures have delighted the Project management team as well as the investigators. First analyses confirm that the spacecraft is extremely stable, the XMM telescopes are focusing perfectly, and the cameras and spectrometers are working exactly as expected. The Science Operations Centre infrastructure, for processing and archiving the science data telemetry from the spacecraft, is also performing well. Initial inspection of the first commissioning images, resented on 9 February, showed some unique X-ray views of several celestial objects. The Calibration and Performance Verification phase for X/WA& science instruments was planned to start on 3 March, with routine science operations beginning in June 2000. (b) Images from X/W-Newton
takes its first pictures
[From ESA Press Release, 2 February
[From ESA Information
20001
Note, 9 February 20001
The first pictures from ESA’s new X-ray Space Observatory (XMM-Newton) fully demonstrate the capabilities of the spacecraft’s telescopes and its science instruments. The images were officially presented on 9 February at the XMWVewton Science Operations Centre in Villafranca, Spain. The images were obtained between 19 and 25 January at the very start of the science payload commissioning process. The spacecraft viewed three regions of the sky: part of the Large Magellanic Cloud (LMC), the Hickson Cluster Group 16
ESA’s X-ray space observatory (XMM-Newton) has taken its very first pictures giving new views on the universe. The commissioning images confirm that the XMM-Newton spacecraft, its X-ray telescopes and science instruments are functioning perfectly. The mission’s Principal Investigators presented spectacular first images at a press conference on 9 February at the ESA Vilspa facility at VillafrancaIMadrid in Spain, where the XMM Science Operations Centre is located. After a successful 17
scopes. Galaxies in Hickson groups have a high probability of interacting. Their study has shed light on the question of galactic evolution and the effects of interaction. Investigation into their gravitational behaviour has also significantly contributed to our understanding of ‘dark matter’, the mysterious matter that most astronomers believe comprises well over 90% of our universe.
(HCG-16), and the star HR 1099. These targets were chosen because they all present a variety of extended and point X-ray sources and are interesting regions. The pictures are ESA Website at available on the http://www.esa.int, then Image Gallery, then News and at http://sci.esa.int/xmm/firstimages. See also page 4 of this Bulletin. The Large Magellanic Cloud, also known as the Nebula Major, is about 20 thousand light years in diameter. Situated 160 thousand light years from Earth, it is one of two irregularly shaped galaxies that are easily seen with the naked eye in the southern hemisphere. These galaxies are satellites of the Milky Way and appear to be slowly spiralling into our own galaxy. The first image obtained by the EPIC-PN X-ray cameras viewed the 30 Doradus region of the Large Magellanic Cloud. Also called the Tarantula Nebula, 30 Doradus is a ‘cauldron of creation’ where exploding stars are releasing vast amounts of matter and where new stars are being born. The image indicates the million degree temperatures of the emitting medium, with blue representing the hottest regions, green intermediate temperatures and red the coldest regions. The images reveal a white and blue arc-like formation, only part of which was known in the past. It has the appearance of a supernova remnant with its expanding glowing-hot gas producing X-rays as it collides with the interstellar medium. The image also shows the remains of a star that exploded as Supernova 1987A on 24 February 1987. It was the first supernova to reach naked-eye brightness since 1604 (Kepler’s star) and remained visible to the naked eye for nearly nine months.
Observation of celestial objects from space over a range of X-ray, ultraviolet and visible wavelengths, is a unique feature of the XMM-Newton mission. The EPIC-PN view of the Hickson 16 group shows a handful of bright X-sources and, in the background, more than a hundred faint X-ray sources that XMM-Newton is revealing for the first time. Juxtaposing the X-ray view of HCG 16 with that of the Optical Monitor reveals one of the great strengths of XMM-Newton in being able to compare the properties of objects at visible, ultraviolet and X-ray wavelengths on a routine basis. Many of the X-ray sources are revealed as elongated ‘fuzzy blobs’ coincident with some of the optical galaxies. Routine access to ultraviolet images is a first for the mission, allowing astronomers to learn much more about individual objects. Obtaining a ratio of the brightness of individual sources seen with different filters (‘filter spectroscopy’) gives some indication of the temperature and composition of these objects. Using XMM-Newton to search for variability from sources such as these will facilitate the hunt for those elusive black holes thought to lurk at the centres of many galaxies. “The performance of our instrument is very much as we expected” said Keith Mason, Principal Investigator for the Optical Monitor. “We have worked for over a decade on this mission and it is very exciting having the first data...The pictures really show the value of the multi-wavelength approach of the XMM design”.
Martin Turner, Principal Investigator for the EPIC cameras, commented “These first pictures are tremendously exciting after so many years of work. They are all that we hoped they would be. In the LMC we can see the elements, which go to make up new stars and planets, being released in giant stellar explosions. We can even see the creation of new stars going on, using elements scattered through space by previous stellar explosions. This is what we built the EPIC cameras for and they are really fulfilling their promise.”
HR 1099 is a sixth magnitude star located about a 100 light years from the Sun only just visible to the naked eye. Its intense brightness in the EPIC-MOS image conceals a binary pair. Whereas our Sun rotates in 30 days, these two stars are whizzing around each other in only 3 days. The rapid motion causes a kind of infernal dynamo, twisting the stars’ magnetic fields into contorted shapes. If one of the stars resembles our own Sun, its partner is infinitely more active than the Sun. It is the scene of intense stellar flares and storms believed to be due to the release of magnetic energy as the fields untwist. Studying the phenomena displayed by HR 1099 and its ilk greatly helps us understand the way our own Sun functions and its effects upon us. The
The Hickson Cluster Group (HCG-16) viewed by EPIC and by the Optical Monitor in the visible and ultraviolet wavelengths is one of approximately a hundred compact galaxy clusters listed by Canadian astronomer Paul Hickson in the 1980s. The criteria for Hickson cluster groups include their compactness, their isolation from other galaxies and a limited magnitude range between their members. Most Hickson cluster groups are very faint, but a few can be observed with modest aperture tele18
X-ray image of HR1099 reveals many serendipitous sources, hitherto unknown.
June. ESA has decided to honour one of the world’s most illustrious scientists by giving the name of Isaac Newton to the XMM mission. The X-ray space telescope is henceforth called the XMM-Newton observatory.
The final two examples of the initial data collected by XMM-Newton and presented by ESA on 9 February take the form of spectra provided by one of the two Reflection Grating Spectrometers (RGS). Just as in optical spectroscopy, different elements absorb and emit light at specific and unique points of the radiation spectrum, the RGS spread these out in the form of two ‘bananas’, the two so-called ‘spectral orders’ of the instrument emission lines appear as distinct features in the rainbow of X-ray colours, acting as signatures that reveal a great deal of information. RGS spectra of HR 1099 were taken and the resulting graphs display peaks or lines that correspond to the various elements present in the source. Different types of iron, oxygen carbon and neon can be distinguished in these spectra and, from an analysis of these data, the temperatures, densities, abundances and velocities of the different materials that are present can be deduced. “Firstly, the nice separation of the two spectral order bands shows the resolution of the RGS CCDs is well up to expectations” commented Bert Brinkman, RGS Principal “For the spectrometers as a Investigator. whole, the resolution which is of prime importance is exactly or marginally better than what we expected after the ground calibrations. The instruments promise a lot for the future”.
The work of Sir Isaac Newton (1642-1727) in the field of mathematics, optics and physics laid the foundations for modern science. He made a major impact on theoretical and practical astronomy and today one cannot evoke an apple, a reflecting telescope, a light-splitting prism or a sextant without recalling Newton’s contributions to science. “We have chosen this name because Sir Isaac Newton was the man who invented spectroscopy and XMM is a spectroscopy mission” Roger Bonnet explained. “The name of Newton is associated with the falling apple, which is the symbol of gravity and with XMM I hope that we will find a large number of black hole candidates which are of course associated with the theory of gravity. There was no better choice of name than XMM-Newton for this mission”. On the occasion of the presentation of the X-ray observatory’s first images, ESA launched ‘Stargazing’, the third XMM-Newton competition. European youngsters, 16 to 18 years old at the end of secondary school, will be able to win observing time using the X-ray telescope. “We are extending the concept of backyard astronomy” said Professor Bonnet. “Through this telescope’s ability to be operated from the ground in a friendly way, young people will be offered a unique opportunity to learn how to operate and manage an observatory as complex as XMM-Newton. I would be very surprised if this contest does not trigger some new vocations”. The competition follows the ‘What’s new Mr Galileo’ essay contest which allowed over 400 lucky winners to visit French Guiana, and the ‘Draw me a telescope’ competition in which young children designed the XMM launch logo. ‘Stargazing’ will allow school classes throughout Europe to make proposals for observation in conjunction with scientists working on the XMM-Newton mission. The deadline for proposals is 12 May 2000. As from June, two schools per country will be selected. In July-August 2000, two students from each class will be visiting the XMM-Newton Science Operations Centre in Villafranca, Spain in order to finalize their proposals. The best four observation proposals will be selected and will be carried out by the XMM-Newton science team at the end of the year and early 2001. The results will be presented at the following Le Bourget Air Show in mid-June 2001.
All the images reveal hitherto unknown X-ray sources. Faint point sources barely perceptible with previous X-ray space telescopes appear in all their splendour. Understanding everything they show is not yet possible as the XMM-Newton instruments have yet to be calibrated. XMlM Project Scientist Fred Jansen said: “As these are the very first astronomical data and we are already observing lots of new science, XMM-Newton holds a very clear promise for an exciting and scientific future.” ESA’s Director of Science Professor Roger Bonnet was equally impressed: “I am amazed by the quality of the pictures as compared to previous X-ray missions. We see on them a lot of new sources, especially in the parts of the spectrum which correspond to the hottest temperatures and we see that the universe is hotter than we thought and that many new sources are appearing. We are very hopeful that many more objects will be discovered and that by extending the temperature measurements of the universe to many objects, we will have a much better picture of the history and the hectic behaviour of stars at the end of their life”. The Calibration and Performance Verification phase for X/I&I&Newton’s science instruments was scheduled to begin on 3 March, with routine science operations starting in
Further information about the competition and its rules can be found at: http://sci.esa.int/xmm/competition 19
SCIENTIFIC SPACE MISSION NEWS
3.1.
Ulysses, launched 6 October 1990, Out of Ecliptic Interplanetary Medium Mission
[From ESA 19991
Information
Note,
As grains of this particular size travel towards the Sun, they are repelled constantly by the sunlight. This causes them to lose speed until eventually they come to a halt at a distance of four times the Earth-Sun distance. At distances closer than twice the Earth-Sun distance, the findings are unreliable because interstellar and solar system dust are more difficult to tell apart.
17 December
The discovery says something about the optical properties of the banished dust grains. So Landgraf and his colleagues decided to consult tables that list the strength of radiation pressure needed to deflect same-sized grains of different types of material. The best match, they found, was with a mixture of silicates detected in interstellar clouds elsewhere in the Milky Way, suggesting that we are moving through an identical cloud. “We were very excited when we found that the composition fits” commented Landgraf. The notion that we are travelling through an interstellar cloud is not new, as Ulysses had discovered previously that a cloud of gas was moving through the solar system. By 1995, Ulysses had detected enough galactic dust grains to see that they were travelling through the solar system in the same direction as the gas, suggesting that the cloud consists of dust as well as gas.
The force of sunlight is keeping part of our solar system dust free at least free from a particular type of dust. Markus Landgraf, now working at ESA’s operations centre ESOC in Germany together with his international team, made this discovery after poring over data collected by the dust detector on board the Uysses spacecraft. In a paper in Science, they show how their findings lend support to the view that our solar system is moving through a cloud of dust and gas that is made of the same stuff as interstellar clouds observed elsewhere in our galaxy. Landgraf and his colleagues made the discovery when looking at the mass distribution of dust particles collected by the detector between February 1992 and April 1996 as Uysses swept along its solar polar orbit. They were interested in interstellar dust, which can be distinguished from dust originating in the solar system by its speed and direction of travel.
The composition of dust grains in distant interstellar clouds can be measured with telescopes from the way in which light is absorbed and scattered by the clouds. However, dust grains in our local interstellar cloud are too sparse and close to us for such measurements.
Interstellar dust travels very fast, and can be found outside the ecliptic, whereas solar system dust tends to travel more slowly in the plane of the planets’ orbits. “When I got the print out on my desk, it was obvious immediately that there was something unusual about the mass distribution. It was a big surprise” said Landgraf. Interstellar dust grains of a particular size not too big and not too small were missing from the volume of space between two and four times the distance of the Earth from the Sun. After eliminating all other possible explanations, the team concluded that the pressure of sunlight was keeping the dust grains out of this region. The particles were just the right size for sunlight to have this effect. “If the particles are very small, light doesn’t see them because they are smaller than the wavelength of light. If they are very big, they absorb and reflect light, but the light doesn’t push them away because they’re too heavy. The particles being pushed away are large enough to absorb and reflect light, but they don’t have enough inertia to stay still” explained Landgraf.
The findings of the team at ESOC show that there are indirect ways and means of deducing their composition. “The evidence is stacking up for our own local interstellar dust and gas cloud, though the origin of this cloud just isn’t known. We don’t know the whole history of these grains, which is why they are so intriguing. They could have originated in supernovae explosions, or they could be the outflow of old stars which give out star dust when they get old, much like a candle produces soot when it becomes too cold” speculated Landgraf.
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3.2.
Hubble S ace Telesco e, launched 2 B April 1990, As Pronomical Telescope
Ed Weiler, NASA Associate Administrator for Space Science. “I think there is no better proof than these pictures that NASA’s capability to send humans into space to work on Hubble has had a vital role in space science and [in] the renaissance in astronomv we’re now seeing.”
(a) Hubble placed into Safe Hold [From NASA News, 15 November 19991 NASA’s Hubble Space Telescope (HST) was placed into a safe hold on 13 November 1999 when gyroscope #l ceased operation. With only two operational gyros remaining, the science programme was suspended until the completion of Servicing Mission 3A, in December 1999. This gyro situation was not expected to impact the servicing mission due at the end of 1999. In fact, anticipation that another gyro could fail was the primary reason that the HST managers scheduled an early repair mission and split the third servicing mission activities into two flights: Servicing Mission-3A (Decemand Servicing Mission-3B ber 1999) (mid-2001).
“After a two-month hiatus, it is a tremendous boost to all of astronomy to see Hubble back in action. NASA has restored the observatory to a condition that was better than it was even before the fourth gyroscope failed” said Steven Beckwith, director of the Space Telescope Science Institute, the Hubble science operations centre in Baltimore, MD. To verify the telescope’s refurbishment, astronomers resumed operations by aiming it at two scientifically intriguing and photogenic celestial targets. One object is an intricate structure of shells and streamers of gas around a dying Sun-like star 5000 light-years away. Designated NGC 2392, it is dubbed the ‘Eskimo’ Nebula because, as seen through ground-based telescopes, it resembles a face inside a furry parka. In Hubble’s sharp view, the ‘furry’ features resemble giant comets all pointing away from the central star, like the spokes of a wheel.
The telescope was not at risk as the safehold mode had been thoroughly tested and used twice since Hubble’s launch in 1990. This protective safe mode allows ground control of the telescope, though with only two gyros working, Hubble cannot be aimed with the precision necessary for scientific observations of the sky. Consequently, the aperture door was closed to protect the optics, and the spacecraft was aligned to the Sun to ensure adequate power was received by the solar panels.
“The clumps that form the comet heads all seem to be located at a similar distance from the star. This fact will be important in developing a theory of why the clumps formed in the first place,” said planetary nebula expert J. Patrick Harrington of the University of Maryland, College Park, MD. “Of all the planetary nebulae imaged by the Hubble Space Telescope, this new image is unsurpassed in subtle beauty.” (see 1 .l, page 4).
Engineers are investigating the cause of the gyro loss. (The gyro was returned to ground after the servicing mission). Additional information on the servicing mission and on Hubble is available at: http:Nhubble.gsfc.nasa.gov/ (b) HubMe Recommissioned [From NASA News, 24 January
A second target is a massive cluster of galaxies called Abell 2218, which acts like a giant zoom lens in space. The gravitational field of the cluster magnifies the light of more distant galaxies far behind it, providing a deep probe of the very distant universe. The cluster was imaged in full colour, providing a spectacular and unique new view of the early universe.
20001
NASA’s Hubble Space Telescope is back in business, as has been made dramatically evident in stunning new pictures of remote galaxies and a colourful dying star. The images were taken between 10 and 13 January 2000, as part of the activities to recommission the Earth-orbiting telescope. The pictures are a culmination of the successful Space Shuttle servicing mission (STS-103) in December 1999, which restored NASA’s premier optical space observatory to its full capability with a crystal-clear view, and beefed it up with new electronics and critically needed replacement gyroscopes. “Thanks to the great work by the astronauts, Hubble is better than new” said Dr
“For the first time, we can view the internal colour structure of some very distant galaxies. This gives us new insight into details of what young galaxies are like,” said Professor Richard Ellis at the California Institute of Technology, Pasadena, CA, and a co-investigator on the original (black-and-white) Hubble image of Abell 2218 taken in 1994. The colour of a distant source is preserved by gravitational lensing. By matching images of the same
12
ture, but this new evidence certainly makes the argument for the presence of an ocean far more persuasive.” It appears that the ocean lies beneath the surface somewhere in the outer 60 miles (about 100 km), the approximate thickness of the ice/water layer. Kivelson explained that ‘Jupiter’s magnetic field at Europa’s position changes direction every 5% hours. This changing magnetic field can drive electrical currents in a conductor, such as an ocean. Those currents produce a field similar to Earth’s magnetic field, but with its magnetic north pole - the location toward which a compass on Europa would point - near Europa’s equator and constantly moving. In fact, it is actually reversing direction entirely every 5% hours. On previous Europa flybys, Galileo identified a magnetic north pole, but did not determine whether its position changes with time. “We wondered ‘was it possible that the north pole did not move?“’ Kivelson said.
colour, families of multiple images produced by the lensing process can be identified. An unusual red feature in the field particularly fascinates Andrew Fruchter, leader of the team that took the early-release observations. “This extraordinary object has colours which indicate it is one of two things, either a rare, extremely cool dwarf star in our own galaxy, or one of the most distant objects ever viewed by Hubble lensed into visibility by the mass of the cluster” said Fruchter. Further observations will be needed to confirm the identity of this unusual object. Spacecraft operators report that all the new equipment installed on the telescope in December is working perfectly, including the new computer, solid state recorder, and fine guidance sensor. In particular, the new gyroscopes are allowing Hubble to point reliably with exquisite precision at celestial objects. Two key science instruments, the Wide Field and Planetary Camera 2 and the Space Telescope Imaging Spectrograph, are now being used for routine science observations to probe everything from planets to black holes and far flung galaxies.
The new evidence was gathered during a flyby specially planned so that the observed position of Europa’s north pole would make it clear whether or not it moves. In fact, the most recent data showed that its position had moved, thus providing key evidence for the existence of an ocean. It is not likely that the electric currents on Europa flow through solid surface ice as ice is not a good carrier of currents. However, Kivelson pointed out that “melted ice containing salts, like the sea water found on Earth, is a fairly good conductor. There is no other likely current-carrying material near Europa’s surface. Currents could flow in partially melted ice beneath Europa’s surface, but that makes little sense, since Europa is hotter toward its interior, so it’s more likely the ice would melt completely. In addition, as you get deeper toward the interior, the strength of the current-generated magnetic field at the surface would decrease”.
The Space Telescope Science Institute is operated by the Association of Universities for Research in Astronomy, Inc. for NASA, under contract with NASA’s Goddard Space Flight Center, Greenbelt, MD. The Hubble Space Telescope is a project of international cooperation between NASA and ESA. Images are available on the Internet at: http://oposite.stsci.edu/pubinfo/latest.html and http://oposite.stsci.edu/ pubinfo/pictures.html.
3.3.
Galileo, launched 18 October 1989, Jupiter Probe
[From NASA News, 10 January
20001 These latest findings are consistent with previous Galileo images and data showing a tortured surface seemingly formed when Europa’s surface ice broke and was reconfigured while floating on an underlying sea. Further theoretical work is under way to analyse the fluid layer and its properties. “It will be interesting to see whether this same type of phenomenon occurs at Jupiter’s moon Ganymede” Kivelson said. Galileo is tentatively scheduled to fly by Ganymede twice this year.
When NASA’s Galileo spacecraft swooped past Jupiter’s moon Europa, it picked up powerful new evidence that a liquid ocean lies beneath Europa’s icy crust. As the spacecraft flew 218 miles (351 km) above Europa on 3 January, its magnetic field was recorded by the magnetometer which observed directional changes in the field consistent with the presence of a shell of electrically conducting material, such as a salty, liquid ocean. “1 think these findings tell us that there is indeed a layer of liquid water beneath Europa’s surface” said Dr Margaret Kivelson, principal investigator for the Galileo magnetometer (at the University of California, Los Angeles). “I’m cautious by na-
Additional information Galileo are available at http://galileo.jpl.nasa.gov.
13
and pictures taken by
The Galileo mission is managed for NASA’s Office of Space Science, Washington, D.C. by JPL, a division of the California institute of Technology, Pasadena, CA.
3.4.
SOHO (Solar and Heliospheric Observatory), launch 2 December 1995, Solar and Heliospheric mission
[From NASA News, 8 February 20001 In just four years of operation, the Solar and Heliospheric Observatory (SOHO) spacecraft has found 102 comets, making it by far the most successful comet-hunter in history. Calculations have shown that the latest comets discovered with SOHO are previously unknown with the 102nd comet observed by Dr Douglas Biesecker (SM&A, Vienna, VA and NASA’s Goddard Space Flight Center, Greenbelt, MD), a member of the SOHO team personally responsible for 45 of the discoveries. A cooperative project between ESA and NASA, SOHO has revolutionized solar science. It also has revealed an amazing number of ‘suicidal’ comets plunging into the solar atmosphere. Like nearly all of SOHO’s comet discoveries, the latest comet showed up in images from and Spectrometric Large Angle the Coronagraph (LASCO) instrument. This is a set of coronagraphs that view the space around the Sun out to 12.5 million miles, while blotting out the bright solar disk with masks. LASCO watches out for ejections of electrically charged gas from the Sun that threaten to disturb the Earth’s space environment. As an unexpected bonus, it also proved ideal for recording objects falling into the Sun. Still pictures and movies from LASCO are freely available on the Internet, and even amateur astronomers have used them to discover comets.
“SOHO is seeing fragments from the gradual breakup of a great comet, perhaps the one that the Greek astronomer Ephorus saw in 372 BC” said Dr Brian Marsden of the Center for Astrophysics in Cambridge, MA. “Ephorus reported that the comet split in two. This fits with my calculation that two comets on similar orbits revisited the Sun around AD 1100. They split again and again, producing the sungrazer family, all still coming from the same direction. The sungrazers’ ancestor must have been enormous by cometary standards.” “The rate at which we’ve discovered comets with LASCO is beyond anything we ever expected” said Bieseeker. “We’ve increased the number of known sungrazing comets by a factor of four. This implies that there could be as many as 20 000 fragments”. Life is perilous for a sungrazer. The mixture of ice and dust that makes up a comet’s nucleus is heated like the proverbial snowball in hell, and it can only survive its visit to the Sun if it is quite large. What is more, the strong tidal effect of the Sun’s gravity can tear the looselyglued cometary nucleus apart. The disruption that created the many SOHO sungrazers was similar to the fate of Comet Shoemaker-Levy 9, which went too close to Jupiter and broke up into many pieces that eventually fell into the planet in 1994. The history of splitting gives clues to the strength of comets, which will be of practical importance if ever a comet seemed likely to hit the Earth. Also, the fragments seen as SOHO comets reveal the internal composition of comets, freshly exposed as it were, in contrast to the much-altered surfaces of objects such as Halley’s comet that have visited the Sun many times. The count of SOHO’s comet discoveries would be one fewer without a late bonus from SOHO’s Solar Wind Anisotropies (SWAN) instrument, which looks away from the Sun to survey atomic hydrogen in the solar system. In December 1999, the International Astronomical Union retrospectively credited SOHO with finding Comet 1997 K2 (SOHO # 93) in SWAN full-sky images from May to July 1997. It remained outside the orbit of the Earth even at its closest approach to the Sun, and thus did not vaporize entirely.
Ten comets discovered by SOHO, including the ones identified as SOHO # 100, 101 and 102, passed the Sun at a safe distance from Earth. However, the rest of the SOHO comets vaporized in the solar atmosphere. Near misses are well known. One hundred years ago, Heinrich Kreutz in Kiel, Germany, realized that several comets seen buzzing the Sun seemed to have a common origin, because they came from the same direction among the stars. These comets are now called the Kreutz sungrazers, and the 92 vanishing SOHO comets belong to that class.
More information and images are on the Internet at: http://sungrazer.nascom.nasa.gov/soholOO and at http://pao.gsfc.nasa.gov/gsfc/ spacesci/sunearth/sunearth.htm#soho
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3.5.
FUSE (Far Ultraviolet S ectroscopic Explorer), launc I: ed 24 June 1999
[From NASA News, 12 January
the 62 guest investigators from around the world selected by NASA for the first year of operations. We are continuing to tune the instrument” Moos added. “In the spring, we expect to begin a comprehensive study of the abundance of deuterium, a fossil atom left over from the Big Bang. As our team becomes more practised, we need less time to optimize the instrument, and the amount of time we can spend on scientific observations will go up. This means higher scientific productivity.” FUSE is able to detect interstellar gas and determine its composition, velocity and distance by viewing bright celestial objects further away. The intervening gas selectively absorbs the light from these objects in a unique pattern of colours, depending on the composition of the gas. The spectrograph on FUSE separates the light into its component colours, the resulting patterns identifying the gas - like optical fingerprints. When the patterns shift to different colours, velocity and distance measurements can be inferred.
20001
The extended halo of half-million-degree gas that surrounds the Milky Way was generated by thousands of exploding stars, or supernovae, as our galaxy evolved, according to new observations by NASA’s Far Ultraviolet Spectroscopic Explorer (FUSE) spacecraft. The spacecraft has nearly completed its shakedown phase, and its first results are already providing a wealth of new information about the material that becomes stars, planets and ourselves. The hot gas halo which surrounds our galaxy extends about 5000 to 10 000 light years above and below the galactic plane and thins with distance (one light year is almost six trillion miles). “The hot gas halo has been known for some time, but we weren’t sure how it got there or stayed hot” said FUSE co-investigator Dr Blair Savage of the University of Wisconsin in Madison. “The new FUSE observations reveal an extensive amount of oxygen VI (oxygen atoms that have had five of their eight surrounding electrons stripped away) in the halo. Some scientists thought that ultraviolet radiation from hot stars could produce the halo, but the only way to make the observed amount of oxygen VI is through collision with the blast waves from exploding stars, called supernovae.”
The 1400 kg spacecraft carries a 2.4 m focal length telescope with a primary mirror made of four separated segments; two of these are coated with silicon carbide (to reflect radiation at wavelengths between 90 and 110 nm) and the other two with aluminum and lithium fluoride (to reflect 100 - 119 nm radiation). The focused beams then fall onto four separate (correspondingly coated) Rowland gratings that disperse the spectrum into four separate photon - counting microchannel flat- plate detectors. A separate star tracking Fine Error Sensor (FES) facilitates location of the source and a pointing stability within 0.5 arcseconds for large integration times. While there have been other far UV satellites such as Copernicus and HST, the investigative thrust on the FUSE data will be intergalactic clouds and interstellar clouds which may well carry the signature of pristine (Big Bang) deuterium ions that have escaped being consumed in stellar cores. The deuterium/hydrogen ratios so obtained may approximate to the status of the universe minutes after the Big Bang.
“Stars destined to explode don’t live long, compared to stars like our Sun, so star explosions are actually a record of star formation” said Dr George Sonneborn, FUSE project scientist at NASA’s Goddard Space Flight Center, Greenbelt, MD. “By comparing supernova-generated halos among galaxies, we may be able to compare their star formation histories.” “FUSE measures the pulse of the lifeblood of our galaxy, the thin gas between stars” said Dr Warren Moos, FUSE principal investigator at Johns Hopkins University in Baltimore. “This interstellar gas courses through our veins, because dense clouds of it collapsed to form new stars and planets, including our solar system.”
The FUSE spectrograph is at least 100 times more powerful than previous instruments and should help reveal a large number of new atomic and molecular features in interstellar gas.
“The FUSE observatory is now open for business” Moos said. “After an extended onorbit checkout and debugging period, common for complex space observatories, we are now performing observations on a routine basis for members of the principal investigator team and
New images related to this investigation, and more information about FUSE, can be found on the Internet at: http:/fuse.pha.jhu. edul
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3.6.
Chandra, launched 22 July 1999, X-ray Astronomy Observatory
black hole, and the evidence that the explosion from the gas near the black hole is pushing the hot gas around”. Indeed, combined radio and X-ray observations suggest that a vast bubble of high energy particles is pushing the hot gas aside, creating the Hydra-like loops of hot gas. Similar processes are likely to be at work in other galaxy clusters, and in newly forming galaxies that are collapsing from a cloud of gas. By using images from Char&a and other telescopes, astronomers may eventually conquer a ‘monstrous’ problem of cosmic significance.
(a) The Heart of the Hydra A Galaxy Cluster [From NASA News 9 December
19991
NASA’s Chandra X-ray Observatory image of the Hydra A galaxy cluster has revealed a possible solution to a Herculean puzzle about the fate of the largest objects in the universe. For years astronomers have been searching unsuccessfully for large quantities of matter they believed must be flowing into the central regions of galaxy clusters. The Char&a image of Hydra A displays long snake-like strands of 35 million degree gas extending away from the centre of the cluster. These structures show that the inflow of cooling gas is deflected by magnetic fields produced by explosions from a central black hole.
The Observatory Smithsonian/Harvard centre in Cambridge (b) Chandra background
is operated by a joint team working at a control MA.
resolves
the universe’s
[From NASA News, 13 January
X-ray
20001
While taking a giant leap toward solving one of the greatest mysteries of astronomy the nature and source of the X-ray background, NASA’s Char-&a X-ray Observatory may also have revealed the most distant objects ever seen in the universe and discovered two new, but puzzling, types of cosmic objects.
The X-ray image also reveals a bright wedge of hot multimillion-degree gas pushing into the heart of the cluster. Like the legendary Hercules, who had to contend with the multiple heads of the monstrous Hydra, astrophysicists now know they must deal with the effects of magnetic fields, star formation, rotation and black holes if they are to understand what is happening in the inner regions of the galaxy cluster. As the largest gravitationally bound objects in the universe, galaxy clusters provide crucial clues for understanding the origin and fate of the universe. Each large cluster such as Hydra A contains hundreds of galaxies and enough gaseous material to make a thousand more galaxies. One intriguing question has been the ultimate fate of this colossal gas reservoir. Early X-ray observations indicated that the gas in the inner regions of Hydra A should be cooling and slowly settling into the centre of the cluster to form new galaxies or hundreds of trillions of dim stars. As astronomers began searching for this cool matter, they were puzzled to find that the new galaxies and stars were not detected in sufficient numbers. The Chart&a results on Hydra A, which is 840 million light years from Earth, may point to a resolution of this problem. The inflow of cooling gas may be deflected by magnetic fields, and even pushed back into the cluster by explosions from the vicinity of a supermassive black hole at the core of the central galaxy.
Char&a has resolved most of the X-ray background, a pervasive glow of X-rays throughout the universe, which was first discovered in the early days of space exploration. Until the arrival of Chandra, it has not been possible to discern the origin of the hard, or high-energy, X-ray background, because no telescope had the necessary resolution. Commenting on the findings with Chart&a, Dr Alan Bunner, Director of NASA’s Structure and Evolution of the Universe science theme said “This is a major discovery. Since it was first observed 37 years ago, understanding the source of the X-ray background has been a holy grail of X-ray astronomy. Now, it is within reach”. The results of the observations with Chandra were presented, by Dr Richard Mushotzky of NASA’s Goddard Space Flight Center, Greenbelt, MD, Dr Lennox Cowie and Dr Amy Barger at the University of Hawaii, Honolulu and Dr Keith Arnaud of the University of Maryland, College Park, at the 195th national meeting of the American Astronomical Society in Atlanta, GA and have been submitted for publication in Nature. “We are all very excited by this finding” said Mushotzky. “The resolution of most of the hard X-ray background during the first few months of the Char&a mission is
“In Hydra, you can see the whole cycle” said Brian McNamara of the Harvard-Smithsonian Center for Astrophysics. “You have the hot gas cloud, the disk of material feeding the
16
a tribute to the power of this observatory and bodes extremely well for its scientific future”. The Chandra team looked at a small section of the sky, a circle about one-fifth the size of a full moon, and resolved about 80% of the X-ray glow in this region into specific light sources. Stretched across the entire sky, this adds up to approximately 70 million sources, most of which are galaxies. One-third of the sources are galaxies the cores of which shine bright in X-rays, yet do not shine in visible light. There may be tens of millions of these ‘veiled galactic nuclei’ in the universe. Each of these galaxies quite possibly harbours a massive black hole at its core that produces X-rays as gas is pulled toward it at nearly the speed of light. A second new class of objects, comprising approximately one-third of the sources, is to be ‘ultra-faint galaxies’. assumed Mushotzky said that these sources might emit little or no optical light, either because the dust around the galaxy blocks the light totally or because the optical light is eventually absorbed during its long journey across the universe. In the latter scenario, Mushotzky commented that these sources may be well over 14 billion light years away and, thus, the earliest (most distant) objects ever identified. Resolution of the X-ray background relied on a 27.7-hour Chandra observation using the Advanced CCD Imaging Spectrometer in early December 1999, and also utilized data from the Japan-US Advanced Satellite for Cosmology and Astrophysics. For further information on Chandra, including images, see http://chandra.nasa.gov
3.7.
XMM (X-ray Multi-Mirror Mission), launched 10 December 1999, X-ray Observatory
(a) XMM-Newton
launch from Kourou on Ariane 504 on 10 December 1999, XMM was delivered into its final operational orbit in the following week. The telescope doors on the X-ray Mirror Modules and on the Optical Monitor telescope were opened on 17/l 8 December. The Radiation Monitor was activated on 19 December and the spacecraft was put into a quiet mode over the Christmas and New Year period. The mission’s scientific data are being received, processed and dispatched to astronomers by the XMWVewton Science Operations Centre in Villafranca. Operations with the spacecraft were restarted on 4 January when, as part of the commissioning phase, all the science payloads were switched on one after the other for initial verification. After a series of engineering exposures, between 19 and 24 January, several views of two different extragalactic regions of the universe were taken. These featured a variety of extended and Xray point sources, and were chosen to demonstrate the full functioning of the observatory. This initial series of short and long duration exposures have delighted the Project management team as well as the investigators. First analyses confirm that the spacecraft is extremely stable, the XMM telescopes are focusing perfectly, and the cameras and spectrometers are working exactly as expected. The Science Operations Centre infrastructure, for processing and archiving the science data telemetry from the spacecraft, is also performing well. Initial inspection of the first commissioning images, resented on 9 February, showed some unique X-ray views of several celestial objects. The Calibration and Performance Verification phase for X/WA& science instruments was planned to start on 3 March, with routine science operations beginning in June 2000. (b) Images from X/W-Newton
takes its first pictures
[From ESA Press Release, 2 February
[From ESA Information
20001
Note, 9 February 20001
The first pictures from ESA’s new X-ray Space Observatory (XMM-Newton) fully demonstrate the capabilities of the spacecraft’s telescopes and its science instruments. The images were officially presented on 9 February at the XMWVewton Science Operations Centre in Villafranca, Spain. The images were obtained between 19 and 25 January at the very start of the science payload commissioning process. The spacecraft viewed three regions of the sky: part of the Large Magellanic Cloud (LMC), the Hickson Cluster Group 16
ESA’s X-ray space observatory (XMM-Newton) has taken its very first pictures giving new views on the universe. The commissioning images confirm that the XMM-Newton spacecraft, its X-ray telescopes and science instruments are functioning perfectly. The mission’s Principal Investigators presented spectacular first images at a press conference on 9 February at the ESA Vilspa facility at VillafrancaIMadrid in Spain, where the XMM Science Operations Centre is located. After a successful 17
scopes. Galaxies in Hickson groups have a high probability of interacting. Their study has shed light on the question of galactic evolution and the effects of interaction. Investigation into their gravitational behaviour has also significantly contributed to our understanding of ‘dark matter’, the mysterious matter that most astronomers believe comprises well over 90% of our universe.
(HCG-16), and the star HR 1099. These targets were chosen because they all present a variety of extended and point X-ray sources and are interesting regions. The pictures are ESA Website at available on the http://www.esa.int, then Image Gallery, then News and at http://sci.esa.int/xmm/firstimages. See also page 4 of this Bulletin. The Large Magellanic Cloud, also known as the Nebula Major, is about 20 thousand light years in diameter. Situated 160 thousand light years from Earth, it is one of two irregularly shaped galaxies that are easily seen with the naked eye in the southern hemisphere. These galaxies are satellites of the Milky Way and appear to be slowly spiralling into our own galaxy. The first image obtained by the EPIC-PN X-ray cameras viewed the 30 Doradus region of the Large Magellanic Cloud. Also called the Tarantula Nebula, 30 Doradus is a ‘cauldron of creation’ where exploding stars are releasing vast amounts of matter and where new stars are being born. The image indicates the million degree temperatures of the emitting medium, with blue representing the hottest regions, green intermediate temperatures and red the coldest regions. The images reveal a white and blue arc-like formation, only part of which was known in the past. It has the appearance of a supernova remnant with its expanding glowing-hot gas producing X-rays as it collides with the interstellar medium. The image also shows the remains of a star that exploded as Supernova 1987A on 24 February 1987. It was the first supernova to reach naked-eye brightness since 1604 (Kepler’s star) and remained visible to the naked eye for nearly nine months.
Observation of celestial objects from space over a range of X-ray, ultraviolet and visible wavelengths, is a unique feature of the XMM-Newton mission. The EPIC-PN view of the Hickson 16 group shows a handful of bright X-sources and, in the background, more than a hundred faint X-ray sources that XMM-Newton is revealing for the first time. Juxtaposing the X-ray view of HCG 16 with that of the Optical Monitor reveals one of the great strengths of XMM-Newton in being able to compare the properties of objects at visible, ultraviolet and X-ray wavelengths on a routine basis. Many of the X-ray sources are revealed as elongated ‘fuzzy blobs’ coincident with some of the optical galaxies. Routine access to ultraviolet images is a first for the mission, allowing astronomers to learn much more about individual objects. Obtaining a ratio of the brightness of individual sources seen with different filters (‘filter spectroscopy’) gives some indication of the temperature and composition of these objects. Using XMM-Newton to search for variability from sources such as these will facilitate the hunt for those elusive black holes thought to lurk at the centres of many galaxies. “The performance of our instrument is very much as we expected” said Keith Mason, Principal Investigator for the Optical Monitor. “We have worked for over a decade on this mission and it is very exciting having the first data...The pictures really show the value of the multi-wavelength approach of the XMM design”.
Martin Turner, Principal Investigator for the EPIC cameras, commented “These first pictures are tremendously exciting after so many years of work. They are all that we hoped they would be. In the LMC we can see the elements, which go to make up new stars and planets, being released in giant stellar explosions. We can even see the creation of new stars going on, using elements scattered through space by previous stellar explosions. This is what we built the EPIC cameras for and they are really fulfilling their promise.”
HR 1099 is a sixth magnitude star located about a 100 light years from the Sun only just visible to the naked eye. Its intense brightness in the EPIC-MOS image conceals a binary pair. Whereas our Sun rotates in 30 days, these two stars are whizzing around each other in only 3 days. The rapid motion causes a kind of infernal dynamo, twisting the stars’ magnetic fields into contorted shapes. If one of the stars resembles our own Sun, its partner is infinitely more active than the Sun. It is the scene of intense stellar flares and storms believed to be due to the release of magnetic energy as the fields untwist. Studying the phenomena displayed by HR 1099 and its ilk greatly helps us understand the way our own Sun functions and its effects upon us. The
The Hickson Cluster Group (HCG-16) viewed by EPIC and by the Optical Monitor in the visible and ultraviolet wavelengths is one of approximately a hundred compact galaxy clusters listed by Canadian astronomer Paul Hickson in the 1980s. The criteria for Hickson cluster groups include their compactness, their isolation from other galaxies and a limited magnitude range between their members. Most Hickson cluster groups are very faint, but a few can be observed with modest aperture tele18
X-ray image of HR1099 reveals many serendipitous sources, hitherto unknown.
June. ESA has decided to honour one of the world’s most illustrious scientists by giving the name of Isaac Newton to the XMM mission. The X-ray space telescope is henceforth called the XMM-Newton observatory.
The final two examples of the initial data collected by XMM-Newton and presented by ESA on 9 February take the form of spectra provided by one of the two Reflection Grating Spectrometers (RGS). Just as in optical spectroscopy, different elements absorb and emit light at specific and unique points of the radiation spectrum, the RGS spread these out in the form of two ‘bananas’, the two so-called ‘spectral orders’ of the instrument emission lines appear as distinct features in the rainbow of X-ray colours, acting as signatures that reveal a great deal of information. RGS spectra of HR 1099 were taken and the resulting graphs display peaks or lines that correspond to the various elements present in the source. Different types of iron, oxygen carbon and neon can be distinguished in these spectra and, from an analysis of these data, the temperatures, densities, abundances and velocities of the different materials that are present can be deduced. “Firstly, the nice separation of the two spectral order bands shows the resolution of the RGS CCDs is well up to expectations” commented Bert Brinkman, RGS Principal “For the spectrometers as a Investigator. whole, the resolution which is of prime importance is exactly or marginally better than what we expected after the ground calibrations. The instruments promise a lot for the future”.
The work of Sir Isaac Newton (1642-1727) in the field of mathematics, optics and physics laid the foundations for modern science. He made a major impact on theoretical and practical astronomy and today one cannot evoke an apple, a reflecting telescope, a light-splitting prism or a sextant without recalling Newton’s contributions to science. “We have chosen this name because Sir Isaac Newton was the man who invented spectroscopy and XMM is a spectroscopy mission” Roger Bonnet explained. “The name of Newton is associated with the falling apple, which is the symbol of gravity and with XMM I hope that we will find a large number of black hole candidates which are of course associated with the theory of gravity. There was no better choice of name than XMM-Newton for this mission”. On the occasion of the presentation of the X-ray observatory’s first images, ESA launched ‘Stargazing’, the third XMM-Newton competition. European youngsters, 16 to 18 years old at the end of secondary school, will be able to win observing time using the X-ray telescope. “We are extending the concept of backyard astronomy” said Professor Bonnet. “Through this telescope’s ability to be operated from the ground in a friendly way, young people will be offered a unique opportunity to learn how to operate and manage an observatory as complex as XMM-Newton. I would be very surprised if this contest does not trigger some new vocations”. The competition follows the ‘What’s new Mr Galileo’ essay contest which allowed over 400 lucky winners to visit French Guiana, and the ‘Draw me a telescope’ competition in which young children designed the XMM launch logo. ‘Stargazing’ will allow school classes throughout Europe to make proposals for observation in conjunction with scientists working on the XMM-Newton mission. The deadline for proposals is 12 May 2000. As from June, two schools per country will be selected. In July-August 2000, two students from each class will be visiting the XMM-Newton Science Operations Centre in Villafranca, Spain in order to finalize their proposals. The best four observation proposals will be selected and will be carried out by the XMM-Newton science team at the end of the year and early 2001. The results will be presented at the following Le Bourget Air Show in mid-June 2001.
All the images reveal hitherto unknown X-ray sources. Faint point sources barely perceptible with previous X-ray space telescopes appear in all their splendour. Understanding everything they show is not yet possible as the XMM-Newton instruments have yet to be calibrated. XMlM Project Scientist Fred Jansen said: “As these are the very first astronomical data and we are already observing lots of new science, XMM-Newton holds a very clear promise for an exciting and scientific future.” ESA’s Director of Science Professor Roger Bonnet was equally impressed: “I am amazed by the quality of the pictures as compared to previous X-ray missions. We see on them a lot of new sources, especially in the parts of the spectrum which correspond to the hottest temperatures and we see that the universe is hotter than we thought and that many new sources are appearing. We are very hopeful that many more objects will be discovered and that by extending the temperature measurements of the universe to many objects, we will have a much better picture of the history and the hectic behaviour of stars at the end of their life”. The Calibration and Performance Verification phase for X/I&I&Newton’s science instruments was scheduled to begin on 3 March, with routine science operations starting in
Further information about the competition and its rules can be found at: http://sci.esa.int/xmm/competition 19