Alan MacRobert, Sky and Telescope (November 30, 2010)
"In the latest breakthrough for exoplanet science, a team using one of the European Southern Observatory's 8.2-meter Very Large Telescope reflectors has obtained a crude spectrum for the atmosphere of a super-Earth orbiting a dim red dwarf star 40 light-years away. The planet's upper atmosphere is apparently dominated by steam or cloudy haze.
"The star, 14.7-magnitude GJ (Gliese-Jahreiss) 1214 in Ophiuchus, is 300 times dimmer than the Sun with a spectral type of M4.5. Its planet was discovered in 2009 when the MEarth Project detected the planet's silhouette periodically dimming the star. The planet has 6.5 Earth masses, as determined later by the star's gravitational wobbles, and it circles the little star very closely in just 38 hours. The transits reveal the planet's diameter to be 2.6 times Earth's - making its average density very low, only about a third of Earth's density...."
The Lemming's mentioned GJ 1214b before. (December 2, 2010) The Sky and Telescope article gives a bit more information about the exoplanet - and a little more about where it is. At 40 light years, it's practically in our back yard - by galactic standards.
Finding water in GJ 1214b's atmosphere was possible, given today's technology, because the planet is a transiting exoplanet. Its orbit carries it across GJ1214's face, as seen from Earth.
The water could be water vapor; or high-altitude clouds, or haze.
Analyzing an exoplanet's atmosphere is a big deal. With more of that sort of data, astronomers will be able to start classifying worlds around other stars.
About GJ 1214b, detecting water in its upper atmosphere narrowed the possibilities for what the place is like considerably. Back to the article.
"...Before this observation, astronomers had suggested three possible atmospheres for GJ1214b. The planet could be shrouded by water - which, given its high temperature so close to the star (200ºC; 400ºF), would be in the form of steam. Or it could be a rocky world with an atmosphere of mostly hydrogen obscured by high clouds or hazes. Or it might be a mini-Neptune, with a small rocky core and a deep hydrogen-rich atmosphere, the upper part of which would be clear.
"The measurements clearly show no sign of hydrogen and thus rule out the third option. So the atmosphere is either rich in steam or blanketed by clouds or hazes. The planet's low density, meanwhile, indicates that it's a waterworld.
" 'Although we can't yet say exactly what that atmosphere is made of, it is an exciting step forward to be able to narrow down the options for such a distant world to either steamy or hazy,' says Bean. 'Followup observations in longer-wavelength infrared light are needed to determine which of these atmospheres exists on GJ 1214b.' "
"Waterworld," in this context, doesn't mean that GJ1214b is inhabited by folks who look like Kevin Costner. It's a sort of planet that, according to today's models for planetary formation, could exist. And, given the number of planets we're finding, how common hydrogen and oxygen are, and the size of the universe, probably does exist.
A real waterworld isn't so much covered by water, like Earth, as it is made mostly of water. If GJ 1214b is a waterworld, its ocean could be around 15,000 kilometers deep or more. The planet's around 33,020 kilometers in diameter. Those numbers aren't typos. A waterworld's oceans would be deep.
By comparison, Earth is about 12,700 kilometers in diameter; with the Pacific ocean floor at a depth of around 4.3 kilometers/4,300 meters.
There's serious doubt that life could exist on a waterworld. Life-as-we-know it needs water, but everything from microcritters that live in geysers to polar bears and moss need other elements and compounds, too. Which would be in mighty short supply anywhere in a waterworld, about the ocean floor. Which would probably be solid water. Not the sort of ice that's on the ground here in central Minnesota. More likely ice VII - a (very) high pressure sort of solid water. And that's another topic.
Related posts:
- "Gliese 581 System's Habitable Zone: New Numbers"
(December 22, 2010) - "GJ 1214b: Super-Earth, With an Interesting Atmosphere"
(December 2, 2010) - "HR 8799b: Unexpectedly Hot and Cloudy: And About 130 Light Years Away"
(September 2, 2010) - "'More Than 100 Earth-Like Planets' Found? Well, No: Not Really"
(July 24, 2010) - "Life Around a Red Dwarf Star? Could be"
(July 7, 2010)
- "Waterworld planet is more Earth-like than any discovered before"
Ian Sample, Science, guardian.co.uk (December 16, 2009)
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