Exoplanets, Let Me Show You Some

You can't have aliens without an alien planet. Fortunately, astronomers the world over have been providing planets for roughly 18 years, and they're not looking to stop anytime soon.

Of the 453 planets* confirmed to date, here are some highlights:

• "free-floating" planets, including S Ori 70, though it's debated whether these are really planets
• B1620-26 b, in a circumbinary orbit around a pulsar and white dwarf, and which also happens to be the oldest planet known
• Mu Arae c, the first terrestrial** planet discovered orbiting a main sequence star
• Gliese 876 d, the first super-Earth orbiting a main sequence star
• OGLE-2006-BLG-390Lb, the first icy super-Earth around a main sequence star
• Gliese 581 d, which may be an ocean planet
• WASP-17b, the first planet with a retrograde orbit
• PST B1257+12's three-planet*** system, the first system discovered
• Upsilon Andromedae's three planets, the first system around a main sequence star, and the first around a binary
• HD 209458 b, whose atmosphere we've learned a lot about
  
• HD 149026 b, which has a giant core
• TrES-4, the planet with the lowest known density (equivalent to balsa wood)
• HD 189733 b, which has water and methane, but is sadly a gas giant
• HR 8799, whose three planets have been imaged
• COROT-9b, the first known temperate planet (again, a gas giant)

I love how we're getting a wider range of planet types these days, and how we're able to study atmospheres long-distance. I also love that we're getting more accurate and refined, and finding smaller planets as a result. Hopefully we'll reach the stage where Earth-sized planets are commonly in the headlines, rather than the gas giants we're best able to detect at the moment. I'm also looking forward to our first long-distance detection of a planet with a moon.

Something else that's cool? Extrasolar planets don't have to orbit in the same plane, or follow the direction of the star's rotation.

Want to look up exoplanets? It seems to be a popular pastime, because there's exoplanetology.com, exoplanets.org, the Star and Exoplanet Database, and the Extrasolar Planets Encyclopedia.

Want to participate? It's not quite out yet, but there's a computer program in the works.

*and counting
** maybe
*** planet #4 currently unconfirmed