Three Neptunes, Asteroid Belt Circle Southern
Star
(From the July/August
2006 issue of StarDate magazine)
A team of astronomers led by Christophe Lovis of Geneva Observatory
has discovered that a dim, southern-hemisphere star only 41 light-years
away hosts three Neptune-mass planets. Slightly less massive
than the Sun, HD 69830 is visible with the unaided eye.
Artist's concept shows three planets and a plethora of asteroids
in HD 69830.
After monitoring the star for more than two years with the European Southern Observatory’s 3.6-meter telescope at La Silla, Chile, the team concluded that this system has a lot in common with our own solar system.
Each of the three planets has a minimum mass of 10 to 18 times Earth’s mass. They have orbits of 8.7, 31.6, and 197 days. One of the planets lies in the so-called “habitable zone,” where water could exist in liquid form. Astronomers using Spitzer Space Telescope recently discovered a possible asteroid belt around this star.
Based on computer simulations, Lovis’ team thinks that the innermost planet is probably rocky, the middle planet is made of rock and gas, and the outermost planet has a rock and ice core surrounded by a massive envelope of gas. This outermost planet is the first known Neptune-mass planet to reside in the habitable zone. — Rebecca Johnson
» More information about extrasolar planets
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