To find out what water might look like on alien worlds, a group of researchers decided to see how Earth's oceans would appear from afar, as if from another planet.

Using the Deep Impact/EPOXI spacecraft, currently headed for a rendezvous next year with Comet Hartley 2, they peered back at Earth from more than 30 million miles (50 million kilometers) away, tracking the way reflected light changes as oceans rotate in and out of view.

From that distance, Earth's surface features were blurred [see photo at left], but the presence of water passing through the spacecraft's view increased the planet's blueness. Landmasses, on the other hand, lent a reddish hue. The team of researchers was able to assemble from those color variations a rough map of the liquid and land boundaries on Earth, presented in a paper set to be published in the Astrophysical Journal.

The Kepler spacecraft, launched by NASA in March to look for cousins of Earth—those planets around other stars that have the right conditions for life—is now on the job. The spacecraft is in position, trailing Earth in an orbit around the sun, and has completed a tune-up of its instruments.

"Now the fun begins," Kepler principal investigator Bill Borucki of the NASA Ames Research Center in Moffett Field, Calif., said in a statement. "We are all really excited to start sorting through the data and discovering the planets."

As the hunt for Earth-size planets around other stars ratchets up, some researchers are already investigating how to test those planets for habitability once they are found.

A team of U.S. and Australian scientists reports successfully testing an approach that could be used to look for water on so-called extrasolar planets, or exoplanets. The researchers tried out their technique, described this week in a paper submitted to arxiv.org to be published in Astrobiology, on the only Earth-like planet we know of: Earth.

Late tomorrow night, NASA's Kepler spacecraft will—conditions permitting—lift off from Cape Canaveral Air Force Station in Florida on its unprecedented mission to find habitable, Earth-like planets around distant stars.

The $600-million venture will train Kepler's photometer on a group of 100,000 stars several hundred to a few thousand light-years away and track them for more than three years. As the planets believed to reside there pass between their stars and Kepler's detector, the spacecraft will register a slight dip in stellar brightness. Over time these dips can be used to compile a profile of the planetary systems in Kepler's view, which, according to prevailing models of planetary formation, should include several Earth-like planets. Once astronomers know how common Earths are and where in the galaxy they can be found, follow-up missions will be able to refine their searches for extraterrestrial life.

It was front-page news when astronomer Paul Kalas of the University of California, Berkeley, and his team produced the first photographic evidence of a planet orbiting another star last month. (Another team, publishing simultaneously, announced similar results around a different star.) But at least one person in the field was not surprised: astronomer Alice Quillen of the University of Rochester had predicted the existence of just such a planet, in just such an orbit, in the Monthly Notices of the Royal Astronomical Society: Letters in October 2006.

Two years ago, Quillen examined the debris disk around a star 25 light-years away known as Fomalhaut. She hypothesized that the features of the disk implied that there ought to be a planet, whose mass lay between that of Neptune and Saturn, orbiting nearby, some 119 astronomical units (AU) from Fomalhaut. (An astronomical unit is roughly the distance between Earth and the sun.)

A poorly kept secret is now official: the Hubble Space Telescope has discovered carbon dioxide (CO₂) in the atmosphere of a planet outside our solar system. That's a first in the study of extrasolar planets, or exoplanets, which have been quite the hot topic this year.

The exoplanet HD 189733 b, roughly the mass of Jupiter, orbits a star 63 light-years away in extremely close company. Although the planet can't be seen directly, scientists used Hubble data to analyze its atmospheric composition and turn up CO₂ as well as carbon monoxide (CO). They did this by comparing the light spectrum from the star with that from the star and planet combined, as the planet passes in front of its star.

Although HD 189733 b is way too steamy for life as we know it—roughly 1,950 degrees Fahrenheit (1,065 degrees Celsius) by one estimate—the finding, leaked to media outlets two weeks ago, shows that techniques exist to find markers of life on other planets. (The paper has been submitted to Astrophysical Journal Letters.)

Astronomers have discovered a new planet in another solar system orbiting a red giant star that provides clues into what may happen to our own solar system five billion years from now when our own, younger sun becomes a gigantic old star. 

The exoplanet (a planet in another solar system) is about six times the mass of Jupiter and orbits about 40 percent closer to its star, dubbed HD 102272, than Earth does around the sun. Scientists say this is apparently the shortest distance that a planet can be from a red giant (a large, relatively cool, elderly star) without burning up.

On the heels of the first photographs of planets orbiting other stars comes another first for so-called extrasolar planets: an atmosphere containing carbon dioxide (CO₂). Nature News and Science News report that a forthcoming journal article will detail the discovery of CO₂ around HD 189733 b, a planet roughly equivalent to Jupiter in mass that orbits a star some 63 light-years away.

HD 189733 b, discovered in 2005, has already yielded other exoplanet milestones: it was the first found to host an atmosphere containing methane and was also among the first found to harbor water vapor. All of these discoveries have been made without seeing the planet in the conventional sense: to ascertain a planet's traits, the light spectrum of the parent star is compared with the star's emission as the planet passes in front of it. In the latest finding, the data came from the Hubble Space Telescope.