Hervé Morin, Mars, a new object for ‘Curiosity’.
translation : Doxa-louise
It is the most ambitious scientific mission to Mars yet : Curiosity rover (Mars Scientific Laboratory, for the scientific jargon), which was launched Saturday November 26 at 16 hours (Paris time) by an Atlas V rocket from Cape Canaveral (Florida), is a concentrate of technology.
Loaded with ten scientific instruments, it will have to survive one martian year (ninety-eight terrestial weeks) and cover some twenty kilometers looking for rocks to analyse, for the design teams from the Jet Propulsion Laboratory - JPL - (NASA, Caltech University) to be satisfied. But the scientists world-wide associated with this adventure are hoping that the engine, the largest of its kind, will be more enduring.
Before embarking on its scientific travails, Curiosity will have to survive a long journey and most importantly a landing, slated for august 2012, where the modalities are yet untried. Too massive (900 kgs) to soft land with the aid of air bags, as certain of its predecessors have, it will be lowered to the martian soil by a kind of spatial ‘elevator’, a structure with built-in retro-rockets that will deposit it at the end of ropes. If this method is successful, it will be used again in future missions to transport to Mars ever heavier equipment.
Then will come the time of the scientific mission itself. NASA has resisted so far the temptation to «oversell» the mission, which will cost no less than 2,5 billon dollars. It has made clear from the start that Curiosity will not be looking for life on Mars. One need than not expect images of micro-organisms alive or fossil. But it will attempt to determine if this planet could have known that convergence of conditions favourable to its appearance. The key word? Liveability.
The difficulty arises from the fact that the conditions favourable to the emergence of life are at the same time the ones least favourable to conserving its traces : the rarity of fossils on earth attests to this. On Mars, one is not looking for Tyrannosaurus marsii, but rather for any clues left behind by possible germ colonies : hard to imagine in what shape after many billions of years of petrification.
NASA recognizes that knowing wether or not life has ever existed on Mars is still an open question. Its slogan of the 1990s, «Follow the water», proved a disappointment. Certainly, for life to appear H2O is necessary. But it must have time to interact with its environment. The rovers Spirit and Opportunity confirmed that water was present in the past. They showed us the traces left on the soil, the sulfates that prove that evaporation occured.
Yet for Jean-Pierre Bibring, from the Institut d’astrophysique spatiale d’Orsay (CNRS, université Paris-XI), looking for life where water flowed and sculpted rock is without doubt a false start : volcanic phenomena could well have heated water percolating underground to make it flow above ground on the occasion of certain events. But, by those far-gone times, tha martian atmosphere was already too thin for this water to stagnate and permit reactions leading to life. «One has to go back well before that, not long after the formation of planets, he assures us. Before the end of the great bombing at the beginnings of the solar system. Before volcanism had time to form the great plains of northern Mars, while this planet was still covered by oceans.»
To his mind, Mars is «an open window on the past of the Earth». Our planet, more massive, has gone through a tectonic activity which led to the disappearance of the more ancient rocks, pulled back into the mantle. On Mars, these vestiges of the first ages subsist, in the form of clays, born of rocks which ‘played’ in water for a very long time. «Perhaps that, here on Earth, it is under those conditions that life emerged », he puts forward. It is the instrument Omega, for which he is responsible on the European Mars Express probe, which brought out, in the middle of the decade 2000, these diluvian clays. This discovery has altered our understanding of the history of Mars. And for NASA’s orientation, now become «Follow the carbon», which for Curiosity translates to «Follow the clay».
The rover should find some without much trouble in the Gale crater, where it is expected to land. Choice of the site became the object of an intense struggle, mixing together scientific, technical (safety for landing) and as well, marketing considerations. «This crater has a known stratification, which is well understood, informs us Francis Rocard, in charge of programs for the exploration of the solar system at the Centre national d’études spatiales (CNES). It offers as well a rather spectacular aspect, with a mount to be scaled which promises beautiful landscapes».
Jean-Pierre Bibring would have preferred another site, Mars vallis, certainly less pictoresque, but where Curiosity could have easy access to primordial clay rocks. From within the crater, it will be necessary to leave the’ellipsis’, the zone where landing is considered secure, to reach them - «which might take up to two years», he states sadly.
The astronomer Sylvester Maurice (Observatoire Midi-Pyrénés, Toulouse) is less harsh : «The site agreed upon brings together two approaches, mineralogy (the composition of rocks) and morphology (the manner in which they are stratified)», he says. Surprises are not impossible : «Every time we predicted something, Mars showed she had more imagination than we did.»
In concert with teams from the American laboratory at Los Alamos, this Frenchman is responsible for one of the most spectacular instruments on Curiosity, the ChemCam. It is a laser capable of vaporising rock at up to 7 meters for analysis at a distance. «With this laser saber, we have the benefit of what Anglo-Saxons call a ‘cool factor’, he says gaily. Other instruments are meant to give precision measures, with clenches, ovens, chromatographs (notably French), spectroscopes, etc. «In total, we have 80 kgs for scientific exploration on a 900 kg engine, and we expect a lot from such equipment», indicates Francis Rocard.
For Sylvester Maurice and his colleagues, the initial challenge was that of reducing the mass of the instrument from 10 kgs to 700gs. «At the beginning, it was too long, one couldn’t close the trunk of the rocket», he recounts. Each superfluous gram has a snowball effect on the rest of the equipment. The necessary slimming exercise is «a great Monopoly, where one exchanges mass, length, power, all within the extraordinary master guidelines of the Americans».
Pause after the launch? Not at all, for the time of crossing to Mars will be used to develop software : «The rover is not yet complete, it will be much more intelligent on arrival than at departure», indicates Sylvester Maurice. These nine months will be used profitably to train men to use it. «We are going to end up with a 900 g car, with ten instruments each refined by tens of individuals, tells us the researcher. Potentially, we have 400 to 500 pilots for a single joystick.»
How should this situation be managed, what choice for the rocks to be analysed, the work to be done? ChemCam, directed from France, will analyse the surrounding rocks, transmitted to the JPL in California, who will decide which ones need more work, on contact.» «The programming will occur almost in real time, with as well a definition of further down strategic objectives», notes Sylvester Maurice.«This requires an awesome level of organisation, as complex as that for the construction of the instruments.» Thus Curiosity, a robot whose condition is finally rather human.
