NASA发现“超级地球” 或存在生命

After completing its first year of observations in the southern sky, NASA’s Transiting Exoplanet Survey Satellite has spotted some intriguing new exoplanets only 31 light-years away from Earth.

Multiple exoplanets — planets orbiting stars outside our solar system — were discovered orbiting an M-dwarf star, called GJ 357 in the Hydra constellation. The star is 40 percent cooler than our sun and only about a third of the sun’s mass and size. A study describing the three planets was published this week in the journal Astronomy & Astrophysics.

The first exoplanet discovered around the star was GJ 357 b.

The exoplanet is 22 percent larger and 80 percent more massive than Earth, making it a super-Earth. The researchers estimate that it has an average temperature of 490 degrees Fahrenheit. It completes one orbit around the star every 3.9 days.

“We describe GJ 357 b as a ‘hot Earth,’” said Enric Palle, study co-author and astrophysicist at the Institute of Astrophysics of the Canary Islands. “Although it cannot host life, it is noteworthy as the third-nearest transiting exoplanet known to date and one of the best rocky planets we have for measuring the composition of any atmosphere it may possess.”

GJ 357 d, a super-Earth that is 6.1 times the Earth’s mass, is the most intriguing because it orbits the star at a distance where the temperature might be just right to support liquid water on the surface. “GJ 357 d is located within the outer edge of its star’s habitable zone, where it receives about the same amount of stellar energy from its star as Mars does from the sun,” said Diana Kossakowski, study co-author at the Max Planck Institute for Astronomy. “If the planet has a dense atmosphere, which will take future studies to determine, it could trap enough heat to warm the planet and allow liquid water on its surface.”

The researchers don’t know if the super-Earth is rocky like our own planet, but it orbits the star every 55.7 days and has a temperature of negative 64 degrees Fahrenheit. An atmosphere could cause it to be warmer.

If GJ 357 d were to show signs of life, it would be at the top of everyone’s travel list — and we could answer a 1,000-year-old question on whether we are alone in the cosmos.

In the middle of those two planets is GJ 357 c. It’s 3.4 times the mass of Earth and zips around the planet every 9.1 days, reaching a temperature of 260 degrees Fahrenheit.

Words to Learn 相关词汇

【系外行星】xìwài xíngxīng

exoplanet a planet outside our solar system

【宇宙】yǔzhòu

cosmos the universe, regarded as an orderly, harmonious system

美国宇航局的过境系外行星测量卫星

（TESS）在完成对南半球天空的第一年观测后，发现了几颗距离地球仅31光年的有趣的新系外行星。

科学家发现了数颗围绕着长蛇座M矮星GJ 357运行的系外行星，系外行星指的是围绕太阳系外恒星运行的行星。这颗恒星的温度比太阳低40%，质量和体积只有太阳的三分之一左右。一项描述这三颗行星的研究本周发表在《天文学与天体物理学》期刊上。

科学家发现的首颗围绕这颗恒星运行的系外行星是GJ 357 b。这颗系外行星体积比地球大22%，质量比地球高80%，使之成为“超级地球”。研究人员估计它的平均温度为490华氏度（约合254摄氏度）。这颗行星的公转周期为3.9天。“我们将GJ 357 b描述为一个‘热地

球’，”研究的合作者、加那利群岛天体物理研究所的天体物理学家恩里克·怕列说。“尽管它不能承载生命，但值得注意的是，它是迄今为止已知的‘第三近程’过境系外行星，也是可以用来测量其拥有的任何大气成分的最佳岩质行星之一。”

另一颗“超级地球”GJ357d的质量是地球的6.1倍，最令研究人员感兴趣，因为它围绕恒星运行的距离使其表面的温度可能刚好适宜液态水的存在。“GJ 357 d位于其恒星宜居带的外边缘，它从恒星接收到的能量与火星从太阳接收到的能量差不多，”马克斯普朗克天文研究所的研究合著者戴安娜·科萨科夫斯基说。“如果这颗行星有稠密的大气层，它可能会捕获足够的热量使自身变暖，表面就可以留存液态水，而是否存在大气层还需要进一步研究。”

科学家尚不清楚这颗“超级地球”是否和地球一样属于岩质行星，但它的公转周期为55.7

天，温度为零下64华氏度（约合零下53摄氏度）。如果行星上有大气层，温度会更高。如果GJ 357 d行星上有生命迹象，它将成为每个人旅行清单上的第一目的地，那个困扰我们上千年的问题或许也将有答案，那个问题就是：人类是不是宇宙中唯一存在的生命。

行星GJ357 c位于这两颗行星中间，质量是地球的3.4倍，公转周期为9.1天，温度达到260华氏度（约合127摄氏度）。

(Chinadaily.com.cn)