Study: Alien worlds have dry atmospheres
Pastor Dale Morgan
Study: Alien worlds have dry atmospheres*
POSTED: 1812 GMT (0212 HKT), February 21, 2007
Story Highlights
• Astronomers: Two extrasolar planets lack water in their atmospheres
• Two-hundred and thirteen planets have been found outside our solar system
• The study of one extrasolar planet found hints of fine
silicate-particle clouds
• Venus lacks water in its atmosphere, Mercury has no atmosphere
WASHINGTON (AP) -- Scientists taking their first "sniffs of air" from
planets outside our solar system are a bit baffled by what they did not
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.
"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 does not 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.
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 is a mere 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 is the one with the strange
silicate cloud.
So where did 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
is 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, Richardson and other scientists said.