Celestia Forums

I am looking at making a new imaginary world, based on Vidal-Madjar's proposed chthonian category of hell-like worlds;

if a hot jupiter strays too close to its sun, it will lose all its atmosphere and be reduced to a rocky core; this will be a hot, high gravity world, and quirte a challenge for future miners or colonists.

However, roughly working out some figures, if such a core were 10x Earth masses, and as dense as iron, it would be approx 24000km diameter with a gravity of only 2.7 gee or so;

disappointing, I had expected higher gravity than that.

Would the molten core of such a largely molten object become more dense than Iron? I would expect some carbon and silicon, not to mention aluminium, nickel etc in the mix perhaps as well; but this is all guesswork.

Any ideas?

Well there is a theory that any carbon at the core of a Jupiter or greater Jovian would be turned to diamond do to the extreme pressures at the core. Also we have evidence of many Jovians orbiting there parent star quite close and still maintaining there mass, ergo atmospheres. Of course there will be a limit to just how close they can get. But one must remember that a Jovian isn't just made up of a gaseous atmosphere and a rocky core. There are many layers to the atmosphere and zones were the hydrogen actually turns to liquid and then to liquid metallic hydrogen before you ever get to the core. That is allot of mater to have to sublimate over time. And if it is a transitional Jovian then you have to take into account how long it has been close to its parent star.
Because Jovians are more like stars than planet they tend to have very strong magnetic fields protecting them. This will give them some ability to hold onto there noble gas atmospheres even when they do get close to a star.

Don. Edwards

HD 209458 b is losing its atmosphere, and the loss of hydrogen can apparently drag heavier molecules with it (carbon and oxygen have been detected in the planet's gas tail).

However HD 209458 b is not close enough to its star and too massive to lose all its atmosphere before its star evolves off the main sequence - it is more likely to be consumed as HD 209458 expands than to become a chthonian planet.

If the mass is getting lost, as far as I understand it the hydrogen is kept in the unusual states (e.g. liquid metallic) by intense pressure, so if the atmosphere was being lost the pressure would decrease and the hydrogen would turn to its more normal gaseous state.

The sort of world I am imagining is very close to its star, and has lost nearly all its atmosphere over several billion years; it may well retain a magnetic field, and so protect some of the atmosphere from sputtering anf other types of loss, but the high temperature would be the main factor.

I am trying to come to a realistic density value, to give an idea of the gravity;
compression into a slightly degenerate state seems to be a factor, according to this link
http://cosmos.colorado.edu/stem/courses ... 5/l5S6.htm

which says the core of Jupiter may be compressed by a factor of 2, while the core of Earth is compressed by a factor of 10%;
so the core of Sisyphos may have been compressed by a factor of ~2 before it lost its atmosphere;

however this imagined world will have had a mass of 300 Earth masses, and has reduced to a mass of 10 Earths;

so this compression will be greatly reduced- perhaps to 20% or so in the central portion only-
(some interesting geological processes taking place in the expansion no doubt)

making the overall density of the world increased by only a few percent over the uncompressed materials.

If it has a large molten core of iron, overlaid by a sial crust and topped by a layer of diamond; it would probably struggle to reach an overall density of 7000 kg/m^3;

for a 10 x Earth mass body, I get a diameter of ~25000 km, and a gravity of about 2.5 gee...

now all I have to do is find a plausible temperature...

And here it is


temperature is 1700 Celsius according to Celestia- sounds a bit low...

The full entry for this world can now be found here;
http://www.orionsarm.com/worlds/Sisyphos.html
Thanks for everyone's help

Check out John Dollan's far superior Eoestremonath as well
http://www.orionsarm.com/worlds/Eostremonath.html

eburacum45 wrote:The full entry for this world can now be found here;
http://www.orionsarm.com/worlds/Sisyphos.html
Thanks for everyone's help

As usual, an outstanding job, Steve. I need to add an entry to the PCL for this world type yet. BTW, do you have this and any other OA add ons for Celestia available?

eburacum45 wrote:Check out John Dollan's far superior Eoestremonath as well
http://www.orionsarm.com/worlds/Eostremonath.html

Heh, thanks! I've had that kicking around for ages. I still need to add a section that deals with daily life in "modern" OA society. It is all supposed to be background dressing for my series of works, "Baseline Diaries".

...John...