NASA’s Perseverance spacecraft has reached an important moment in its mission to Mars. This Tuesday (17), the six-wheeled robot will begin to climb an ancient delta in the crater where it landed.
It will roll uphill, pausing every now and then to examine rocks that seem most likely to have signs of past life on the planet.
On the way back, Perseverance will collect some of these rocks, placing the samples at the base of the delta to be retrieved by later missions. The aim is to bring this material back to Earth in the 2030s for further analysis.
“The delta at Jezero Crater is Perseverance’s main astrobiological target,” the project’s deputy scientist Katie Stack Morgan told the BBC.
“These are the rocks that we believe have the most potential to contain signs of ancient life, and they can also tell us about the climate of Mars and how it evolved over time,” she said.
The spacecraft made a spectacular landing in the middle of the 45 km Jezero Crater on February 18, 2021.
Since then, the spacecraft has been testing tools and instruments, flying an experimental mini-helicopter and collecting an overall impression of the site.
But the robot’s main purpose in going to the site on the Red Planet has always been to study the huge mound of sediment to the west of Jezero.
Based on satellite images, scientists suspect it to be a delta. Perseverance’s initial observations on the ground have now confirmed this assessment.
A delta is a structure that forms from silt and sand dumped by a river as it enters a larger body of water. The sudden deceleration that occurs in the river’s flow allows anything carried in suspension to fall.
In the case of Jezero, the largest body of water was most likely a crater-wide lake that existed billions of years ago.
“Rivers that flow into a delta bring nutrients, which are useful for life, obviously; and so the fine-grained sediment that is brought in and deposited at a high rate in a delta is good for preservation,” explains the mission scientist, Sanjeev Gupta, from Imperial College London, UK.
“Also, if there was life in the interior, it could have been taken downriver and concentrated in a delta.”
In recent days, Perseverance has shifted towards a “ramp” in the delta dubbed the Hawksbill Gap. This is a gentle slope that will take the robot to an elevation of a few tens of meters above the crater floor.
The ascent is a reconnaissance mission. Perseverance will “walk” in search of the most interesting rocks.
“The spacecraft has an incredible set of instruments that can tell us about the chemistry, mineralogy and structure of the delta by examining sediments down to the scale of a grain of salt,” says mission scientist Briony Horgan of Purdue University in the American state of Indiana.
“We’re going to learn about the chemistry of this ancient lake, whether its waters were acidic or neutral, whether it was a habitable environment and what kind of life it might have supported.”
Let’s be clear: no one knows if there was life on Mars, but these three or four rocks that Perseverance will collect at the bottom of the crater could perhaps find signs – if they exist.
It is unlikely that the robot itself will be able to reach definitive conclusions – no matter how clever its instruments. Even on Earth, where we know microbial life has existed for billions of years, evidence for its earliest fossilized forms is difficult to interpret, and still controversial.
Establishing whether there was life on Mars will have to wait until the rocks arrive on Earth for a detailed analysis that only the largest laboratories are equipped to carry out.
“The claim that there is microscopic life on another planet in our Solar System is a huge claim. And so the proof also needs to be huge,” says Jennifer Trosper, NASA’s Perseverance project manager.
“I don’t think the instruments that we have on their own can provide that level of proof. They can provide something like ‘we think this might be it’, and then later, when we bring the samples back to Earth and use more sophisticated instruments, we can sure,” she told BBC News.
At the end of the year, Perseverance is expected to deposit a first set of rocks when it returns to the crater floor. This will include not just the rocks collected during the Hawksbill descent, but four samples collected in the previous months at the bottom of the crater.
NASA, along with the European Space Agency, is in advanced stages of planning the missions needed to pick up these deposited rocks and send them to Earth. Those projects – which involve another probe, a Mars rocket and a carrier spacecraft – are due to launch later this decade.
Perseverance still has years of work ahead of it. After depositing its first stockpile of rocks, the spacecraft will return to Hawksbill Gap to the top of the delta and beyond, to visit rocks that appear to be the shoreline remnants of ancient Lake Jezero.
These deposits are made of carbonate minerals and, again, appear to have formed in an environment conducive to recording past life on Mars – if it ever existed.
