It is more than 50 years since the U.S. probe Mariner 4 succeeded in orbiting Mars in 1964, marking the beginning of robotic exploration of this planetary neighbour. More than 50 missions have been sent since then, and only about half have been successful. Thanks to that handful of orbiters, landers and rovers, we know that Mars is an icy, scree-covered body with a very tenuous atmosphere, that there is water at its poles, and that it may have harboured life in the past (or may continue to do so beneath the surface). All of this raises new questions for scientists, who would like to bring samples of Martian soil and air back to Earth.
The main space agencies are already working on this complex mission. In 2020, NASA will launch a rover to collect and store samples. A second rover will then collect them and a special vehicle will launch them into Martian orbit, where they will be captured and returned to Earth by a third vehicle. The details of the plan are still in the design stage and the most optimistic scenarios speak of a date of return after 2030. It seems difficult, but these are the main reasons why it would be worth trying:
There are better instruments on Earth
The Martian samples could be analysed here with the best possible technology and experiments could be carried out which have been impossible until now. In addition, the samples could be manipulated and prepared for much more precise analysis, which is very complicated for a robot to do.
The scientific instruments used in robotic space missions must be miniaturised to reduce launch weight and must be extremely rugged to overcome the long voyage and the harsh conditions on the red planet. This means that the instruments available on Mars are much less sensitive than their terrestrial counterparts. And there are many others that could not be sent because of their size, energy consumption or other particularities.
Putting the samples into context
Currently on Earth we already have more than 100 meteorites that came from the red planet. It is believed that these rocks were uprooted from Mars and put into orbit by the impacts of large asteroids. Then they would have travelled through space for an indeterminate time until finally falling on our planet.
These meteorites have revealed much about the composition of Mars but have already been studied to the limit. Scientists cannot learn anything more from them, as they lack information to put them in context: for example, they do not know which part of the planet they come from. What’s more, they have suffered alterations due to the force of the impact that sent them into space and many have been contaminated by terrestrial materials. This is why scientists want fresh samples that can be placed in a Martian geological context.
Search for life
The search for life is and always has been the main driving force behind the exploration of Mars. However, since the Viking 1 and Viking 2 probes reached the Martian surface in 1976, no further experiments have been conducted with the explicit aim of seeking microbial life. The tests carried out at that time seemed to confirm the absence of life on the surface, but these experiments have been much questioned as being too geocentric; in other words, they were looking for life as we know it on the Earth’s surface.
Since then, many discoveries have redefined our conception of what life is and what defines a habitable environment. Some examples are microbes found at high pressure and temperature in the Earth’s subsoil or around geothermal vents deep in the ocean.
On the other hand, if life ever existed on Mars —billions of years ago— it is very difficult for the instruments of a robotic vehicle to find evidence. Microbes do not form fossils that are easy to detect and finding traces of organic matter that are billions of years old would require extremely sensitive instruments and very complex sample preparation. Which brings us back to the first reason: only by analysing that Martian material on Earth will it be possible to definitively answer the question of whether there was —or still is— life on Mars.
A necessary step for manned missions
From a technological point of view, a mission to return Martian samples to Earth would be a small-scale version of what is needed for a manned round-trip mission. It would be easier to rely on the success of such a mission if rocks could be recovered before attempting it with humans.
Obtaining samples from Mars would also provide a better understanding of the Martian soil and atmosphere. Many of the plans to send humans to Mars count on being able to take advantage of the resources present in the environment during the stay; for example, extracting oxygen from the air or water from the subsoil, but it is not known how well air filtering or water extraction equipment will work there. The possibility of growing food on Martian soil has also been considered, which would greatly reduce the amount of supplies that would have to be carried. Studying samples of Martian soil would allow us to know whether these plans are viable or not.
It is technically possible
One of the main reasons for carrying out this mission is because it is technically doable. NASA has been planning for a similar mission since the 1970s. However, in recent years the capabilities of space agencies and private space companies have come a long way. For years, unmanned vehicles have been able to meet in space and dock autonomously, and launch technology would already make it possible to create a vehicle capable of taking off from Mars.
In addition, there have been many successes in taking samples from other bodies in the solar system. The Japanese Space Agency’s Hayabusa probe was able to obtain samples of an asteroid and bring them back to Earth in 2010, and its heir, Hayabusa2, is now orbiting the asteroid Ryugu, where it has collected samples and will soon be on his way back. Mars would be the next logical step.
One reason against it: the cost
Despite all the scientific benefits of bringing Martian samples to Earth, one aspect to consider is the cost of the mission. There are no official figures yet, but it is clear that the mission would involve two or three launches from Earth and one from Mars, thereby multiplying the costs. As a reference, the Mars 2020 mission, which will take the next rover to Mars, will cost around $2.5 billion, practically the same as its predecessor, Curiosity, launched in 2012.
This money could be dedicated to a variety of smaller missions to study Mars or for other purposes. Still, advocates point out that this mission would be as revolutionary as the Apollo Program was for lunar science. Almost everything we know today about the origin of the Moon derives from the samples obtained during manned missions to the Moon and the experiments that were conducted on them. Bringing samples from Mars to Earth could lead to a similar scientific revolution.