Exoplanets With Water: Blue Clue

"New Technique Could Reveal Exoplanets with Water"
Space.com (June 1, 2009)

"When it comes to life as we know it, nothing is more important than liquid water. Now scientists have devised a way to spot water on distant planets that can only barely be seen now, which in turn could reveal whether they might be able to support life.

"In the past two decades, astronomers have detected more than 300 planets orbiting alien stars. Although most of these exoplanets are gas giants similar to Jupiter, powerful space telescopes such as the one aboard NASA's recently launched Kepler Mission will make it easier to detect smaller rocky exoplanets similar to Earth...."

The article describes, briefly, how scientists had NASA's Deep Impact spacecraft take two pictures of Earth at two different times, from millions of miles away. Reducing each picture to a single pixel, which is about as big an image of Earth as we're likely to get at this point, they analyzed the color of the pixel.

At one-pixel resolution, Earth is mostly gray. There's a bit of blue, and a bit of red, though: and how much changes, depending on where clouds are - and aren't.

Other chemicals are mostly blue, too: like Neptune's methane. But in Neptune's case, it's equally blue, day in and day out.

Earth's blueness varies with its rotation and cloud cover. So, presumably, would another planet with big patches of water on its surface. And, a planet with that much liquid water might also have life.

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Related posts, at

• "A Serious Search for Other Worlds, Life, and - Maybe - Extra-Terrestrial Intelligence"