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Runaway exoplanets

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Thu, 2012-03-22 16:17

Arenamontanus Arenamontanus's picture

Runaway exoplanets

Here is an interesting possibility: very fast planets that have been thrown out of the galaxy by supermassive black holes. http://www.cfa.harvard.edu/news/2012/pr201206.html http://io9.com/5895598/hypervelocity-planets-are-zooming-out-of-our-gala...

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Mon, 2012-03-26 19:34

Extrasolar Angel Extrasolar Angel's picture

Re: Runaway exoplanets

What would be the consequence of such planet colliding with an asteroid or meteorite swarm, considering its fast speed? Would the result be very explosive or does have no consequences?

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Tue, 2012-03-27 03:36

Arenamontanus Arenamontanus's picture

Re: Runaway exoplanets

Big boom. At 15 000 km/s, a one kilogram impactor has kinetic energy 10^14 joules, or about 26 kilotons. That is twice Hiroshima. To get enough energy to overcome the gravitational binding energy of an Earth-sized runaway exoplanet (that is, to blow it up) you need 2*10^18 kg - about the size of a small moon like Hyperion. I suspect that the exoplanet would have its front side scoured by radiation (hydrogen gas is a proton beam from its point of view) and nuclear impacts, while the back is relatively safe. Unfortunately it likely has a rapid rotation (due to massive torques during the slingshot)... The gatecrashers come out of the gate and find a cold but impressive sight: a galaxy covering much of the sky, a heavily cratered icy landscape. As they investigate they notice a few things: the rotation is quite fast, the galaxy is slightly redshifted, and their seismometer is going bananas for some reason. As the galaxy sets they start to notice strange light flashes near the eastern horizon...

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