Definition of Super-Earth

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Definition of Super-Earth

Post by Stalker on 18th June 2008, 2:57 pm

There is a definition now as a super-earth.
A super-earth is a planet the mass of which is more important than that of the Earth but lower in 10ME

A superb earth can be:
- Rocky (similar composition in the Earth)
- ferrous (similar composition with Mercury)
- oceanic [Covered with water and with ice (supercritical or not)]
- gaseous (mini-Neptune)

Source (French) in "dernières informations"
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Re: Definition of Super-Earth

Post by Edasich on 19th June 2008, 4:57 am

This is an interesting point but it should have been poste in "Planetology subforum". Extrasolar Discoveries section is for newfound substellar/planetary objects' detection.
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Re: Definition of Super-Earth

Post by Stalker on 19th June 2008, 5:44 am

Ok Sorry
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Re: Definition of Super-Earth

Post by Edasich on 19th June 2008, 6:46 am

N.P Wink

RePost it where I said Smile
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Re: Definition of Super-Earth

Post by Sirius_Alpha on 10th September 2008, 7:57 pm

Edasich wrote:This is an interesting point but it should have been poste in "Planetology subforum". Extrasolar Discoveries section is for newfound substellar/planetary objects' detection.

Moved.

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Re: Definition of Super-Earth

Post by Darkness nova on 15th September 2008, 8:38 pm

A super-earth is a planet the mass of which is more important than that of the Earth but lower in 10ME

I don't really understand what that meant. Can somone tell me what may have been lost in translation. "or just lost to me".

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Re: Definition of Super-Earth

Post by Lazarus on 16th September 2008, 12:14 pm

Stalker seems to mean that the mass is greater than that of Earth but less than 10 Earth masses.

There seem to be several rough definitions for super-Earth which are similar but not quite the same. Some define it based on mass - e.g. 1-10 Earth masses, 5-10 Earth masses, etc. Others define it based on whether the planet retains a hydrogen atmosphere: a planet more massive than Earth but lacking a substantial hydrogen atmosphere counts as a super-Earth.
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Re: Definition of Super-Earth

Post by Darkness nova on 17th September 2008, 1:00 am

Ah this makes sense.

However I wonder. Why would a 2 earth mass planet be a super earth stalker? Sounds like a really good idea but I still think it needs a bit of tweaking. Actually to be really honest with you I think a group of people from several countries need to sit down online or elsewhere and come up with a good definition using both the ones outlined here as a platform or outlne and there own judgement.

Someone other than the IAU. No offense to them but I'd rather they figure out the whole planet thing first. ((note the irony in this statement))

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Re: Definition of Super-Earth

Post by Sirius_Alpha on 17th September 2008, 7:13 pm

As opposed to the debate over what is, and what isn't, a planet, I think that a debate over the definition of "Superearth" is rather pointless.

Super means "larger", Sub means "smaller". So why not just have SubEarths, Earths, and SuperEarths? This is assuming we have to make a distinction.

If we must distinguish on mass, then what's the point? I'm sure a 0.99 Earth-mass planet and a similar 1.01 Earth-mass planet aren't too distinguishable. Is there really a need to really define "SuperEarth"?

If we go with what Lazarus' pointed out, defining them by atmosphere, then we won't know what planets we find are superEarths and what aren't until atmospheric investigations are made. Even after that there's still the prospect of a lower-mass planet still retaining a hydrogen atmosphere. Would we have superEarths less massive than non-superEarths?

If we define "SuperEarth" based on mass, I think we all agree that we would have to choose an abritrary value. If we define "SuperEarth" based on physical properties, then there are ambiguities from uncertanties, as well as issues with overlapping types (i.e. a SuperEarth being less massive than a non-SuperEarth).

Another issue is the term itself. If we have "SuperEarth", it's easy for an unaware person to assume that the planet resembles a large Earth -- i.e. a habitable Earth-like planet. With a step below that an "Earth" would, understandably, generate a lot of similar confusion. "An Earth found orbiting Gliese ###" for example... well people are going to think it's habitable. Perhaps "SuperTerrestrial", "Terrestrial", and "SubTerrestrial" would be more appropriate.

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Re: Definition of Super-Earth

Post by Lazarus on 17th September 2008, 7:36 pm

If we want to throw another definition into the mix, consider the model for Mu Arae c proposed in the discovery paper

Thus, we expect this object to have a massive, essentially rocky core (as opposed to icy), surrounded by a gaseous envelope with ∼5-10% of its mass. It therefore probably qualifies as a super-Earth and not as a failed ice-giant.

This model seems remarkably similar to the structure of Uranus and Neptune, except with a rocky core instead of an icy one. Uranus/Neptune-analogues as super-Earths? The terms "rock giant" or "rocky giant" don't exactly appear in the literature...

As for super-Earths more massive than low mass ice giants, no real problem in this - after all, HD 149026b indicates that there may be "super-Neptunes" reaching Saturn mass, which are indeed predicted in some simulations of accretion (pdf).
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