Saturday science subject: Planet-gazing


— 11:52 AM on November 15, 2008

Astronomers have been detecting planets beyond our solar system for a while now, but most extra-solar planets are too small and far away to see directly with telescopes. As ScienceDaily reports, however, a team of astronomers at the W.M. Keck Observatory in Hawaii has caught the first ever direct image of multiple planets orbiting a distant star.

The host star (a young, massive star called HR 8799) is about 130 light years away from Earth. Comparison of multi-epoch data show that the three planets are all moving with, and orbiting around, the star, proving that they are associated with it rather than just being unrelated background objects coincidentally aligned in the image. HR 8799 is faintly visible to the naked eye, but only to those who live well away from bright city lights or have a small telescope or even binoculars, see online finder charts here.

The planets, which formed about sixty million years ago, are young enough that they are still glowing from heat released as they contracted. Analysis of the brightness and colors of the objects (at multiple wavelengths) shows that these objects are about seven and ten times the mass of Jupiter. As in our solar system, these giant planets orbit in the outer regions of this system – at roughly 25, 40, and 70 times the Earth-Sun separation. The furthest planet orbits just inside a disk of dusty debris, similar to that produced by the comets of the Kuiper Belt objects of our solar system (just beyond the orbit of Neptune at 30 times the Earth-Sun distance). In some ways, this planetary system seems to be a scaled-up version of our solar system orbiting a larger and brighter star.

For the record, Jupiter's mass is over 300 times greater than the Earth's, so these extrasolar planets are pretty massive indeed. ScienceDaily notes that HR 8799 has about 1.5 times the mass of our Sun and is five times brighter, too. Finding planets closer to the Earth's size will involve "specialized space telescopes that are still on the drawing board."

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