Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

October 19, 1996

Lalande 21185: The Nearest Planetary System?
Credit and Copyright: John Whatmough, Extrasolar Visions

Explanation: What's the closest extrasolar planetary system? It may well be planets of the dim red dwarf star catalogued as Lalande 21185 -- a mere 8 light years distant. This star is too faint to be seen by the naked eye and its planets have not been imaged directly. Instead, their presence is inferred by a long series of telescopic observations, tracking the star as it wiggles and wobbles in mutual gravitational response to the masses of its orbiting planets. Our own planetary system would be detectable by such a technique ... Using data obtained from frequent observations of this star over the last 50 years, University of Pitsburgh astronomer George Gatewood recently announced that much of Lalande 21185's wobble is most likely due to an unseen planet with approximately 90% of the mass of Jupiter and an orbital period of 5.8 years. His work also indicates that a second and possibly third planet of similar mass could well be present in the system. Massive planets orbiting a red dwarf star would be very different from the Earth -- as illustrated in this artist's vision of a Jupiter-sized planet with rings and moons lit by a cool, dim sun. Nevertheless, the existence of a planetary system so near our own suggests the intriguing possibility that planets are common in our galaxy.

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