Next: A color portrait
A true-color painting of the planet may soon be possible.
Charbonneau and Brown are now using Hubble to examine faint starlight reflected
off the planet just as it passes behind the edge of its star. The results, based
on a barely measurable amount of starlight, could reveal the color and reflectivity
of the planet and indicate whether clouds of dust or metallic elements might
be present.
Computers have made conflicting predictions of what the planet ought to look
like, based on what's known about its size and distance from the star.
"In some computer models, this planet is blacker than coal," said Brown. "In
others, it's bright white, like Venus. Only observations can tell us what's
real."
In detecting sodium, the astronomers actually saw less of it than predicted.
They figure high-altitude clouds in the alien atmosphere may have blocked some
of the light, reflecting it back into space.
"That should encourage those astronomers using related techniques to seek reflected-light
detections that it's worth keeping on digging," said Cameron, the St. Andrews
researcher.
By developing the technique further, Charbonneau and Brown think it could one
day be used to detect chemicals that are only produced as a result of biological
activity -- when life is present. Thus, they say, ET might be found not by visiting
a planet that can't even be seen directly, but by detecting the chemicals emitted
by ET or the things he eats.
Meanwhile, more modest goals are in order.
They have a proposal in to use Hubble next year to search the same planet for
water vapor, carbon monoxide and methane. The latter could be used to pin down
the planet's temperature.
The real goal: Another Earth
Several research groups hunt exoplanets and attempt to study their atmospheres.
The overall goal is to ultimately find potentially habitable planets and probe
them for signs of life.
"Suddenly, discussing searches for Earth-like planets seems quite reasonable,"
Charbonneau said Tuesday.
An actual discovery of another Earth is likely to be a few years away, however.
"But we have a pretty good idea of how to get there," Cameron told SPACE.com. "We may see transits of Earth-sized planets using space-based photometry missions such as NASA's Kepler or the European Space Agency's Eddington within a decade if all goes well."
Studying the atmospheres of possibly habitable planets presents more challenges, however.
Brown said Kepler might be used for this purpose. But other scientists say the effort would require advanced flotillas of spacecraft that operate in concert to effectively create one large telescope. The technique, called interferometry, is only now being perfected on Earth.
NASA has not yet committed to building a space-based interferometer, but an early model that would test the concept under a limited budget, a craft dubbed StarLight, could fly in 2006 if funding comes through.
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