We have been exploring the surface of Mars for a good few decades now, and in the process have discovered evidence for water and an ancient habitable environment. One thing remained elusive though – any signs of the building blocks of life.
Now that looming problem has been solved by the Curiosity rover.
Reporting in the journal Science, researchers have announced that the rover’s Sample Analysis at Mars (SAM) instrument has successfully detected organics on Mars, a major breakthrough in our search for life on the Red Planet. A second paper also reports some interesting findings about methane.
“It’s a really, really big stepping stone,” Sanjeev Gupta from Imperial College London in the UK, one of the co-authors on the study, told IFLScience. “It gives us great confidence that future missions have the potential to discover life.”
Using the SAM instrument, the team led by Jennifer Eigenbrode from NASA’s Goddard Space Flight Center examined samples of Martian soil about three years ago from mudstone in Gale Crater. It was collected by Curiosity’s drill from 5 centimeters (2 inches) beneath the surface, preserved in sulfur and dating back in time between 3.2 and 3.8 billion years, when water was once present here.
While we have seen organics on Mars before, this is the first time they have been linked to larger molecules that could be indicative of life.
Gale Crater on Mars, pictured, is thought to have once hosted a lake. NASA/JPL-Caltech
Heating the sample in the instrument, the team found evidence for several organic materials, including thiophene, methanethiol, and dimethyl sulfide. These are not compounds directly related to life, but they are signatures of larger molecules that could have been produced by life.
Organic molecules are ones that contain carbon and hydrogen. They can come from non-life sources, such as meteorites, and also from interactions with rocks and water. However, they also come from living matter. So we needed to find some on Mars to prove we were heading in the right direction.
“The detection of organic matter on Mars is the next step in the search for life on Mars,” Eigenbrode told IFLScience. “If the organic matter we discovered was derived from life, then it could contain signatures of that ancient life.”
Previous attempts to find organics on Mars, including the Viking missions in 1976 and the Phoenix lander in 2008, had been inconclusive. Curiosity’s discovery marks the first time we have truly known about organic compounds on the surface of Mars.
It’s important to stress that this is not a detection of life, nor is it proof that past or present life exists on Mars. It instead gives us ever-growing evidence that parts of Mars, such as Gale Crater in which Curiosity now resides, was capable of supporting life as we know it.
Thanks to this discovery, we now know that Mars once had all of the basic ingredients we know life needs. This will give scientists planning future missions confidence that they are on the right track in the search for life.
It poses another question though, specifically if life did not arise. If Mars had all the same conditions as Earth, including water and organics, then why did life spring up on our planet but not on our neighbor?
“If there’s no life on Mars, even though conditions are so similar, what made Earth so special?” Inge Loes ten Kate from Utrecht University, who was not involved in either study, told IFLScience.
Curiosity will not be able to answer this question definitively. But future missions may very well be able to give us a better picture, including ESA’s ExoMars rover in 2020. This will be able to drill up to 2 meters (6.5 feet) under the surface, 40 times further than Curiosity, to depths where material is more shielded from radiation.
At these depths, it may be possible to find even more organic compounds like this. But it will probably not be until we actually return Mars rocks to Earth, as NASA is planning in the 2020s, that we will really be able to answer if life arose on the Red Planet.
“This discovery gives us confidence that we’re not wasting our time,” said Sanjeev.
NASA’s Mars 2020 rover will leave samples on Mars for an uncrewed mission to one day return them to Earth. NASA/JPL-Caltech
In the second paper also released today, researchers led by Christopher Webster from NASA’s Jet Propulsion Laboratory (JPL) measured methane levels on Mars. They used an instrument on Curiosity called the Tunable Laser Spectrometer over five years to make the discovery.
The most interesting finding is that methane levels on Mars seem to change with the seasons. In the winter levels drop down to about 0.2 parts per billion, but in the summer they raise three-fold to 0.6 parts per billion. It might sound small, but this rise is hugely important.
“Very few gases on Earth change by a factor of three,” Webster told IFLScience. “So this huge change allows us to rule out some things and causes.”
This is exciting for another ESA mission, one that’s currently in orbit around Mars, called the Trace Gas Orbiter (TGO). Scientists are using this spacecraft to study gases in the atmosphere of Mars and pinpoint some of the sources of them on the surface.
ESA’s Trace Gas Orbiter (illustrated) will look more closely for methane. ESA/D. Ducros
It’s thought this methane has been trapped in reservoirs underground, and over the summer as temperatures increase, it is released from the surface into the air. Where this methane came from isn’t clear, and it may simply be the result of geological processes on Mars.
But one other source of methane is, of course, life. Coupled with the first paper, it paints a tantalizing picture of what might be happening on Mars. And if you let your mind wander, things certainly do get a bit interesting.
“You can hypothesize that there might have been early life, and the organics might have been the remnants from that, and those organics might have produced methane, and that methane is being stored in the surface of Mars,” said Kate.
It will be years before we truly know if that might have been the case. But this latest discovery tells us that, for all the billions of dollars we’ve spent exploring Mars, it just might be hiding the answer to the question we’ve wanted to know all along: Are we alone, and if so, why?