Nine planet solar system found, with room to grow
By John Timmer |
Astronomers have pulled off an interesting magic trick and made two planets appear. Since they appeared in a planetary system that already had seven, it gives that planetary system a total of nine, making it the most planet-rich system we're aware of (since our own has only eight). It may further its lead in the future, as well, as the authors conclude that there's not enough data yet to identify an Earth-sized planet.
How does one make a planet appear? In this case, it's the result of their method of discovery. Most planet candidates these days are coming from Kepler, the space-based telescope that watches for planets that orbit in front of their host star from Earth's perspective. This results in a small fraction of the star's light being bocked out on a periodic basis, with the size of the fraction being roughly proportional to the size and orbit of the planet.
Prior to Kepler, most exoplanets were discovered by looking for their gravitational influence on the host star. Planets don't actually orbit around an immovable host star; they both orbit around their collective center of mass. It's just that the star is so much more massive, the center of mass is typically within its radius. Nevertheless, that's enough to pull the star slightly in various directions as the planets orbit from one side of the star system to another. That motion is enough to allow the Doppler effect to shift the light of the star to slightly different wavelengths.
Detecting these Doppler shifts is easy when there's just one planet, since they should change with a period that corresponds the the planet's orbit. As the number of planets grow, however, the signals get increasingly complex. On one orbit, a set of planets could all pull together, creating a large shift. A few orbits later, those same planets may be scattered across the system, largely canceling each other out. Periodic changes within the star itself can also complicate the analysis.
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http://arstechnica.com/science/news/2012/04/new-analysis-adds-two-more-planets-to-an-already-crowded-system.ars
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