A geological mission to Mars
Can Curiosity match the exploits of Earth Scientists?
On the 16th of July 1965, Mariner 4, NASA’s fourth in a series of spacecraft designed to investigate the planets of our inner solar system, completed the first successful flyby of the Martian surface. The Mariner 4 mission was one of huge success among a string of other, not-so-lucky (or perhaps not as well executed), missions carried out in the 1960s; primarily by NASA and the USSR’s Soviet Space Program – including the latter stages of the Sputnik Program. The initial pictures returned from Mariner 4 depicted a heavily cratered, baron surface of the red planet – quashing the initial excitement of ‘life on Mars’.
Since Mariner 4, a mission of many firsts, the exploration of Mars has moved on significantly: there have been over thirty spacecraft launched to investigate the red planet since 1965, including eleven that planned to land. Of these, six can be classified as ‘true rovers’, including the British-built, Beagle 2, and twin rovers Spirit and Opportunity, built for NASA’s Mars Exploration Rover (MER) project for launch in 2003. Now, in 2012, NASA’s latest incarnation, Curiosity – dubbed by some as a robot-geologist – builds upon the success of the MER project, taking on board many of the best features of Spirit and Opportunity: six-wheel drive, a rocker-bogie suspension system and cameras mounted on a mast. Whilst Curiosity is in many ways similar to its predecessors, a lot has changed since 2003 and its differences are what set it apart as a truly cutting-edge machine. For instance, Curiosity carries twice as many scientific instruments and its entire science payload is over ten times the weight of Spirit and Opportunity’s. Despite being a bigger, more powerful, technologically advanced machine, NASA still managed to decrease the landing ellipse (an area in which they are 99% certain they can land the craft) by 75%!
Curiosity landed on the Martian surface, inside its designated landing site, Gale Crater, at 05:31 UT on the 6th of August 2012. “We always knew it was going to be a great landing site…It’s not until you’re on the ground that you realise that something like this is going to be like driving around in western Utah – it’s going to be spectacular”. John Grotzinger, project scientist (and geologist), summed up his excitement after seeing some of the first ground-level images from Curiosity. Some may find “driving around in western Utah” a little underwhelming for a trip to Mars but it seems Grotzinger was trying to convey the 3D nature of the area surrounding the landing site, as all images up to this point had been from an aerial perspective.
Curiosity was built and is operated by the NASA mission team, Mars Science Laboratory (MSL), who are in-turn part of the Mars Exploration Program. The Mars Exploration Program’s overall science strategy is ‘following the water’. The MSL team will be seeking to contribute to this strategy by following specific objectives, with a view to reaching four main goals: (1) Determine whether life arose on Mars, (2) Characterise the climate of Mars, (3) Characterise the geology of Mars and (4) Prepare for human exploration. The primary goal of determining whether life arose on Mars is the driving force behind this mission and sees NASA go ahead with what is their first astrobiology mission since the Viking landers.
With one of four main goals of the MSL being to characterise the geology of Mars, Curiosity has been provided with a subset of instructions under the heading of geological and geochemical objectives. These are: to investigate the chemical, isotopic and mineralogical composition of the Martian surface and near surface geological materials; and to interpret the processes that have formed and modified rocks and soils.
So why is geology so important in what is essentially a search for life? Well, NASA itself has admitted that the question of whether life has existed on Mars is one which this mission alone cannot answer: “Curiosity does not carry experiments to detect active processes that would signify present-day biological metabolism, nor does it have the ability to image microorganisms or their fossil equivalents”. This means that Curiosity is not looking for life itself, but signals in the environment that suggest a suitable habitat for life. For example, one of the main strategies is to search for carbon-containing compounds known as organic molecules: an important ingredient for life that Curiosity can detect. This ability, along with many other facets of knowledge that can be coaxed from the rocks on Mars is what makes geology so integral to this mission. Geology is the link between the distant past and what we see today; if there’s a time in Mars’ history when life did exist, the only record of that will be in its rocks. That’s why Gale Crater was selected as the landing site: it is, in NASA’s opinion, the place where the rocks are most likely to paint a picture about the history of life on Mars.
Curiosity possesses instrumentation that far exceeds some of the world’s most well-equipped Earth Science laboratories, and eclipses the comparatively rudimentary tools used by field geologists. Among its arsenal is a laser-equipped, spectrum-reading camera – for vaporising rock surfaces; and an Alpha Particle X-ray Spectrometer for determining the relative abundance of selected elements. The more familiarly named (to the geologically inclined at least) Mars Hand Lens Imager – or MAHLI for short – is arguably the most important tool, if only for the wealth of fundamental knowledge it can provide. In the field, the hand-lens to a geologist is indispensable: it is imperative to build the basis of understanding, from which all other inferences proliferate. The application of a hand-lens in the study of a rock can provide information on properties such as colour, texture, cleavage, crystal size, crystal shape, sorting and composition; all of which have implications for such factors as how, why, at what rate and via which processes selected rocks were formed.
With a seemingly superfluous supply of equipment at its disposal, Curiosity seems destined for greatness, but can this one ton, $1.8 billion behemoth really match up to the achievements of the geologists and geoscientists on Earth?
Well this has been pondered, and scientists – including NASA’s own Shawn Domagal-Goldman at this year’s Cheltenham Science Festival – have discussed this very subject. Each will have their own views; many will say that the ability of an Earth Scientist to recognise the subtleties in an outcrop, to move around a site to get the perfect view of things or to create such detailed observations required for a top-notch geological sketch are simply unrivalled by mere machines. However, the fact of the matter is, we can’t put a human geologist on Mars, which makes the whole man vs. machine argument close to irrelevant. What we do have is a machine with the ability to carry out world-class research on a planet 127 million miles away. That is something which cannot be rivalled by anything attempted before.
The information provided by MAHLI and the other science instruments will be analysed by geologists, geochemists and other NASA scientists; as with most of science, the resulting conclusions will be up for debate. Not least because these rocks are alien to everyone; no one has ever touched a rock from Mars and how do we know what the products of over four billion years of geological processes on Earth’s neighbour will look like? Of course we will use our knowledge of Earth geology as an analogue, but what effect will physical and environmental characteristics have on the geology? For instance, there are crucial differences in how we distinguish wind-blown from water-lain sediments on Earth, but are these applicable on Mars? With Mars’ gravity being only 38% as strong as Earth’s and an atmospheric pressure less than 1/100th of that on our own planet, who’s to say that Martian sediments won’t portray their depositional histories in a way that misleads us…Only time will tell.
Looking to the future
NASA has had by far the most success when it comes to deciphering the geological history of Mars. It’s testament to the team at NASA’s Jet Propulsion Laboratory, California that the US government and president Obama continue to support missions of this size and expense, whilst others have fallen by the wayside. Just this week NASA announced plans to send a new spacecraft, InSight, to Mars in 2016. The craft will be equipped with seismic instruments, allowing for experiments on ‘marsquakes’ and the internal structure of the planet. InSight will undoubtedly build on the knowledge gained from the work of Curiosity and once again push the boundaries of planetary science to a whole new echelon of understanding.
Before then, Curiosity has important work to do and all eyes will be firmly fixed on the rover’s voyage of discovery en route to its primary destination, Mount Sharp; which the NASA mission team hope to at the base of a year from now.
Whatever happens during Curiosity’s operations on Mars, the results will be ground-breaking; Mars is an enigma waiting to be deciphered and each and every day will teach us something we didn’t know about one of our closest neighbours.