英語時差：冰冷的24 Themis小行星（上）

One of the most intriguing questions in science is where the earth’s oceans came from. Did the planet always have water? Or did it come from somewhere else? A discovery suggests that Earth owes its watery nature at least in part to extraterrestrial sources. Namely, asteroids. A team of scientists published a report showing that one of the largest known asteroids in the solar system, called 24 Themis, has frozen water on its surface. Scientists have long suspected that asteroids contain water. But until now, they’ve had to estimate how much water a given asteroid may have had by measuring the minerals found in meteorites.