Re: Solar System around 55 Cancri

On Thu, 8 Nov 2007, Rumpelstiltskin wrote:

Lehrer's newshour yesterday had an unusual segment about a nearby solar system around a star 40 light years away, in the constellation Cancer. The interesting thing is that there are apparently five planets so far around this star, which is evidence supporting the idea that solar systems are common. The planets around 55 Cancri are huge by our solar system's standard, the four smaller ones being about the size of Neptune and the more distant large one being four times the size of Jupiter, or we wouldn't be able to detect them yet. We haven't actually "seen" the planets, we just know they're there by analyzing the wobble of the star that we can see. Similarly, our own sun would move slightly back and forth as see from a distance, because Jupiter pulls on the sun as it orbits around it. http://www.sciencedaily.com/releases/2007/11/071106133058.htm Analyzing the components of the wobble of 55 Cancri based on five large planets pulling on it seems to me quite a difficult project, because of the exactness required about the change of position of the star over a period of time needed to allow multivariate analysis of what components would be contributing to its complex resultant pattern of motion.

55 Cancri is a yellow dwarf like our sun, and in addition to its planetary system it has a red dwarf companion 1000 AU away: http://en.wikipedia.org/wiki/55_Cancri

40 light years is fairly close to us. The closest star system to Sol is the Alpha Centauri system four light years away, so there are (ball-park) only about (40/4) cubed = 1000 stellar systems that close to us.

Hope we get to communicate with one of these one of these days!

If the orbits are as large as in our system, then I agree that it's a difficult job to identify the planets from the wobble. But it may be that the peculiar wobble is just a way to identify stars which are different from binary star wobble which is when two stars revolve arround each other. Some of the distant planet orbits may be decades long.

I would guess that spectroscopic data would show multiple light sources at different temperatures-- all at a lower temperature than the sun of course. And the intensity of the sources would be an indication of their size. Look to the infrared spectrum and a way to block out the solar infrared-- with good enough optical resolution I guess. To close the question, a calculation to show that there exists a given set of orbits such that the observed planets are sufficient to explain the peculiar wobble.
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