Warm and windy nights

摘要

In May this year astronomers announced the first weather report for an alien world. Although fairly crude, it hints that some pretty wild weather is blowing on a giant Jupiter-like planet. HD 189733b was discovered in 2005. Seen from Earth, it transits its star, passing in front of it and then behind it on each 2.2-day-long orbit. Like most planets that are very close to their stars, HD 189733b has one side always facing its star in perpetual daytime while the other is permanently dark. The cooler, night side of HD 189733b faces us when the planet is in front of its star and the hotter day side rotates into view just before the planet disappears behind its host.