WASHINGTON - The first "sniffs of air" of two huge far-away planets reveal that they seem to be missing water, a surprising finding amid weather unlike any planets in our solar system with blast furnace-like gusts amid supersonic winds.
The absence of water from the atmosphere of both these Jupiter-sized gaseous bodies upsets one of the most basic assumptions of astronomy.
One of the researchers, Harvard University astronomy professor David Charbonneau, called the planets "very different beasts ... unlike any other planets in the solar system."
So far, scientists have found 213 planets outside our solar system — they are called exoplanets. But only eight or nine are in the right orbit and location for the type of study reported by three teams using
NASA's Spitzer Space Telescope.
The closest of the two planets studied, HD 189733b, is 360 trillion miles from Earth in the constellation Vulpecula. The other planet, HD 209458b, is about 900 trillion miles away in the constellation Pegasus and it has a strange cloud of fine silicate particles. Two different research teams studied it.
The two suns the planets orbit closely have hydrogen and oxygen, the stable building blocks of water. The 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.
"We had expected this tremendous signature of water ... and it wasn't there," said Carl Grillmair of the California Institute of Technology and Spitzer Science Center. He and Charbonneau studied the closer of the two planets, and their work is being published online in The Astrophysical Journal Letters.
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.
But consider the atmosphere on the second of the two exoplanets, the one 900 trillion miles away: "Weather today on 209458 is hot, dry, probably cloudy with a chance of wind," study team leader Mark Swain of NASA's Jet Propulsion Lab said in a Wednesday teleconference.
How hot? Try 1,500 degrees Fahrenheit. How windy? Somewhere between 500 and 2,000 mph.
Another research team found indications that the atmosphere has grains of silicon-oxygen compounds. That team, led by L. Jeremy Richardson of NASA's Goddard Space Flight Center in Maryland, is reporting its research in Thursday's issue of Nature.
But the key finding is dry.
"In NASA's search for life beyond Earth, the mantra has been to follow the water," said Carnegie Institution of Washington astronomer Alan Boss, who wasn't involved in any of the research.
Scientists say it's possible the water is hiding beneath dust clouds or that all the airborne water molecules are 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 very fact that we've been surprised here is a wake-up call. We obviously need to do some more work," Grillmair said.
Charbonneau said these surprising "sniffs of air from an alien world" tell astronomers not to be so Earth-centric in thinking about other planets. "We're limited by our imagination in thinking about the different avenues that these atmospheres take place in," he said.
Swain called the results "a very important stepping stone for our ultimate goal of characterizing planets around other stars where life could exist."
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On the Net:
Spitzer Space Telescope:
http://www.spitzer.caltech.edu/Nature:
http://www.nature.com.
The Astrophysical Journal Letters:
http://www.journals.uchicago.edu/ApJ/rapid.htmlBy SETH BORENSTEIN, AP Science Writer
