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Cristian Monea

16 Iun 2009 23:16



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Possible planets

Observations from the James Clerk Maxwell Telescope in 1997 revealed an "elongated bright central region" that peaked at 9″ (70 AU) to the northeast of Vega. This was hypothesized as either a perturbation of the dust disk by a planet or else an orbiting object that was surrounded by dust. However, images by the Keck telescope had ruled out a companion down to magnitude 16, which would correspond to a body with more than 12 times the mass of Jupiter. Astronomers at the Joint Astronomy Centre in Hawaii and at UCLA suggested that the image may indicate a planetary system still undergoing formation.

Determining the nature of the planet has not been straightforward; a 2002 paper hypothesizes that the lumps are caused by a roughly Jupiter-mass planet on an eccentric orbit. Dust would collect in orbits that have mean-motion resonances with this planet—where their orbital periods form integer fractions with the period of the planet—producing the resulting clumpiness.

In 2003 it was hypothesized that these lumps could be caused by a roughly Neptune-mass planet having migrated from 40 to 65 AU over 56 million years, an orbit large enough to allow the formation of smaller rocky planets closer to Vega. The migration of this planet would likely require gravitational interaction with a second, higher mass planet in a smaller orbit.

Using a coronagraph on the Subaru telescope in Hawaii in 2005, astronomers were able to further constrain the size of a planet orbiting Vega to no more than 5–10 times the mass of Jupiter. Although a planet has yet to be directly observed around Vega, the presence of a planetary system can not yet be precluded. Thus there could be smaller, terrestrial planets orbiting closer to the star. The inclination of planetary orbits around Vega is likely to be closely aligned to the equatorial plane of this star. From the perspective of an observer on a hypothetical planet around Vega, the Sun would appear as a faint 4.3 magnitude star in the Columba constellation.

(c) http://en.wikipedia.org/wiki/Vega