[John]

I have a story in planning stages, but I want to know how viable it is (not that it's going to stop me from going through with it).  Let's say there are two equally-sized planets (= in mass) orbiting each other, but at some point the gap closes between them to the point where they collide and form a new planet. 

A. How long would it take for the new planet to have a stable spherical shape? and
B. What about the water and atmosphere? 
C. Temperature?  How much heat would it produce?

The tentative idea is to have two twin planets collide, while at least two survivors are in a ship close to the shared atmosphere of the two planets.  How long would they have to be in orbit until the planet is livable?  The ships could be like self-sustaining space stations.  I just hope it isn't some span beyond 20 years, because it would ruin the plan for my story.  I calculated that two planets, having equal masses and densities before collision, and equal densities before and after, would make a new planet where everything is 1.26 times heavier than on the original two planets.  Therefore, my original proposition for the ships to crash back onto the bigger planet will have to be reworked.

If all else fails. I could always just put the characters into suspended animation until the new planet is ready, and supply their ships with advanced terraforming tools. 

It won't be the first apocalyptic muscle story I've made, but it will be the first from this approach. 

[Solarian, aka LordDaroth]

First: those cahnces are beyond astronomical (but earth and moon is a fine example of planetary collosion)

Second: Millions and millions if not a billion year…

[luvmuslgirls]

I'm afraid Solarian's approximations are fairly accurate on the reality of the circumstances that would occur in your proposed scenario. The collision would be cataclysmic and anything within a certain distance would probably be destroyed. Whew! sorry. Slipped into my Doctor Who/Carl Sagan mode there. ::)

Anyway, if you want realism, you will need to change something of your idea. Maybe the characters are not of that region of space? Maybe they had an unmanned probe monitoring the planetary system from light years distance. What are the characters setting? Do they have advanced technology? Some kind of hyperdrive space travel? Or they have a generation ship or something like a stasis field as they travel a million, billion years to the planetary system? Just some suggestions.  🙂

[John]

OK, thanks.  I tried Googling the answer and it was just one of those searches that yields results totally unrelated to the question I was going for.  Like I said, the relative speed is practically non-existent; they aren't going right at each other, but slowly meeting.  I guess if they got within a certain range the g*M[1]*M[2]/r^2 value would skyrocket, and would cause a great deal of gravitational acceleration and a big crash.  I was fearing something to the scale of millions of years. for fusion into a stable planetary body.  Time travel is an option, but not one I'm crazy about using in this case.

Maybe I'll work it so the two planets with another one in between, kind of like the Venus-Earth-Mars set up.  It would kind of mess up the symbolic idea I'm going for, but I want to make the story somewhat plausible.

BTW, they are supposed to be pre-space stage, but need to develop a vessel to escape the planetary doom – both planets.  I haven't put much thought into their techs beyond that.

[Holiday]

That’s a scary premise, MuskelGrothe. I don’t think anything can survive such a collision, regardless of technology. If it were a catastrophic asteroid or meteroite attack, some people might be able to be kept in stasis. But on the planetary surface anything more than 100 kg. would die. That’s according to theory one scientist had about the last Ice Age.

[Fett]

I think it would matter greatly on the planet’s themselves (density for example) and their proximity to their sun, as well as what stage the sun’s development is in.

Also, for the people on the planets, they’d feel strange effects that would probably wipe them out before the planet collided due to the forces of gravity involved. The two Earths would pull at each other, lifting buildings right from their foundations probably.

[Holiday]

This reminds me of a superhero idea I had that reflects the primordial origins in ancient myths. What if a huge battle between superheroes and supervillains ended up with a huge explosion (like in DC’s Kingdom Come). A few weeks the area is still off-limits. Then suddenly a new generation of superhumans emerged from the blasted earth. Their minds are initially blank, despite having fully developed bodies.

[Solarian, aka LordDaroth]

Resurrecting a three month old dead thread…

[Holiday]

Solarian, aka LordDaroth wrote:

Resurrecting a three month old dead thread…

I don’t browse this part of the website often. So when I do I look for subjects that interest me.

[AlexG]

Don’t know about collisions, but if it was on the subject of planets blowing-up I’d recommend Tom Van Flandern as a reference source. Yrs back, he use to be reg guest (along w/ Richard C Hoagland) on Coast to Coast AM w/ Art Bell.

“I like a good story well told. That is the reason I am sometimes forced to tell them myself.”
~ Mark Twain / Samuel Clemens (1907)

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