SSS 2010-04-29

（单词翻译）

This is Scientific American's 60-Second Science. I'm Karen Hopkin. This’ll just take a minute.

Any school kid can tell you that comets are made of ice. That frozen water burning off is what gives comets their characteristic tails. But asteroids² were generally thought to be dry. Or at least frost-free. Now two studies published in the journal Nature suggest that notion may be all wet. Because at least one asteroid¹ appears to be coated by a thin layer of ice. And just that kind of asteroidal³ frosting could have been the source of our water here on Earth.

The asteroid belt just outside Mars is home to a lot of rocky bodies…including a behemoth with a diameter of 129 miles. This asteroid, called 24 Themis, is one of the largest in the belt and has attracted the attention of astronomers⁴ because its nearby traveling companions look like comets.

In the latest studies, scientists used an infrared⁵ telescope to spectroscopically examine the asteroid’s surface. And the chemical signature they saw was a good match for water ice, which they found all over the asteroid.

The find provides support for the theory that Earth’s water could have been delivered as ice by an asteroid. Lucky for us we could borrow some from the neighbors.

Thanks for the minute for Scientific American's 60-Second Science. I'm Karen Hopkin.