This has been the talk of the Internet today, so I might well write about it as well... for the first time, scientists were able to capture images (in visible light, no less) of not one, but four extrasolar planets orbiting around two separate "normal" stars (we had already seen images of a planet orbiting a brown dwarf star).
First, we have star HR8799, a young star that is a bit larger than our Sun (1.5 times as massive and 5 times as bright) and that lies 130 light years away in the constellation Pegasus. Images taken with the Keck and Gemini North telescopes in Hawaii show three large planets orbiting this star; one is about seven times and other two are 10 times as massive as Jupiter. They orbit the start at distances ranging from 24 to 67 AU (the planetary limits of our own solar system are around 30 AU).
Apart from the historical value of directly imaging these planets, this event is significant for other reasons: this star is very similar to our own, and these large planets are orbiting it at a large distance, leaving space closer to the star for small rocky worlds; in other words, this might be a solar system similar to our own, which is something of a rarity among the hundreds of other solar systems we've already found.
Secondly, we have Fomalhaut, a larger star (2.3 times as massive and 16 times as bright as the Sun) 25 light years away in the constellation Pisces Austrinus, the southern fish. It's been known for a while that this star is surrounded by a large dust disk; in fact, the very sharp inner edge of this disk was a clue that there was a planet there, cleaning out debris just inside the disk. And, indeed, Hubble images do show a bright planet located there, in a very wide orbit around the star. The planet seems to be about twice as massive as Jupiter, and its brightness may indicate it is surrounded by a very large ring system.
The planet orbits the star once every 872 years at a distance that is almost four times the distance from Neptune to our Sun, but since Fomalhaut is brighter than our Sun its appearance would be similar to how the Sun appears when seen from Neptune. Just as is the case with HR 7899, Fomalhaut is a very young star and its solar system is still being formed, which helps in the detection of the planets: they're still hot enough that they radiate brightly in the infrared.
Both stars are visible with the naked eye from a dark sky site, and Fomalhaut should be easily visible even from a urban setting. If you are in Melbourne (or any place at the same latitude), Fomalhaut will be almost directly overhead today soon after sunset — it's bright enough that you can't really miss it. HR 7899 will be a bit harder to find; Pegasus will be visible on the northern sky in the middle of the night, and the Lowell Observatory press release has a diagram that will help you find the right star (it's likely you will need a binocular or small telescope, though).
For more details and images, in addition to the links in the text above, see the (very enthusiastic) Bad Astronomy blog and Centauri Dreams.
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