It looks pretty conclusive:
"We're thrilled to have identified clear signs of water on a planet that is trillions of miles away," said study leader Giovanna Tinetti of the Institut d'Astrophysique de Paris in France.
Called HD 189733b, the planet belongs to a class of gas giants called "hot Jupiters," which orbit their stars from a distance closer than Mercury is to our sun.
With average temperatures over 1300 degrees Fahrenheit (more than 700 Celsius), it's unlikely that this planet supports any life -- water or no water. Still, if there's water on one planet out there, it's looking more likely that there will be water on others. From the example of our own solar system, we know that some (perhaps most?) planetary systems include both gas giants and little rocky planets. And we know that there are little rocky planets out there, that such bodies are not unique to our own neighborhood. It's a matter of time, now, before we find the first little rocky planet with water, a nice distance from its sun. That will be quite a discovery.
Discovering a new planet used to be a big deal. But now that we've found anywhere between 212 and 247 new planets (depending on whom you ask) and we can only suppose that there are trillions upon trillions of them out there. The recent demotion of one of the original nine was treated as a much more significant news story than the discovery of any of the subsequent 200-plus.
To recapture the imagination of a planet-jaded public, we're going to have to find life out there. We're getting closer to having that capability all the time:
In [a] previous study, the scientists looked for spectral absorption lines created by radiation traveling up from the interior of the planet and passing through layers of cool gas that selectively absorb certain wavelengths of light.
Without a temperature difference, no absorption occurs.
In the new study, the researchers observed HD 189733b as it passed in front of, or "transited," its parent star.
Using Spitzer's infrared camera, the team analyzed light that was emitted from the interior of the parent star and which passed through the planet's atmosphere on its way to Earth.
In this case, absorption occurs because of the temperature difference that exists between the star's atmosphere and that of the planet.
We discovered extrasolar planets by observing the stars they orbit and extrapolating -- when a star wobbles just so, we know that a planet is out there tugging on it. Getting a hint as to what that planet is made of is a big step forward, but we're still figuring out what we can about the planets by looking at the stars. This is like trying to describe the fish based on the way it tugs on the fishing line.
There are a number of initiatives underway that will help us to continue to improve our understanding of extrasolar planets. And one of these days, we'll be able to look at these distant planets directly. Then things are going to really get interesting.