NASA發現"超級地球" 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.

美國宇航局的過境系外行星測量衛星（TESS）在完成對南半球天空的第一年觀測後，發現了幾顆距離地球僅31光年的有趣的新系外行星。

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% 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.

科學家發現了數顆圍繞着長蛇座M矮星GJ 357運行的系外行星，系外行星指的是圍繞太陽系外恆星運行的行星。這顆恆星的溫度比太陽低40%，質量和體積只有太陽的三分之一左右。一項描述這三顆行星的研究本週發表在《天文學與天體物理學》期刊上。

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

科學家發現的首顆圍繞這顆恆星運行的系外行星是GJ 357 b。

The exoplanet is 22% larger and 80% 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.

這顆系外行星體積比地球大22%，質量比地球高80%，使之成爲“超級地球”。研究人員估計它的平均溫度爲490華氏度（約合254攝氏度）。這顆行星的公轉週期爲3.9天。

"We describe GJ 357 b as a 'hot Earth,'" said Enric Pallé, 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."

“我們將GJ 357 b描述爲一個‘熱地球’，”研究的合作者、加那利羣島天體物理研究所的天體物理學家恩裏克·怕列說。“儘管它不能承載生命，但值得注意的是，它是迄今爲止已知的‘第三近程’過境系外行星，也是可以用來測量其擁有的任何大氣成分的最佳巖質行星之一。”

The researchers also discovered more signals of exoplanets in the system.

研究人員還在星系中發現了更多系外行星的信號。

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.

另一顆“超級地球”GJ357d的質量是地球的6.1倍，最令研究人員感興趣，因爲它圍繞恆星運行的距離使其表面的溫度可能剛好適宜液態水的存在。

"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."

“GJ 357 d位於其恆星宜居帶的外邊緣，它從恆星接收到的能量與火星從太陽接收到的能量差不多，”馬克斯普朗克天文研究所的研究合著者戴安娜·科薩科夫斯基說。“如果這顆行星有稠密的大氣層，它可能會捕獲足夠的熱量使自身變暖，表面就可以留存液態水，而是否存在大氣層還需要進一步研究。”

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.

科學家尚不清楚這顆“超級地球”是否和地球一樣屬於巖質行星，但它的公轉週期爲55.7天，溫度爲零下64華氏度。如果行星上有大氣層，溫度會更高 。

"This is exciting, as this is humanity's first nearby super-Earth that could harbor life -- uncovered with help from TESS, " said Lisa Kaltenegger, study author, associate professor of astronomy and director of Cornell's Carl Sagan Institute. "With a thick atmosphere, the planet GJ 357 d could maintain liquid water on its surface like Earth and we could pick out signs of life with upcoming telescopes soon to be online."

研究報告的撰寫者、天文學副教授、康奈爾大學卡爾·薩根研究所所長莉薩·柯廷安說：“這很令人興奮，因爲這是人類在TESS的幫助下發現的第一顆可能存在生命的近距離‘超級地球’。如果存在稠密的大氣層，行星GJ357 d可能像地球一樣表面可留存液態水，我們或許可以通過即將上線的望遠鏡找到生命的跡象。

"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."

“如果GJ 357 d行星上有生命跡象，它將成爲每個人旅行清單上的第一目的地，那個困擾我們上千年的問題或許也將有答案，那個問題就是：人類是不是宇宙中唯一存在的生命。”

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.

行星GJ357 c位於這兩顆行星中間，質量是地球的3.4倍，公轉週期爲9.1天，溫度達到260華氏度。