UChicago: Cloudy Weather Observed on an Alien World

[MargaritaMc]

University of Chicago:
Researchers use Hubble Telescope to reveal cloudy weather on alien world

Weather forecasters on exoplanet GJ 1214b would have an easy job. Today's forecast: cloudy. Tomorrow: overcast. Extended outlook: more clouds.

A team of scientists led by researchers in the Department of Astronomy and Astrophysics at the University of Chicago report they have definitively characterized the atmosphere of a super-Earth class planet orbiting another star for the first time.

The scrutinized planet, which is known as GJ1214b, is classified as a super-Earth type planet because its mass is intermediate between those of Earth and Neptune. Recent searches for planets around other stars ("exoplanets") have shown that super-Earths like GJ 1214b are among the most common type of planets in the Milky Way galaxy. Because no such planets exist in our Solar System, the physical nature of super-Earths is largely unknown.
The scrutinized planet, which is known as GJ 1214b, is classified as a super-Earth type planet because its mass is intermediate between those of Earth and Neptune. Recent searches for planets around other stars (“exoplanets”) have shown that super-Earths like GJ 1214b are among the most common type of planets in the Milky Way galaxy. Because no such planets exist in our Solar System, the physical nature of super-Earths is largely unknown.

Previous studies of GJ 1214b yielded two possible interpretations of the planet’s atmosphere. Its atmosphere could consist entirely of water vapor or some other type of heavy molecule, or it could contain high-altitude clouds that prevent the observation of what lies underneath.

But now a team of astronomers, led by UChicago’s Laura Kreidberg and Jacob Bean, have detected clear evidence of clouds in the atmosphere of GJ 1214b from data collected with the Hubble Space Telescope. The Hubble observations used 96 hours of telescope time spread over 11 months. This was the largest Hubble program ever devoted to studying a single exoplanet.

The researchers describe their work as an important milestone on the road to identifying potentially habitable, Earth-like planets beyond our Solar System. The results appear in the Jan. 2 issue of the journal Nature.*

read more at:
http://news.uchicago.edu/article/2013/1 ... lien-world

*Clouds in the atmosphere of the super-Earth exoplanet GJ 1214b," by Laura Kreidberg, Jacob L. Bean, Jean-Michel Désert, Björn Benneke, Drake Deming, Kevin B. Stevenson, Sara Seager, Zachory Berta-Thompson, Andreas Seifahrt, & Derek Homeier.

http://hubblesite.org/news/2014/06

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[BDanielMayfield]

GJ 1214b was a good place to look for cloud cover, given what was already known about this exoplanet. The star M4.5 Red Dwarf star GJ 1214 is only about 42 light years away. Its “b” planet was discovered in 2009 with a 40 cm telescope by the transit method.

Lots of things can be learned about exoplanets whose orbits cross the face of their stars. GJ 1214b’s year is only 1.5804 days long, which makes it a “hot” planet, but not extremely hot since the star it orbits is only 0.15 Solar masses. The planet’s surface (or cloud top?) temperature is thought to be about 520 K. (For comparison the surface temp of Venus is 737 K.) From the amount of light that the planet blocks when it transits the radius has been determined to be 2.79+or-0.20 Earth radii, and from the way it pulls its star around the planet’s mass was found to be 6.3+or-0.9 Earth masses. This allows the planet’s density to be computed to be about 1.6+or-.2 g/cm^3.

That’s an extremely light density! It’s only about 30% of Earth’s density. GJ 1214b is thought to be a water world, or maybe a steam puff. So finding it to be covered in clouds was quite likely.

Bruce

[MargaritaMc]

That's really interesting, Bruce. When you say 1.5804 "days", I'm presuming that you mean Earth days. Thinking about it, I realise that it couldn't be the rotation of the planet in question, as presumably there is no possible way of knowing that (yet)?
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[BDanielMayfield]

Yes, GJ 1214b’s year is 1.5804 of our “Earth days” long. Astronomers expect that all bodies in tight “hot” orbits will be tidally locked. What that means is that such planets’ rotational period is the same as the orbital period. This means that one side of this planet always faces the star while the other side is always in darkness. This must make for some really strange weather on these worlds, since one side bakes up close to the star while the other side is in perpetual night.

Our Moon is tidally locked to Earth. The only way we can see the far side of the Moon is from lunar orbiters. One solar day on the Moon is about 29 of our days long. The moon used to be much closer to the Earth, and tidal forces would have been much stronger. Over time the Moon’s rotation rate was slowed by tidal friction until it matched the orbital period.

Tidal locking has happened to other moons in our solar system too, and it is expected that it would have to happen to many exoplanets as well.

Bruce

[MargaritaMc]

I confess that I originally posted the OP because I was intrigued that it was possible to detect the "weather" on an exo planet, but now am finding that there is such a lot more of interest! Thank you, Bruce!

I've come across this astrobite from 2011 that has helpful info PLUS some informative links about techniques used in the various studies:
http://astrobites.com/2011/11/28/an-upd ... h-gj1214b/

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