An Earth-size planet has been spotted orbiting a nearby star at a distance that would makes it not too hot and not too cold - comfortable enough for life to exist, researchers announced September 29.

　　If confirmed, the exoplanet, named Gliese 581g, would be the first Earth-like world found residing in a star's habitable zone - a region where a planet's temperature could sustain liquid water on its surface. And the planet's discoverers are optimistic about the prospects for finding life there。

　　"Personally, I would say, my own personal feeling is that the chances of life on this planet are 100 percent," said Steven Vogt, a professor of astronomy and astrophysics at the University of California. "I have almost no doubt about it."

　　Gliese 581g is one of two new worlds the team discovered orbiting the red dwarf star Gliese 581, bumping that nearby star's family of planets to six. The other newfound planet, Gliese 581f, is outside the habitable zone, researchers said。

　　The star is located 20 light-years from Earth in the constellation Libra. Red dwarf stars are about 50 times dimmer than our sun. Since these stars are so much cooler, their planets can orbit much closer to them and still remain in the habitable zone. Estimates suggest Gliese 581g is 0.15 astronomical units (One astronomical unit is the average distance between the Earth and sun) from its star, close enough to its star to be able to complete an orbit in just less than 37 days。

　　Gliese 581g has a mass three to four times Earth's, the researchers estimated. From the mass and estimated size, they said the world is probably a rocky planet with enough gravity to hold onto an atmosphere. Just as Mercury is locked facing the sun, the planet is tidally locked to its star, so that one side basks in perpetual daylight, while the other side remains in darkness. This locked configuration helps to stabilize the planet's surface climate, Vogt said. Between blazing heat on the star-facing side and freezing cold on the dark side, the average surface temperature may range from minus 31 to minus 12 degrees Celsius, the researchers said。

　　据美国太空网9月29日报道，研究人员最新宣称探测到一颗类似地球的行星，其环绕邻近恒星距离适中，得以保持适宜的气候和温度——舒适程度足以让生命存活下来。

　　如果得以证实，这颗被命名为“Gliese 581g”的系外行星将成为第一颗类似地球的世界——该行星的温度可维持表面存在液态水。而探测者们则因此对找到外星生命充满希望。

　　“就个人角度而言，我认为这颗行星上存在生命的概率为100%，”美国加州大学圣塔克鲁兹分校天体物理学家史蒂文-沃格特说。“对此我几乎毫不置疑。”

　　Gliese 581g是环绕红矮星Gliese 581两颗行星中的其中一颗，它的发现使该行星系内行星数量增加至6颗。研究人员称，另一颗新发现的行星是Gliese 581f，位于适宜居住区域之外。

　　而红矮星Gliese 581位于天秤星座，距离地球20光年，大约比太阳昏暗50倍。由于这样的恒星温度相对较低，它的行星在近距离环绕其运行的同时还能保持着适宜的气候和温度。初步分析认为Gliese 581g与恒星的距离为0.15个天文单位(一个天文单位约等于地球至太阳的平均距离)，较近的轨道距离使得该行星公转一周只需37天。

　　研究人员估测Gliese 581g行星的质量大约是地球的3到4倍。基于该行星的质量和预测体积，研究人员称该行星很可能是一颗岩石行星，具有足够的引力维持大气层。与水星总有一半固定地面对太阳相似，该行星总是始终保持一面朝向恒星，使得星球的一半永久处于阳光之中，而另一半则永久位于黑暗。沃格特称，这种特征有助于稳定行星的表面气候。研究人员还称，在炽热和寒冷的两个半球之间，该星球平均表面温度为零下31摄氏度至零下12摄氏度。