Ice on Asteroid Suggests Earth's Water Came From SpaceAP: Scientists have found lots of life-essential water -- frozen as ice -- in an unexpected place in our solar system: an asteroid between Mars and Jupiter.
The discovery of significant asteroid ice has several consequences. It could help explain where early Earth first got its water. It makes asteroids attractive to explore... And it even muddies the definition between comets and asteroids...
This asteroid has an extensive but thin frosty coating. It is likely replenished by an extensive reservoir of frozen water deep inside rock once thought to be dry and desolate, scientists report in two studies in the journal Nature... What they found on 24 Themis, a rock more than 200 miles wide with temperatures around 100 degrees below zero Fahrenheit, was more than they ever expected...
Furthermore, scientists didn't find just ice; they found organic molecules, similar to what may have started life on Earth... Earth, when it formed billions of years ago was dry, scientists say. So where did the water come from? One leading theory is from crashing comets... But comets come from the outer reaches of the solar system and tend to have more heavy hydrogen than the water in our oceans... Icy asteroids between Mars and Jupiter might have the right heavy oxygen ratio to match what's on Earth...
The icy asteroid also just makes a mess of the differences between asteroids and their cosmic cousin, the comet. The general definition has been that asteroids are dry rocks and comets icy snowballs. Now it seems to be more a continuum of dry and icy with not much difference.
