The aging Sun-like star HD 69830 has three planets and an asteroid belt orbiting it less than 1 astronomical unit away. The three planets are at least as large as Neptune, with minimum masses of 10, 12, and 18 times Earth's. Credit: European Southern Observatory
Scientists Discover a Very Familiar-Looking Planetary SystemTwo years of close observations of the star HD 69830 have revealed that it is orbited by no less than three low-mass planets, with a minimum mass only 10-18 times that of Earth. Furthermore, scientists strongly suspect that HD 69830 is also host to an asteroid belt.
The Planetary Society
30 May 2006
The system around HD 69830, the authors explain, is unlike any of the other 17 planetary systems discovered so far. All other known systems are dominated by at least one giant Jupiter-sized planet, with a mass hundreds of times that of the Earth. In contrast, the newly discovered system is composed of planets of roughly equal size - all with masses similar to that of our neighbor Neptune. The innermost of the three planets orbits its star in just under 9 days, whereas the two outer ones complete each revolution in 32 days and 197 days respectively. Intriguingly, this places the outermost planet just inside the star's "habitable zone" the region in space in which liquid water is stable.
Asteroid Belt Like Ours Spotted Around Another StarThe scientists have not actually seen any asteroids around Zeta Leporis, a young star twice as massive as the Sun and 60 to 70 light-years away. Instead they have studied the temperature and position of the star's swirling mass of debris, which they say shows evidence of chaotic collisions among rocks that creates the dust needed to sustain such a disk... Zeta Leporis, also called HR 1998, is between 50 million and 400 million years old, compared to our middle-aged Sun, which is about 4.5 billion years old. Along with some other young stars, it was found in the 1980s to have a ring of dusty debris. And in 1991 astronomers learned that this debris ring was unusually warm and close to its parent star, unlike other disks that are farther out, and hence colder. This dust, given its known properties, should spiral into a star within 20,000 years, according to current theories of physics and star formation, scientists say. But this star is much older.
by Robert Roy Britt
4 June 2001