GJ 1214b: Probing the Atmospheres of Super Earths
December 2, 2010 Leave a comment
Meet GJ 1214b: one of the most Earth-like planet ever found outside oursolar system. It’s not exactly Earth’s twin: It’s about six times bigger, a whole lot hotter and made mostly of water. But compared to the giant gas balls that account for nearly every other extrasolar planet everfound, it’s pretty darn close. And through a fortunate happenstance of cosmic geometry, astronomers will be able to study GJ 1214b in great detail.
GJ 1214b, first discovered in December 2009, is 2.7 times the size of Earth and 6.5 times as massive. Previous observations ofthe planet’s size and mass demonstrated it has a low density for its size, leading astronomers to conclude the planet is some kind of solid body with an atmosphere. The planet orbits close to its dim star, at a distance of 0.014 astronomical units. An astronomical unit is the distance between Earth and the sun, approximately 93 million miles. Its host star lies about 40 light-years from Earth in the constellation of Ophiuchus (the Serpent Bearer). It is a faint star, but it is also small, which means that the size of the planet is large compared to the stellar disc, making it relatively easy to study. The planet travels across the disc of its parent star once every 38 hours as it orbits at a distance of only two million kilometres: about seventy times closer than the Earth orbits the sun. GJ 1214b circles too close to its star to be habitable by any ‘Earthly’ life forms.
[Image Details: Using a ground-based telescope, astronomers, including two NASASagan Fellows, made the first characterizations of a super-Earth’s atmosphere. A super-Earth is a planet up to three timesthe size of Earth and up to 10 times the weight.]
The atmosphere around a super-Earth exoplanet has been analysed for the first time by an international team of astronomers using ESO’s Very Large Telescope. The planet, which is known as GJ 1214b, was studied as it passed in front of its parent star and some of the starlight passed through the planet’s atmosphere. We now know that the atmosphere is either mostly water in the form of steam or is dominated by thick clouds or hazes. The findings, reported are a significant milestone toward eventually being able to probe the atmospheres of Earth-like planets for signs of life.
To study the atmosphere, the team observed the light coming from the star as the planet passed in front of it. During these transits, some of the starlight passes through the planet’s atmosphere and, depending on the chemical composition and weather on the planet, specific wavelengths of light are absorbed. The team then compared these precise new measurements with what they would expect to see for several possible atmospheric compositions. This same type of technique has been used to study the atmospheres of distant “hot Jupiters,” or Jupiter-like planets orbiting close to their stars, and found gases like hydrogen, methane and sodium vapor.
In the case of the super-Earth, no chemical fingerprints were detected; however, this doesn’t mean there are no chemicals present. Instead, this information ruled out some possibilities for GJ 1214b’s atmosphere, and narrowed the scope to either an atmosphere of water steam or high clouds. Astronomers believe it’s more likely the atmosphere is too thin around the planet to let enough light filter through and reveal chemical fingerprints.
The team determined the planet, GJ 1214b, is either blanketed with a thin layer of water steam or surrounded by a thick layer of high clouds. If the former, the planet itself would have an icy composition. If the latter, the planet would be rocky or similar to the composition of Neptune, though much smaller.
This is the first super-Earth known to have an atmosphere. But even with these new measurements, we can’t say yet what that atmosphere is made of. This world is being very shy and veiling its true nature from us. A steamy atmosphere would have to be very dense – about one-fifth water vapor by volume — compared to our Earth, with an atmosphere that’s four-fifths nitrogen and one-fifth oxygen with only a touch of water vapor. During the next year, we should have some solid answers about what this planet is truly like.
That list of ingredients raises at least the possibility of life. With an estimated temperature of 370 degrees Fahrenheit, GJ 1214b is an unlikely incubator (Earth’s toughest extremophile, a microbe that lives in deep-sea volcanic vents, maxes out at 284 degrees) but it’s not impossible.