天文學家發現「最豐富」的太陽系外星系

天文學家發現「最豐富」的太陽系外星系
更新時間 2010年 8月 25日, 格林尼治標準時間17:14
HD10180星系跟太陽系相似，但有其獨特之處。

天文學家發現一個由至少5顆行星組成的太陽系外星系。

這些行星圍繞一顆名為HD 10180的類似太陽的恆星旋轉，距地球127光年，位於水蛇座南方。

研究人員稱這是迄今為止發現的「最豐富」的太陽系外星系。

負責觀測研究這一星系的瑞士日內瓦大學天文學家路易說，這個星系包含的行星可能是已經發現的類似星系中最多的。

他說，他領導的研究小組的成果表明人類科技水平已經從對單個行星的研究發展到對複雜的恆星系的研究。

研究顯示HD 10180星系有若干特殊之處。

它至少有5顆跟海王星類似的行星繞恆星旋轉軌道的半徑跟火星繞太陽旋轉半徑相仿。這意味著它的星系「內圈」的行星數量比太陽系更多。

而且，所有的行星運轉軌道看來幾乎都是正圓型的。

通過研究該星系中行星運動的規律，科學家可以發現它們之間的相互引力作用，由此推測整個星系的長期演變。

除了5顆行星，研究人員還發現了可能是該星系中第6、第7顆行星發出的「較模糊」的信號。

它們的密度估計是地球的1.4倍，離位於星系中心的恆星HD 10180的距離只有地球和太陽之間距離的2%，即地球上的1.2天等於那個星球上的1年。

http://www.bbc.co.uk/zhongwen/trad/world/2010/08/100825_exoplanet_discovery.shtml

專家：可能是迄今發現最小的系外行星
Experts: Exoplanet Could Be Smallest Ever Found
Updated:
21 hours 20 minutes ago

GENEVA (Aug. 24) -- Scientists say they've identified a sun-like star with as many as seven different planets - including one that might be the smallest ever found outside the solar system.

If confirmed, the planetary system around HD 10180, a star more than 100 light years distant, would be the richest ever discovered. One astronomer says it's part of a growing body of evidence that the universe is full of planets - and that several could be similar to our own.

"The really nice thing about finding systems like this is that it shows that there are many more out there," said Alan Boss, of the Washington-based Carnegie Institution for Science, who wasn't involved with the find. "Mother Nature really had fun making planets."

Although most of the planets identified are large - about 13 to 25 times the mass of our home - those behind the discovery, announced Tuesday at an international conference in France, say they're nearly certain they've identified one only 1.4 times the size of Earth.
This artist's impression shows the remarkable planetary system around the Sun-like star HD 10180. The large crescent is the third world in the system (HD 10180d), which is comparable to the planet Neptune in mass. The two inner planets appear as silhouettes in transit across the bright disc of the star. The outer planets in the system appear in the background sky

Planets found outside the solar system are called "exoplanets" and this would be the smallest one ever spotted.

Scientists have been successfully hunting exoplanets for about 15 years, and they've now catalogued some 450. But most finds have been limited to one or two or three planets per star, usually gargantuan balls of gas similar to Jupiter or Saturn.

But at up to seven planets, the new discovery nearly matches our own solar system, which counts eight.

Christophe Lovis of Geneva University, one of the scientists behind the find, said the first five were most comparable to Neptune.

"They are made essentially of rocks and ice. They have a solid core. But on top of that is a layer of gas, of hydrogen and helium most likely," he said. "They are probably not habitable."

The sixth is possibly a Saturn-like planet, while the seventh, the smallest, would be so close to its star that its "year" would take just over a day.

Lovis and his team haven't been able to observe the planets directly, which is typical. Few planets can be seen against the blazing light given off by their much more massive parent stars. The European Southern Observatory compares the challenge to "spotting a dim candle in front of a raging forest fire."

So the scientists used the observatory's 3.6 meter (11.8 foot) telescope at La Silla, Chile, to study the star itself. Over six years, they took 190 measurements, checking it for the telltale wobbling caused by the gravitational forces of nearby planets.

Boss noted that the method was "biased toward finding the big guys" because the greater the planet, the greater its gravity and the more it made its parent star wobble. But he said the discovery showed that finding smaller planets was still possible.

"This field has gone from zero to close to 500 planets in just 15 years," he said. "Fifteen years ago we did not know about the big guys. Earth-like planets are going to be quite commonplace."

The find was made by researchers from Switzerland, France, Germany, and Portugal and has been submitted to the journal Astronomy and Astrophysics.

Satter reported from London.
http://www.aolnews.com/science/article/experts-spot-smallest-planet-outside-solar-system/19606576