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Forum » SpaceEngine » Feedback and Suggestions » Suggestion: Protoplanetary Disks
Suggestion: Protoplanetary Disks
apenpaapDate: Wednesday, 29.10.2014, 16:32 | Message # 16
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Given the amount of white dwarfs, I'm sure there must indeed be one somewhere where a planet happened to migrate into a habitable zone orbit, yeah. It's certainly an interesting thought. I wonder if, at that point, any terrestrial planet wouldn't have lost its internal heat yet, though considering it's got to be quite old. I'm also wondering if it could still have any kind of potentially life-bearing atmosphere too, considering it's unlikely to pick up a new atmosphere near the white dwarf.

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HirnsausenDate: Thursday, 30.10.2014, 05:29 | Message # 17
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Having planets again inside the very narrow habitable zone could happen probably because of two reasons
- catching a wandering planet from somewhere
- a previous outer planet, unstable orbit due to destruction of inner planets, came closer and stabilized

An atmosphere is subject of development and/or change.
- Change: the planet had already an atmosphere but the new heat changes surface reactions that also change atmosphere
- New: no atmosphere before, but the new heat causes evaporation on surface, thus creating an atmosphere

Type of atmosphere:
Anything is possible, from poisonous to habitable, depends on the materials that created the new atmosphere.

Since white dwarfs endure much longer than regular suns, if life found its way on a planet, it will have an even much longer life time to develop. If such habitable worlds around white dwarfs really can exist, habitable planets might be very old, life on them might be very ancient and ultra-highly developed. Who knows - maybe white dwarfs are the hosts for the wisest of all civilizations? Or the best-developed species. Not sure, how much the emissions of a white dwarf would cause mutations inside the DNA (if they use such) of the local species.
WatsisnameDate: Thursday, 30.10.2014, 07:03 | Message # 18
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The "catching a wandering planet from somewhere" sounds plausible at a first glance, but nearly impossible at a second. An object falling in towards a star from infinity has a tremendous amount of energy -- it starts out as mostly gravitational potential, then is converted to kinetic for an enormous increase in speed. If total energy is conserved, the object just swings right back out into interstellar space. Oops.

So for the object to be captured, a mechanism is necessary to transfer/dissipate that energy. This usually implies a dense medium of some sort. Furthermore, the mechanism must cease at the right time, or else the orbit will continue to decay until the planet falls too close to the white dwarf and is destroyed. To end up in a 'habitable zone' orbit, this process must be exceedingly precise. It is very hard to imagine it ever working out this way in nature.

It would be much easier for planets that were originally orbiting the star (though far enough to survive the prior giant phases) to decay into smaller orbits. This could happen gradually over large timescales, perhaps by planet-planet interactions.

As for forming a new atmosphere, yes, this could happen. For example, perhaps a rock and ice planet migrates inward to the point where its surface ices sublime, starting with methane. The methane atmosphere raises surface temperature and pressure, allowing water to achieve liquid phases. Perhaps then the planet is capable of supporting life.

There is another avenue to consider here, which is the possibility of habitable moons around a white dwarf, which can totally negate the meaning of 'habitable zones', or even the necessity of atmospheres. There is a lot of reasonable conjecture about life in the subsurface ocean of Europa, which is tidally heated by the other Galilean moons. One could imagine an analogous world around a white dwarf, with the life not even noticing that their star died.

Aside: I'd proffer this scenario for Europa's future, though I'm not sure how well it fares during the sun's giant phases. Quick calculation suggests Europa's surface temperature exceeds 373K (not that STP boiling point of water matters much for Europa's atmosphere). Maybe its oceans even boil away completely.

HarbingerDawnDate: Thursday, 30.10.2014, 13:55 | Message # 19
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Quote Watsisname ()
I'm not sure how well it fares during the sun's giant phases

I created a red giant Solar system in Celestia one time (I think I may have done it in SE too), and Europa was something like 1000K. Even Pluto was too hot. I recall that only Eris was a reasonable temperature. I should note that I created this to simulate the most luminous period of the red giant phase.

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Edited by HarbingerDawn - Thursday, 30.10.2014, 13:57
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