The race is on to discover a second Earth
IN 1995, when Michel Mayor of the University of Geneva detected the first exoplanet (a planet that orbits a star other than the sun) he started a race that has gained pace ever since. Some 360 such planets have now been detected, but none is exactly equivalent to the Earth.
The closest so far is Gliese 581c, which was discovered in 2007 by Dr Mayor’s colleague, Stéphane Udry. It is both rocky and orbits its parent star at a distance where liquid water could reasonably be expected to exist. However, since its parent star is a red dwarf—a far smaller and fainter object than the sun—that orbit is, in fact, much smaller that the Earth’s around the sun. That, in turn, suggests Gliese 581c is likely to be tidally locked to its orbital period, so that one side of the planet always faces the star and the other never does. Having half a planet in permanent daylight and the other half in permanent darkness does not sound like a good recipe for life.
As astronomers heard this week at the International Astronomical Union meeting in Rio, two new missions—a French one launched in December 2006 and an American one launched on March 6th—are in the process of trying to add to the list. Dr Mayor told the meeting that the French mission, CoRoT, has now found 80 exoplanets. It does so by watching for small diminutions in the amount of light from a star as the planet in question passes in front of it, a phenomenon known technically as a transit. The details of all but seven of these transiting planets are still unpublished, but Dr Mayor gave the meeting a preview.
The planets discovered so far by CoRoT typically have a mass that is less than 30 times that of Earth, making them likely to have a solid, rocky surface. But they also orbit their stars rapidly, typically taking two or three months, rather than a year, to do so. For those who hanker after extraterrestrial life that is a pity. Such rapid orbits mean the planets in question are close to their parent stars, and thus likely to be tidally locked.
Other news from CoRoT is better, though. Some 80% of the planets Dr Mayor has found have siblings. The existence of so many neighbours suggests that planetary systems tend to be stable, and stability is good for the evolution of life. Dr Mayor described a system he has seen that has five rocky planets in it. They have masses of 11, 14, 26, 27 and 76 times that of the Earth. He concluded his talk by saying, “I am really confident that we have an Earth-like planet coming in the next two years.”
He and his team may, however, be pipped at the post. On August 6th America’s space agency, NASA, announced that its Kepler planet-detector (named after the man who worked out the laws of planetary motion, as this article explains) is also behaving well. A paper published in Science by William Borucki of the NASA Ames Research Centre based in Moffett Field, California, and his colleagues showed that Kepler, which also uses the transit-detection technique, has confirmed the existence of a Jupiter-like planet
discovered in 2007 and provided more precise details of that planet’s mass and orbital period. And Kepler’s instruments are more sensitive than CoRoT’s, so it should be capable of finding Earth-sized planets more easily than its French cousin.
Yet such space probes are not the only way of searching for other Earths. As part of his efforts to find new worlds, Dr Mayor is using the HARPS spectrograph, which is based at the European Southern Observatory in La Silla, Chile. He and his colleagues are training HARPS on ten nearby, bright and quiet stars three times a night, for 15 minutes at a time, for 50 nights a year, for at least two years, in the hope of spotting a nearby Earth-sized planet. The device works by detecting the tiny wobble given to a parent star when a planet passes it by. The spectrograph has already found 16 planets.
Meanwhile, David Bennett of the University of Notre Dame in Indiana wants to use a technique called gravitational microlensing to spot planets that might be missed by other methods. He told the conference that his approach would pick up not only small rocky planets orbiting at great distances from their parent stars, but also planets that had been ejected from their orbits. The idea would be to stare at a distant star and report instances when its light had been bent by the gravity of a planet passing in front of it. Such signals would be brief and rare, but they would also be strong and unmistakable. Sooner or later, then, an Earth-sized planet will turn up. How Earth-like it will be in other ways, remains to be seen.
Source of Information : The Economist August 15 2009
Showing posts with label Astronomy. Show all posts
Showing posts with label Astronomy. Show all posts
Wednesday, September 9, 2009
Monday, September 7, 2009
Galaxies in the early universe - Rocking the cradle
The discovery of some massive infants forces a rethink of galactic evolution
IN THE crazy world of Dr Seuss, an American children’s author, a bird called a Pelf lays eggs that are three times as big as herself. At this week’s meeting of the International Astronomical Union, astronomers were asked to entertain equally odd thoughts when they were presented with the latest evidence that some early galaxies, although smaller than their more recent counterparts, contain much more mass. It is like being handed a baby that weighs three times as much as its mother.
The objects in question are “red compact” galaxies, in particular a well-studied one called 1255-0 that formed just 3 billion years after the Big Bang. As the universe is thought to be 13.7 billion years old, the light reaching Earth from this galaxy shows what it was like some 10.7 billion years ago, when it was the equivalent of a newborn. Images suggest that the galaxy is 3,000 light years across—just a fifth of the size of the Earth’s home galaxy, the Milky Way—but about four times as massive.
To check how compact 1255-0 really was, a group of astronomers led by Pieter van Dokkum of Yale University analysed the speed at which its stars were moving. The researchers reasoned that if it really was as small and as massive as it appeared, those stars would be whizzing round its centre at high velocity.
They were able to calculate the speed of the stars in question using the Doppler effect—the change in frequency, and thus in colour, that a light wave undergoes according to whether the thing that emitted it is moving towards or away from the observer. (The changing pitch of an ambulance siren is the equivalent effect for sound.) The Doppler shifts of the light from different parts of 1255-0 showed Dr van Dokkum and his colleagues that the average orbital velocity of this galaxy’s stars was 510 kilometres a second, the highest value ever recorded. This suggests that previous estimates of its size and mass are right.
Growing and shrinking
Red compact galaxies are thought to evolve by growing into blob-shaped galaxies called ellipticals, which are common today, and there are also several of these near 1255-0. Although ellipticals are bigger than red compacts, they are usually less massive. That makes the process of transition from one to the other problematic. Mergers are ruled out. Though they would make the babies bigger, they would also make them heavier, rather than lighter. The shock involved would create new, younger stars as well, and these do not appear to be there.
One possibility discussed at the meeting is whether the distribution in space of dark matter might help explain what happens. It may be that the red compacts are heavy not because they contain more stars but because they contain more of this substance, whose nature remains unknown, but which can be detected by its gravitational effects, and which seems to be about six times as abundant as the familiar matter of atoms and molecules. Yet this explanation is not terribly satisfactory either. Existing observations suggest that dark matter was smoothly distributed around elliptical galaxies by some 8 billion or 9 billion years ago. If extra dark matter is what is making earlier galaxies particularly massive, then something must have happened to redistribute the stuff between 10 billion years ago (when it clumped together in baby galaxies) and 9 billion years ago (by which time it was no longer lumpy).
That something would have to have been strange indeed, though—possibly a shift in the value of a fundamental constant such as the speed of light—to have caused compact galaxies to inflate while losing weight. Dr Seuss’s hero never did find out how the Pelf learned to pull off her egg-laying trick. Perhaps astronomers will have better luck.
Source of Information : The Economist August 15 2009
IN THE crazy world of Dr Seuss, an American children’s author, a bird called a Pelf lays eggs that are three times as big as herself. At this week’s meeting of the International Astronomical Union, astronomers were asked to entertain equally odd thoughts when they were presented with the latest evidence that some early galaxies, although smaller than their more recent counterparts, contain much more mass. It is like being handed a baby that weighs three times as much as its mother.
The objects in question are “red compact” galaxies, in particular a well-studied one called 1255-0 that formed just 3 billion years after the Big Bang. As the universe is thought to be 13.7 billion years old, the light reaching Earth from this galaxy shows what it was like some 10.7 billion years ago, when it was the equivalent of a newborn. Images suggest that the galaxy is 3,000 light years across—just a fifth of the size of the Earth’s home galaxy, the Milky Way—but about four times as massive.
To check how compact 1255-0 really was, a group of astronomers led by Pieter van Dokkum of Yale University analysed the speed at which its stars were moving. The researchers reasoned that if it really was as small and as massive as it appeared, those stars would be whizzing round its centre at high velocity.
They were able to calculate the speed of the stars in question using the Doppler effect—the change in frequency, and thus in colour, that a light wave undergoes according to whether the thing that emitted it is moving towards or away from the observer. (The changing pitch of an ambulance siren is the equivalent effect for sound.) The Doppler shifts of the light from different parts of 1255-0 showed Dr van Dokkum and his colleagues that the average orbital velocity of this galaxy’s stars was 510 kilometres a second, the highest value ever recorded. This suggests that previous estimates of its size and mass are right.
Growing and shrinking
Red compact galaxies are thought to evolve by growing into blob-shaped galaxies called ellipticals, which are common today, and there are also several of these near 1255-0. Although ellipticals are bigger than red compacts, they are usually less massive. That makes the process of transition from one to the other problematic. Mergers are ruled out. Though they would make the babies bigger, they would also make them heavier, rather than lighter. The shock involved would create new, younger stars as well, and these do not appear to be there.
One possibility discussed at the meeting is whether the distribution in space of dark matter might help explain what happens. It may be that the red compacts are heavy not because they contain more stars but because they contain more of this substance, whose nature remains unknown, but which can be detected by its gravitational effects, and which seems to be about six times as abundant as the familiar matter of atoms and molecules. Yet this explanation is not terribly satisfactory either. Existing observations suggest that dark matter was smoothly distributed around elliptical galaxies by some 8 billion or 9 billion years ago. If extra dark matter is what is making earlier galaxies particularly massive, then something must have happened to redistribute the stuff between 10 billion years ago (when it clumped together in baby galaxies) and 9 billion years ago (by which time it was no longer lumpy).
That something would have to have been strange indeed, though—possibly a shift in the value of a fundamental constant such as the speed of light—to have caused compact galaxies to inflate while losing weight. Dr Seuss’s hero never did find out how the Pelf learned to pull off her egg-laying trick. Perhaps astronomers will have better luck.
Source of Information : The Economist August 15 2009
Sunday, September 6, 2009
The future of astronomy - Black-sky thinking
SINCE time immemorial man has looked at the stars in awe and wonderment. No longer. The observatories where light is collected are now run by robots that neither dirty the instruments nor take night-time naps. Does it matter? Some of the astronomers at this year’s meeting of the International Astronomical Union (IAU), held in Rio de Janeiro from August 3rd to 14th, think it does. They discussed what could be done to halt their subject’s trend towards mining data gathered by computers rather than peering into telescopes.
The Rio meeting is the high point of what has been dubbed by the union as the International Year of Astronomy. The reason for picking 2009 to receive this honour is that it is exactly 400 years since Galileo Galilei turned his telescope on the heavens to study what the naked eye could not disclose, and also since Johannes Kepler revealed to the world that planetary orbits are ellipses, not circles. These two events can be seen, in retrospect, as the beginning of modern astronomy.
The pace of discovery has not slowed down. Indeed, more than one participant in the meeting described the present as a “golden age”. The rate of discoveries has been increasing, along with the means to keep up with the details. That has, in turn, led to bigger and more expensive telescopes, and the introduction of management techniques intended to ensure the smooth running of large projects. But it is that managerialism that is beginning to worry some of the more thoughtful members of the union. They fear that although it brings short-term benefits, it may, in the long run, crush individual flair.
Simon White of the Max Planck Institute for Astrophysics in Garching, Germany, is one such worrier. He observes that in the 19th century and for most of the 20th, too, scientific progress usually came from brilliant individuals formulating and testing hypotheses using data accumulated by relatively modest means.
Big science has its place, of course. For one thing, enormous amounts of data allow subtle effects to be detected statistically. But Dr White suggests astronomers should ensure small science can flourish alongside its larger counterpart by, for example, ensuring that telescopes designed to look for big fish can also be used for projects that might be considered as small fry.
Thinking space
Another way to encourage gifted individuals might be to reform the way time on telescopes is allocated. The IAU’s new president, Robert Williams of the Space Telescope Science Institute in Baltimore, Maryland, is a supporter of this idea. He reckons decisions about who gets what observing time should be made by the directors of observatories, answerable to a governing body, rather than by groups of the great and good, as tends to happen now.
“High-risk, high-reward projects require hard decisions that are best made by individuals, not committees,” he says. And he should know. As director of the Space Telescope Science Institute he was, in 1995, allocated ten days on Hubble (pictured above), America’s most famous eye in the sky. Instead of using that time on a project with a preordained objective, he asked, in what might be seen as an act of either modesty or bravura, that the telescope be pointed at a typical patch of sky and left there for the whole period, to see what it could see.
The result was the Hubble Deep Field, a fantastically detailed image of a small region in a constellation called Ursa Major. The field of view is so narrow that only about 20 stars from the Milky Way, the galaxy in which the Earth resides, lie within it. What it shows instead is almost 3,000 galaxies, some of which are the most distant (and hence the youngest) ever observed. The image demonstrates that the universe is, indeed, uniform over large scales and that the Earth occupies a typical region of it. It is unlikely that a committee would have had the guts to allocate so much time to what was a speculative punt.
Yet despite the professed desire of some to do so, astronomers cannot turn their backs on big science. In particular, to see faint, distant objects at the dawn of time, as Dr Williams did with Hubble, you need to collect a lot of light. That means your telescopes need big mirrors. And big mirrors do not come cheap.
Back on Earth, the biggest mirrors in prospect belong to three telescopic projects that will, by coincidence, all come to fruition in 2018, if their backers get their way. The Giant Magellan Telescope, a joint effort by America, Australia and South Korea that is to be built in the Atacama Desert in Chile, would have seven mirrors, each 8.4 metres across, giving an effective diameter of 25 metres. An even larger beast, dubbed the Thirty Metre Telescope, for obvious reasons, is a collaboration between American and Canadian universities. It has been on the drawing board since 1990. Last month its project board announced that, if funding were forthcoming, it would be built on Mauna Kea in Hawaii.
The third, the European Extremely Large Telescope, is the suggested replacement for the Overwhelmingly Large Telescope, a proposal rejected by the European Southern Observatory three years ago when it discovered that the bill would also be overwhelmingly large. Its mirror would be 42 metres across, and it would probably be built either on one of the Canary Islands or in Chile.
Besides these new conventional telescopes, completely novel ways of doing Big Astronomy are likely to emerge to tempt astronomers back into its clutches. Several projects are already under way to detect gravitational waves—ripples in the fabric of spacetime itself—although none has yet caught its quarry. Should they, or their successors, eventually do so, it would open up a new window on the universe, allowing astronomers to study massive objects such as colliding black holes in unprecedented detail.
Astrophysicists have also begun to be able to detect the directions from which streams of subatomic particles called neutrinos arrive, and progress is being made as well on interpreting cosmic rays. Once these are better understood, astronomers could use them to study the universe in the way they now use light and radio waves.
Yet astronomers are still right to want space for the small. The two most exciting recent findings—the discovery of “dark energy”, which pushes space itself apart, and of planets beyond the solar system—were made using modest equipment. It is the very success of the small that promotes the growth of the big.
Source of Information : The Economist August 15 2009
The Rio meeting is the high point of what has been dubbed by the union as the International Year of Astronomy. The reason for picking 2009 to receive this honour is that it is exactly 400 years since Galileo Galilei turned his telescope on the heavens to study what the naked eye could not disclose, and also since Johannes Kepler revealed to the world that planetary orbits are ellipses, not circles. These two events can be seen, in retrospect, as the beginning of modern astronomy.
The pace of discovery has not slowed down. Indeed, more than one participant in the meeting described the present as a “golden age”. The rate of discoveries has been increasing, along with the means to keep up with the details. That has, in turn, led to bigger and more expensive telescopes, and the introduction of management techniques intended to ensure the smooth running of large projects. But it is that managerialism that is beginning to worry some of the more thoughtful members of the union. They fear that although it brings short-term benefits, it may, in the long run, crush individual flair.
Simon White of the Max Planck Institute for Astrophysics in Garching, Germany, is one such worrier. He observes that in the 19th century and for most of the 20th, too, scientific progress usually came from brilliant individuals formulating and testing hypotheses using data accumulated by relatively modest means.
Big science has its place, of course. For one thing, enormous amounts of data allow subtle effects to be detected statistically. But Dr White suggests astronomers should ensure small science can flourish alongside its larger counterpart by, for example, ensuring that telescopes designed to look for big fish can also be used for projects that might be considered as small fry.
Thinking space
Another way to encourage gifted individuals might be to reform the way time on telescopes is allocated. The IAU’s new president, Robert Williams of the Space Telescope Science Institute in Baltimore, Maryland, is a supporter of this idea. He reckons decisions about who gets what observing time should be made by the directors of observatories, answerable to a governing body, rather than by groups of the great and good, as tends to happen now.
“High-risk, high-reward projects require hard decisions that are best made by individuals, not committees,” he says. And he should know. As director of the Space Telescope Science Institute he was, in 1995, allocated ten days on Hubble (pictured above), America’s most famous eye in the sky. Instead of using that time on a project with a preordained objective, he asked, in what might be seen as an act of either modesty or bravura, that the telescope be pointed at a typical patch of sky and left there for the whole period, to see what it could see.
The result was the Hubble Deep Field, a fantastically detailed image of a small region in a constellation called Ursa Major. The field of view is so narrow that only about 20 stars from the Milky Way, the galaxy in which the Earth resides, lie within it. What it shows instead is almost 3,000 galaxies, some of which are the most distant (and hence the youngest) ever observed. The image demonstrates that the universe is, indeed, uniform over large scales and that the Earth occupies a typical region of it. It is unlikely that a committee would have had the guts to allocate so much time to what was a speculative punt.
Yet despite the professed desire of some to do so, astronomers cannot turn their backs on big science. In particular, to see faint, distant objects at the dawn of time, as Dr Williams did with Hubble, you need to collect a lot of light. That means your telescopes need big mirrors. And big mirrors do not come cheap.
Back on Earth, the biggest mirrors in prospect belong to three telescopic projects that will, by coincidence, all come to fruition in 2018, if their backers get their way. The Giant Magellan Telescope, a joint effort by America, Australia and South Korea that is to be built in the Atacama Desert in Chile, would have seven mirrors, each 8.4 metres across, giving an effective diameter of 25 metres. An even larger beast, dubbed the Thirty Metre Telescope, for obvious reasons, is a collaboration between American and Canadian universities. It has been on the drawing board since 1990. Last month its project board announced that, if funding were forthcoming, it would be built on Mauna Kea in Hawaii.
The third, the European Extremely Large Telescope, is the suggested replacement for the Overwhelmingly Large Telescope, a proposal rejected by the European Southern Observatory three years ago when it discovered that the bill would also be overwhelmingly large. Its mirror would be 42 metres across, and it would probably be built either on one of the Canary Islands or in Chile.
Besides these new conventional telescopes, completely novel ways of doing Big Astronomy are likely to emerge to tempt astronomers back into its clutches. Several projects are already under way to detect gravitational waves—ripples in the fabric of spacetime itself—although none has yet caught its quarry. Should they, or their successors, eventually do so, it would open up a new window on the universe, allowing astronomers to study massive objects such as colliding black holes in unprecedented detail.
Astrophysicists have also begun to be able to detect the directions from which streams of subatomic particles called neutrinos arrive, and progress is being made as well on interpreting cosmic rays. Once these are better understood, astronomers could use them to study the universe in the way they now use light and radio waves.
Yet astronomers are still right to want space for the small. The two most exciting recent findings—the discovery of “dark energy”, which pushes space itself apart, and of planets beyond the solar system—were made using modest equipment. It is the very success of the small that promotes the growth of the big.
Source of Information : The Economist August 15 2009
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