Although NASA’s newDragonfly mission泰坦将是首次返回土星系统以跟进卡西尼任务的发现,天文学家已经准备好返回土星卫星的另一个卫星Ecceladus。
土卫is only 500 kilometres across, but it carries outsized importance in the list of places in our solar system where extraterrestrial life might be found. In a series of flybys between 2005 to 2015,卡西尼discovered it to be venting geyser-like jets of water from a subsurface ocean that might be warm and nutrient-rich enough to support life.
And while neither NASA nor any other space agency plans to return to Enceladus in the near future, astrobiologists are brainstorming ways to determine if its ocean might truly be habitable, and/or currently contain life.
A preliminary issue, however, is how long this ocean might have existed, says Marc Neveu, a planetary scientist and astrobiologist at NASA’s Goddard Space Flight Centre in Greenbelt, Maryland, US.
他告诉上周的生活AbSciCon 19astrobiology science conference in Bellevue, Washington, there must be a source of energy for its biochemistry, and the most likely source of this is from chemicals created by reactions between the water and the moon’s hot, rocky core. Similar reactions are what fuel flourishing ecosystems surrounding hydrothermal vents deep beneath the surface of Earth’s.
但是土卫座很小,其这种化学物质的储层受到限制。尼弗说,如果海洋太老了,那么产生它们的反应可能会消退,从而剥夺了其中的生物(如果存在)。如果海洋太年轻,它可能没有足够长的时间来生存 - 或者至少无法检测到的水平 - 他指出,“我们真的在乎我们是否要发送航天器”。
To figure out how old the ocean might be, he modelled the evolution of Enceladus over billions of years, looking to see how its interactions not only with Saturn’s enormous gravity, but also with other moons and the rings, would cause its interior to either warm or cool. “You have to account for all of that,” he says. “There’s a lot of parameters.”
他说,基于这一点,埃斯塔努斯的海洋似乎已有十亿年了。他说:“可能是两个,或者可能是五十亿年。”但最重要的是,它既不是超人(与太阳系的45亿年历史相比,也不是超级年轻。
One of the interesting things about Enceladus is that it is jetting water directly into space, where a spacecraft carrying the right instruments can dip through the plume and take samples. Cassini did this several times, but when it was designed, nobody dreamt that worlds like Enceladus might have life, and its instruments weren’t designed as life-sign detectors.
加利福尼亚州帕萨迪纳(Pasadena)的分析化学研究人员杰西卡·凯普尔(Jessica Creamer)表示,一种可以完成该任务的方法是一种用激光诱导的荧光检测,称为毛细血管电泳。
它首先要使航天器通过羽流潜水,收集几微米材料。然后将其熔化,用荧光染料标记,并溶解在导电溶剂中。然后通过50微米直径的毛细管将其施加固定电压。
不同的化学物质以不同的速率流过管道,将带有激光照亮的条带分开。
“商业系统大约是洗碗机的大小,”奶精说。“我们的鞋子大小。”
Most importantly, she says, it is capable of distinguishing organic molecules such as amino acids based on whether their geometry is “left-handed” or “right-handed.” That’s important, because abiotic processes tend to produce a 50/50 mix of the two, whereas biological ones tend to favour one or the other (left-handed for Earth organisms).
But it would also be useful to deploy one or more landers, says Steven Vance, a JPL astrobiologist. These could carry instruments like seismometers (for landers) or gravity sensors (for an orbiter) that are capable of peering beneath Enceladus’s surface to learn more about its interior ocean and the processes within it that might support life.
Whatever such a mission might find, Neveu says, it would be an important contribution to astrobiology. Perhaps, it would make history by finding evidence of life – or reveal a seemingly habitable world that is nevertheless lifeless.
后者会令人失望,但是当涉及到我们是否独自一人在宇宙中的一个大问题时,他说:“我认为同样有意义”。
And, while Dragonfly is the mission now under development, it’s a good reminder that Saturn has not one, but two moons capable of supporting life. “Follow the water,” NASA once said in developing its goals for searching for extraterrestrial life in the Solar System. And in the case of Saturn, that leads not only to Titan, but also to Enceladus.
Originally published by宇宙as生物学家still have eyes for Enceladus
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