With regards to this story in UT: http://www.universetoday.com/am/publ...th.html?542006

It got me wondering whether this type of collision between 2 planets or proto-planets would be detectable from Earth. If say it happened in a solar system within 100 light years of Earth, would we be able to detect it in any way? I would imagine the explosion to be simply huge.

Also, how many starts are there within 100 light years of Earth?

I know thats 2 question just wondering if one of you brainy people could help?

Many Thanks

There are about 110 stars within 20 light years of Earth. Assuming the same density, there would be about 13,750 (110*(100/20)^3) stars within 100 light years.

I'm skeptical about being able to see such an event due to the vast distances involved, but perhaps someone here can do the math and possibly correct me.

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Actually I'd guess that an infrared telescope would have little trouble observing the heat and debris from such a collision. I'll do some calculations for a more detailed estimate, to see how two Mercurys colliding compares with the IR output of the Sun. I'm guesing that for ten minutes or so it will be more than a few percent of the Sun's output.

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Actually, I remember reading something like this in S&T (I think it was) several years ago, about how some astronomers theorized that planet collisions should be common in very young systems, and easily detected from Earth. I think the example they simulated was a terrestrial planet (Earth or Mars-sized) hitting a gas giant (Jupiter-sized), something which would leave noticeable aftereffects for perhaps millennia afterward. They acknowledged that you'd have to observe a *lot* of young systems to have a good chance of observing one, though.

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"Call me old-fashioned, but I think fire is magic. And it scares me a lot."

--The State

Wow - I thought the explosion would be big! but a few percent of the Suns output! Jeez that is one HUGE amount of energy!

This is what I had in mind... If we were to look for these collisions surely we would be able to find out how common they are in young systems.

thanks for the reply's guys

I even found a reference!

http://www.citebase.org/cgi-bin/cita...tro-ph/0308218

__________________
"Call me old-fashioned, but I think fire is magic. And it scares me a lot."

--The State

Excellent link Romanus - thanks