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No star unturned
No star unturned ●
TODAY, there is hardly a place on Earth that remains uncharted, unnamed or unclaimed. Just go online and you can view a satellite image of anywhere on the planet – the summit of Everest, say, the South Pole or a maze of streets in Timbuktu. Satellites and silicon have created an awesome picture of our world. For some people, namely astronomers, the world is not enough. They’d love to map the whole night sky with the same vigour, and that dream is not far off thanks to several allsky surveys in the pipeline. By around 2020, astronomers say, practically all the asteroids, stars and galaxies that ground-based telescopes could possibly see will be ticked off and catalogued. “In my mind, it’s very much analogous to maps of the Earth,” says John Tonry from the University of Hawaii’s Institute for Astronomy (IfA) in Honolulu. “In the 13th century, practically nothing was known of the New World. By the 16th century, there was still a lot to discover. But today you can pull up an image of any place on the Earth. In 2020, that’s the analogue of what we’ll have of the sky.” The transformation is taking place thanks to the advent of ambitious digital mapping projects that mine the night sky for everything they can find. The first to blaze the trail was the Sloan Digital Sky Survey, which maps a fifth of the sky from Apache Point Observatory in New Mexico. It began in 2000 and snapped nearly 200 million celestial objects in its first five years of operations. The successors to Sloan have the whole sky in their sights. One is a project called SkyMapper, under construction at the Australian National University’s Siding Spring Observatory in New South Wales. Aiming to map all the sky south of the equator at visible wavelengths over five years, SkyMapper 26 | NewScientist | 15 December 2007
should begin observations in mid-2008. It will use a 1.3-metre telescope and a 268-megapixel digital camera, and will generate 500 terabytes of data – the amount of information on more than 100,000 standard DVDs. Meanwhile, an even more ambitious project called Pan-STARRS (Panoramic Survey Telescope and Rapid Response System) began in August on the Hawaiian island of Maui, using a fairly modest 1.8-metre telescope. Several times each month until 2010, the telescope will map the whole of the sky visible from Hawaii – about three-quarters of the total. But Pan-STARRS 1, the first incarnation of the project, has a secret weapon: its monumental digital camera, that allows it to image vast swathes of sky faster than ever before. With 1.4 billion pixels, the camera is the biggest in the world, more than four times the size of any other telescope camera. “That’s really overwhelming,” says Tonry, who led the camera development team. It should discover billions of new stars and galaxies, as well as millions of asteroids in our solar system. And if all goes well, a follow-up survey called Pan-STARRS 4, running from around 2010 to 2020, will continue the work using four copies of the
20
billion astronomical objects charted by 2020
AUDE VAN RYN
If the sun’s evil twin or killer asteroids are out there, we’ll nail them, says Hazel Muir
1.8-metre scope at the higher, clearer site of Mauna Kea on Hawaii’s Big Island. By then, we should have a virtual universe containing a mind-boggling mass of data. The Pan-STARRS contribution alone will spew out some 40 petabytes, enough to fill more than 8.5 million standard DVDs, a stack higher than Mount Everest. “Essentially, we’ll know the positions of things down to a gnat’s ass,” Tonry told a May meeting of the American Astronomical Society in Honolulu. The surveys will record everything they can find, whether nearby or billions of light years away. In our own solar system, they will hunt www.newscientist.com
1.4
billion pixels in Pan-STARRS’s camera
down undiscovered dwarf planets and should find millions of new asteroids. In fact, by the end of next year, Pan-STARRS 1 should have spotted more new asteroids than have been officially catalogued in the whole of human history. To date, roughly 600,000 asteroids have been observed, if you count those seen on at least two nights and ignore iffy “one-night stands”, according to Brian Marsden, former director of the International Astronomical Union’s Minor Planet Center in Cambridge, Massachusetts. “Pan-STARRS may well record several hundred thousand minor planets in a www.newscientist.com
month or two of operation,” he says. These sightings will require follow-up observations over several years, but Marsden expects that we will have a million numbered asteroids in catalogues in 5 to 10 years’ time. “When we do, provided that competition remains minimal, Pan-STARRS should be credited with the discoveries of more than half of them,” he says. Knowing the positions and orbits of so many chunks of rock will make it much easier for scientists to rewind the solar system’s history and figure out how the sun and its motley crew of planets formed. The Pan-STARRS team will pay special
attention to killer asteroids that threaten to collide with Earth. Estimates suggest that 50-metre rocks strike the Earth every 1000 years or so. When an asteroid this size exploded in the sky above the Tunguska river valley in Siberia in 1908, the blast wave flattened around 2000 square kilometres of forest. A similar strike above London would wipe out everything within its M25 orbital motorway. Even more devastating explosions occur every couple of hundred thousand years, when a kilometre-sized rock heads our way. Simulations suggest these can trigger devastating tsunamis. So a few hours’ warning alone could save lives by allowing people to retreat to high ground. “If you can simply say exactly where and when it’s coming down, that’s really important,” says Tonry. “It’s incumbent on us to look.” The survey might also unveil new planets in the solar system. Given that Pluto has been reclassified as a “dwarf planet” due to its small size, these would be the first new planets since Neptune was discovered in 1846. PanSTARRS will spot any Jupiter-sized planets that lie less than 1700 astronomical units (AU) from the sun, 1 AU being the distance between the sun and the Earth. It will detect new Neptunes up to 980 AU from the sun, new Earths up to 640 AU distant and even new Plutos up to 250 AU away (New Scientist, 23 July 2005, p 29). It could also confirm or lay to rest speculation that the sun has a dim dwarf companion, dubbed the “death star” or Nemesis. Since the 1980s, a handful of scientists have backed the controversial idea that a hypothetical star orbits the sun at a distance of 50,000 to 100,000 AU and periodically disturbs comets in the outer solar system, nudging them inwards, possibly on a collision course with Earth. It would 15 December 2007 | NewScientist | 27
explain why mass extinctions appear to have a 26-million-year cycle – if indeed they do; that’s also controversial. But with Pan-STARRS on the case, a death star will have nowhere to hide. “If Nemesis is out there, we’ll find it,” says the IfA’s Ken Chambers, director of the Pan-STARRS consortium, a collection of institutions in the US, Germany, the UK and Taiwan that have financed the project, along with the US air force and NASA. “We don’t know what the odds are, but it’s not completely crazy.” Beyond the solar system, the survey will do a great job of finding all the bright stars in the Milky Way, whose light is not blocked by dust. “We’ll certainly see all the solar-type stars throughout our galaxy,” says Tonry. And the telescope will keep an eye on the Milky Way’s most magnificent neighbour, the Andromeda galaxy. It lies 2.9 million light years away and is the only large galaxy in our cosmic backyard. For five months, Pan-STARRS will image Andromeda twice every night. These frequent visits should bag a host of stars that vary in brightness on short timescales, as well as microlensing events, when the gravity of a star bends and briefly magnifies light from some distant galaxy behind it. These microlensing events could reveal the first planets to be detected outside the Milky Way, according to the IfA’s Nick Kaiser, principal investigator for Pan-STARRS. If a lens star in Andromeda has a planet orbiting around it, the planet’s gravity could create a telltale “spike” in the microlensing event, a hallmark that has
BRETT SIMPSON
The Pan-STARRS 1 telescope in Maui should double the number of known asteroids
already allowed astronomers to spot planets in the bustling centre of our own galaxy. As well as shedding light on the invisible part of the universe (see “Invisible skies”), the surveys should also turn up what Tonry calls “things that go bump in the night”. Through monitoring such large areas of sky repeatedly, astronomers are bound to see some rare oddities, needles in the cosmic haystack that you would never find unless you’ve looked everywhere. Amateur astronomers have reported curious flashes of light that are never seen from the same patch of sky again. Could they be sudden flare-ups from black holes or colliding neutron stars? “There are very rare things that people know might be happening,” says Tonry. “But there are also things that nobody has ever
Invisible skies The new breed of telescopes will reveal much about the invisible stuff that makes up most of the universe. For starters, the PanSTARRS telescope in Hawaii will provide the most detailed map yet of the large-scale structures in the universe, including the copious “dark matter” whose identity astronomers are desperate to pin down. Dark matter is invisible, but maps from Pan-STARRS will reveal its landscape by recording how its gravity distorts background galaxies. Then there is the mysterious dark energy. It first came to light in 1998 when astronomers analysed dozens of supernovae and deduced from them that the expansion of
28 | NewScientist | 15 December 2007
the universe is speeding up, not slowing down as previously assumed. Now Pan-STARRS will bag “ridiculous numbers” of supernovae, according to John Tonry from the University of Hawaii’s Institute for Astronomy in Honolulu. The Pan-STARRS 1 telescope will find more than 3000 a month. In Australia, the SkyMapper survey aims to bag up to 50,000 supernovae over five years. That dwarfs the few hundred currently discovered each year by all the world’s telescopes combined. Both projects aim to monitor some of the supernovae as they evolve, but the majority will need follow-up observations by
astronomers elsewhere. “We can just flood the rest of the world with things to look at,” says Tonry. With so many supernovae under the spotlight, astronomers hope to get a much better picture of what triggers these explosions in the first place and tease out any subtle variations (New Scientist, 25 October, p 52). That could in turn fine-tune measurements of dark energy and hopefully shed light on what drives it. Understanding the nature of dark energy will allow astronomers to answer the biggest cosmic question of all: what are the universe’s future expansion plans? Will it expand forever or ultimately collapse in a “big crunch”?
thought of – just weird stuff. When the Hubble Space Telescope was built, it wasn’t exactly clear what it would do but it was pretty obvious it would do something neat, and in fact it has. But the greatest results from HST were never thought of when it was launched.” Beyond Pan-STARRS and SkyMapper, astronomers have plans for an even more ambitious project called the Large Synoptic Survey Telescope (LSST). Operating from around 2014 to 2024, it will be an 8.4-metre telescope on Cerro Pachón in northern Chile. The LSST will be able to map three-quarters of the whole sky over just three nights, generating more than 30 terabytes of image data every night, equivalent to the amount of text in around 30 million books. By 2020, the surveys should together have charted some 20 billion astronomical objects that astronomers can tour at the click of a mouse. That’s pretty much every object that a ground-based telescope could ever see. Effectively, they will end the era Galileo began when he used the first astronomical telescope to spy on Jupiter’s posse of moons. It’s testament to the staggering leaps in computer technology. Astronomers are no longer fazed by handling the 10 terabytes of data that Pan-STARRS 1 will churn out every week. The data rate from Pan-STARRS 4 will be five times that. This is feasible thanks to Moore’s law, the trend for the power of computers to double roughly every two years – more bang for your buck, as it were. “It’s just astonishing that silicon has taken over the universe,” Tonry told the American Astronomical Society. “We think the universe is so vast and yet it’s just a little backyard compared to the intellectual depths that we’re going through in the computer revolution.” “Moore’s law has met the universe,” he added, “and Moore’s law has won.” ● www.newscientist.com
TODAY, there is hardly a place on Earth that remains uncharted, unnamed or unclaimed. Just go online and you can view a satellite image of anywhere on the planet – the summit of Everest, say, the South Pole or a maze of streets in Timbuktu. Satellites and silicon have created an awesome picture of our world. For some people, namely astronomers, the world is not enough. They’d love to map the whole night sky with the same vigour, and that dream is not far off thanks to several allsky surveys in the pipeline. By around 2020, astronomers say, practically all the asteroids, stars and galaxies that ground-based telescopes could possibly see will be ticked off and catalogued. “In my mind, it’s very much analogous to maps of the Earth,” says John Tonry from the University of Hawaii’s Institute for Astronomy (IfA) in Honolulu. “In the 13th century, practically nothing was known of the New World. By the 16th century, there was still a lot to discover. But today you can pull up an image of any place on the Earth. In 2020, that’s the analogue of what we’ll have of the sky.” The transformation is taking place thanks to the advent of ambitious digital mapping projects that mine the night sky for everything they can find. The first to blaze the trail was the Sloan Digital Sky Survey, which maps a fifth of the sky from Apache Point Observatory in New Mexico. It began in 2000 and snapped nearly 200 million celestial objects in its first five years of operations. The successors to Sloan have the whole sky in their sights. One is a project called SkyMapper, under construction at the Australian National University’s Siding Spring Observatory in New South Wales. Aiming to map all the sky south of the equator at visible wavelengths over five years, SkyMapper 26 | NewScientist | 15 December 2007
should begin observations in mid-2008. It will use a 1.3-metre telescope and a 268-megapixel digital camera, and will generate 500 terabytes of data – the amount of information on more than 100,000 standard DVDs. Meanwhile, an even more ambitious project called Pan-STARRS (Panoramic Survey Telescope and Rapid Response System) began in August on the Hawaiian island of Maui, using a fairly modest 1.8-metre telescope. Several times each month until 2010, the telescope will map the whole of the sky visible from Hawaii – about three-quarters of the total. But Pan-STARRS 1, the first incarnation of the project, has a secret weapon: its monumental digital camera, that allows it to image vast swathes of sky faster than ever before. With 1.4 billion pixels, the camera is the biggest in the world, more than four times the size of any other telescope camera. “That’s really overwhelming,” says Tonry, who led the camera development team. It should discover billions of new stars and galaxies, as well as millions of asteroids in our solar system. And if all goes well, a follow-up survey called Pan-STARRS 4, running from around 2010 to 2020, will continue the work using four copies of the
20
billion astronomical objects charted by 2020
AUDE VAN RYN
If the sun’s evil twin or killer asteroids are out there, we’ll nail them, says Hazel Muir
1.8-metre scope at the higher, clearer site of Mauna Kea on Hawaii’s Big Island. By then, we should have a virtual universe containing a mind-boggling mass of data. The Pan-STARRS contribution alone will spew out some 40 petabytes, enough to fill more than 8.5 million standard DVDs, a stack higher than Mount Everest. “Essentially, we’ll know the positions of things down to a gnat’s ass,” Tonry told a May meeting of the American Astronomical Society in Honolulu. The surveys will record everything they can find, whether nearby or billions of light years away. In our own solar system, they will hunt www.newscientist.com
1.4
billion pixels in Pan-STARRS’s camera
down undiscovered dwarf planets and should find millions of new asteroids. In fact, by the end of next year, Pan-STARRS 1 should have spotted more new asteroids than have been officially catalogued in the whole of human history. To date, roughly 600,000 asteroids have been observed, if you count those seen on at least two nights and ignore iffy “one-night stands”, according to Brian Marsden, former director of the International Astronomical Union’s Minor Planet Center in Cambridge, Massachusetts. “Pan-STARRS may well record several hundred thousand minor planets in a www.newscientist.com
month or two of operation,” he says. These sightings will require follow-up observations over several years, but Marsden expects that we will have a million numbered asteroids in catalogues in 5 to 10 years’ time. “When we do, provided that competition remains minimal, Pan-STARRS should be credited with the discoveries of more than half of them,” he says. Knowing the positions and orbits of so many chunks of rock will make it much easier for scientists to rewind the solar system’s history and figure out how the sun and its motley crew of planets formed. The Pan-STARRS team will pay special
attention to killer asteroids that threaten to collide with Earth. Estimates suggest that 50-metre rocks strike the Earth every 1000 years or so. When an asteroid this size exploded in the sky above the Tunguska river valley in Siberia in 1908, the blast wave flattened around 2000 square kilometres of forest. A similar strike above London would wipe out everything within its M25 orbital motorway. Even more devastating explosions occur every couple of hundred thousand years, when a kilometre-sized rock heads our way. Simulations suggest these can trigger devastating tsunamis. So a few hours’ warning alone could save lives by allowing people to retreat to high ground. “If you can simply say exactly where and when it’s coming down, that’s really important,” says Tonry. “It’s incumbent on us to look.” The survey might also unveil new planets in the solar system. Given that Pluto has been reclassified as a “dwarf planet” due to its small size, these would be the first new planets since Neptune was discovered in 1846. PanSTARRS will spot any Jupiter-sized planets that lie less than 1700 astronomical units (AU) from the sun, 1 AU being the distance between the sun and the Earth. It will detect new Neptunes up to 980 AU from the sun, new Earths up to 640 AU distant and even new Plutos up to 250 AU away (New Scientist, 23 July 2005, p 29). It could also confirm or lay to rest speculation that the sun has a dim dwarf companion, dubbed the “death star” or Nemesis. Since the 1980s, a handful of scientists have backed the controversial idea that a hypothetical star orbits the sun at a distance of 50,000 to 100,000 AU and periodically disturbs comets in the outer solar system, nudging them inwards, possibly on a collision course with Earth. It would 15 December 2007 | NewScientist | 27
explain why mass extinctions appear to have a 26-million-year cycle – if indeed they do; that’s also controversial. But with Pan-STARRS on the case, a death star will have nowhere to hide. “If Nemesis is out there, we’ll find it,” says the IfA’s Ken Chambers, director of the Pan-STARRS consortium, a collection of institutions in the US, Germany, the UK and Taiwan that have financed the project, along with the US air force and NASA. “We don’t know what the odds are, but it’s not completely crazy.” Beyond the solar system, the survey will do a great job of finding all the bright stars in the Milky Way, whose light is not blocked by dust. “We’ll certainly see all the solar-type stars throughout our galaxy,” says Tonry. And the telescope will keep an eye on the Milky Way’s most magnificent neighbour, the Andromeda galaxy. It lies 2.9 million light years away and is the only large galaxy in our cosmic backyard. For five months, Pan-STARRS will image Andromeda twice every night. These frequent visits should bag a host of stars that vary in brightness on short timescales, as well as microlensing events, when the gravity of a star bends and briefly magnifies light from some distant galaxy behind it. These microlensing events could reveal the first planets to be detected outside the Milky Way, according to the IfA’s Nick Kaiser, principal investigator for Pan-STARRS. If a lens star in Andromeda has a planet orbiting around it, the planet’s gravity could create a telltale “spike” in the microlensing event, a hallmark that has
BRETT SIMPSON
The Pan-STARRS 1 telescope in Maui should double the number of known asteroids
already allowed astronomers to spot planets in the bustling centre of our own galaxy. As well as shedding light on the invisible part of the universe (see “Invisible skies”), the surveys should also turn up what Tonry calls “things that go bump in the night”. Through monitoring such large areas of sky repeatedly, astronomers are bound to see some rare oddities, needles in the cosmic haystack that you would never find unless you’ve looked everywhere. Amateur astronomers have reported curious flashes of light that are never seen from the same patch of sky again. Could they be sudden flare-ups from black holes or colliding neutron stars? “There are very rare things that people know might be happening,” says Tonry. “But there are also things that nobody has ever
Invisible skies The new breed of telescopes will reveal much about the invisible stuff that makes up most of the universe. For starters, the PanSTARRS telescope in Hawaii will provide the most detailed map yet of the large-scale structures in the universe, including the copious “dark matter” whose identity astronomers are desperate to pin down. Dark matter is invisible, but maps from Pan-STARRS will reveal its landscape by recording how its gravity distorts background galaxies. Then there is the mysterious dark energy. It first came to light in 1998 when astronomers analysed dozens of supernovae and deduced from them that the expansion of
28 | NewScientist | 15 December 2007
the universe is speeding up, not slowing down as previously assumed. Now Pan-STARRS will bag “ridiculous numbers” of supernovae, according to John Tonry from the University of Hawaii’s Institute for Astronomy in Honolulu. The Pan-STARRS 1 telescope will find more than 3000 a month. In Australia, the SkyMapper survey aims to bag up to 50,000 supernovae over five years. That dwarfs the few hundred currently discovered each year by all the world’s telescopes combined. Both projects aim to monitor some of the supernovae as they evolve, but the majority will need follow-up observations by
astronomers elsewhere. “We can just flood the rest of the world with things to look at,” says Tonry. With so many supernovae under the spotlight, astronomers hope to get a much better picture of what triggers these explosions in the first place and tease out any subtle variations (New Scientist, 25 October, p 52). That could in turn fine-tune measurements of dark energy and hopefully shed light on what drives it. Understanding the nature of dark energy will allow astronomers to answer the biggest cosmic question of all: what are the universe’s future expansion plans? Will it expand forever or ultimately collapse in a “big crunch”?
thought of – just weird stuff. When the Hubble Space Telescope was built, it wasn’t exactly clear what it would do but it was pretty obvious it would do something neat, and in fact it has. But the greatest results from HST were never thought of when it was launched.” Beyond Pan-STARRS and SkyMapper, astronomers have plans for an even more ambitious project called the Large Synoptic Survey Telescope (LSST). Operating from around 2014 to 2024, it will be an 8.4-metre telescope on Cerro Pachón in northern Chile. The LSST will be able to map three-quarters of the whole sky over just three nights, generating more than 30 terabytes of image data every night, equivalent to the amount of text in around 30 million books. By 2020, the surveys should together have charted some 20 billion astronomical objects that astronomers can tour at the click of a mouse. That’s pretty much every object that a ground-based telescope could ever see. Effectively, they will end the era Galileo began when he used the first astronomical telescope to spy on Jupiter’s posse of moons. It’s testament to the staggering leaps in computer technology. Astronomers are no longer fazed by handling the 10 terabytes of data that Pan-STARRS 1 will churn out every week. The data rate from Pan-STARRS 4 will be five times that. This is feasible thanks to Moore’s law, the trend for the power of computers to double roughly every two years – more bang for your buck, as it were. “It’s just astonishing that silicon has taken over the universe,” Tonry told the American Astronomical Society. “We think the universe is so vast and yet it’s just a little backyard compared to the intellectual depths that we’re going through in the computer revolution.” “Moore’s law has met the universe,” he added, “and Moore’s law has won.” ● www.newscientist.com