Planetary system looks very like our own

Posted by Kate Taylor

With the discovery of a fourth giant planet, astronomers are hailing the HR 8799 system as remarkably similar to our own.

The international team has imaged a fourth giant planet in the system, showing it to be a supersized version of our solar system.
 
"Besides having four giant planets, both systems also contain two 'debris belts' composed of small rocky or icy objects, along with lots of tiny dust particles," says Benjamin Zuckerman, a UCLA professor of physics and astronomy.
 
He's referring to Jupiter, Saturn, Uranus and Neptune, along with the asteroid belt between the orbits of Mars and Jupiter and the Kuiper Belt beyond Neptune's orbit.
 
The newly-discovered fourth planet orbits HR 8799, which lies some 129 light years from Earth and is faintly visible to the naked eye.

But while its layout resembles our solar system, it's much larger: astronomers estimate that the combined mass of its four giant planets may be 20 times greater than the mass of all the planets in our solar system. The debris belts also contain much more mass than our own.
 
Three previously discovered planets were the subjects of a 2008 paper in Science, as the first-ever images of a planetary family orbiting a star other than our sun.
 
All four planets orbiting HR 8799 are similar in size, probably between five and seven times the mass of Jupiter. The latest discovery orbits HR 8799 more closely than the other three; if it were in orbit around our sun, the astronomers say, it would lie between the orbits of Saturn and Uranus.
 
The astronomers used the Keck II telescope at Hawaii's  Keck Observatory to obtain images of the fourth planet.
 
The origin of thee four giant planets remains a puzzle; neither of the two main models of planet formation can account for all four.
 
It's perfectly possible that the system contains additional planets closer to the star - quite possibly rocky, Earth-like planets, Zuckerman said. However, these would be hard to detect.

The report appears in Nature.