Sunday, February 28

‘Perseverance’: How to find life on Mars | Science



The next, most difficult, objective of exploring Mars is to find native life. Or, at least, his remains. The ship that is entrusted with that mission, Perseverance from NASA, is about to reach its destination: its landing is scheduled for today around 10 p.m. Spanish peninsular time.

The first serious attempt in this direction dates back to 1976, when two ships from the series landed there. Viking. Each one carried a miniaturized biological laboratory. Specifically, it could perform three types in tests aimed at detecting some characteristics of any living being: metabolism, respiration and growth.

The idea was to collect small soil samples and supply them with nutrients that any terrestrial organism would find palatable. It could be an amino acid soup or a mixture of radioactively labeled gases. The eventual Martian bugs – if they existed – should assimilate them and emit metabolic products that would be analyzed by other instruments on board.

The paradox is that to detect life it would have to be destroyed. The Viking they had a pyrolytic furnace in which to incinerate the samples to analyze the combustion products. Man’s first contact with the Martians would have ended in extermination. Although it were modest microorganisms.

The results of the Viking they were ambiguous. One of the experiments came back positive, too positive. The other two, negative. Many scientists – Joan Oró among them – pointed out that they were probably due to chemical reactions between the soil and nutrients, not metabolic processes. The soil of Mars had reactive properties that masked the results and, at the same time, made the presence of microorganisms more unlikely. The search for life on Mars promised to be a much more complicated undertaking.

From that point on, NASA adopted more systematic search procedures. First, characterize the Martian environment to decide if it had been favorable to life in the past. In particular, clarify once and for all whether liquid water ever existed on the surface. The aerial photographs showed unmistakable signs: large rivers now dry, traces of large-scale erosion … But confirmation on the ground was needed.

Some evidence suggests that there was so much water in that crater that it overflowed over the rim

Step by step evidence accumulated. First, thanks to the two twin vehicles Spirit Y Opportunity; later, with a probe sent to the polar regions. And, finally, with the data transmitted by the robot Curiosity, still active. He has been exploring inside Gale Crater for more than two years, an ancient lake that preserves mineral deposits whose origin requires the presence of water. Long ago, perhaps 3.5 billion years ago, Mars had a more benign climate, with a denser atmosphere, mighty rivers, lakes, and even shallow oceans.

The new robot explorer, Perseverance, goes in search of even more direct evidence. You will land in the dry delta of an ancient river that emptied into a lake formed inside the Jezero crater. Some evidence suggests that there was so much water that it overflowed over the edge of the crater.

It is possible to suppose that in its course, the river dragged minerals and –perhaps- remains of organisms, if any. Over the millennia, they should have focused on the alluvial fan, precisely where the NASA robot is going to move.

The Perseverance It has an articulated arm at the end of which the analysis instruments are housed. There are two of them, designed to detect traces of primitive biological activity. It is not about finding living microorganisms, but at least their remains.

One of the two instruments is an X-ray spectrometer. It works by bombarding rock samples with a beam of radiation which causes some luminescence. The colors of that light (technically, its spectrum), depend on its chemical composition. It can identify almost thirty elements in minute quantities (calcium, sodium, phosphorus …) and also other more exotic ones such as rubidium, strontium or zirconium.

The other works according to a similar concept, except that it uses ultraviolet light to illuminate the samples and thus elicit a response from their molecules. In this case, the Perseverance He carries two Raman spectrometers. One, in the robotic arm, which can approach rocks up to a few millimeters away. It is especially sensitive to the presence of chains and rings of carbon atoms, whose origin could be biological. The other works further afield: it uses a laser to remotely vaporize small amounts of rock and analyze the emitted gas cloud.

The Perseverance it carries a small drill and a robotic manipulator on its lower chassis. When some particularly promising terrain is spotted, he will take a sample and store it in one of forty sealed tubes. Some will be left on the ground, in well-located places; others will be stored on board.

In both cases the goal is the same: in the future (perhaps six or seven years from now) another robot will pick them up and bring them to Earth. Its design is barely outlined, but it will be a collaboration between NASA and the European Space Agency. NASA will put the landing vehicle and ESA, the autonomous stroller that, like a Martian Tom Thumb following the trail of breadcrumbs, will collect the sample capsules scattered on the ground.

Once collected, it will put them in a capsule at the end of a small rocket that will put it into orbit. There, another probe will pick up the cargo and bring it to Earth. It will be – with the permission of the Chinese – the first time that scientists can touch pristine material collected directly from the red planet.

Why resort to such a complicated scheme? Question of specialization. Perseverance, which weighs about a ton, is designed to study the area where the samples will be collected, but not to bring them in. A return rocket – apart from the added complexity – would weigh too much. The future collection vehicle will not carry analysis equipment; just the essential mechanisms to collect the capsules and check them in to Earth.

Hopefully the project is not delayed. The collecting device will be powered by solar cells. Perfect for operating on a meteorologically calm Mars. But by 2028 it is estimated that the storm season could begin. It will not be the first time that dust clouds have been raised that cover the entire planet, as happened in 1971 and 2001. That reduces the available lighting which would greatly affect the future robot. Your trip may have to be delayed until the middle of the next decade. Or redesign it to replace solar cells with a nuclear generator, immune to dust, which would not be an easy or cheap operation.

Rafael Clemente He is an industrial engineer and was the founder and first director of the Museu de la Ciència de Barcelona (now CosmoCaixa). He is the author of ‘A small step to [un] man ‘(Dome Books).

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