A new analysis of organic molecules found in dried Martian mud in Gale Crater has revealed interesting organics. Scientists have come to the conclusion that we cannot rule out – these molecules are actually of biological origin.
Although our understanding of Martian molecules is limited and incomplete, the information we have indicates the possibility of life on the Red Planet billions of years ago.
The molecules were actually extracted by the Curiosity rover from a section of mudstones in Gale Crater called the Murray Formation; research on the discovery was published in 2018. The first experiments identified a number of molecules, including a group of aromatic compounds called thiophenes.
#BREAKING @NASA news! @MarsCuriosity rover found organic molecules on Mars! While this doesn’t mean that we’ve found concrete evidence of life on Mars, it is a good sign in our continuing search. We’re sending the Mars 2020 rover to dig deeper! https://t.co/sU0wYlkZSu
– Jim Bridenstine (@JimBridenstine) June 7, 2018
Here on Earth, these connections are usually found in some pretty interesting places. They are found in crude oil – from compressed and overheated dead organisms such as zooplankton and algae; and coal from compressed and overheated dead plants.
The compound is believed to be formed abiotically, that is, through a physical rather than biological process when sulfur reacts with organic hydrocarbons at temperatures above 120 degrees Celsius (248 ° F), a reaction called thermochemical sulfate reduction (TSR).
However, although this reaction is abiotic, hydrocarbons and sulfur can be of biological origin. So scientists began to investigate how thiophenes could have formed on Mars.
“We have identified several biological pathways for thiophenes that seem more likely than chemical ones, but we still need proof,” said astrobiologist Dirk Schulze-Makuch of Washington State University.
“If you find thiophenes on Earth, you would think they are biological, but on Mars, of course, the bar to prove this should be slightly higher.”
There are several ways thiophenes could have appeared on Mars without the need for life. For example, thiophenes have been found in meteorites; so extraterrestrial stones could carry molecules in them.
Geological processes can also generate the heat needed to reduce sulfate, especially when Mars was volcanically active; and volcanic activity, of course, also produces sulfur.
But there is something interesting about the Martian thiophenes. The processes described above require the sulfur to be nucleophilic, that is, the sulfur atoms donate electrons to form a bond with their reaction partner. However, most of the sulfur on Mars exists as non-nucleophilic sulfates.
They can be reduced to nucleophilic sulfides. But there is another possibility – biological sulfate reduction (BSR). Some bacteria – and even white truffles, although you probably won't find them on Mars – can synthesize thiophenes.
It is therefore entirely possible that when Mars was warmer and wetter than it is today, about 3 billion years ago, bacterial colonies existed and produced thiophenes. This can happen even at subzero temperatures.
Unfortunately, the sample was slightly damaged. Curiosity uses a method of analysis called pyrolysis, which heats samples to 500 degrees Celsius. So there is a limit to the knowledge we can learn from what has survived.
But the Rosalind Franklin rover, scheduled for release in July, will have a much less destructive instrument on board. Thus, any thiophenes he digs up from the Martian soil may be more intact when applied.
In addition, the isotopes of carbon and sulfur can also be indicative. This is because living organisms prefer lighter isotopes; if thiophenes contain lighter isotopes, this may also indicate biological processes.
“I think it will take us to actually send people there, and the astronauts can see moving microbes through a microscope, to accurately prove the existence of life on Mars.”
The study was published in Astrobiology.
Sources: Photo: NASA / JPL / Arizona State University, R. Luk
