Celestia Forums

A new planet around Gliese 876... this is the smallest planet apart from the pulsar planets discovered outside our solar system.

Link

way kool, it would probaly be a hothouse planet, tidaly locked..... not a place to set up a resort....

http://www.space.com/scienceastronomy/050613_super_earth.html

Arlington, Va.. Taking a major step forward in the search for Earth-like planets beyond our own solar system, a team of astronomers has announced the discovery of the smallest extrasolar planet yet detected. About seven-and-a-half times as massive as Earth, with about twice the radius, it may be the first rocky planet ever found orbiting a normal star not much different from our Sun.

The team measures a minimum mass for the planet of 5.9 Earth masses, orbiting Gliese 876 with a period of 1.94 days at a distance of 0.021 astronomical units (AU), or 2 million miles:

Astronomers Announce the Most Earth-Like Planet Yet Found Outside the Solar System

Extrasolar.ssc file update

I'm skeptical of the idea that it's a rocky planet. I mean, it's about 7 earth masses, orbits about 0.02 AU from its primary for a blackbody temperature of about 385K (albedo and greenhouse affect would modify this). And of course it'd be tidelocked.

If it was rocky like Earth and had earth's density, it could have a radius of 12200 km and be 7 earth masses, but then the minimum molecular weight its atmosphere could hold would be about 2.07, just over what's necessary to hold hydrogen, but easily able to hold Helium. So it'd hold all gases in the atmosphere except hydrogen, which would stay for a while but slowly leak away into space. But then, if it could hold onto Helium, its atmosphere would be quite thick wouldn't it?

It could have marslike density (3500 kg/m3) and be 14,200 km in radius and have an MMW retention of 2.4, which would be about the same as described above.

Or it could have a ganymede-like density (2000 kg/m3) and be 17,100 km in radius and retain an MMW of 2.9. Again, the same sort of thing.


Either way, it appears that we may be looking at a 'helium subgiant' that can hold onto helium but not hydrogen. That sounds more realistic to me than just 'a big earth'.

OMFG!!!!!

that is the EXACT SAME SYSTEM that I put an earthlike planet in on celestia!!!!!!!!

Man! That is an AWESOME coincidence!!!

EDIT: Alrighty, i'm over the initial excitement now, lol. anyhoo, really though, the earthlike planet that I created is really just a moon of the innermost gas giant, which (in celestia, of course), although barely, seems to be in the habitable zone of Gliese 876.

Actually I have got an inhabited moon around the c planet too, in the Orion's Arm universe (Aardwolf).
(although it is not very Earth-like)
Here is an image of the new d planet in Celestia -

I have guessed the radius as 12000km, assuming it has a rocky core and a fairly thick atmosphere- it would have a gravity of around 2 gee.

Helium subgiant, eh? Interesting type, Doc!

...unfortunately tidal forces bode ill for Earthlike moons of planet c - it seems that the maximum moon mass around Gl 876 c is about Pluto-size, and that's pushing it some...

Out of interest, how do you go about working out molecular weight retained, and what are the results for Mu Arae d/Rho1 Cancri e?

If the pressure is high enough, could there be an ocean of water on this world? If the temperature is 200 celsius, that would not be entirely impossible, especially with a thick helium atmosphere.

If the pressure is a couple of megapascals or so (20X Earth's atmospheric pressure) there could be liquid water at 470K - how thick would the atmosphere need to be I wonder.

Now that I have downloaded Grant's update, I see he has made the radius 600km greater than my estimate- otherwise the .ssc is essentially the same. I think he is probably right- this planet might have a rocky core as dense as Earth's or Mercury's, but will have quite a dense atmosphere over the top of that.

But greenhouse effect would probably rule out liquid water, I think.

Is this the default Celestia "venuslike.jpg" texture or did you do any modification?It looks different,specially the colour.

eburacum45 wrote:Actually I have got an inhabited moon around the c planet too, in the Orion's Arm universe (Aardwolf).
(although it is not very Earth-like)
Here is an image of the new d planet in Celestia -

I have guessed the radius as 12000km, assuming it has a rocky core and a fairly thick atmosphere- it would have a gravity of around 2 gee.

No I didn't alter it. If you download the Celestia add on from Sourceforge yours would look similar, although the radius is 12600 km, in the official version.

http://cvs.sourceforge.net/viewcvs.py/c ... asolar.ssc



Because it orbits a red dwarf Celestia tints it in a pinkish tone.
Actually in Celestia v.1.4.0 the colours of the red dwarf stars are quite realistic; but the colour of the light they cast on planets and spacecraft is a little too red.

Actually the current thinking at Extrasolarvisions is that GL 876 d is too hot to have clouds; that might only leave Rayleigh scattering,and a blueish/greenish tint (a mixture of the blue sky effect and the red/yellow colour of the dwarf light.