[BRIEF NOTE] On GJ 1214b
Dec. 18th, 2009 08:53 am![[personal profile]](https://www.dreamwidth.org/img/silk/identity/user.png){kind=small}
rfmcdonaldCentauri Dreams' summary of what's known about the newly discovered and very broadly Earth-like world GL 1214b works for me.
Apart from the fact that this world can be found with a small ground-based telescope--who knew planet-finding could be so easy just a couple of decades ago?--this ocean planet could be quite typical: "Planetary objects that form in the outer solar system begin as a comet-like mixture of roughly 50% water and 50% rock by weight. Simulations of solar system formation have shown that planets are likely to migrate inward or outward as they form, presenting the possibility that icy planets could wind up in orbits where their ice melts into liquid form, turning them into ocean planets."
By comparison, GJ 1214b's density would make it 50% denser than the ice-rock Jovian moons of Callisto or Ganymede and is comparable to that of famed Europa. GJ 1214b's much too hot to be a Europa, sadly, but at least there's some interesting chemistry going on.
At a distance of 1.3 million miles, the planet orbits its star every 38 hours, with an estimated temperature a little over 200 degrees Celsius. Because GJ 1214b transits the star, astronomers are able to measure its radius, which turns out to be 2.7 times that of Earth. The density derived from this suggests a composition of about three-fourths water and other ices and one-fourth rock. Some of the planet’s water should be in the form of exotic materials like Ice VII, a crystalline form of water that is found at pressures greater than 20,000 Earth atmospheres:“Despite its hot temperature, this appears to be a waterworld,” said Zachory Berta, a graduate student at the Harvard-Smithsonian Center for Astrophysics (CfA) who first spotted the hint of the planet among the data. “It is much smaller, cooler, and more Earthlike than any other known exoplanet.”
That’s quite a find for the MEarth Project, which uses an array of eight 16-inch telescopes that monitor a list of 2000 red dwarf stars. The MEarth array is located at the top of Mount Hopkins, Arizona. MEarth looks for the tiny drop in brightness that indicates a transit, using data processing technologies to extract the planetary signature. If ever there was a find that should galvanize the amateur astronomy community, it’s this one, as David Charbonneau (CfA), who heads MEearth, is quick to note:“Since we found the super-earth using a small ground-based telescope, this means that anyone else with a similar telescope and a good CCD camera can detect it too. Students around the world can now study this super-earth!”
Sifting through this material, what stands out is that the radius measured for GJ 1214b is larger than expected by current models. Remember, this is the second time we’ve found a transiting super-Earth, the first being CoRoT-7b. The latter has a similar mass but the radius of GJ 1214b is much larger. Indications are that a surrounding atmosphere some 200 kilometers thick is adding to the drop in stellar light measured in these transits. Charbonneau again:“This atmosphere is much thicker than that of the Earth, so the high pressure and absence of light would rule out life as we know it, but these conditions are still very interesting, as they could allow for some complex chemistry to take place.”
Apart from the fact that this world can be found with a small ground-based telescope--who knew planet-finding could be so easy just a couple of decades ago?--this ocean planet could be quite typical: "Planetary objects that form in the outer solar system begin as a comet-like mixture of roughly 50% water and 50% rock by weight. Simulations of solar system formation have shown that planets are likely to migrate inward or outward as they form, presenting the possibility that icy planets could wind up in orbits where their ice melts into liquid form, turning them into ocean planets."
By comparison, GJ 1214b's density would make it 50% denser than the ice-rock Jovian moons of Callisto or Ganymede and is comparable to that of famed Europa. GJ 1214b's much too hot to be a Europa, sadly, but at least there's some interesting chemistry going on.
