The BBC has a report that evidence has been found in lunar rock samples of a planetismal (called Theia) that was thought to have crashed into the Earth to form the Moon. The conclusion is based on a difference in oxygen isotope ratios detected in lunar rock samples returned from the Apollo space missions versus terrestrial samples.
The report is published in the journal Science [abstract]; report is paywalled.
(Score: 2) by Alfred on Friday June 06 2014, @05:11PM
This is an interesting idea. You get me to thinking...
Assuming that enough kinetic energy turns to heat then things could melt. And not everything would have to melt, just enough to ease the action of going to a round shape. And even though debris would be flying everywhere our scenario only worries about what is left.
However:
I think that it would take a lot of energy to melt all those solids into liquids. The fracturing of solids would take considerably less energy and thus be more likely. Kinda like hitting a rock with a hammer, the rock will break before it melts.
hmm...
/HypotheticalRambling
(Score: 0) by Anonymous Coward on Friday June 06 2014, @10:47PM
Do you have any idea just how big space is, how big planets are, or how fast things go in space? The earth itself is moving around the sun at about 30 kilometers per second. Thats somewhere around 66,500 miles per hour. For the sake of simplicity, lets just use that as the average speed for anything in orbit around the sun. The earth's mass is something like 6 x10^24 (a 6 followed by 24 zeros), and its a small planet. So if earth were to impact something else, the kinetic energy involved from just the earth alone (Force = 0.5 x Mass x Velocity x Velocity) is a mind-bogglingly huge number, more than enough to melt a whole lot of rock.
I dont mean to sound condescending, but this is some pretty basic stuff, and its incredibly fascinating if you start looking into it (which I really encourage you to do!)