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View Full Version : Super-Earths: How Much Are They Like Earth?



Fraser
2008-Jun-17, 04:20 PM
With yesterday's announcement about finding a batch of so-called “super-Earths” - rocky alien worlds a few times more massive than our own - as well as another announcement back in May that 45 relatively low mass planets had been found, it's obvious astronomers are constantly improving on their techniques to find new worlds. While [...]

More... (http://www.universetoday.com/2008/06/17/super-earths-how-much-are-they-like-earth/)

neilzero
2008-Jun-17, 09:25 PM
We may soon be able to detect worlds as small as Earth and farther from their star. These hot super earth's may be tide locked = keep the same face toward the star. If so, the unlighted side may be cool or even cold. If cold, the water and possibly the atmosphere may be frozen into a great glacier centered on the dark side. If warm or cool, there may be habitable locations in the twilight zone. If more than four times the mass of Earth, the surface gravity is likely too much for humans to thrive, but a few of us might be able to tough out weighing twice as much. Likely it is not exactly square law. Neil

JohnBStone
2008-Jun-18, 08:47 PM
If more than four times the mass of Earth, the surface gravity is likely too much for humans to thrive, but a few of us might be able to tough out weighing twice as much. Likely it is not exactly square law.
It's proportional to mass divided by square of the radius - so density is important. Though I guess heavier planets have bigger cores which pushes the density up. I calculate a planet with four times the mass would need to be 40% denser than Earth to have 2G surface gravity - though that doesn't seem particularly unlikely. Even with double Earth's density it would only be 2.6G.

Try feeding numbers into this http://www.transhuman.talktalk.net/iw/Geosync.htm

I think if humans ever reach there they will have figured a way to survive the gravity...

a-l-e-x
2008-Jun-18, 09:38 PM
We'll see a multitude of new discoveries, especially when the new space telescope goes into orbit. The resolution should be high enough to even detect the presence of water and oxygen in the atmospheres of these planets.

GOURDHEAD
2008-Jun-19, 12:44 PM
Quoted from the link:
Super-Earths are planets that have [than] ten times or less the mass of Earth. The three planets around the star HD 40307 have masses of 4.2, 6.7, and 9.4 times the mass of the Earth. They orbit their star with periods of 4.3, 9.6, and 20.4 days, respectively. That's a short orbital period, meaning they are very close to the star. Since they are close to the star, astronomers believe its likely they are terrestrial, rocky-type planets rather than gas giants like Jupiter and Saturn. But also, being so close to the star means they are very warm – perhaps 1000 degrees Celsius. This would not be a pleasant or probable environment for life as we know it to take a foothold. But we don't know for sure, and since we are curious creatures, we want to know more about these planets. The cited periods imply orbital semi-major axes that are very similar in magnitude and seem to impose a high degree of circularity, else these planets would mutually scatter each other away from or into the parent star. If this characterization proves accurate, it would seem to greatly enlarge the probability of stable planetary systems with systems of multiple stars. This bodes well for the likelihood of finding planets in the AC system. Has HARPS been trained on AC yet?

timb
2009-Jan-14, 10:10 PM
According to The HD 40307 Planetary System: Super-Earths or Mini-Neptunes? (http://arxiv.org/abs/0901.1698) the planets, in particular HD 40307b, are unlikely to be rocky. The authors come to this conclusion by analysing the tidal evolution of the system.