Wednesday, December 16, 2009

Another world - this one watery

Another week, another world. This one is wet (emphases mine) ...
.... The alien world known as GJ 1214b orbits a red dwarf star one-fifth the size of our own sun, 40 light-years away in the constellation Ophiuchus, the astronomers reported in Thursday's issue of the journal Nature.

Super-Earths - planets that are roughly two to 10 times Earth's mass - represent the hottest frontier in the years-long search for worlds beyond our solar system...

... Those planets orbit stars like our own sun, but the brightness of GJ 1214b's parent star is hundreds of times dimmer. The planet is also much closer to the star than any of our own solar system's planets, orbiting at a distance of only 1.3 million miles (2 million kilometers). That combination suggests that the planet's surface temperature would be about 400 degrees Fahrenheit (200 degrees Celsius), Charbonneau's research team reported.

... GJ 1214b was detected thanks to an innovative telescope system, a cleverly focused observation campaign - and perhaps a little bit of luck. The eight-telescope array, dubbed the MEarth Project, was set up at the Whipple Observatory on Mount Hopkins in Arizona. The telescopes were programmed to gaze at 2,000 low-mass stars and check for slight, regular dips in light that could be caused by a dark planet's transit across the star's disk.

Relatively dim, relatively close stars were favored because the planet's dimming effect would be more noticeable than it would be with brighter, bigger, farther-out stars.

Just a few months after the MEarth Project began, graduate student Zachory Berta spotted the signature of GJ 1214b's 38-hour orbit. Based on the pattern of the dimming, the team figured out that the planet was 2.7 times as wide as Earth.

The astronomers then turned to another instrument, the HARPS spectrometer on the European Southern Observatory's La Silla telescope in Chile, to figure out the planet's mass. Such mass calculations depend on another technique that checks for the slight wobble in a star's motion caused by a planet's gravitational pull. The HARPS observations indicated that the planet was 6.55 times as massive as Earth.

Putting those measurements together, the team was able to model the planet's density and composition. The best fit for the data was a mixture consisting of about three-quarters water and other ices, one-quarter rock and a gaseous atmosphere.

... Although the surface temperature on GJ 1214b would be well above water's boiling point on Earth's surface, Charbonneau said the planet could nonetheless possess an exotic form of liquid water due to extreme atmospheric pressure at the surface. In today's news release, Berta said the pressure may turn at least some of the water into a rare crystalline form known as ice-seven.

"Despite its hot temperature, this appears to be a water world," Berta said.

On Earth, organisms have been found living near deep-sea hydrothermal vents, where superheated water is held under high pressure. But Charbonneau said he wouldn't want to bet that life could endure under GJ 1214b's crushing conditions.

In fact, it's too early to bet heavily on any detailed description of GJ 1214b. Fortunately, Charbonneau said, the star is close enough that the Hubble Space Telescope could someday analyze the composition of the planet's atmosphere. "That will make it the first super-Earth with a confirmed atmosphere - even though that atmosphere probably won't be hospitable to life as we know it," he said...

... The larger implication of the Nature study is that other super-Earths may be waiting out there with just the right conditions for life. "We found this planet in the first six months," Charbonneau noted. "We had only looked at a small fraction of the stars that we planned to look at through the entire project. That means that either we got really lucky - which is possible - or these planets are common."
Red dwarf planets are tidally locked, so one side would be very hot and another side very cold. In between?

The next two years are expected to bring news of hundreds of planets - maybe thousands. We're filling in terms in the Drake equation, and making the "great quiet" ever more unsettling.
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