King of Mars
An Australian geologist’s role in NASA’s latest mission
Early on the morning of August 6, a group of scientists held their breath as Curiosity, NASA’s latest Mars rover, streaked through the thin Martian atmosphere in ball of fire. One of those scientists was Dr Penny King a geologist currently working at the Australian National University.
“It’s the opportunity of a lifetime to be involved in a mission that explores new areas in our solar system,” Dr King says, “And based on past missions, we expect to find out that the Martian surface is more diverse and interesting than we could ever have imagined.”
Although the possibility of life on Mars is a strong driver for exploration of the red planet, Curiosity’s primary mission isn’t to look for that life directly. Instead, it will assess how suitable the environment of Mars is for supporting life either in the present or at some point in the distant past.
Dr King is part of a small team of scientists that will be working with one of the instruments on curiosity, the Alpha Particle X-Ray Spectrometer (APXS), which is sponsored by the Canadian Space Agency. The APSX’s job is to identify elements present in rocks enabling geologists to identify those rocks and build that information into a detailed picture of the geological history of Mars.
The APSX works by bombarding the exposed rock surface with alpha particles and x-rays generated by a radioactive Curium 244 source in its probe. The radiation causes the atoms of the rock to emit their own characteristic x-ray signature rather like fluorescent paint glowing under ultraviolet light.
By looking at the peaks in the returned spectrum, scientists like Dr King can determine the composition of the rocks and identify other materials that may be on the surface of the rocks. “This is the third mission on which an APXS has been used so it has a well established and successful record. This latest version will have a couple of advantages over the previous ones though.”
One is that the detector stage will have active cooling which will increase the rate at which measurements can be made and enable the detector to work round the clock. The other is a contact sensing tip. “This enables us to know with great accuracy the distance from the radioactive source to the sample rock.” Dr King says,” And that will make it possible to use some tricks in the science to detect the presence of light elements like oxygen that don’t directly show up in the fluorescence signals.”
Analysing data from Curiosity isn’t a simple matter though. “Mars has very different chemistry to the Earth with lots of sulphur, chlorine and bromine.” Dr king says, “You can’t think about Earth processes. It’s a kind of mind game, you have to put aside a lot of what you know about geology on Earth and keep thinking ‘Mars’.”
To solve this complex analysis puzzle, the scientists will not have to rely on APSX alone. It will be complemented by a battery of other on-board science tools including a laser that can vaporise points on the surface of rocks and spectrometers that analyse the resulting flash for chemical signatures in the visible and near infrared spectrum.
From a geologists point of view, the best place for Curiosity to explore is an area known as Gale Crater in which there are some deep ravines that expose rocks from various points in Mars’ geological history. But there’s a catch. None of the existing Mars landing techniques could safely drop the rover with such precision into a deep crater. So NASA came up with something entirely new and perhaps a little crazy.
Hitting the atmosphere at around 20,000 km/h the lander was initially slowed by friction with the thin Martian atmosphere, deploying a heat shield to protect the rover. Once the speed was down to around 1000 km/h, a supersonic parachute opened reducing its speed to 200km/h. Finally a rocket descent stage took the rover close to the surface from where it was gently lowered to the ground on a tether.
In the end it was the NASA engineers that had the last laugh. Crazy or not, it worked! But pinpointing a specific landing zone was just one of the reasons for reinventing the way probes are landed on Mars.
“If we’re really going to get to grips with all that’s going on with Mars and any biology there, the holy grail is sample return.” Dr King explains, “If we can get Mars rocks back in the labs here on Earth, we’ll be in a much better scientific position. Now if you want to land a sampling vehicle then have it take off again, you have to be able to soft land it in a very specific level place.”
“The trouble with bouncing ball landing systems is it’s a lot like golf – your lander tends to end up in a hole! So apart from its own science mission, the curiosity landing technique was a great test of a system that has the potential to land a vehicle that can then blast off again and ultimately return samples to Earth.”
Dr King will be spending the first 90 days of the mission in the USA uploading instructions to curiosity and selecting targets for analysis. “ We’re operating on the Martian day,” she says, “And that’s about 40 minutes longer than an Earth day. So over the course of the mission our shift schedules drift later and later.”
“The Curiosity rover will search for life, specifically traces of organic matter. We will take a close look at the Gale Crater which likely has some of the ingredients that we think are important to life including water, energy and carbon, as well as rocks that might preserve organic matter,” Dr King says.
Of course with increasing numbers of probes being sent to Mars, one of the key things that has to be avoided is accidental contamination of Mars with microorganisms from Earth hitching a ride aboard the spacecraft. “There are actually quite strict international agreements in place to prevent that happening,” Dr King explains, “Any vehicle that will land on Mars has to be cleaned and sterilised to very exacting standards.”
Even the flight path was chosen with contamination avoidance in mind - the spacecraft’s trajectory aiming to miss the planet. At the last minute a correction manoeuvre directed the lander towards Mars whilst the remaining propulsion stage cruised off into space. That way if there was a malfunction, the entire craft would head off into deep space rather than crashing on and potentially contaminating Mars.
It’s not likely that we’ll be meeting any little green men soon, but the possibility of an encounter with microbial life from another planet grows stronger with each mission. As does the complexity and ingenuity of the spacecraft design.