外太空最黑暗的真空中有生命(下)
The gravitationAl tug of large planets,like Jupiter and Saturn, could sling some planets on "escapetrajectories", propelling them off beyond their solar system into theempty space between stars.
木星和土星等大行星的引力拖曳, 可把某些行星拋擲到“逃逸軌跡上”，把它們推出其自身的太陽系外，進入空曠的星際空間。
That might seem to consign them to a coldand barren future. But some scientists believe that the first life on Earth wasnot powered by sunlight, but by volcanic energy released from the planet'sinterior at hot vents in the deep sea.
這看起來似乎是把它們交付給了一個寒冷而荒蕪的未來。但一些科學家認爲，地球上最初的生命並不是由太陽提供能量的，而是由深海熱液噴口噴出的地球內部釋放的火山能量驅動的。
All of the rocky planets in the inner solarsystem come with two internal heat sources.
太陽系的所有巖態行星都有兩個內部熱源。
First, each planet has a fiery core stillhot from the primordial fury of its formation. On top of that, they containradioactive elements. Primordial heat and radioactive decay inside rocky rogueplanets could warm them for billions of years – perhaps enough to keep theplanets volcanically active and provide the energy for life to start.
第一，每個行星都有炙熱核心，仍然保持着形成過程中的原始狂暴產生的熱量。除此之外，它們還含有放射性元素。巖態的流浪行星內部的原始熱能和放射性衰變，可溫暖它們數十億年– 也許足夠保持行星上的火山活躍，爲生命的開始提供能量。
Rogue planets could also have dense,heat-retaining atmospheres. Compared with gas giants like Jupiter and Saturn,Earth's atmosphere is thin and tenuous, because the Sun's heat and light havestripped away lighter gases like hydrogen. Mercury is so close to the Sun thatit barely has any atmosphere at all.
流浪行星還可有稠密儲熱的大氣層。與木星和土星等氣態巨星相比，地球的大氣層稀薄，因爲太陽的熱和光除去了氫氣等較輕的氣體。水星離太陽如此之近，以致幾乎沒有任何大氣層。
Yet on an Earth-sized rogue planet, farbeyond its parent star's influence, much of the original atmosphere mightremain in place. The resulting temperature and pressure could be enough tosustain liquid water at the surface, even without any sunlight.
然而在地球大小的流浪行星上，因爲遠離母恆星的影響，原始大氣層可能大體保持了原樣。由此產生的氣溫和壓力可能足以在星球表面維持液態水，即使沒有任何陽光。
What's more, rogue planets would not beplagued by giant meteorite impacts, as Earth has been.
而且，流浪行星不會受到巨隕石撞擊的困擾，像地球曾經遭受的那樣。
If these ideas are right, then outside oursolar system rogue planets in interstellar space could be the closest placeswhere extraterrestrial life exists.
若這些想法對頭，那麼在我們的太陽系外，星際空間的流浪行星可能是離我們最近的外星生命存在的地方。
