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300B

January 24th, 2007

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The 200-odd extrasolar planets that have been discovered with the radial velocity method are orbiting stars that lie within a few hundred light years of the Sun. The light we now see coming from GJ 876 left that red dwarf back in early August 1991. When you’re in the bars drinking to celebrate the periastron passages of HD 80606 b, it’s easy to forget that last December’s periastron passage actually occurred in September 1817.

By galactic standards, however, a distance of 300 light years is still right next door. For every star within 300 light years of the sun, the Milky Way contains roughly 300,000 additional stars that are farther away. All told, adopting the latest rules on what constitutes a planet, our galaxy likely contains about 300 billion planets, of which perhaps 500 million are hot Jupiters.

Right now, 51 Peg, HD 209458, Upsilon Andromedae, et al. count among the Sun’s local galactic neighbors, but this hasn’t always been the case. The velocity dispersion of stars in the solar neighborhood is ~20 kilometers per second. A kilometer per second is a parsec per million years, which means that in a mere 15 million years, the roster of nearby planets will contain very few familiar names. HD 209458b is transiting now, but in a few hundred thousand years, it’s likely that the line of sight to the system will no longer allow Earthbound observers to watch that dip every 3.5247542 days.

So get out there while there’s still time! Due to a computer glitch, the transitsearch candidates table failed to get its nightly update for the past several nights. I’ve fixed the problem, and the ephemerides are all up to date.

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