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Full Version: Gliese 581g: 3-Earth-mass planet in the habitable zone
Unmanned > Beyond.... > Telescopic Observations
Announced today by Steven Vogt of UC Santa Cruz and Paul Butler of the Carnegie Institution, bringing the total count of planets around that phenomenal little star (just 20 light years away, too!) to six or seven.
Discovery paper
Press release
Announcement press conference at the National Science Foundation
Good summary from Science
Let the mass misinterpretations begin (see headline)!!!
We are all reminded to review the forum guidelines, particularly section 1.3

Discussion of observations and classifications (zones, temperatures, composition) of planetary bodies from those observations is acceptable, but let's not stray into anything more than that.
Words to post by, Dan.
It is said that this planet is probably tidally locked. But where it's always dawn and always windy as hell, I'm sure it's paradise.
Is there any method of actually confirming whether a planet is tidally locked or not, short of computer models (which are theoretical) and direct imaging (which isn't quite in our capabilities for something this small)?

Infrared spectroscopy might be able to do it by looking at surface temperature.

When it is on the opposite side of the star from us, it would look hotter, when it is on the same side of the star as us, we'd be looking at more of the backside, it should look cooler.

'Course, this would be totally ignoring any atmospheric effects (e.g. Venus).

BUT, I don't know what sort of telescope would be required to resolve this planet to a "magic pixel" to get the desired spectrum.

What type of space telescope would be able to do this? Would the TPF be able to eventually do it?
Time to revive projects Icarus, Daedalus and Longshot ... noticeably unmanned space missions rolleyes.gif
There was a paper posted on Arxiv in the last couple months saying that tidally locked planets might not get baked/frozen if they have a substantial atmosphere to transport heat away from the subsolar point. Jim Kasting was a coauthor. I'll try to find it later. It certainly stands to reason that a super-Earth would probably have a thick atmosphere.

Explorer...the physical models are far more than theoretical. They certainly make some assumptions (e.g., it's a rocky planet), but no assumptions that strain credibility. They can easily include the tidal forces from the other planets in the system which could keep the planet out of tidal lock.
QUOTE (Drkskywxlt @ Sep 30 2010, 10:36 AM) *
It certainly stands to reason that a super-Earth would probably have a thick atmosphere.

Not necessarily, tectonic recycling or oceanic chemistry could sequester some atmospheric gases in sediments and rocks. Earth and Venus have very different atmospheric thicknesses, one factor being that Earth has a smooth running tectonic machinery, and Venus doesn't. (The water cycle is another big factor - water also may lube Earth's tectonic cycle - so water and tectonics are intertwined at least for smaller planets like Earth and Venus).

Here's a paper that suggests that super-Earths are more likely to have an active tectonic cycle. The authors suggest that evidence against a tectonic cycle on a distant world would be the detection of a thick CO2 atmosphere:

Valencia et al. The Astrophysical Journal, 670 (2007) L45L48. "Inevitability of Plate Tectonics on SuperEarths." Article freely available here.
Despite Dan reminding you all in this very thread - already there have been several posts culled that clearly breach rule 1.3

Juramike...I've seen some papers like that. Many folks have speculated that super-Earth's would have lots of H2O vapor in their atmospheres, and hence a strong greenhouse effect from it. Tectonics wouldn't impact that the same way it could with CO2.
Mercury was thought for many years to be tidally locked towards the Sun as well, and it turned out to be in 3:2 resonance. This new planet orbits in less then half the time of Mercury though, so it's still anyone's guess what's going on over there...
That was before we understood spin-orbit resonances. After the situation with mercury was discovered, it didn't take long for it to be explained. For a circular orbit, the spin-orbit resonance will tend to 1:1 -- synchronous rotation.
Does anyone know if a moon would be detected by the technique they used to find the planet?

This could have implications as far as the rotation speed.

Also considering the distance and mass of 581 d and c there may be some resonance caused by them on g, couldn't there?
QUOTE (dmuller @ Sep 30 2010, 01:00 PM) *
Time to revive projects Icarus, Daedalus and Longshot ... noticeably unmanned space missions rolleyes.gif

Also TPF and its followon PI (Planet Imager).
QUOTE (scalbers @ Sep 30 2010, 04:47 PM) *
Also TPF and its followon PI (Planet Imager).

Anything with a goal of studying specific planets (rather than discovering them) will certainly have some benchmarks now.
Excellent point.
If it's tidally locked, can you still catch waves?
QUOTE (bjb @ Sep 30 2010, 09:19 PM) *
Does anyone know if a moon would be detected by the technique they used to find the planet?

No, a moon would not have been detectable. A planet-plus-moon would have produced exactly the same radial velocity signature from the parent star as a moonless planet with the same total mass. In the case of planets discovered by observing planetary transits of the star there is the prospect of detecting moons through small timing irregularities in the transits, but the radial velocity method is blind to the presence of moons.
The media are going to make 'Astronomers find the first Earth-like planet!' the new 'Water discovered on Mars!' laugh.gif
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