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Introduction

For a long time now, Mars has been the object of desire for many missions from a range of different space agencies. Many of them have been very successful (like the incredible story of the NASA rover Opportunity, whose proposed mission life cycle was 90 days yet is still gathering and sending data after 13 years), and some not-quite-so successful (the poor Beagle 2, long believed to have been destroyed upon landing but recently discovered to have been inactive simply because two solar panels failed to deploy, blocking the communications antenna). Though Mars has a reputation for making missions difficult for various reasons (roughly two-thirds of probes sent to Mars have failed before their missions could be completed), at the present time there are no less than eight different active vehicles sent by mankind either in orbit or on the Martian surface itself.

One of these vehicles, the most recent successful arrival on the surface, has given us more data than ever about the Martian environment. It is assessing the climate, analyzing geology, offering possible conclusions on whether or not life of any kind once existed on Mars, and perhaps most importantly, looking to answer a fundamental question:

If we were to visit Mars in the future…how hospitable would it truly be?

In the early 2000s, NASA began work on a project that would eventually become known as the Mars Science Laboratory (MSL) mission. The idea was to determine once and for all the current and past habitability of Mars for organisms both complex and simple.

The centerpiece of this mission was the rover that the MSL carried with it, right down to the Martian surface itself: the vehicle named Curiosity.

The Curiosity Mission, Now and Into the Future

Early Stages to Landing

In 2004, NASA began taking proposals for the various parts that the probe would take to Mars, and within four years most of the instrumentation had been completed and was being tested. Though the project did run over-budget during development and NASA had to simplify many of the instruments in order to make a revised launch date, the rover – given the name Curiosity thanks to sixth-grader Clara Ma from Kansas – took flight from Cape Canaveral in late 2011; the beginning of a ten-month journey to Mars.

The MSL mission had, and still has, several basic objectives – chief among them to identify possible “biosignatures” or features that imply that a biological presence had once been on Mars. The mission also performs detailed geological testing of the area to identify exactly what kind of rocks and soil may be found on the Martian surface. And finally, it records and analyses radiation levels both during the journey to Mars and once on the surface. That data, of course, would be potentially crucial for planning a future human Mars mission – and more on that later.

On August 6th, 2012, Curiosity landed successfully in the Gale Crater, very close to the equator of Mars. After a tense 14 minute wait, news of this reached the waiting mission staff, and very soon after that the world knew that the most complex and elaborate rover yet designed for Mars missions would soon begin its exploration. The choice of Gale Crater had been carefully considered beforehand; the site for the landing had to include both a variety of different materials for geological analysis and also the kind of rocks capable of indicating the evidence of past water and (maybe, just maybe) ancient fossils. From past observations of the surface, that particular location satisfied all these requirements – and its close proximity to the Martian equator would help with communication.

On the Surface

Once on the ground, Curiosity got to work, using a variety of instruments to assess the Martian surface in pursuit of its mission. Though the initial thoughts regarding what the rover could carry had been limited by budget and time constraints, a wide variety of instruments were fitted to the rover for use.

These included:

– a spectrometer designed to assess the chemical makeup of rocks using alpha particle radiation and X-rays, ideal for getting an accurate composition of the sample.

– an X-ray diffraction analyser, designed to target specific minerals within rocks and identify whether or not any particular rock might have had water involved in its creation or its development. Past or present water, is, of course, a key indicator of possible life.

– an instrument for analysing the few gases in the Martian atmosphere, looking in particular for specific oxygen and carbon signatures within carbon dioxide and methane that would tell if those gases were produced chemically or organically.

– a radiation detector, switched on at launch in order to measure the radiation doses given to the mission both by the Sun and by other possible sources.

– a weather package designed to measure wind speed, temperature, humidity and other important values.

– a variety of different cameras – five for imaging the surface and other interests, and 12 for supporting the movement of the rover itself.

With all of this instrumentation on one vehicle, Curiosity is by far the most complex rover ever sent to a body outside of Earth orbit and land successfully.

Within a few months of landing, the rover made a rather spectacular success when it came across what was described as an “ancient stream-bed.” This indicated that there had, at one time, been a wide-flowing and vigorous river system, at least in that area. Though the existence of flowing water in the past had been heavily touted since the Mariner missions of the 1970s, this added further weight to the idea that Mars did, in recent history, contain flowing liquid water – and by extension, possibly life. Further discoveries the following year of abundantly accessible water in soil samples added more credence to this theory.

In early 2013, a sample of rock taken by Curiosity at Gale Crater detected water, carbon dioxide, oxygen, sulphur dioxide and hydrogen sulphide. This is a chemical combination very well-suited for the existence of microbe life, thereby adding further weight to the idea that Mars was, once upon a time, potentially habitable for simple forms of life.

In late 2014, the rover detected a spike in methane levels ten times higher than the baseline value in the Martian atmosphere, as well as other organic compounds within rock samples. While the source of these compounds is debatable, it is entirely possible that they could have been produced by ancient microbial processes.

In late 2015, there was enough data gathered by Curiosity for a conclusion to be made that the landing area of Gale Crater was once either a large lake, or stream, or both, billions of years ago.

Finally, in late 2016, NASA gave a summation of the mission so far, where they confirmed the relative success of at least one objective of the mission. In their opinion, the Gale Crater site once contained an ancient river or lake, with a chemical energy source and all the chemical ingredients needed for life to have once existed there. Their conclusions were definitive – while Mars likely does not have life now and possibly did not in the past, the conditions were extremely favourable for life to have existed there once upon a time.

From the time of its launch, the rover has measured the doses of radiation from galactic cosmic rays as well as energised particles emitted by the Sun. The findings, however, were sobering: the dose that the rover took in the time frame that a human Mars mission would entail (860 days total: 360 days traveling back and forth and 500 days on the surface) was almost twice what NASA deems an unacceptable lifetime limit for its astronauts in orbit around the Earth.

Future of Curiosity

Though the initial plan was for the rover and the mission to be active for just two years, within a few months of landing the mission plan for Curiosity was extended indefinitely. This didn’t come as a surprise to most familiar with the sheer durability and toughness of such rovers: the story of the NASA rover Opportunity, as shown above, pays testament to that.

Presently, Curiosity is to be found exploring the surfaces of Mount Sharp, looking for further clues as to

Martian history and in particular how the planet moved from a relatively habitable abode for simple life to one incapable of supporting it. Still in excellent working order with only a couple of minor technical difficulties to inhibit it, the rover has traveled over 16.5 kilometres from its landing site.

Right now, the key objective that the rover is focusing on as it climbs Mount Sharp is to discover exactly how and when the lakes and rivers upon Mars dried out, thereby giving possible clues as to why it happened.

On its fifth “birthday,” the rover even played a little “Happy Birthday” tune to itself – and with any luck, Curiosity will continue to roll on in the course of its mission for many years to come.

What Does It All Mean For Future Missions?

In the roughly five year timeline since Curiosity first landed on Mars, this probe has given NASA and the world a treasure trove of information regarding surface and atmospheric conditions on Mars, some of which confirmed what previous missions had hinted, and some of which was entirely new. It has, by all accounts, been a remarkable success – and no doubt there is still much more to be found and more information to be sent back by the durable, brilliant rover.

However, the thirst is for more than just robotics to set their wheels on the surface of our nearest planetary neighbour. As has been mentioned in previous entries, more than one organization on Earth has the hunger to put humans on Mars and to do it soon. But to do that, we need a lot of information about conditions there – both for the sake of mission parameters and for the safety of the astronauts that would go.

So, in light of that, what has the Curiosity mission told us about a potential human Mars mission that is noteworthy?

Well, the first discovery is possibly the most difficult factor discovered by the mission, and the one most likely to put serious holes in a lot of Martian ambitions – the high radiation levels.

As was noted earlier, the maximum accepted lifetime dose of radiation by NASA for its low Earth orbit astronauts is one that will give a three percent additional risk of fatal cancer development. The readings from the rover show a total dose of around 1 sievert of radiation during an 860-day Mars mission, which corresponds to a five percent additional risk – almost double what NASA deems acceptable. And this, of course, does not take into account other missions that the astronaut may have been on previously in their lifetime, nor the (likely) vital time in a zero-G environment that they would need for the purposes of training for such a Mars mission. This finding, showing that the total dose was higher than many people expected, indicates that serious consideration is going to have to be given to radiation shielding for any astronauts involved in such a mission.

There are, of course, solutions to this problem – increased radiation shielding for the craft involved, as well as the choice of building a habitat for this purpose (likely essential for long-term habitation of Mars anyway) once on the surface that would be likewise shielded. Such shielding does increase the potential weight of any mission sent, and so increases the cost and possible complexity. Such things will have to be carefully considered in the planning of any future human mission.

The second discovery involves the landing of the rover itself, where a rather unique system was used. Rather than just one system – thrusters, an airbag or parachutes – being used to arrest the fall of the rover to the surface, Curiosity instead used a unique combination. Initially, a heat shield was used to reduce speed during the initial entry into the thin Martian atmosphere. This was followed by a parachute once further down, and thrusters once within around two kilometers of the ground. Finally, and most uniquely, a “sky-crane” system was used, where cables helped lower the rover away from the rest of the descent vehicle until touchdown, at which point the cables separated and the other part of the lander flew away to land elsewhere. Such a system was entirely novel and was deemed one of the few possible ways that a wheeled rover as large as Curiosity could be landed safely – that is, without causing damage to vital systems through impact or the dust cloud generated by such a landing.

The success of this principle demonstrated that heavy yet delicate payloads can be deposited on the Martian surface, and as any human mission is going to require an awful lot of heavy yet delicate equipment, this method is a useful possibility for getting materials down to the surface.

The Curiosity rover has also confirmed beyond reasonable doubt that while organic compounds exist on Mars, organic life likely does not at this point in time, which has connotations for precautions that any crew might have to take if it came to encountering simple life there – such as increased anti-contamination procedures and the like.

All of these, along with various discoveries that have been made regarding chemical and organic findings on Mars by the rover, mean that this mission has been given a wealth of information that will prove useful if and when humanity decides to send some of its own representatives to the Red Planet.

Conclusion

Almost five years after its landing, the Curiosity rover is still almost fully functional, rolling away through the Martian landscape, testing and sampling all the time. A testament to the ingenuity of those who helped place it there as well as the durability of the rover itself, it should continue to supply incredibly useful data for many years to come.

By far the heaviest and most complex vehicle ever to land on the surface of a planet that is not our own, it has spent the last half a decade giving us a wealth of information. Through discoveries made by this one rover, we now have a much better idea of the best method to deliver heavy payloads to the Martian surface, the previous habitability of Mars, and the likely dose of radiation that a human mission to Mars might face, and more. Even now, it seeks to answer another question about Martian history by attempting to discover at least a rough idea of the time at which liquid water there might have vanished.

In the next couple of decades, it is possible that a human Mars mission will finally result in human feet upon that planet. Maybe, just maybe, when they do…

…there will be a tough little rover, battered but still working…rolling up to greet them.

More from Ross:

The Road To Mars: Our Past and Our Future

Going To Mars, Part 1: The Human Element

Going to Mars, Part 3A: Orion, The Next Generation of Travel

Ross Wakefield is a freelance science writer, communicator and consultant, with specialized expertise in the field of current and historical space developments. Ross has a Bachelors degree in Physics with Astrophysics from the University of Leicester and a CMCU in Astronautics and Space Engineering from Cranfield University and is a member of the Institute of Physics and British Mensa. Ross is currently beginning a series of articles with The Mars Generation on various space-related topics. When he’s not glued to a computer screen, he enjoys playing and watching sport, reading various books and trying to find where the nearest good pool table is in the United States. Find Ross on his Twitter.