Ice/HMC Hybrid

[Reido]

I've recently come across two HMC planets that are rather puzzling, They're very cold at 20K and 27K and have some ice, yet they have "hot" volcano's i.e. Silicate Vapour Geysers.

Here's the first one and some extra info:

Main star: K8 VA, Age 10006, Temp 3862
Secondary: M9 VI, Age 10006, Temp 2042

Spoiler

Here's the second one:

Main Star: M7 VA, Age 4566, Temp 2444

Spoiler

I've scanned and looked at hundreds of these, but I took a break from the game in July so I'm assuming that these are "new".

With my limited knowledge, these don't seem plausible. The systems might be too old for radioactivity to be the cause of the internal heating and these planets aren't close enough to anything else for tidal forces to be a major factor.

Is there a plausible reason for these to exist, or are they another "Glitch in the Matrix"


CMDR Andrew Reid

 

[iain666]

The second one is only the same age as earth, and quite a bit bigger. It would certainly retain enough heat to be active.

The first one is older, but is also more massive. I honestly don't know how long you could expect a planet of that mass to remain active but 10Ga doesn't feel ridiculous to me.

You would expect them both to be pretty cold despite their volcanism because they've got very little warming by insolation and not a lot of atmosphere.

 

[Reido]

Thanks for the reply.

Since I can't make heads or tails out of this type of planet, for now I'm just going to chalk them up as a glitch in the Stellar Forge unless someone else chimes in.


CMDR Andrew Reid

 

[iain666]

I'm a geologist, not an astrophysicist.

As a geologist they work just fine as planets (I've since gone off and done some reading and it looks like Earth could stay active for at least another 3-4Ga - although there are scenarios that could lead to a mechanical gumming up of plate tectonics breaking the system before it gets too cold - so a larger planet being geologically active at 10Ga is just fine). The hot volcanism is a result of that internal heat (radioactive heating plays a role but the residual heat of gravitational collapse is much more important, and it takes a very long time for that to radiate away from a planet of a few earth masses). The cold surface is a result of being so far from the star(s), most of our surface temperature comes from solar input, the heat coming off the earth itself is pretty negligible - even the heat from an erupting volcano is next to nothing when considered as the amount it directly warms the entire planet.

Whether their existence at all is consistent with how we currently think solar systems form I can't be confident on.

 

[Reido]

I've found a few more samples of this type of planet along with some extra data.

Here's a few common elements among them:

-Very cold 20K-43K
-Hot volcano's
-Helium atmospheres
-Orbital Inclination and Eccentricity are high

Those last two bits of information might be the key to explaining these planets.

The way I understand it is that ALL planetary orbits are inherently unstable over the long term with some orbits being more stable and others less stable.

What I think I'm seeing with these planets is a snapshot of a planet that has in it's past been close enough to it's star to have kept it's internal temperature high due to heat from it's star and/or tidal forces, but due to it's unstable orbit has now migrated far out in it's system enough to make the surface temperature drop to Ice world temps but not enough time has elapsed for the internal temp to drop as well.

The ages for the systems these are in are all over the place from 394M to 12.8B and all the common star types as well.

Here's some new samples:

Spoiler

Most of them certainly stick out like a sore thumb and I'm sure I would have noticed these when I was doing planetary surveys up to v1.4 and I don't see anything in the spreadsheet I have from that time that looks even close to these, so I'm reasonably sure these have been added since v2.0

It's always nice to come across little surprises like this to keep exploration interesting


CMDR Andrew Reid

 

[SpaceMonkeyz]

Fascinating. +1 rep for broaching such an interesting topic that I know very little of. I love how this game can be a tool for learning too.

Keep up the research Commander, maybe I will see you at BP

 

[iain666]

What I think I'm seeing with these planets is a snapshot of a planet that has in it's past been close enough to it's star to have kept it's internal temperature high due to heat from it's star and/or tidal forces, but due to it's unstable orbit has now migrated far out in it's system enough to make the surface temperature drop to Ice world temps

The internal heat of a planet is a consequence of gravitational collapse. It radiates that into the vacuum over time. Tidal forces and internal radiation can slow that cooling but they are not dominant and insolation has a pretty negligible effect. It is almost entirely a function of mass.

Mars (~0.1 earths by mass) stayed geologically active for two or three billion years, Earth will keep going for probably 8-10Ga in total and bigger planets will keep going for longer.

There really is no mystery to a planets of this size being geologically active (and having hot volcanic events) at any orbital range.

Surface temperature, on the other hand, is dominated by insolation so we would expect near absolute zero surface conditions with the atmosphere mostly freezing out despite being refreshed by volcanic activity.

There might be some reason from an astrophysicist why we wouldn't expect an HMC to form that far out and this must therefore have formed further in and migrated out - but the current internal heat of the planet is definitely not that reason.

 

[Reido]

I should have been more clear in my last post that the mechanism behind the internal heat and volcanism is not in dispute.

I was just trying to come up with a plausible explanation for the peculiar positions of these HMC planets. I don't normally look at the orbital data for planets so needed to collect data on a few more to see if they all followed the same trend of unstable orbits.

I came across another one last night that was over 22,000ls from the entry point in it's system.


CMDR Andrew Reid