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  • Deep in our solar system,

  • a new era of space exploration is unfolding.

  • Beneath the thick ice of Europa,

  • in the vapor plumes on Enceladus,

  • and within the methane lakes of Titan,

  • astrobiologists are on the hunt for extraterrestrial life.

  • We've honed in on these three moons because each is an 'ocean world,'

  • an environment that contains a liquid ocean

  • and liquid can support the formation of life.

  • Living organisms have to be able to grow, reproduce, and feed themselves,

  • among other things.

  • All of those functions require the formation of complex molecules

  • from more basic components.

  • Liquids such as water allow chemical compounds to remain in suspension

  • instead of sinking under the force of gravity.

  • This enables them to interact frequently in a 3-dimensional space and,

  • in the right conditions,

  • go through chemical reactions that lead to the formation of living matter.

  • That alone isn't enough;

  • the small but complex biomolecules that we're familiar with

  • are sensitive to temperature

  • too hot or cold, and they won't mix.

  • Liquid water has an additional advantage

  • in that it's relatively temperature-stable,

  • meaning it can insulate molecules against large shifts in heat.

  • On Earth, these and other conditions in aquatic environments

  • may have supported the emergence of life billions of years ago.

  • Tantalizingly, the same could be true in other parts of our solar system,

  • like these three icy moons.

  • Europa, which is a moon of Jupiter,

  • is probably the most intriguing ocean world.

  • Beneath a surface layer of ice thicker than Mount Everest,

  • there exists a liquid ocean as much as 100 kilometers deep.

  • Astrobiologists think this hidden ocean could harbor life.

  • Thanks to the Galileo probe,

  • we can deduce that its potential salt content

  • is similar to that of some lakes on Earth.

  • But most of its characteristics will be a mystery until we can explore it further.

  • Like Jupiter, Saturn also has moons that might have the right conditions for life.

  • For instanceEnceladus is a tiny ball of ice that's small enough to nestle

  • within the surface area of the Gulf of Mexico.

  • Similarly to Europa, it likely contains an ocean deep under the ice.

  • But Enceladus also has geysers

  • that frequently vent water vapor and tiny ice grains into space.

  • Astrobiologists are curious about whether these geysers

  • are connected to the ocean below.

  • They hope to send a probe to test whether the geysers' plumes of vapor

  • contain life-enabling material from that hidden sea.

  • Although it's the best known substance for nurturing life,

  • water isn't necessarily the only medium that can support living things.

  • Take Titan, Saturn's largest moon,

  • which has a thick nitrogen atmosphere

  • containing methane and many other organic molecules.

  • Its clouds condense and rain onto Titan's surface,

  • sustaining lakes and seas full of liquid methane.

  • This compound's particular chemistry means it's not as supportive a medium as water.

  • But, paired with the high quantities of organic material

  • that also rain down from the sky,

  • these bodies of liquid methane could possibly support unfamiliar life forms.

  • So what might indicate that life exists on these or other worlds?

  • If it is out there, astrobiologists speculate that it would be microscopic,

  • comparable to the bacteria we have on earth.

  • This would make it difficult to directly observe from a great distance,

  • so astrobiologists seek clues called biosignatures.

  • Those may be cells, fossils, or mineral traces left behind by living things.

  • And finding any biosignatures will be challenging for many reasons.

  • One of the biggest concerns

  • is to make sure we sterilize our probes extremely thoroughly.

  • Otherwise we could accidentally contaminate ocean worlds

  • with Earth's own bacteria,

  • which could destroy alien life.

  • Titan, Enceladus, and Europa

  • are just three of possibly many ocean worlds that we could explore.

  • We already know of several other candidates in our solar system,

  • including Jupiter's moons Callisto and Ganymede,

  • Neptune's Triton, and even Pluto.

  • If there's this much potential for life to exist in our own tiny solar system,

  • what unimagined secrets might the rest of the universe contain?

Deep in our solar system,

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太陽系には地球外生命体が存在するかもしれない - アウグスト・カルバリド (There may be extraterrestrial life in our solar system - Augusto Carballido)

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    April Lu に公開 2021 年 01 月 14 日
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