Is it possible for two planets to merge and still sustain life?

[Lonewolf27]

Hi people!

Strange request but not having much luck in anything specific to what I'm doing, either that or I'm not sure what i should be searching for...

I'm making a fantasy world for a book and wanting to create a single planet that is still distinguishable as having been 2 separate planets at a previous time. (similar to the bubbles above, but separated more). I've toyed with ideas on what may or may not work and realized its a bit over my knowledge level.

My reason I am seeking help is to find out several things:

- Could the 2 partially merged planets sustain this state? (maybe they could be still orbiting each other while physically attached)
- Could pre-existing life survive even a minor collision of the 2 planets?
- How would gravity work at different points on the planet?
- What would you expect the planets rotation to be like?
- What would happen along the "rub" points as the 2 planets synchronised their rotations? (would there be a large valley or a volcanic ridge)

Strange question I know, but I think its a cool concept for a world and want to get as much out of it as possible in regards to scenarios and further ideas.

Any help is appreciated, even if only to tell me where to look or what book i should be reading.

Cheers,
Lonewolf

 

[Naty1]

Could the 2 partially merged planets sustain this state? (maybe they could be still orbiting each other while physically attached)
its possible
- Could pre-existing life survive even a minor collision of the 2 planets?

unlikely http://en.wikipedia.org/wiki/Impact_event

- How would gravity work at different points on the planet?

much like it does on earth...everything on th surface is attracted to the center of gravity (mass)

- What would you expect the planets rotation to be like?

it would have to be gentle enough so as to no separate any parts...gravity would have to hold the planets together...

- What would happen along the "rub" points as the 2 planets synchronised their rotations? (would there be a large valley or a volcanic ridge)

the planets would rub in a such as way as to minimize the gravitational potential energy...that is the centers of mass would tend to move as close together as possible but would be opposed from doing so by friction...

 

[JDługosz]

There's no such thing as a "minor" collision.

Check out the double-planet Roche/Ewe that share an atmosphere, in Robert Forward's novels set there.

 

[granpa]

you would need to make one a moon and have it slowly spiral inward till it reached the roche limit.
At that point I am not sure what would happen.
of course they would have to be tidally locked at all times

 

[JesseC]

I suppose the planets would have to be reasonably small (or just not too dense). Too big and the gravitational forces would pull them into a sphere.

Although still presumably big enough to retain an atmosphere if you're thinking of life there?

Gravity would be stronger where there is more ground underneath... so on the 'ends' of the double planet.

Due to conservation of angular momentum i would expect the object to be rotating fast...

 

[Lonewolf27]

Thanks for your replies

You've given me some ideas and concepts to think about. The current concept I have is as follows:

- Planet A Is in orbit around its sun. Planet B is on the same orbit but slightly faster, shadowing planet A.
- They eventually have a cosmic collision and planet B becomes a Satellite of planet A
- Due to the masses/velocities of the 2 planets, Planet B's falling orbit, it eventually makes contact with planet A once more.
- Any liquid water on both planets would touch before any landmass does, this would cool the landmass's friction of each planet when they actually touch, preventing the mantle being breached, and also Planet B's falling orbit
- The Axis of rotation they are on in all likely hood would be different, causing a massive climate change to the worlds as they synchronised. But as both had pre-existing atmospheres before the second collision took place they would both be capable of supporting life, but maybe not the pre-existing life.

Possible phenomena
- As mentioned by Granpa Most of the liquid water on one planet would be following the other planet, likely leaving the only water source as a single ocean around the merge point. An Ice age on both planets prior to the 2nd contact might explain why water is still abundant. The water would still want to collect at that point, and would be lethally hot as friction disperses its heat into the water, causing it to evaporate, the lack of sunlight in the area causing it to cool quickly back to its water state.
- Just like with the water, the atmospheres would move to the merging point, this would leave the furthest point of each planet with relatively thin atmospheres
- The planet you would be on would have the dominant gravity, but with a strong influence from the other planet's pull, meaning there would be some sideways pull unless you were standing on the furthest point on either planet.

Is that close to believable? Any obvious flaws in logic?

Thanks again for your feedback,
Lonewolf

 

[Chronos]

A classic 3 body problem in space. There is no absolute solution, only approximations. Add more gravitating bodies and you get a bigger mess [but can still be approximated].

 

[JDługosz]

Is that close to believable? Any obvious flaws in logic?

The amount of energy released would melt both bodies to magma. There's just know way to have a "soft landing"!

After they are in common orbit and the orbit decays (why?), it will reach Roche's Limit where the tidal forces rip it apart. Think Saturn here. A large body would not stay intact all the way down.

In "low orbit" you are moving at some 17000 miles per hour. The planet's rotation will be much slower, so it will make quite a scrape when it lands, if that much were possible.

"Same orbit" and "slightly faster" are mutually exclusive. If they are in orbits that are very close together, they will interact over time and swap places, as is seen with at least one set of moons in our own solar system.

 

[JDługosz]

You said it's a "fantasy world", so don't worry about making it hard science fiction. Just say a powerful wizard did it.

 

[RocketSci5KN]

The best you could probably do is to have the rotational speed of PlanetA match the orbital speed of PlanetB so there is no relative velocity between the two near surfaces. And of course, PlanetB would need to be tidally locked to A. I have no idea if this would be even semi-stable for any size of A and B. Obviously, your best story would be if A and B were about the same mass and 'almost' touching, say 25mi apart, so you could trap an atmosphere between the two and have very low gravity between them.