我们不知道的“超级地球”

What is a super-Earth? Exactly what it sounds like: It's a planet that's similar to Earth but larger. And astronomers are realizing that super-Earths may be one of the most common planets in our galaxy.

什么是“超级地球”?顾名思义：和地球相似、但比地球大的行星。天文学家发现，“超级地球”可能是银河系中最普遍的行星类型之一。

Astronomers have found dozens of potentially habitable planets outside of our solar system. That's dozens of chances to discover the first alien life! Or plenty of places we could park our first interstellar colonies!

迄今为止，天文学家已经发现了数十个可能宜居的太阳系外行星。这可是数十个发现外星生命的机会啊!也是数十个人类可能建立首个星际殖民地的对象!

But with so many options, how do we know which is best? You might think the most Earth-like planets should be top of our list. After all, we've got water, land, an atmosphere, and trillions of life forms lapping it all up.

那么，面对这么多选项，究竟哪个才是最佳选择呢?你也许认为，最像地球的行星肯定是首选。毕竟，地球形成了海洋、陆地、大气层以及无数种生命形式。

But according to a small group of researchers, there are bigger and better planets out there. They're called super-Earths.

然而，一些研究人员表示，银河系里存在更大、更好的行星，即“超级地球”。

Super-Earths may be some of the most common planets in our galaxy. Since 2009, the Kepler Space Telescope has discovered about 4,000 exoplanets. 30% of them are super-earths. And a few percent of those super-earths orbit within their host star's habitable zone:

它可能是银河系里最普遍的行星类型之一。自2009年以来，开普勒太空望远镜发现了大约4000颗太阳系外行星，其中30%是“超级地球”。在这些“超级地球”里，大约有百分之几位于母星的宜居带内。

That's a Goldilocks zone where the planet's surface is just the right temperature for liquid water. Not too cold or too hot. Now, there's a chance that some of these super-Earth's aren't rocky worlds like Earth. The larger ones could be made of mostly hydrogen and helium gas like Jupiter and Saturn which would not be hospitable for life.

在宜居带里，行星表面温度恰好能够形成液态水，既不太热、也不太冷。不过，有些位于宜居带的超级地球可能不是固态行星。较大的行星可能主要由氢气和氦气构成，像木星和土星一样，这不适合生命的生存。

But the reality is, astronomers are still gathering details as more data comes in. So, in the meantime, we'll explore what life on a rocky, habitable super-Earth might be like.

针对这个问题，天文学家还在收集更多数据，探究更多细节。与此同时，我们也在探究宜居的、固态的超级地球上的生命会是怎样的面貌。

Liquid water is just the start. These planets can be almost double Earth's radius and up to 10 times more massive. And all that extra mass is what researchers think could really make super-Earth's the perfect home. Because more massive planets have a stronger gravitational pull.Super-Earth Kepler 20b, for example, is nearly double the size of Earth and is 10 times more massive. Making its surface gravity almost 3 times stronger. That stronger gravity means the planet can hold on to more air molecules forming a thicker atmosphere.

液态水只是个开端。这类行星的半径可能是地球的两倍，质量可能是地球的十倍。研究人员认为，超级地球之所以成为理想家园，正是由于质量大——质量越大，引力越大，吸引的气体分子越多，形成的大气层越厚。

Which is great for protection against harmful space radiation. It also means mountains and hills would erode faster leaving a relatively flatter surface compared to Earth.

厚厚的大气层能够隔绝有害的太空辐射，同时也意味着山地和丘陵的侵蚀速度更快，能够形成相对平坦的地表。

Which might sound boring but scientists think this could actually spawn dozens of shallow islands across the planet.Which, in turn, could be the perfect place for life to form and evolve. "Just as biodiversity in Earth's oceans is richest in shallow waters near coastlines, such an 'archipelago world' might be enormously advantageous to life."

这听起来无聊，但却可能使星球形成许多浅岛，而这可能是生命形成和演化的理想场所。就像在地球上，海洋生物多样性最丰富的场所是海岸附近的浅滩。因此，“群岛世界”可能极其有利于生命。

There's just one problem leaving this tropical paradise would be extremely difficult. The escape velocity on Kepler 20b is more than double compared to Earth's. Which means either rockets would need more fuel to reach their destinations. For example, a mission similar to the Apollo moon landings would require twice the amount of fuel or, rockets could only carry a fraction of the payload.

不过，这也会造成一个问题，即星球的“逃逸速度”增大。这样一来，火箭需要消耗更多燃料——要么增加燃料，要么减少有效负荷。

For instance, SpaceX's Falcon Heavy can launch 50,000 kilograms of payload into Earth's orbit whereas it could only launch 40 kilograms into orbit around a super-Earth like Kepler 20b. That's about the weight of a German Shepherd.

举例而言，SpaceX的“重型猎鹰”运载火箭能够将5万千克的有效负荷送上地球轨道;但在Kepler 20b(超级地球，体积是地球的1.865倍、质量是地球的8.58倍、引力是地球的近3倍)上，它只能够发射40千克的东西——大约相当于一只德国牧羊犬的体重。

Suffice it to say, leaving a super-Earth would be a far greater challenge.

简而言之，离开超级地球比离开地球困难得多。