Since the discovery of the first exoplanet in January of 1992, astronomers have identified over 5,500 of them, with nearly a thousand of the systems analyzed having more than one detected planet. It now appears that at least one of the variables in the Drake equation -- fp, the fraction of stars that have planets -- is far higher than anyone might have expected.
What has come as an additional surprise is how varied these worlds are. Having grown up on a steady diet of Lost in Space, Star Trek, and Star Wars, I kind of had exoplanets pictured as mostly Earth-like, with lots of big rocks and maybe an odd-colored sky:
The truth is, every new one we find holds some sort of surprise. Some of the odder ones are:
- TrES-2b, which holds the record as the least-reflective planet yet discovered. It's darker than a charcoal briquet. This led some people to conclude that it's made of dark matter, something I dealt with here at Skeptophilia a while back. (tl:dr -- it's not.)
- CoRoT-7b, one of the hottest exoplanets known. Its composition and size are thought to be fairly Earth-like, but it orbits its star so closely that it has a twenty-day orbital period and surface temperatures around 3000 C. This means that it is likely to be completely liquid, and experience rain made of molten iron and magnesium.
- 55 Cancri e, nicknamed the "diamond planet." Another "hot super-Earth," this one is thought to be carbon rich, and that because of the heat and pressure, much of the carbon could be in the form of diamonds. (Don't tell Dr. Smith.)
- PSR J1719−1438, a planet orbiting a pulsar (the collapsed, rapidly rotating core of a giant star). It has one of the fastest rates of revolution of any orbiting object known, circling its host star in only 2.17 hours.
- V1400 Centauri, a planet with rings that are two hundred times wider than the rings of Saturn. In fact, they dwarf the planet itself -- the whole thing looks a bit like a pea in the middle of a dinner plate.