火星上發(fā)現(xiàn)的有機(jī)分子可能是古代生命存在的證據(jù)

火星上發(fā)現(xiàn)的有機(jī)分子可能是古代生命存在的證據(jù)

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.

許多登陸者和漫游者在火星上的調(diào)查發(fā)現(xiàn)，在這顆紅色星球上存在著幾種有機(jī)化合物。一個(gè)新發(fā)現(xiàn)的類型，被稱為硫代苯，引起了華盛頓大學(xué)研究人員的注意?？茖W(xué)家們認(rèn)為，在2018年“好奇號”收集的樣本中發(fā)現(xiàn)的分子是由生物過程而非化學(xué)過程產(chǎn)生的，這暗示著火星上有古代生命。

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.

硫代苯是由四個(gè)碳原子和一個(gè)硫原子組成的五邊形環(huán)。在地球上，這些分子分別存在于煤、原油(分別由死去的植物和有機(jī)體組成)和白松露中。這種化合物被認(rèn)為是通過熱化學(xué)過程形成的，但是細(xì)菌也可以創(chuàng)造它。古代細(xì)菌會在火星上創(chuàng)造它嗎?這是發(fā)表在《天體生物學(xué)》雜志上的一篇新論文的重點(diǎn)。

"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."

論文合著者Dirk Schulze-Makuch在一份聲明中說:“我們發(fā)現(xiàn)了幾種似乎比化學(xué)途徑更可能產(chǎn)生硫代嘌呤的生物途徑，但我們?nèi)匀恍枰C據(jù)。”“如果你在地球上發(fā)現(xiàn)了硫代苯，那么你會認(rèn)為它們是生物性的，但在火星上，證明這一點(diǎn)的門檻肯定要高得多。”

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.

研究人員說，如果這是一種生物反應(yīng)，它可能與古代細(xì)菌有關(guān)，這些細(xì)菌或者促進(jìn)了這些碳環(huán)和硫環(huán)的組裝，或者實(shí)際上分解了這些分子。如果這些化合物是通過非生物反應(yīng)形成的，也就是說它們是物理的而不是生物的，所以不需要生命形式，那就有點(diǎn)極端了。

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.

硫代苯可以通過熱化學(xué)硫酸鹽還原法生成，這需要120°C(240°F)的溫度才能工作?；鹦巧嫌谢鹕胶推渌嚓P(guān)的地質(zhì)過程，所以他們可能產(chǎn)生了這些物質(zhì)，就像隕石撞擊一樣。然而，研究小組并不認(rèn)為這些過程可以解釋“好奇號”探測到的硫代苯的數(shù)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.

到目前為止，我們還不能肯定地證實(shí)火星上是否曾經(jīng)有過生命。盡管這一新發(fā)現(xiàn)似乎表明古代細(xì)菌是更有可能的答案，但還需要進(jìn)一步的證據(jù)。更有力的例子是通過研究分子的同位素組成。同位素是一種重量略有不同的相同化學(xué)元素的變體。當(dāng)談到它們使用的同位素時(shí)，生命形式有偏好，我們可能很快就能在這些分子中發(fā)現(xiàn)它們，這將更清楚地表明它們是否是生物起源。

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

“有機(jī)體“很懶惰”，他們更愿意使用這種元素的輕同位素變化，因?yàn)檫@樣消耗的能量更少。”舒爾茨-馬庫奇解釋道。

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.

“好奇號”無法利用船上的儀器進(jìn)行分析，但歐洲航天局和俄羅斯宇航局將于今年夏天發(fā)射的羅莎琳·富蘭克林漫游者可以。當(dāng)“好奇號”于2018年在蓋爾隕石坑的默里地層的泥漿中挖掘出樣本時(shí)，它使用了一種需要將樣本加熱到500°C的技術(shù)來分析它。羅莎琳德·富蘭克林將攜帶一種破壞性小得多的儀器，所以我們可能很快就會發(fā)現(xiàn)更多關(guān)于硫代苯及其起源的信息。