Eight new planets have been discovered in the 'Goldilocks' zone of their stars, orbiting at a distance where oceans and life could exist.
科学家已经发现了8个新的可能有海洋和生命的行星 。它们位于这些行星的恒星的适居带内 。
The discovery doubles the number of small planets less than twice the diameter of Earth which are believed to be in the habitable zone of their parent stars.
Among these eight, astronomers say there are two that are the most similar to Earth of any known exoplanets to date.
天文学家说 ，在这8个行星中 ，有两个是迄今已知所有外行星中和地球最像的 。
'Most of these planets have a good chance of being rocky, like Earth,' said lead scientist Dr Guillermo Torres, from the Harvard-Smithsonian Centre for Astrophysics in Cambridge, US.
The two most Earth-like planets, known as Kepler-438b and Kepler-442b, both orbit red dwarf stars that are smaller and cooler than the sun.
那两个最像地球的行星分别是Kepler-438b和Kepler-442b 。它们都绕红矮星轨道运行 。这些恒星（红矮星）不仅比太阳小 ，还比太阳冷 。
With a diameter just 12 per cent bigger than Earth, Kepler-438b has a 70 per cent chance of being rocky, the scientists have calculated.
科学家估计 ，直径只比地球长12%的Kepler-438b有岩石的几率是70% 。
Kepler-442b is about one-third larger than Earth, and the likelihood of it being rocky is around 60 percent.
Kepler-442b只比地球大三分之一 ，有岩石的几率约是60% 。
To be in the habitable zone, also known as the 'Goldilocks zone', a planet must be not too hot or too cold and receive roughly as much sunlight as Earth.
如果一个行星处在可居住带内 ，就必然不太热或不太冷 ，还会像地球一样受到充沛阳光的照射 。
Too much heat from its star, and any water would boil away as steam. Too little, and the water would freeze solid.
如果行星从恒星那里得到过多热量 ，行星上的任何水都会像蒸汽一样蒸发 。如果得到的热量太少 ，水就会冻成固体 。
'For our calculations we chose to adopt the broadest possible limits that can plausibly lead to suitable conditions for life,' Dr Torres added.
托雷斯表示：“为了计算 ，我们选择使用了似乎都可以导致适和生命存在条件的最广泛的限制标准 。”
Kepler-438b receives about 40 per cent more light than the Earth giving it a 70 per cent probability of having a habitable zone orbit. In comparison, baking hot Venus has twice as much.
考虑到Kepler-438b有一个可居住带轨道的几率是70% ，这个行星受到的太阳照射可能比地球多了约40% 。相比之下 ，非常炎热的金星受到的太阳照射可能是地球的两倍 。
Co-author Dr David Kipping, also from the Centre for Astrophysics, said: 'We don't know for sure whether any of the planets in our sample are truly habitable. All we can say is that they're promising candidates.'
研究负责人之一同时又是哈佛-史密森天体物理学中心科学家的大卫·基平表示：“我们不能确定我们样本中的任何行星是不是适于居住 。我们只能说它们是很有希望的候选者 。”
Neither of the planets are our close neighbours. Kepler-438b is located 470 light-years from Earth while the more distant Kepler-442b is 1,100 light-years away.
这两个行星都不是地球的近邻 。Kepler-438b距地球470光年 ，而更远的Kepler-442b距地球1100光年 。
The team, whose findings were presented at the American Astronomical Society's annual meeting in Washington DC, studied planetary candidates first identified by Nasa's Kepler space telescope.
这个科研组研究了美国宇航局开普勒太空望远镜最早识别的行星候选者 。改组的科学家还在华盛顿举行的美国天文学会年会上提出他们的发现 。
All the planets were too small to confirm by measuring their masses. Instead, they were validated using a computer program that determined they were statistically likely to be planets.
所有这些行星都太小 ，所以不能通过测量它们的质量进行确认 。但科学家用一个决定它们在统计学上可能是行星的电脑程序进行了这项工作
After the analysis, follow-up observations showed that four of the planets were in multiple star systems.
分析后 ，后续的观测结果显示 ，这些行星中有4个处在多重星系中 。
The research is also published in the Astrophysical Journal.