Have any planets outside our Solar System been spotted by telescope?

2M1207 b (the red one) orbiting 2M1207 (the blue one)
Question posed by David.

As of 8th August 2011 (the time of writing) 573 planets have been found outside of our own Solar System. Of these, only 24 have been discovered by direct imaging with telescopes. The vast majority of "extrasolar" planets are discovered using other techniques as, due to the relative closeness of a planet to its parent star along with the massive difference in brightness, it is usually very difficult to notice the planet: try taking a photograph of a pinhead next to a streetlamp at night!

Until recently (very recently- we're talking 2010 onwards, here) for a planet to be photographed orbiting its sun, it needed to be very large (the bigger the better), very young and hot (so that it emits a lot of infrared radiation), and with as wide an orbit as possible. Now, though, techniques and equipment are being developed that allows more planets to be imaged directly.

The information I'm about to quote comes from the Extrasolar Planets Encyclopaedia, which cites its last update as being today. I won't name all 24 directly imaged exoplanets to date; you can visit the Encyclopaedia yourself for that! I'll just pick out what I see as being some interesting ones:

The first exoplanet to be directly imaged was 2M1207 b (pictured above!), discovered in 2004 orbiting the star imaginatively named 2M1207, a brown dwarf in the constellation Centaurus. The planet is four times the mass of Jupiter (deonted "4 MJ" from now on).

Five planets have been discovered by direct imaging this year. They are:
  • CD-35 2722 b (mass = 31MJ)
  • CFBDS 1458 b (mass = 6.5 MJ)
  • HIP 78530 b (mass = 23.04 MJ)
  • SR 12 AB c (mass = 13 MJ)
  • WD 0806-661B b (mass = 8 MJ)

CD-35 2722 b is the largest exoplanet to have been discovered by direct imaging. The smallest is Formalhaut b, with a mass less than 3 MJ, orbiting Formalhaut in the constellation Piscis Austrinus, discovered in 2008.


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