Jul 21st 2020
AROUND 3.5BN years ago conditions on Earth and Mars were similar. Both had thick atmospheres and liquid water on their surfaces. Both, in other words, had the conditions required to sustain life. And on one of those planets life was, indeed, sustained. Precisely when biology began on Earth remains obscure. But by 3.5bn years ago, a billion years after the solar system formed, it was well established there and has since evolved into the lush abundance of complex forms seen today. Mars, meanwhile, became a freezing desert.
The question nevertheless remains: given that the conditions needed for life to emerge on Earth also seem to have pertained for a time on Mars, might life have evolved there, too? And, if it did, might it still survive in some form, even if only in vanishingly rare amounts?
On July 30th NASA, Americas space agency, hopes to launch its latest Mars rover, Perseverance, which will try to answer at least the first of those questions. It is aimed at a 45km-wide crater called Jezero that was, 3.5bn years ago, home to a lake. Its main goal is to look for signs of ancient life. But it is also the opening gambit in a decade-long plan to bring Martian rocks to Earth. Nor will Perseverance be alone in its quest. It will be accompanied either now or soon by European, Chinese and other robots intent on finding out just what it was that happened on Mars.
Once upon a time...One such mission is already on its way. On July 20th the United Arab Emirates (UAE) joined the list of countries that have launched probes towards extraterrestrial bodies. That was when Al Amal, meaning hope, rose from Japans spaceport on Tanegashima, off the southern tip of Kyushu. Al Amals purpose is to study Marss weather and also how the Martian atmosphere is leaking into space.
All being well, Perseverance will follow soon from Americas principal spaceport, at Cape Canaveral, in Florida. This one tonne, six-wheeler, which cost $2.4bn to build and launch and will take another $300m to operate during its mission, will be the most sophisticated vehicle yet sent by America to the Martian surface.
Jezero, the crater around which it will trundle, sits on the inner rim of Isidis Planitia, one of the largest impact basins on Mars, which was excavated 3.9bn years ago. One source of the water which formed the lake that once lay within Jezero seems to have been a river leading to a well-preserved delta (see picture). The layers of sediment in this feature are prime targets in the search for Martian biology.
On Earth, some of the oldest evidence for life comes in the form of stromatolites. These stratified structures form in shallow water when colonies of microbes grow layer upon layer, trapping minerals as they do so. The most ancient examples are thought to be those found in Greenland in 2016, which have been dated to 3.7bn years before the present day. If there was sufficient time for stromatolite-forming organisms to evolve on Earth by this date then there is no obvious reason why they might not also have evolved on Mars.
Spotting stromatolite-like layers in rocks will not, though, be enough on its own. Researchers will also need to consider the textures of the rocks concerned and the distribution within them of minerals and potentially telltale organic molecules. Confusingly, in chemistry-speak, an organic molecule is not necessarily of biological origin. The term just means that it is built around carbon atoms, so organic molecules can also originate inorganically, as it were. The biological nature of an organic molecule has thus to be justified by other evidence. As Kathryn Stack Morgan, a geologist who is the Perseverance missions deputy project scientist, observes, This is exactly the type of thing that we do here on Earth to make a case for biosignatures in our own rock record, and for the very first time using our instruments we can do that on the surface of Mars.
Rocks and hard placesPerseverance carries two instruments in particular that are intended to examine the surfaces of rocks which the rover encounters. Both will look for pertinent minerals and organic molecules. SHERLOC, situated at the end of the rovers robotic arm, will shine a laser onto tiny grains in rocks it comes across. By analysing the spectrum of the light that is scattered back, this instrument will be able to identify molecules in the grains under scrutiny. WATSON, a camera, will then take close-ups of rocks that SHERLOC deems worthy of further study.
Mapping SHERLOCs chemical analyses onto WATSONs high-resolution images will show how different mineral layers are arranged and textured. That will be a big improvement over the instruments on board NASAs current operational Mars rover, Curiosity, which arrived in 2012. These are capable only of grinding up rocks to work out whether or not organic molecules are present in the bulk material. If there are stromatolites (or even fossils of more complex creatures) Perseverance will be able to see them, both chemically and optically.
As did Curiosity, Perseverance will rely on an autopilot to guide it through the atmosphere to the planets surface, after arriving at a velocity, relative to its target, of 19,500km per hour. We refer to it as the seven minutes of terror, says Matt Wallace, an engineer who is the missions deputy project manager. The rovers autonomy will then carry over to its everyday operations. Because of the time it takes radio waves to travel from Earth to Mars, Perseverance will receive instructions from its controllers only once a day. On the ground in Mars it will need to find and avoid awkwardly placed rocks, and also more serious hazards, such as cliffs, by processing, in real time, pictures coming from its dozens of cameras. This autonomy, NASA is confident, will permit the new rover to cross the Martian surface routinely and safely at a speed of around 150 metres per hour, double that at which Curiosity is usually allowed to travel.
As well as eyes, Perseverance has ears. A pair of microphones on board will permit people to hear the winds of Mars for the first time. They will also be able listen to the whirr of the rovers gears, the crunch of its wheels as it moves across the regolith (the crushed rock that passes for soil on Mars) and the percussive sounds of the drill at the end of its arm as it chips out samples of rocks to study.
Not all of those samples will be discarded after investigation. Some will be packed for eventual dispatch to Earth by a project called the Mars Sample Return mission. This is a collaboration between NASA and the European Space Agency, ESA, that involves launching five separate spacecraft over the course of a decade. Perseverance is the first, and its collaboration-related job is to seal samples of Martian rock that its operators think worthy of further investigation into one of around 30 titanium tubes which it carries. As the illustration overleaf presages, it will leave these on the surface to be picked up by an ESA-designed fetch rover that could arrive as early as 2028. Once collected, the tubes will be brought back to Earth by a system of relay craft, and their contents analysed.
Perhaps most intriguingly of all, Perseverance will also carry a 1.8kg helicopter, called Ingenuity. If this manages to fly in Marss thin atmosphere (which has about 1% of the density of Earths at the surface), it will represent the first controlled flight, beyond the landing and lift-off of a spacecraft, to take place on another heavenly body. And if that happens, it will pave the way for more sophisticated drones on future mission to act as scouts.
The life-seeking instruments on Perseverance are more advanced than anything that has come before them, but this was not the original plan for the next phase, after Curiosity, of NASAs attempt to find life on Mars. In February 2012, while Curiosity was still making its way there, Barack Obamas administration slashed NASAs planet-exploration budget by a fifth. At the time, American scientists had been developing a programme called ExoMars, in collaboration with ESA. This was to involve an orbiter and several rovers being launched from 2016 onwards, with a combination of tools intended to look for signs of life.
Mr Obamas cuts killed American involvement in ExoMars and, by the time Curiosity reached Mars in August 2012, NASA had no plans to send any future rovers. The overwhelmingly positive public reaction to Curiositys nail-biting landing, however, helped persuade the agencys chiefs to reconsider their priorities and put together a scaled-back version of previous plans that required no increase in the budget. The result, the mission now known as Perseverance, was announced a few months later.
Every contact leaves a traceMeanwhile, ESA had kept its part of the ExoMars programme alive, turning to Russia for help with launching and hardware. In 2016, the Europeans delivered the first part of the programme, the Trace Gas Orbiter, to its destination. Its goal is to measure the precise concentrations in Marss atmosphere of substances, including methane, water vapour, nitrogen oxides and acetylene, that each form less than 1% of the atmospheres total volume but which might be signs of biological activity.
Methane is of particular interest since its presence varies with both time and location on the planets surface. Methane does not live long in the Martian atmosphere, suggesting there is an active source of the gas. On Earth, living things emit methane as they digest nutrients. But purely geological processes can also liberate the stuff.
The next step in ESAs ExoMars programme is a rover, called Rosalind Franklin. This was also scheduled for launch about now, to take advantage, like the Perseverance and Al Amal missions, of the current alignment of Earth and Mars that allows for a quick, six-month journey between the two. However, a combination of technical delays and the effect of covid-19, which has meant the multinational team of engineers involved could not easily travel to complete the manufacture and testing of the rover, has pushed the launch date back to the next favourable alignment, in 2022.
When Rosalind Franklin eventually does arrive on Mars (which will be in 2023, if this timetable is adhered to), the craft will crawl over an area called Oxia Planum. This has clays that date back around 4bn years, which will make it the oldest site yet explored on Mars. Since clay minerals require water to form, there are high hopes that Oxia Planum may once have been a life-friendly region.
Rosalind Franklins scientific payload will be capable of much more sophisticated analyses than Perseverances. In particular, the Mars Organic Molecule Analyser (MOMA) will be able to extract organic molecules from rocks and regolith more effectively than before.
Previous attempts to study organic molecules on Mars have been plagued by the presence of chemicals called perchlorates. These were first seen in 2008, by NASAs Phoenix lander, and were confirmed by Curiosity half a decade later. Those missions baked their Martian samples in ovens, to release the organics. That also released chlorine and oxygen from the perchlorates, and these oxidised most of the organic molecules present. moma will circumvent this problem by using an ultraviolet laser that will knock organic molecules off rock samples so fast that any perchlorates present will not have time to decompose.
Rosalind Franklins most important tool, however, will be a drill that can collect samples from two metres below the surface. This is crucial for recovering material in which organic molecules can be found in a good state of preservation. The thin Martian atmosphere is easily penetrated by ionising radiation from space. This slams into the surface and even penetrates a little way beneath. As Jorge Vago, ExoMarss lead scientist, observes, Over many millions of years, this ionising radiation acts like gazillion little knives slowly cutting away the functional groups of the organic molecules you would like to hopefully discover. Use a drill to go deep enough, though, and any material collected will have been protected from radiation by several metres of rock. ESAs modelling suggests that samples from 1.5 metres down would be scientifically interesting. The deepest any mission has so far sampled under the surface of Mars is a few centimetres.
The jackpot of this treasure hunt would be to find things like sugars, phospholipids (constituents of the membranes of cells), nucleotides (the letters of genetic material) or amino acids (the building blocks of proteins) that are characteristic of life on Earth. But consolation prizes might be available in the form of less direct signals of biology within the chemistrytraces of the actions of enzymes, for example. As Dr Vago observes, the way fatty acids are synthesised biologically on Earth means that they usually have an even number of carbon atoms, although there is nothing in their underlying chemistry which favours that in abiotic syntheses. Finding a pattern like this, or something equally chemically striking, in Martian organic molecules would be encouraging to those who hope that Mars has or once had life.
Many handsAmerica and Europe have long histories of studying Mars. The uae is a newcomer. But it is not alone in that. Another country also wants to use the current launch window to join the Mars club: China.
Tianwen-1 (heavenly questions) is a combined mission consisting of an orbiter, a lander and a rover. It is built and operated by the China National Space Administration (CNSA) and is also scheduled for imminent launch. Chinese officials have been tight-lipped about the exact timing and have also declined to release much detail about the missions scientific aims. This is not Chinas first attempt at Martian space flight, however. In 2011 a Chinese craft called Yinghuo-1 attempted to hitch a ride with Phobos-Grunt, a Russian probe. Unfortunately, the rockets intended to propel the combined mission on its way malfunctioned, and it never left Earth orbit.
The little that is known of Tianwen-1 suggests that it will study the distribution of ice on Mars and examine how the planets habitability has changed over time. The various craft involved will host around a dozen scientific instruments, including cameras, chemistry sets, magnetometers and radars. Officials from the CNSA have said that the mission would make detailed surveys of the Martian surface. A ground-penetrating radar, for example, will measure the thickness and composition of layers within the regolith and identify any ice that is within 100 metres of the surface.
It will be a sophisticated spacecraft, if the details revealed about the missions landing system are accurate. Zhang Rongqiao, the chief designer, told Chinese television-viewers in 2019 that the lander would separate from the crafts main body at an altitude of 70 metres and hover until it found a safe landing spot. Cameras and laser scanners will help this lander avoid obstacles as it makes its way to the surface.
Whether the lander will be capable of the sorts of biology-detecting activity planned for Perseverance and, after it, Rosalind Franklin, is unclear. But even if it is not, those other two vehicles, combined with the forthcoming ESA and NASA Mars sample-return mission, do now offer a realistic possibility of answering the question of whether there is, or was, life elsewhere than on Earth. A failure to find it would be a disappointment, although the search would no doubt go on, both on Mars and elsewhere. But an answer in the affirmative, even were that life only bacterial and extinct, would surely transform humanitys view of itself as profoundly as did the discoveries of Nicolaus Copernicus and Charles Darwin.
See the article here:
Is there life on Mars? - The Economist
