我們不知道的“超級地球”

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“超級地球”?顧名思義：和地球相似、但比地球大的行星。天文學家發(fā)現(xiàn)，“超級地球”可能是銀河系中最普遍的行星類型之一。

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!

迄今為止，天文學家已經(jīng)發(fā)現(xiàn)了數(shù)十個可能宜居的太陽系外行星。這可是數(shù)十個發(fā)現(xiàn)外星生命的機會啊!也是數(shù)十個人類可能建立首個星際殖民地的對象!

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，面對這么多選項，究竟哪個才是最佳選擇呢?你也許認為，最像地球的行星肯定是首選。畢竟，地球形成了海洋、陸地、大氣層以及無數(shù)種生命形式。

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

然而，一些研究人員表示，銀河系里存在更大、更好的行星，即“超級地球”。

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:

它可能是銀河系里最普遍的行星類型之一。自2009年以來，開普勒太空望遠鏡發(fā)現(xiàn)了大約4000顆太陽系外行星，其中30%是“超級地球”。在這些“超級地球”里，大約有百分之幾位于母星的宜居帶內(nèi)。

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.

在宜居帶里，行星表面溫度恰好能夠形成液態(tài)水，既不太熱、也不太冷。不過，有些位于宜居帶的超級地球可能不是固態(tài)行星。較大的行星可能主要由氫氣和氦氣構成，像木星和土星一樣，這不適合生命的生存。

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.

針對這個問題，天文學家還在收集更多數(shù)據(jù)，探究更多細節(jié)。與此同時，我們也在探究宜居的、固態(tài)的超級地球上的生命會是怎樣的面貌。

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.

液態(tài)水只是個開端。這類行星的半徑可能是地球的兩倍，質(zhì)量可能是地球的十倍。研究人員認為，超級地球之所以成為理想家園，正是由于質(zhì)量大——質(zhì)量越大，引力越大，吸引的氣體分子越多，形成的大氣層越厚。

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.

厚厚的大氣層能夠隔絕有害的太空輻射，同時也意味著山地和丘陵的侵蝕速度更快，能夠形成相對平坦的地表。

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."

這聽起來無聊，但卻可能使星球形成許多淺島，而這可能是生命形成和演化的理想場所。就像在地球上，海洋生物多樣性最豐富的場所是海岸附近的淺灘。因此，“群島世界”可能極其有利于生命。

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.

不過，這也會造成一個問題，即星球的“逃逸速度”增大。這樣一來，火箭需要消耗更多燃料——要么增加燃料，要么減少有效負荷。

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.

舉例而言，SpaceX的“重型獵鷹”運載火箭能夠?qū)?萬千克的有效負荷送上地球軌道;但在Kepler 20b(超級地球，體積是地球的1.865倍、質(zhì)量是地球的8.58倍、引力是地球的近3倍)上，它只能夠發(fā)射40千克的東西——大約相當于一只德國牧羊犬的體重。

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

簡而言之，離開超級地球比離開地球困難得多。