火星上发现的有机分子可能是古代生命存在的证据

火星上发现的有机分子可能是古代生命存在的证据

Investigations by the many landers and rover on Mars have uncovered the presence of several organic compounds on the Red Planet. A newly discovered class, known as thiophenes, has caught the attention of researchers at the University of Washington. The scientists believe the molecules found in samples scooped up by Curiosity in 2018 were created by biological processes rather than by chemical ones, hinting at ancient life on Mars.

许多登陆者和漫游者在火星上的调查发现，在这颗红色星球上存在着几种有机化合物。一个新发现的类型，被称为硫代苯，引起了华盛顿大学研究人员的注意。科学家们认为，在2018年“好奇号”收集的样本中发现的分子是由生物过程而非化学过程产生的，这暗示着火星上有古代生命。

Alfredo Carpineti

Thiophenes are molecules made of four carbon atoms and a sulfur atom forming a pentagon-shaped ring. On Earth, these molecules are found in coal and crude oil – made up of dead plants and organisms, respectively – and white truffles. This compound is thought to form through a thermochemical process, but bacteria can create it too. Could ancient bacteria have created it on Mars? That is the focus of a new paper published in the journal Astrobiology.

硫代苯是由四个碳原子和一个硫原子组成的五边形环。在地球上，这些分子分别存在于煤、原油(分别由死去的植物和有机体组成)和白松露中。这种化合物被认为是通过热化学过程形成的，但是细菌也可以创造它。古代细菌会在火星上创造它吗?这是发表在《天体生物学》杂志上的一篇新论文的重点。

"We identified several biological pathways for thiophenes that seem more likely than chemical ones, but we still need proof," co-author Dirk Schulze-Makuch said in a statement. "If you find thiophenes on Earth, then you would think they are biological, but on Mars, of course, the bar to prove that has to be quite a bit higher."

论文合著者Dirk Schulze-Makuch在一份声明中说:“我们发现了几种似乎比化学途径更可能产生硫代嘌呤的生物途径，但我们仍然需要证据。”“如果你在地球上发现了硫代苯，那么你会认为它们是生物性的，但在火星上，证明这一点的门槛肯定要高得多。”

If it was a biological reaction, the researchers say, it would have involved ancient bacteria that either facilitated the assembling of these carbon and sulfur rings, or actually breaks down these molecules. If the compounds were formed through an abiotic reaction, meaning physical rather than biological, so not requiring lifeforms, it's a bit more extreme.

研究人员说，如果这是一种生物反应，它可能与古代细菌有关，这些细菌或者促进了这些碳环和硫环的组装，或者实际上分解了这些分子。如果这些化合物是通过非生物反应形成的，也就是说它们是物理的而不是生物的，所以不需要生命形式，那就有点极端了。

Thiophenes can be created through thermochemical sulfate reduction, which requires a temperature of 120°C (240°F) to work. Mars had volcanos and other related geological processes, so they could have produced these substances, as could meteorite impacts. The team, however, doesn’t think that these processes can explain the amount of thiophenes detected by Curiosity.

硫代苯可以通过热化学硫酸盐还原法生成，这需要120°C(240°F)的温度才能工作。火星上有火山和其他相关的地质过程，所以他们可能产生了这些物质，就像陨石撞击一样。然而，研究小组并不认为这些过程可以解释“好奇号”探测到的硫代苯的数量。

Currently, we still can't prove definitively if there has ever been life on Mars. Despite this new discovery, which appears to point to ancient bacteria being the more likely answer, further evidence is needed. A stronger case for it would come by studying the isotopic composition of the molecules. Isotopes are a version of the same chemical elements that have slightly different weights. Lifeforms have preferences when it comes to the isotopes they use and we might soon detect them in these molecules, which would indicate with more clarity if they are of biological origin or not.

到目前为止，我们还不能肯定地证实火星上是否曾经有过生命。尽管这一新发现似乎表明古代细菌是更有可能的答案，但还需要进一步的证据。更有力的例子是通过研究分子的同位素组成。同位素是一种重量略有不同的相同化学元素的变体。当谈到它们使用的同位素时，生命形式有偏好，我们可能很快就能在这些分子中发现它们，这将更清楚地表明它们是否是生物起源。

"Organisms are 'lazy'. They would rather use the light isotope variations of the element because it costs them less energy," Schulze-Makuch explained.

“有机体“很懒惰”，他们更愿意使用这种元素的轻同位素变化，因为这样消耗的能量更少。”舒尔茨-马库奇解释道。

Curiosity can’t run this analysis with the instruments on board, but ESA and Roscosmos' Rosalind Franklin rover, which will launch this summer, can. When Curiosity dug the sample out of the mud of the Murray Formation in Gale Crater in 2018, it used a technique to analyze it that requires heating the samples to 500°C. Rosalind Franklin will be carrying an instrument that is much less destructive, so we might be finding more about thiophenes and their origin soon.

“好奇号”无法利用船上的仪器进行分析，但欧洲航天局和俄罗斯宇航局将于今年夏天发射的罗莎琳·富兰克林漫游者可以。当“好奇号”于2018年在盖尔陨石坑的默里地层的泥浆中挖掘出样本时，它使用了一种需要将样本加热到500°C的技术来分析它。罗莎琳德·富兰克林将携带一种破坏性小得多的仪器，所以我们可能很快就会发现更多关于硫代苯及其起源的信息。