Given the extravagant profusion of moons in our own Solar System, it seems likely that there are way more exomoons out there in the Universe than there are exoplanets. We're yet to conclusively find one - but astronomers just found a signal that could mean the presence of an exomoon.
考慮到太陽系中大量的衛星，似乎宇宙中有比外行星更多的外行星。我們還沒有最終找到一個——但天文學家剛剛發現了一個信號，這可能意味著外行星的存在。
Not just any exomoon, either, but something akin to a jacked-up version of the Jovian moon Io, the most volcanically active object in the Solar System.
不僅是任何外行星，而是類似於木星的衛星木衛一的升級版，木衛一是太陽系中火山活動最活躍的天體。
And we really do mean jacked. Not only would the exomoon itself be covered in volcanoes spewing lava, it would be orbiting a hot planet - WASP-49b, a massive gas giant planet known as a hot Jupiter, hurtling around yellow dwarf star WASP-49 once every 2.8 days.
我們的意思是被劫持。這顆外行星不僅會被噴湧熔岩的火山所覆蓋，還會圍繞著一顆熱行星WASP-49b運行。WASP-49b是一顆巨大的氣態巨行星，被稱為熱木星，每2.8天繞黃色矮星WASP-49旋轉一次。
"It would be a dangerous volcanic world with a molten surface of lava, a lunar version of close-in Super Earths like 55 Cancri-e," said astrophysicist Apurva Oza of the Physics Institute of the University of Bern.
伯爾尼大學物理研究所的天體物理學家阿普爾瓦·奧扎說：“這將是一個危險的火山世界，熔岩的熔融表面，類似於月球上的近地天體，如55 Cancri-e。”
But don't go packing your lava suits just yet. The team didn't detect the exomoon directly. They have inferred it exists based on data from the planet itself - from stuff detected in its upper atmosphere.
但現在不要去收拾你的熔岩服。研究小組沒有直接探測到外行星。他們根據行星本身的數據推斷出它的存在，這些數據來自於在其高層大氣中探測到的物質。
When a paper describing the atmosphere of WASP-49b was published in 2017, researchers noted the presence of a thick layer of sodium at unusually high altitudes free of clouds. This sodium layer made Oza's international team look more closely.
2017年，當一篇描述WASP-49B大氣的論文發表時，研究人員注意到在異常高的高度上存在著一層厚厚的鈉，沒有云層。這一鈉層使奧扎的國際團隊看起來更近。
"The neutral sodium gas is so far away from the planet that it is unlikely to be emitted solely by a planetary wind," he said.
他說：“中性的鈉氣體離地球太遠，不太可能僅僅由行星風排放。”
We know, based on observations closer to home, that volcanic activity on Io produces pretty hefty amounts of potassium and sodium (among a few other things). These do not cling in significant quantities to the moon, but get swept up into Jupiter's complex magnetosphere, resulting in a torus of material ringing the planet.
我們知道，根據離地球較近的觀測，木衛一上的火山活動產生了相當多的鉀和鈉(以及其他一些物質)。這些物質並不會大量地附著在月球上，而是會被捲入木星複雜的磁層中，形成一個環繞著行星的物質環面。
We also know that, without the intense gravitational interplay between Io and Jupiter generated by the moon's elliptical orbit - the varying tidal forces that create friction and thus heat in the moon - it would not be volcanically active.
我們還知道，如果沒有月球橢圓軌道產生的木衛一和木星之間的強烈引力相互作用——月球上產生摩擦和熱量的潮汐力各不相同——它就不會有火山活動。
In 2006, a different team of researchers extrapolated that the presence of a torus of material around a planet could imply the presence of a moon or other orbiting body.
2006年，另一組研究人員推斷，行星周圍存在一個物質環面，可能意味著存在一個月球或其他軌道物體。
So, the team crunched some numbers. And they found that a volcanically active exomoon could actually release more potassium and sodium than the planet it orbits.
所以，小組計算了一些數字。他們發現，火山活動的太陽系外行星，實際釋放的鉀和鈉比它所運行的行星多。
The sodium and potassium around WASP-49b, in the quantities and at the strange altitude detected, Oza's team concluded, could have plausibly been spewed out by a volcanic hell-moon. But it's also plausible that other processes or phenomena are responsible - a ring of ionised gas, for example.
奧扎的研究小組得出結論，WASP-49b周圍的鈉和鉀的含量，以及在這個奇怪的高度所探測到的含量，都有可能是由一個火山地獄般的月亮噴發出來的。但也有可能是其他過程或現象造成的，比如電離氣體環。
Once again, more observation would help find answers - analysing the planet's spectrum in greater detail. Sodium and potassium lines on the spectrum are both very strong; by searching more closely, the researchers hope to find the weaker signals of other volcanic volatiles in the planet's atmosphere, such as sulphur and oxygen.
再一次，更多的觀察將有助於找到答案——更詳細地分析行星的光譜。鈉和鉀的光譜線都很強;通過更仔細的搜索，研究人員希望能找到地球大氣中其他火山揮發物質的微弱信號，如硫和氧。
In addition, it provides yet another excellent reason to probe the atmospheres of exoplanets - a task at which we hope the next generation of telescopes will excel.
此外，它還為探測系外行星的大氣層提供了另一個很好的理由——我們希望下一代望遠鏡，能夠在這項任務上取得卓越的成就。
"While the current wave of research is going towards habitability and biosignatures, our signature is a signature of destruction," Oza said. "The exciting part is that we can monitor these destructive processes in real time, like fireworks."
奧扎說:“雖然目前的研究浪潮正在向宜居性和生物特徵發展，但我們的特徵是破壞的特徵。令人興奮的是，我們可以實時監控這些破壞性的過程，就像煙花一樣。”
The research has been accepted into The Astrophysical Journal.
這項研究已被《天體物理學雜誌》接受。
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