Science News and Notes
Thursday, November 13, 2008
Now in Sight: Far-Off Planets
NYT 14Nov2008-Dennis Overbye
A little more of the universe has been pried out of the shadows. Two groups of astronomers have taken the first pictures of what they say — and other astronomers agree — are most likely planets going around other stars. The achievement, the result of years of effort on improved observational techniques and better data analysis, presages more such discoveries, the experts said, and will open the door to new investigations and discoveries of what planets are and how they came to be formed.
“It’s the tip of iceberg,” said Christian Marois of the Herzberg Institute of Astrophysics in Victoria, British Columbia. “Now that we know they are there, there is going to be an explosion.” Dr. Marois is the leader of a team that recorded three planets circling a star known as HR 8799 that is 130 light-years away in the constellation Pegasus. The other team, led by Paul Kalas of the University of California, Berkeley, found a planet orbiting the star Fomalhaut, only 25 light-years from Earth, in the constellation Piscis Austrinus.
In an interview by e-mail, Dr. Kalas said that when he finally confirmed his discovery last May, “I nearly had a heart attack.” In scratchy telescope pictures released Thursday in Science Express, the online version of the journal Science, the planets appear as fuzzy dots that move slightly around their star from exposure to exposure. Astronomers who have seen the new images agreed that these looked like the real thing.
“I think Kepler himself would recognize these as planets orbiting a star following his laws of orbital motion,” Mark S. Marley of the Ames Research Center in Mountain View, Calif., wrote in an e-mail message elaborating on HR 8799. More than 300 so-called extrasolar planets have been found circling distant stars, making their discovery the hottest and fastest-growing field in astronomy. But the observations have been made mostly indirectly, by dips in starlight as planets cross in front of their home star or by wobbles they induce going by it. Astronomers being astronomers, they want to actually see these worlds, but a few recent claims of direct observations have been clouded by debates about whether the bodies were really planets or failed stars. “Every extrasolar planet detected so far has been a wobble on a graph,” said Bruce Macintosh, an astrophysicist from Lawrence Livermore National Laboratory in California and a member of Dr. Marois’s team. “These are the first pictures of an entire system.”
The new planetary systems are anchored by young bright stars more massive than our own Sun and swaddled in large disks of dust, the raw material of worlds. The three planets orbiting HR 8799 are roughly 10, 9 and 6 times the mass of Jupiter, and orbit their star in periods of 450, 180 and 100 years respectively, all counterclockwise. The Fomalhaut planet is about three times as massive as Jupiter, according to Dr. Kalas’s calculations, and is on the inner edge of a huge band of dust, taking roughly 872 years to complete a revolution of its star. Both systems appear to be scaled-up versions of our own solar system, with giant planets in the outer reaches, leaving plenty of room for smaller planets to lurk undetected in the warmer inner regions. Dust rings lie even farther out, like the Kuiper belt of icy debris extending beyond the orbit of Neptune.
“This is a window into what our own solar system might have looked like when it was 60 million years old,” Dr. Marois said. Sara Seager, a planetary theorist at the Massachusetts Institute of Technology, said it was significant that the planets in both cases seemed to be associated with disks of dust, particularly Fomalhaut, one of the brightest and closest stars known to be host to a massive disk. “Fomalhaut is like a Hollywood star to astronomers, so we have some personal excitement here,” Dr. Seager said. “It feels like finding out that one of your four closest friends just won the lottery big time” Alan Boss, a planetary theorist at the Carnegie Institution of Washington, said the triple-planet system in Pegasus was particularly promising, “as we expect planets to form in systems in general, whereas spurious background interlopers will generally appear as single ‘planets.’ ” But he and others cautioned that much more study of these objects was necessary and that the masses imputed to them were still highly uncertain. Being able to see planets directly opens the door to spectroscopic observations that can help determine the composition, temperature and other physical characteristics of planets and allow for comparisons with one another and with their parent stars. Dr. Macintosh said he hoped to train a spectroscope on his new planets as early as Monday.
The new images are the fruits of a long campaign by astronomers to see more and more of the unseeable. In particular, it is a triumph for the emerging technology of adaptive optics, in which telescope mirrors are jiggled and warped slightly many times a second to compensate for the atmospheric turbulence that blurs star images. The problem in seeing other planets is picking them out of the glare of their parent stars, which are millions of times brighter, at least in visible light. As a result, planet hunters usually look for infrared, or heat radiation, which is emitted copiously by planets still shedding heat from the process of formation. For their observations, Dr. Marois and his colleagues used the 8-meter in diameter Gemini North and the 10-meter Keck telescopes on Mauna Kea in Hawaii, both of which had been fitted with adaptive optics. Then they processed the images with a special computer program, which Dr. Marois described as “a software coronagraph,” for processing the images. The team first spied a pair of dots about four billion and six billion miles out from HR 8799 in October last year. Following up, they discovered a third planet closer in, at about two billion miles. Then they discovered an old observation from 2004, which also showed the planets and how far they had moved around the star in three years. “Seeing the orbit is one of the coolest things,” Dr. Macintosh said.
Dr. Kalas did his work with the Hubble Space Telescope, which is immune to turbulence because it is in space. He used a coronagraph to block light from the actual star. He said he had been driven to look for a planet around Fomalhaut after Hubble photographs in October 2004 showed that a dust ring around the star had a suspiciously sharp inner edge, often a clue that the ring is being sculpted by the gravity of some body orbiting nearby. A second set of Hubble observations, in July 2006, revealed a dot moving counterclockwise around the star. “I basically held my breath for three days until I could confirm the existence of Fomalhaut in all of my data,” Dr. Kalas recalled.
Fomalhaut is also a young star, about 200 million years old, and its dust ring extends 11 billion to 20 billion miles from its planet, Dr. Kalas said. In order not to disturb or roil the dust ring, Fomalhaut’s planet must be less than three Jupiter masses, well within regulation planet size, Dr. Kalas and his collaborators calculated. A more detailed analysis, with another team member, Eugene Chiang of the University of California, Berkeley, as lead author will appear in the Astrophysical Journal, Dr. Kalas said. In an e-mail message, Dr. Kalas pointed out that Fomalhaut was the closest exoplanet yet discovered, “close enough to contemplate sending spacecraft there.”
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Report Sees New Pollution Threat
- Andrew Jacobs NYT November 14, 2008
BEIJING — A noxious cocktail of soot, smog and toxic chemicals is blotting out the sun, fouling the lungs of millions of people and altering weather patterns in large parts of Asia, according to a report released Thursday by the United Nations. The byproduct of automobiles, slash-and-burn agriculture, cooking on dung or wood fires and coal-fired power plants, these plumes rise over southern Africa, the Amazon basin and North America. But they are most pronounced in Asia, where so-called atmospheric brown clouds are dramatically reducing sunlight in many Chinese cities and leading to decreased crop yields in swaths of rural India, say a team of more than a dozen scientists who have been studying the problem since 2002. “The imperative to act has never been clearer,” said Achim Steiner, executive director of the United Nations Environment Program, in Beijing, which the report identified as one of the world’s most polluted cities, and where the report was released.
The brownish haze, sometimes in a layer more than a mile thick and clearly visible from airplanes, stretches from the Arabian Peninsula to the Yellow Sea. In the spring, it sweeps past North and South Korea and Japan. Sometimes the cloud drifts as far east as California. The report identified 13 cities as brown-cloud hot spots, among them Bangkok, Cairo, New Delhi, Tehran and Seoul, South Korea.
It was issued on a day when Beijing’s own famously polluted skies were unusually clear. On Wednesday, by contrast, the capital was shrouded in a thick, throat-stinging haze that is the byproduct of heavy industry, coal-burning home heaters and the 3.5 million cars that clog the city’s roads. Last month, the government reintroduced some of the traffic restrictions that were imposed on Beijing during the Olympics; the rules forced private cars to stay off the road one day a week and sidelined 30 percent of government vehicles on any given day. Over all, officials say the new measures have removed 800,000 cars from the roads.
According to the United Nations report, smog blocks from 10 percent to 25 percent of the sunlight that should be reaching the city’s streets. The report also singled out the southern city of Guangzhou, where soot and dust have dimmed natural light by 20 percent since the 1970s. In fact, the scientists who worked on the report said the blanket of haze might be temporarily offsetting some warming from the simultaneous buildup of greenhouse gases by reflecting solar energy away from the earth. Greenhouse gases, by contrast, tend to trap the warmth of the sun and lead to a rise in ocean temperatures.
Climate scientists say that similar plumes from industrialization of wealthy countries after World War II probably blunted global warming through the 1970s. Pollution laws largely removed that pall.
Rain can cleanse the skies, but some of the black grime that falls to earth ends up on the surface of the Himalayan glaciers that are the source of water for billions of people in China, India and Pakistan. As a result, the glaciers that feed into the Yangtze, Ganges, Indus and Yellow Rivers are absorbing more sunlight and melting more rapidly, researchers say.
According to the Chinese Academy of Sciences, these glaciers have shrunk by 5 percent since the 1950s and, at the current rate of retreat, could shrink by an additional 75 percent by 2050. “We used to think of this brown cloud as a regional problem, but now we realize its impact is much greater,” said Veerabhadran Ramanathan, who led the United Nations scientific panel. “When we see the smog one day and not the next, it just means it’s blown somewhere else.” Although the clouds’ overall impact is not entirely understood, Mr. Ramanathan, a professor of climate and ocean sciences at the University of California, San Diego, said they might be affecting precipitation in parts of India and Southeast Asia, where monsoon rainfall has been decreasing in recent decades, and central China, where devastating floods have become more frequent. He said that some studies suggested that the plumes of soot that blot out the sun have led to a 5 percent decline in the growth rate of rice harvests across Asia since the 1960s.
For those who breathe the toxic mix, the impact can be deadly. Henning Rodhe, a professor of chemical meteorology at Stockholm University, estimates that 340,000 people in China and India die each year from cardiovascular and respiratory diseases that can be traced to the emissions from coal-burning factories, diesel trucks and wood-burning stoves. “The impacts on health alone is a reason to reduce these brown clouds,” he said.
-- Andrew C. Revkin contributed reporting from New York.
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