相比之下，类地行星最多只有稀薄的大气层。
By comparison, the terrestrial planets have meager atmospheres at best.
美国科学家多年来一直在使用仪器寻找类地行星。
American scientists have been using instruments for years to look for earth-like planets.
然而，如今的类地行星与木星不同，几乎没有轻气体和冰。
However, unlike Jupiter, the terrestrial planets today are nearly void of light gases and ices.
这些小行星像类地行星一样，主要由岩石物质和金属构成。
These asteroids are like the terrestrial planets, in that they're composed mostly of rocky material and metals.
类地行星主要是岩石：密度大的石块和金属物质，同时会有少量的气体。
The terrestrial planets are mostly rocks: dense rocky and metallic material, with minor amounts of gases.
这些岩态行星被称为“类地行星”。
这些空间站将为人类访问火星或其他类地行星以及以后的生活做准备。
These stations will prepare humans to visit and later live on Mars or other earthlike planets.
类地行星和类木行星之间最明显的区别是它们的大小。
The most obvious difference between the terrestrial and the Jovian planets is their size.
巴特勒说：“这个星系内部有一堆岩石，有点像类地行星。”
"The galaxy has an inner clutch of rocky, sort of terrestrial-like planets," Butler says.
诸如火星和地球这样的类地行星主要由岩石和金属构成，而木星则是大型气态行星。
The terrestrial planets—like Mars and Earth—composed largely of rocks and metals, and the large gas giants, like Jupiter.
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.
类地行星的密度的平均值大约是水的密度的五倍，而类木行星的密度平均值只有水的密度的1.5倍。
The densities of the terrestrial planets average about 5 times the density of water, whereas the Jovian planets have densities that average only 1.5 times the density of water.
最大的类地行星地球的直径仅仅是最小的类木行星海王星的四分之一，而且地球的质量仅仅是其质量的十七分之一。
The largest terrestrial planet, Earth has a diameter only one quarter as great as the diameter of the smallest Jovian planet, Neptune, and its mass is only one seventeenth as great.
它要拍摄第一批类地行星的图片。
在这方面，汞不同于其他类地行星。
In this, mercury differs from the other terrestrial planets.
新消息：类地行星能够维持生命。
你认为我们什么时候可以看到第一课类地行星？
模拟图描绘了类地行星，有岩石表面、海洋和大气。
This artist's depiction shows a possible Earth-like planet with a rocky surface, oceans and an atmosphere. See more space tourism images.
水星的秘密和其对类地行星形成演化的意义将被揭开。
Mercury's secrets, and the implications they hold for the formation and evolution of Earth-like planets, are about to be revealed.
这些由银河系众多恒星锻造出的重元素正是类地行星的构建模块。
Forged by the Milky Way's abundant stars, such heavy elements are the building blocks of terrestrial planets.
天文学家对水星感兴趣是因为它是类地行星而非类木行星。
Astronomers are interested in Mercury, the closest planet to the sun, because it is a terrestrial like Earth, not gassy like Jupiter.
最接近它的四颗行星是石质的类地行星——水星、金星、地球和火星。
The four planets nearest it are rocky, terrestrial worlds — Mercury, Venus, Earth and Mars.
这可能是类地行星的演化方式，月球正在期待我们回去探索，让真相水落石出”。
This could be the way terrestrial planets evolve and the Moon is begging us to go back and explore to figure that out.
相信除了地球之外，类地行星火星和金星在它们形成后不久可能就有海洋的形成。
It's believed that in addition to Earth, the terrestrial planets Mars and Venus may have had oceans soon after their formation.
对于一个真正的类地行星来说，它存在了多久也许是最关键的特征之一。
For a planet to be truly Earthlike, how long it has been around might be one of its most important features.
七个类地行星的外星世界，浸润在他们所属恒星凉爽、红色的阳光之中。
Seven alien, Earth-sized worlds bask in the cool, red light of their parent star.
那些关于类地行星形成与类地行星可居住性的概念将需要从头开始重新进行评估。
Those ideas about terrestrial planet formation and habitability of terrestrial planets will need to be re-evaluated from scratch.
这同样意味着，在银河系其他地方的类地行星可以是任何的情况，但不会很稀少。
It's also a sign that Earth-like planets elsewhere in the galaxy may be anything but rare.
但旧金山州立大学的德布拉菲斯切说，日益精密的技术扩大了找到类地行星的机会。
But Debra Fischer, of San Francisco State University, says the growing sophistication of the technique increases the chances of finding planets more like our own.
但旧金山州立大学的德布拉菲斯切说，日益精密的技术扩大了找到类地行星的机会。
But Debra Fischer, of San Francisco State University, says the growing sophistication of the technique increases the chances of finding planets more like our own.
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