第三，巨大的外行星的引力屏障虽然非常有效，但偶尔也会无法保护地球。
Third, the gravitational shield of the giant outer planets, while highly efficient, must occasionally fail to protect Earth.
这是119颗太阳系外行星中的一颗。这些行星围绕除太阳外的其他星体运行。
The planet is one of 119 known extra-solar planets, objects that orbit stars other than the sun.
大多数已知的太阳系外行星都居住在高度拉长而非圆形的轨道上。
Most known extrasolar planets reside in highly elongated, not circular, orbits.
同样，由于它们的相对位置，四颗类木行星被称为外行星，而类地行星被称为内行星。
Also, because of their relative locations, the four Jovian planets are known as the outer planets, while the terrestrial planets are known as the inner planets.
这个系外行星的质量是地球的几倍，但是它足够小，能够由岩石构成，而不是像木星是一团巨大的气体。
The exoplanet is a few times the mass of Earth, but it should still be small enough to be rocky rather than a gas giant like Jupiter.
外行星是具有气体外层的巨大行星。
The outer planets are giant worlds with thick outer layers of gas.
发现系外行星的“黄金时代”。
目前用于寻找太阳系外行星的技术包括
The primary techniques currently used to find exoplanets include
不，这绝对是个地外行星。
这一发现可能会开创系外行星研究新标向。
The finding might chart a new course for extrasolar planet research.
但是我们不能对太阳系外行星做到这一点。
而对太阳系外行星的研究也引发了新的谜题。
And research into exoplanets is raising new mysteries as well.
这么多的外行星当中又有多少是有生命存在的？
这看起来越来越象一个探索系外行星的黄金时代。
This is looking more and more like a golden age of exoplanet discovery.
为了研究系外行星，天文学家必须非常有创造性。
In order to study exoplanets, astronomers have had to be quite inventive.
1991年以前，科学家一个系外行星都还没发现。
Before 1991, scientists hadn't discovered a single exoplanet.
至今为止被发现的外行星已经有超过270颗之多。
天文学家已经发现了将近500颗太阳系以外的地外行星。
Astronomers have found nearly 500 exoplanets - or planets outside our own solar system.
不过纵使如此，天文学家对寻找系外行星已经越来越老练了。
Still, astronomers are becoming more adept at finding exoplanets all the time.
同时，他们还需要更多的时间来观测那些离母星更远的外行星。
Also, it needs more time to detect exoplanets that orbit further away from their stars.
这些发现使已知的太阳系外行星或系外行星总数量增至645个。
The discoveries bring the total number of known extrasolar planets, or exoplanets, to 645.
另外，近期对太阳系外行星的研究结论表示，行星数量并不算少。
Also, recent searches for extrasolar planets have concluded that planets are not rare.
目前太阳系外有三颗“系外行星”被专家认为人类未来可能移居。
There are now three planets outside the system, known as exoplanets , which experts believe could potentially be colonised by future generations.
根据数据已知，比一个软木塞球还轻的行星是最膨胀的外行星之一。
A planet lighter than a ball of cork is one of the puffiest alien planets known to date.
这些太阳系外行星，或外星球大部分是通过两种不同的策略发现的。
Most of these extrasolar planets, or exoplanets, have been found using two different strategies.
直至2007年，在这颗脉冲星周围轨道上已有三颗系外行星被确认。
As of 2007, three extrasolar planets have been confirmed in orbit around this pulsar.
但是这些是被称之为“系外行星”——太阳系以外行星的第一批图像。
But these are the first images of planets outside the Solar System, or exoplanets as they are called.
这些行星叫系外行星，因为它们处于太阳系以外。要找到它们可不容易。
Finding these planets, known as exoplanets since they are located outside of our solar system, is difficult work.
这些行星叫系外行星，因为它们处于太阳系以外。要找到它们可不容易。
Finding these planets, known as exoplanets since they are located outside of our solar system, is difficult work.
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