A curious mission to Mars

The Curiosity rover lifts off on Saturday. Its job is to collect data that will give a picture of what might have happened on the Red Planet, which could further our understanding of the origins of life, writes DICK AHLSTROM

FIND WATER on Earth and you are certain to find life. But does the same hold true for Mars? Does the Red Planet teem with life either hidden from us or too small to see?

We may soon have the answers to these questions, when the Curiosity rover touches down on the Martian surface. The Mars Science Laboratory mission lifts off on Saturday on a 570-million-kilometre journey that will deliver Curiosity at its destination in August 2012.

Everything about this mission is out of the ordinary, according to Kevin Nolan, a lecturer in physics at the Institute of Technology Tallaght. He is something of an expert on Mars, having written a book on the subject, Mars: A Cosmic Stepping Stone.

Curiosity is the most complex planetary rover ever built. Flight controllers hope to drop it into Gale crater on a tiny patch no more than 20km across, which constitutes an amazing piece of precision flying.

It also carries the most powerful selection of experiments ever built for a rover, he says. “It is the biggest and most sophisticated science payload ever landed on Mars.”

Its on-board camera is sensitive enough to see objects the width of a human hand a kilometre away and see tiny objects down to 12 millionths of a metre wide. It also has a powerful laser that will be used to vaporise rocks.

The rover will also carry experiments provided by Russian and Spanish scientists. Nasa’s science mission directorate manages the project, and the Jet Propulsion Laboratory at the California Institute of Technology is the project manager.

Such an elaborate spacecraft comes with a hefty price tag – €1.9 billion, according to Nolan.

One might ask why bother sending yet another space craft to Mars when we have seen no less than eight missions there over the past decade or so. The answer is that this one will be different. It could answer long- pondered questions about conditions on Mars.

“It is a culmination of all the missions that have gone before,” says David Moore, editor of Astronomy Ireland magazine.

Planners preparing experiments for Curiosity and choosing landing sites will have benefited greatly from the discoveries made by orbiting satellites and by the Spirit and Opportunity rovers over the past few years.

Much has been learned about the planet’s surface, its atmosphere and where to find clear signs that liquid water altered the terrain.

With this in mind, planners chose to land Curiosity inside Gale crater, at the foot of a mountain. The mountain appears to have been eroded by water, a scouring effect that has revealed geological layers that can be studied by the six-wheeled rover.

“This is the most interesting site on the planet,” says Nolan. The crater is full of clay deposits, the kind that form when water is abundant and when conditions are non-acidic – something that is more conducive to life.

Curiosity has instruments on board that can vaporise rock surfaces and measure their chemical constituents. It can drill into the surface, reach out and grasp objects with its long arm or dip down into the hidden depths of ancient fissures to sample what lies below.

Its goal is not to search directly for life. Rather, it is to provide hard data about today’s geology on Mars and how this can inform us about what might have happened in the past.

“This is pushing the boundaries of our understanding of the origins of life. It will give us a clearer idea of what does and does not lead to the origins of life,” says Nolan.

“It will be able to assess the site as a habitat. What it will not be able to do is search for direct signs of life. It would have to find a substantial biological community at the site, but we are not expecting this to happen.”

Curiosity’s instruments will be able to give definitive evidence about whether certain organic molecules are present – the kind associated with cells. It can also provide exact information about the surface soils.

“It will provide ground-truth information of the surface. It will also look at the history of water there,” says Nolan.

“It is a very big deal. It will answer the fundamental questions ‘are we unique?’; ‘are we alone?’” says Prof Paul Callanan, an astrophysicist at UCC.

So much effort is going into the search for extra-solar planets. “It really now behoves us to look within our own solar system, to establish whether other planets really do have liquid water and then what implications this has for the potential of life,” Callanan says. “Making this kind of fundamental discovery is intrinsic to humankind.”

Curiosity is twice as long and five times as heavy as the earlier rover twins, Spirit and Opportunity. Such a big buggy needs a big battery, one not dependent on sunshine to make it work. For this reason it is fitted with a “radioisotope power generator”, a device that uses plutonium-238 to produce heat and then convert this into electrical energy.

It will power the rover for at least two years, and, if Curiosity works as well as its predecessors, it will be running about for much longer.

Throughout the long journey controllers will have their fingers crossed that all goes well. This is particularly true of the complex landing procedures for Curiosity (see panel).

“It will be nail-biting stuff,” says Moore.

nasa.gov

Tricky touchdown The precision task of landing the rover on Mars

NASA MUST love a challenge, given the enormous complexity of getting the Curiosity mobile science laboratory on to the planet’s surface. Everything has to work perfectly or the lab will end up as highly expensive space junk.

“The timing of this is scary; it is incredible,” says Kevin Nolan. “All of it will happen within a few minutes.”

Once the spacecraft carrying the rover slams into the thin Martian atmosphere 81km from the surface, the flight controllers can do no more than hope all the computerised decision-making built into it works according to plan. The craft will be controlling itself.

The controllers want to land the craft within a circle no more than 20km across. Previous rovers, including Spirit and Opportunity, bounced on to the planet, protected by huge air bags, but accuracy using this method is measured in greater distances than expected for Curiosity.

Instead it will be slowed first by the atmosphere working as an “air brake”, with its heat shield reaching 2,800 degrees. Four minutes into the descent it will switch to a huge parachute, slowing the craft down to about 400kph. All this has to work perfectly but has been done many times before. What happens next, however, is amazing.

The back shell of the craft pops open and out drops what the flight controllers call a “sky crane”, with the rover held tight by its powerful claw.

Curiosity, at about 900kg, is heavy enough, but the sky crane weighs more than 1,500kg. It has eight small rocket engines around its rim and these will bring the speed down to only two or three kilometres per hour. Now Curiosity and the space crane attempt the final, most challenging part of the journey to the surface. At about 20metres up the crane lowers the rover gently to the surface using three nylon cords.

Curiosity will sever these as soon as its wheels touch down, freeing the sky crane of its burden. Now nearly a ton lighter, it will fly away from the landing site, coming to ground several hundred metres away.

All of this aerial ballet will be controlled by the ferrying spacecraft and the crane. All the while the Mars Descent Imager will be taking video of the landing site, looking for boulders and dangerous terrain so that the crane drops Curiosity in the safest possible location.

Helping things along will be the Mars Reconnaissance Orbiter, which has been in orbit around Mars since 2005 and will track the spacecraft as it ploughs into the atmosphere and then deploys its parachute.

“It is going to talk directly to the space probe,” Mr Nolan says. It will relay information about the descent, data that will be used to adjust the probe’s trajectory. “They built the orbiter with that in mind.”

Watch an animated version of the landing sequence at mars.jpl.nasa.gov