In the next few weeks, a flotilla of probes will be blasted into space from launch pads round the world and propelled towards one of the solar system’s most mysterious objects: the planet Mars. Within days of each other, spacecraft built by the USA, by China and by the United Arab Emirates will be sent on separate, seven-month voyages to investigate the red planet.
Never has so much interplanetary traffic been put en route to Mars at one time - and all of it is intended to help answer a question that has nagged scientists for decades: is there, or was there ever, life on Mars?
“Robot missions over the past decade or so have shown that Mars is not a dead, alien place as we had concluded in the late 20th century. In fact it is a world peppered with old lake beds, dried out river channels and organic material,“ said Profesor Ray Arvidson, of Washington University, St Louis.
“In other words, back in the day, billions of years ago, Mars was warm and wet. Now we are going to find out if those conditions led to the evolution of life on Mars, just as they did on Earth, and to see if some of that life still persists underground.”
In every case, the spacecraft that make up the new Mars flotilla are highly ambitious in design and construction. The US mission - to be launched in early August - will involve dropping a van-sized robot rover called Perseverance into Jezero Crater, near an ancient river delta, in the Syrtis Major region of Mars. It will then examine rocks on the crater floor and collect samples which it will leave in caches to be collected, in several years’ time, by another - as yet unbuilt - robot rover.
The samples will then be placed in a rocket and blasted back to Earth in the hope of bringing around 500g of Martian soil and rock to researchers’ laboratories by 2031. These samples could reveal signs of past or even present Martian life.
In addition, Perseverance will carry a tiny robot helicopter, another first for Mars, and will also attempt to extract oxygen from the carbon dioxide in the Martian atmosphere - as a test of methods for supporting future human explorers of the planet.
Equally ambitious, the Chinese mission, Tianwen-1, is essentially a three-in-one spacecraft consisting of a satellite that will orbit Mars, a lander, and also a rover that will travel across the Martian surface in search of water, ice and other features. China has recently developed considerable expertise in landing spacecraft and robot rovers on the Moon. Now it is scaling up its operations and is crossing interplanetary space to try out its hardware on Mars.
Precise details of the Tianwen-1 mission are scarce, however. Its launch date and landing site on Mars have still not been revealed by the Chinese, for example, and most communications about the mission have been cryptic, to say the least. “Our team is working in the Wenchang launch centre right now, and everything goes smoothly,” was all Wang Chi, director-general of the National Space Science Center (NSSC) in Beijing, had to say about the project in an email to the journal Nature last week.
And finally there is the Emirates Mars Mission, or Hope as it is also known. It is scheduled for launch on Wednesday (15 July) on a Japanese H-2A rocket that will lift off from the Tanegashima Space Centre and is set to become the first interplanetary mission carried out by an Arab nation. The craft will enter Martian orbit in early 2021, marking the 50th anniversary of the birth of the United Arab Emirates, and will study, in detail, the atmosphere of the Red Planet.
The craft is fitted with an infra-red spectrometer for studying Martian clouds and dust storms and ultra-violet detectors for analysing gases in the planet’s upper atmosphere. This data will then be combined and used to produce the first global weather map of the planet.
This mushrooming of Martian missions is remarkable, though the fact that these probes all have launch dates so near each other is also influenced by celestial mechanics, added Open University astrobiologist Susanne Schwenzer.
“Every 26 months, the orbits of Earth and Mars are aligned in a way that makes it relatively easy to send a rocket there,” she told the Observer. “These launch windows last only a few weeks and one is just about to open up - which explains why these different probes are being prepared for launch over such a brief period this summer.”
Blasting three separate probes to Mars is still an extraordinarily ambitious undertaking, however, particularly as these craft are being launched as our own world has been engulfed by an pandemic that has led to widespread suspensions and cancellations of many other scientific efforts. Indeed, had it not been for Covid-19, a fourth mission, a joint European-Russian probe, ExoMars, would have joined the robot fleet heading for the Red Planet this summer. However, it has now been postponed but will not be launched until 2022 when the next launch window for Martion missions opens up. Our interest in the Red Planet is going to continue for some time, it seems.
“There is no doubt that the exploration of Mars is going through a rebirth,” added Arvidson. “In the 1970s, the Viking missions to Mars revealed a world that appeared to be utterly dead and we stopped sending missions to the planet for a couple of decades. However, more recent probes have changed that view.”
These missions - which have included the US robot rovers Spirit, Opportunity and Curiosity - have shown that Mars must once have been lush and warm but was doomed as a cradle for complex life because of its size. The planet’s diameter is half that of Earth’s, which means it has a much smaller core at its heart compared with the one at the centre of our own planet. The Martian core, once molten, cooled and solidified billions of years ago while our larger core has remained hot and molten allowing convection currents within it to generate a magnetic field around the Earth.
And that is crucial. Without a molten core, Mars could no longer generate a magnetic field which had protected it from radiation from the Sun just as Earth’s magnetic field still shields us today. As a result, the Martian atmosphere and its surface water were swept away by this bombardment of solar particles and the planet became barren and hostile.
However, there is still a chance that life evolved there before the Martian climate changed, added Schwenzer. “Mars is relatively small and so it would have cooled down more quickly than Earth after the hot, primordial creation of the solar system 4.6 billion years ago.
“Seas, lakes and rivers would have formed there before they did on Earth and so life may have arrived on Mars before it did on our world. Its grounds for hope, if nothing else. Now we want to find evidence that it did arise and possibly may still be thriving underground.”
Nasa’s robot rover Perseverance bristles with devices for scrutinising the soil of Mars for signs of microbe-like life. One of these, called Sherloc, will zap rocks with an ultraviolet laser to identify signs of organic material or minerals that formed in watery environments, for example.
However, it will be the rocks that Perseverance collects for subsequent return to Earth that offer the best chance to find life, extant or extinct, on Mars, say researchers. These will have to be carefully selected by mission controllers as Perseverance trundles around Jezero Crater in order to give researchers back on Earth the best chance of finding of evidence of life in them. That selection will be crucial for it will shape the direction of Mars science for decades to come.
Nor will it be easy to get those samples back to Earth. “You can’t just shoot these back to Earth in one go. It’s going to take lots of niggly, complicated manoeuvres to do that,” said science writer Nick Booth whose book, The Search for Life on Mars, co-written with Elizabeth Howell, was published last month.
According to the plan devised by US and European space scientists, Perseverance will collect soil samples, place them in small metal tubes, seal them and leave them at designated sites. Then a second robot, to be built by the European Space Agency and known as a fetch rover, will land on Mars, visit these sites, and load the samples into a football-sized canister which it will place in a rocket that will blast it into orbit round Mars. Then a second robot spaceship will capture the canister, head back to Earth, and release it so that it lands, by parachute, in the Utah desert.
There is a great deal that could go wrong, researchers acknowledge, but if we are to discover if there once was life on Mars, and possibly still exists there, this is the kind of ambitious, expensive task that will have to be undertaken, they say.
The crucial point is that finding life on Mars goes beyond revealing the secrets of our own planetary backyard. “It is still not understood how the first replicating metabolising structures that we’d call ‘alive’ arose,” said Astronomer Royal Martin Rees. “This process could be a rare fluke, one that only happened once in our Galaxy - here on Earth. On the other hand, it could be common and it turns out that life is widespread across the cosmos.”
And that is why Mars is of such fascination to scientists – for if they detect living beings in a second location in our own Solar system that would suggest life is not a fluke and is likely to have emerged on billions of planets in our galaxy. Hence the urge to head to Mars. To find out if we are alone or not in the cosmos.
However, there’s one key caveat, added Rees. “We would have to be sure that the origins of life on Mars and life on Earth were completely independent of each other and that poses a problem - for it is possible that meteorites and asteroids crashing on Mars billions of years ago during the birth of the solar system could have sent rocks carrying primitive Martian life into space and some could have reached Earth. These could have seeded our planet. By that token, all lifeforms on Earth, including humans, would have actually originated on Mars. We are all Martians, in short!”
•1964 The US probe Mariner 4 made the first successful fly-by of Mars, returning the first close-up pictures of its surface. They revealed a seemingly cratered, dead world – astronomers had hoped to see signs of vegetation and life.
• 1976 The US landed two Viking probes. Biological tests suggested, to most scientists, that the planet was lifeless.
• 1997 The US Pathfinder probe carried a tiny, robotic rover called Sojourner to the Ares Vallis region.
•2003 Britain’s sole attempt to land a craft on Mars, Beagle 2, was intended to seek evidence in the soil of past life. It was carried there on Europe’s Mars Express spaceship in December 2003, after which Beagle 2 disappeared. The mission was declared lost in February 2004.
• 2012 Nasa’s car-sized rover Curiosity landed with the aim of investigating the planet’s climate and geology over the next two years. The craft is still in operation after spending thousands of Martian days exploring the surface.