For the past decade or so astronomers have been discovering planets around other stars. By discovering I mean inferring, as the process of detecting these bodies involves measuring the wobble in the star's motion or parsing spectroscopic readings of the star as the planet transits in front of it. So far about 200 planets have been found, all of them large ones as you would expect. Jupiter is the first planet you'd notice in our solar system if you didn't live here. Some of those exoJupiters are weird, though. The wobbly-star method tends to find planets with highly eccentric elliptical orbits. It's supposed that solar systems with those don't have small Earth-like planets with life on them because the eccentric giants sweep the small planets into cometary orbits. Other large planets, the "hot Jupiters", orbit in close proximity to their star. If, as is thought, these star-hugging giants spiraled inward from the outer reaches of their solar systems then there probably aren't any small Earth-like planets left in the liquid water zone of those solar systems either.
HD209458b, unofficially Osiris, is a hot Jupiter orbiting a yellow Sun-like star about 150 light-years from here in the constellation Pegasus. The planet is about two thirds the mass of Jupiter though with a larger radius. It is one eighth as far from its star as Mercury is from the Sun, and makes an orbit once every three and a half days. Its surface temperature is something like 1000 degrees celsius. And, as it turns out, it has water. But given the circumstances in which it finds itself, the water's on the boil. The planet has a plume of superheated gas streaming off it that must be an astonishing sight.
So far this century doesn't have much to commend it, but it's discoveries like this that make me happy to be living in it.
For more on this new planet see here and here.
Douglas (Image from ESA via CBC)
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