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Latecomer revs up dark energy race
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NASA/ESA/STSCI
This Thisweek– week–
–Receding faster and faster – but why?–
Latecomer revs up dark energy race An unexpected way to probe the mystery of dark energy could tip the balance in bid for mission cash STEPHEN BATTERSBY
A DARK horse has jumped into the race to solve the mystery of dark energy. NASA has given the nod to a radical new method to probe this unknown force, which is causing the expansion of the universe to accelerate. It involves looking for the imprint of primordial sound waves. NASA’s decision to fund the probe, called ADEPT, stirs up the competition. Until now, the frontrunners were missions that planned to study dark energy by looking for ancient supernovae. That’s scarcely surprising, since it was the study of supernovae in the 1990s that led to the discovery 8 | NewScientist | 12 August 2006
of dark energy. Now ADEPT is set to change all that. “ADEPT came along late. It had not been talked about; there were no white papers available describing it,” says Ronald Hellings of Montana State University in Bozeman, NASA’s programme scientist for the Joint Dark Energy Mission (JDEM). JDEM is a collaboration with the US Department of Energy (DoE), designed to plug what is a vast gap in our understanding of the cosmos. Dark energy makes up more than 70 per cent of the total energy density of the universe, dwarfing the contribution of both ordinary matter and dark matter, but its nature is utterly unknown.
The main aim of JDEM would be to find out if dark energy comes from a “cosmological constant” – an energy density inherent to space – or whether its strength varies over time, as some theories predict. Originally, the DoE planned to launch a mission on its own, but having little experience in space it decided to collaborate with NASA. Whereas the DoE had been content with its first-choice mission proposal, the Supernova Acceleration Probe (SNAP), NASA wanted to make a competition of it. “We try to open up to everyone and pick the best concept,” says Hellings. To this end, NASA is now funding development studies for three potential missions under the JDEM umbrella: SNAP, Destiny and ADEPT. Both SNAP and Destiny aim to plot the expansion history of the universe using
“The observations should allow them to plot the universe’s expansion history over the past 10 billion years”
stellar explosions known as type Ia supernovae. These are “standard candles” – that is, each such supernova has about the same intrinsic brightness, so measuring the apparent brightness of hundreds or thousands of them should reveal just how far away they are, which in turn would give a handle on the expansion history of space. The ADEPT probe will not use standard candles, but a standard ruler, in the form of sound waves that permeated the infant cosmos. Because these waves helped trigger the formation of galaxies, the distribution of galaxies today reveals the original pattern of the waves. It was only in 2004 that astronomers measured a repeating pattern of slight excesses of galaxies in the cosmos, with a wavelength of a few 100 million light years, the direct result of the lowest note that rang through the early universe. “It was one of most elegant cosmological measurements made in recent years,” says ADEPT team member Adam Riess of the Space Telescope www.newscientist.com
IN THIS SECTION ● Reversing evolution, page 11 ● How the universe shed its karma, page 12 ● Grouse shooting and climate change, page 14
www.newscientist.com
Escaped golf grass frees gene genie in the US A NONDESCRIPT grass discovered in the Oregon countryside is hardly an alien invasion. Yet the plant – a genetically modified form of a grass commonly grown on golf courses – is worrying the US Department of Agriculture (USDA) enough that it is running its first full environmental impact assessment of a GM plant. It is the first time a GM plant has escaped into the wild in the US, and it has managed it before securing USDA approval. The plant, creeping bentgrass (Agrostis stolonifera), carries a bacterial gene that makes it immune to the potent herbicide glyphosate, better known as Roundup. The manufacturer, The Scotts Company, Marysville, Ohio, is hoping the grass will provide a turf that makes it easier for golf course
“It could prove extremely popular with the thousands of golf course managers in the US, making it easy for it to spread” owners to manage their fairways and greens by letting them kill competing weedy grasses with glyphosate. Jay Reichman and colleagues at the US Environmental Protection Agency’s labs in Corvallis, Oregon, identified nine escapees out of 20,400 plants of various grass varieties sampled within a 4.8-kilometre radius of the site where the bentgrass is being cultivated, the most distant 3.8 kilometres away. The team showed that the GM grass has spread both by pollinating non-GM plants to form hybrids, and by seed movement. Bentgrass is a perennial, so once out there it regrows year after year, whereas most GM crops – mainly soybeans, maize and canola (oilseed rape) – are annuals, unable to reproduce, harvested each year and replaced with an entirely new crop the next. Another worry is that unlike the other GM crops, bentgrass has many relatives in the US with
which it can cross-breed or hybridise, potentially passing on the glyphosate-resistance gene to other species – with unpredictable results. “It’s a cautionary tale of what could happen with other GM plants that could be of greater concern,” says Reichman. “I suspect that more examples of this will show up.” His report will appear in the October issue of Molecular Ecology. If bentgrass is approved by the USDA, it could prove a hit with the thousands of golf course managers throughout the US, making it easy for the crop to spread far and wide. If it reaches environmentally sensitive wildernesses or establishes itself by waterways, removing it could require weedkillers far more harmful than the relatively benign glyphosate. “It’s definitely a new set of variables we’ve not had to deal with in previous GM crops,” says Eric Baack of Indiana University in Bloomington, who comments on Reichman’s findings in Current Biology (vol 16,
p R1). Still, it isn’t clear whether the gene would have much impact in the wild. “You wouldn’t expect the weedkiller-resistance gene to be a particular advantage in the wild,” says Baack. Also, the USDA doesn’t class conventional bentgrass as a “noxious” weed. There is however the possibility of litigation if the GM grass contaminates other elite grass strains under cultivation. Some 70 per cent of the US’s commercial grass seed is grown in Oregon, so there is the potential for accidental adulteration. The USDA is not taking any chances. “This is a perennial, and has wild and weedy relatives, and it’s something we think we need to know the environmental impact of before it’s deregulated,” says a spokeswoman for the USDA’s Biotechnology Regulatory Services in Riverdale, Maryland. “There’s no current set date for when [the environmental impact assessment] will be finished,” she says. Whether the US public takes any notice of the furore is another question entirely. “I don’t think people will worry about lawns and golf courses if they’ve not shown any worries already about GM food,” says Baack. Andy Coghlan ● ALAMY
Science Institute in Maryland. The idea behind ADEPT is to use this wavelength as a standard ruler. Astronomers can calculate how different expansion histories should change the appearance of the ruler as they look further out into the universe. They can then compare the calculations with what they actually observe with ADEPT to arrive at the expansion rate of space at different distances, allowing them to plot the universe’s expansion history over the past 10 billion years. This should betray the nature of the dark energy that drives the expansion. Did acceleration take off steadily, as it would if a cosmological constant were responsible, or a little more sluggishly, as so-called “quintessence” models of dark energy suggest? Or perhaps the acceleration was more violent? The ADEPT team thinks it can pin down these parameters more precisely than any of the other probes. For instance, one parameter labelled w is a measure of how springy dark energy is, and ADEPT could measure it to within 2 per cent, compared with 4 per cent for SNAP and 5 per cent for Destiny. ADEPT could also be more sensitive to changes in w over time. “It’s a promising method,” admits astronomer Tod Lauer of the University of Arizona in Tucson, who leads the rival Destiny team. Given that it is a late entrant, plans for ADEPT are less developed than for the other two probes, but we do know that it would have a larger field of view, so that over the course of the mission it could scan threequarters of the sky to build up a comprehensive picture of the universe’s large-scale structure. However, it is not yet clear if any JDEM probe will actually fly. The money should be available by 2009, but NASA will probably have to choose between JDEM and four other missions: the gravitational wave detector LISA, the X-ray observatory Constellation-X, the Cosmic Inflation Probe and the Black Hole Finder. ●
–Aiming for the green, finding the rough – 12 August 2006 | NewScientist | 9
NASA/ESA/STSCI
This Thisweek– week–
–Receding faster and faster – but why?–
Latecomer revs up dark energy race An unexpected way to probe the mystery of dark energy could tip the balance in bid for mission cash STEPHEN BATTERSBY
A DARK horse has jumped into the race to solve the mystery of dark energy. NASA has given the nod to a radical new method to probe this unknown force, which is causing the expansion of the universe to accelerate. It involves looking for the imprint of primordial sound waves. NASA’s decision to fund the probe, called ADEPT, stirs up the competition. Until now, the frontrunners were missions that planned to study dark energy by looking for ancient supernovae. That’s scarcely surprising, since it was the study of supernovae in the 1990s that led to the discovery 8 | NewScientist | 12 August 2006
of dark energy. Now ADEPT is set to change all that. “ADEPT came along late. It had not been talked about; there were no white papers available describing it,” says Ronald Hellings of Montana State University in Bozeman, NASA’s programme scientist for the Joint Dark Energy Mission (JDEM). JDEM is a collaboration with the US Department of Energy (DoE), designed to plug what is a vast gap in our understanding of the cosmos. Dark energy makes up more than 70 per cent of the total energy density of the universe, dwarfing the contribution of both ordinary matter and dark matter, but its nature is utterly unknown.
The main aim of JDEM would be to find out if dark energy comes from a “cosmological constant” – an energy density inherent to space – or whether its strength varies over time, as some theories predict. Originally, the DoE planned to launch a mission on its own, but having little experience in space it decided to collaborate with NASA. Whereas the DoE had been content with its first-choice mission proposal, the Supernova Acceleration Probe (SNAP), NASA wanted to make a competition of it. “We try to open up to everyone and pick the best concept,” says Hellings. To this end, NASA is now funding development studies for three potential missions under the JDEM umbrella: SNAP, Destiny and ADEPT. Both SNAP and Destiny aim to plot the expansion history of the universe using
“The observations should allow them to plot the universe’s expansion history over the past 10 billion years”
stellar explosions known as type Ia supernovae. These are “standard candles” – that is, each such supernova has about the same intrinsic brightness, so measuring the apparent brightness of hundreds or thousands of them should reveal just how far away they are, which in turn would give a handle on the expansion history of space. The ADEPT probe will not use standard candles, but a standard ruler, in the form of sound waves that permeated the infant cosmos. Because these waves helped trigger the formation of galaxies, the distribution of galaxies today reveals the original pattern of the waves. It was only in 2004 that astronomers measured a repeating pattern of slight excesses of galaxies in the cosmos, with a wavelength of a few 100 million light years, the direct result of the lowest note that rang through the early universe. “It was one of most elegant cosmological measurements made in recent years,” says ADEPT team member Adam Riess of the Space Telescope www.newscientist.com
IN THIS SECTION ● Reversing evolution, page 11 ● How the universe shed its karma, page 12 ● Grouse shooting and climate change, page 14
www.newscientist.com
Escaped golf grass frees gene genie in the US A NONDESCRIPT grass discovered in the Oregon countryside is hardly an alien invasion. Yet the plant – a genetically modified form of a grass commonly grown on golf courses – is worrying the US Department of Agriculture (USDA) enough that it is running its first full environmental impact assessment of a GM plant. It is the first time a GM plant has escaped into the wild in the US, and it has managed it before securing USDA approval. The plant, creeping bentgrass (Agrostis stolonifera), carries a bacterial gene that makes it immune to the potent herbicide glyphosate, better known as Roundup. The manufacturer, The Scotts Company, Marysville, Ohio, is hoping the grass will provide a turf that makes it easier for golf course
“It could prove extremely popular with the thousands of golf course managers in the US, making it easy for it to spread” owners to manage their fairways and greens by letting them kill competing weedy grasses with glyphosate. Jay Reichman and colleagues at the US Environmental Protection Agency’s labs in Corvallis, Oregon, identified nine escapees out of 20,400 plants of various grass varieties sampled within a 4.8-kilometre radius of the site where the bentgrass is being cultivated, the most distant 3.8 kilometres away. The team showed that the GM grass has spread both by pollinating non-GM plants to form hybrids, and by seed movement. Bentgrass is a perennial, so once out there it regrows year after year, whereas most GM crops – mainly soybeans, maize and canola (oilseed rape) – are annuals, unable to reproduce, harvested each year and replaced with an entirely new crop the next. Another worry is that unlike the other GM crops, bentgrass has many relatives in the US with
which it can cross-breed or hybridise, potentially passing on the glyphosate-resistance gene to other species – with unpredictable results. “It’s a cautionary tale of what could happen with other GM plants that could be of greater concern,” says Reichman. “I suspect that more examples of this will show up.” His report will appear in the October issue of Molecular Ecology. If bentgrass is approved by the USDA, it could prove a hit with the thousands of golf course managers throughout the US, making it easy for the crop to spread far and wide. If it reaches environmentally sensitive wildernesses or establishes itself by waterways, removing it could require weedkillers far more harmful than the relatively benign glyphosate. “It’s definitely a new set of variables we’ve not had to deal with in previous GM crops,” says Eric Baack of Indiana University in Bloomington, who comments on Reichman’s findings in Current Biology (vol 16,
p R1). Still, it isn’t clear whether the gene would have much impact in the wild. “You wouldn’t expect the weedkiller-resistance gene to be a particular advantage in the wild,” says Baack. Also, the USDA doesn’t class conventional bentgrass as a “noxious” weed. There is however the possibility of litigation if the GM grass contaminates other elite grass strains under cultivation. Some 70 per cent of the US’s commercial grass seed is grown in Oregon, so there is the potential for accidental adulteration. The USDA is not taking any chances. “This is a perennial, and has wild and weedy relatives, and it’s something we think we need to know the environmental impact of before it’s deregulated,” says a spokeswoman for the USDA’s Biotechnology Regulatory Services in Riverdale, Maryland. “There’s no current set date for when [the environmental impact assessment] will be finished,” she says. Whether the US public takes any notice of the furore is another question entirely. “I don’t think people will worry about lawns and golf courses if they’ve not shown any worries already about GM food,” says Baack. Andy Coghlan ● ALAMY
Science Institute in Maryland. The idea behind ADEPT is to use this wavelength as a standard ruler. Astronomers can calculate how different expansion histories should change the appearance of the ruler as they look further out into the universe. They can then compare the calculations with what they actually observe with ADEPT to arrive at the expansion rate of space at different distances, allowing them to plot the universe’s expansion history over the past 10 billion years. This should betray the nature of the dark energy that drives the expansion. Did acceleration take off steadily, as it would if a cosmological constant were responsible, or a little more sluggishly, as so-called “quintessence” models of dark energy suggest? Or perhaps the acceleration was more violent? The ADEPT team thinks it can pin down these parameters more precisely than any of the other probes. For instance, one parameter labelled w is a measure of how springy dark energy is, and ADEPT could measure it to within 2 per cent, compared with 4 per cent for SNAP and 5 per cent for Destiny. ADEPT could also be more sensitive to changes in w over time. “It’s a promising method,” admits astronomer Tod Lauer of the University of Arizona in Tucson, who leads the rival Destiny team. Given that it is a late entrant, plans for ADEPT are less developed than for the other two probes, but we do know that it would have a larger field of view, so that over the course of the mission it could scan threequarters of the sky to build up a comprehensive picture of the universe’s large-scale structure. However, it is not yet clear if any JDEM probe will actually fly. The money should be available by 2009, but NASA will probably have to choose between JDEM and four other missions: the gravitational wave detector LISA, the X-ray observatory Constellation-X, the Cosmic Inflation Probe and the Black Hole Finder. ●
–Aiming for the green, finding the rough – 12 August 2006 | NewScientist | 9