Wednesday, April 18, 2007

Getting closer - exo planet with water

We are getting closer to that Exo Earth ... all the time.

Astronomers have detected water in the atmosphere of a planet outside our solar system for the first time.

The finding, to be detailed in an upcoming issue of Astrophysical Journal, confirms previous theories that say water vapor should be present in the atmospheres of nearly all the known extrasolar planets. Even hot Jupiters, gaseous planets that orbit closer to their stars than Mercury to our Sun, are thought to have water.

The discovery, announced today, means one of the most crucial elements for life as we know it can exist around planets orbiting other stars.

“We know that water vapor exists in the atmospheres of one extrasolar planet and there is good reason to believe that other extrasolar planets contain water vapor,” said Travis Barman, an astronomer at the Lowell Observatory in Arizona who made the discovery.

HD209458b is a world well-known among planet hunters. In 1999, it became the first planet to be directly observed around a normal star outside our solar system and, a few years later, was the first exoplanet confirmed to have oxygen and carbon in its atmosphere.

HD209458b is separated from its star by only about 4 million miles (7 million kilometers)—about 100 times closer than Jupiter is to our sun—and is so hot scientists think about it is losing about 10,000 tons of material every second as vented gas.

"Water actually survives over a broad range of temperatures," Barman explained. "It would need to get quite a bit hotter to completely break the water molecules apart."

Using a combination of previously published Hubble Space Telescope measurements and new theoretical models, Barman found strong evidence for water absorption in the atmosphere of the extrasolar planet HD209458b.

Barman took advantage of the fact that HD209458b is a so-called “transiting planet,” meaning it passes directly in front of its star as seen from Earth. It transits every three-and-a-half days.

When this happens, water vapor in the planet’s atmosphere causes the planet to appear slightly larger in the infrared part of the starlight than in the visible portion.

Barman found the water signature after applying new theoretical models he developed to visible and infrared Hubble data collected by Harvard student Heather Knutson last year, which measured the perceived size of the planet over a broad range of wavelengths.

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Other scientist wonder why many exo planets don't have
water - wondering whether they have been to Earth centric.....

Scientists taking their first "sniffs of air" from planets outside our solar system are baffled by what they didn't find: water.

One of the more basic assumptions of astronomy is that the two distant, hot gaseous planets they examined must contain water in their atmospheres. The two suns the planets orbit closely have hydrogen and oxygen, the stable building blocks of water. These planets' atmospheres — examined for the first time using light spectra to determine the air's chemical composition — are supposed to be made up of the same thing, good old H2O.

But when two different teams of astronomers used NASA's Spitzer Space Telescope for this new type of extrasolar planet research, they both came up dry, according to research published in Thursday's edition of Nature and the online version of the Astrophysical Journal Letters.

The study of one planet found hints of fine silicate-particle clouds. Research on the other planet found no chemical fingerprints for any of the molecules scientists were seeking.

Approach too ‘Earth-centric’
"We had expected this tremendous signature of water ... and it wasn't there," said the study leader for one team, Carl Grillmair of the California Institute of Technology and Spitzer Science Center. "The very fact that we've been surprised here is a wake-up call. We obviously need to do some more work."

Grillmair's colleague, Harvard astronomy professor David Charbonneau, said these surprising "sniffs of air from an alien world" tell astronomers not to be so Earth-centric in thinking about other planets.

"These are very different beasts. These are unlike any other planets in the solar system," Charbonneau said. "We're limited by our imagination in thinking about the different avenues that these atmospheres take place in."

Our own solar system has two planets without water in the atmosphere, Grillmair noted: Mercury, which doesn't have an atmosphere, and Venus, which is a different type of planet from the huge gaseous ones that would be expected to have the components of water in the air.

Water may be hiding, scientists suggest
So far, scientists have found 213 planets outside our solar system, but only 14 have orbits that make it possible for this type of study; only eight or nine of those are close enough to see. Grillmair's team studied the closest, which goes by the catchy name HD 189733b. It's a mere 360 trillion miles from Earth in the constellation Vulpecula. The other planet, HD209458b, is about 900 trillion miles away in the constellation Pegasus, and it's the one with the strange silicate cloud.

So where'd the water go?

Maybe it's hiding, scientists suggest. The water could be under dust clouds, or all the airborne water molecules have the same temperature, making it impossible to see using an infrared spectrograph. Or maybe it's just not there and astronomers have to go back to the drawing board when it comes to these alien planets.

The other finding on the more distant of the two planets seems to indicate that the atmosphere is full of silicon-oxygen compounds, said study lead author L. Jeremy Richardson of NASA's Goddard Space Flight Center.

"They'd be like dust grains and they would form clouds," Richardson said. And that cloud of silicates could be blocking the space telescope from measuring lower-lying water, he and other scientists said.

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