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Curiosity initiates next step in Martian exploration
by Amanda Doyle
Posted: 24 November 2011

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NASA’s Curiosity rover is due to launch on its journey to Mars this weekend in order to assess the past and present habitability of the red planet.

Is there life on Mars? It has long since been ruled out that Mars holds an advanced, canal-building civilisation speculated by the likes of nineteenth century astronomers Giovanni Schiparelli and Percival Lowell, since Mariner 4 revealed a barren planet after the first flyby in 1964. But what about microbial life? Microbes have been found in the most bizarre and unexpected places on Earth, so it’s possible that they may have existed on Mars in the past, or even still do exist on the red planet today. On 26 November, NASA will launch its Mars Science Laboratory (MSL) mission, comprising car-sized rover Curiosity, in an attempt to come one step closer to answering this question.

Artist's impression of Curiosity at work collecting samples on Mars. Image: NASA/JPL-Caltech.

Upon landing in Gale Crater in August 2012, Curiosity will quickly get to work using its ten scientific instruments to decipher if the conditions were ever right for microbial life, by looking for the building blocks of life, such as complex carbon compounds. These are essential for life to form, though they are not solely formed by life. Such organic compounds could also have been delivered to Mars via carbonaceous meteorites. Directly detecting microbes would be a difficult task according to Paul Mahaffy, principal investigator for the Sample Analysis at Mars (SAM) experiment aboard MSL. “To detect microbes themselves on Mars the mission would need to be designed to eliminate with a high probability the possibility of a false positive from an Earth microbe that went along for the ride. This could add significant cost and complexity to the mission design. Then who is to say that the Mars microbes could be detected with the same tools that we use to detect Earth microbes.”

Even if organics did exist on Mars, it might be very difficult to detect them because they are very difficult to preserve. However, sedimentary rocks can trap organics if conditions were right at the time and Curiosity can drill into these rocks.

Curiosity’s SAM experiment has the job of seeking out the carbon based building blocks of life. The Viking experiments in 1976 returned a disappointing null result on organic material. However the Viking landers were stationary, while Curiosity can roam. The Viking landers also only had access to the soil around them, where as Curiosity can examine the inside of rocks. SAM is also much more sensitive than the instruments aboard the Viking landers as well as being able to detect a greater range of organic compounds.

Schematic showing the range of science instruments aboard the Mars Science Laboratory. Image: NASA/JPL-Caltech.

One hot Martian debate currently raging is whether or not methane exists on Mars, along with the origin of the methane. Microbes are a key source of methane on Earth, but there are other sources such as comet impacts and the vaporisation of methane ice. Mahaffy is confident that MSL will help to resolve this debate. “The Tunable Laser Spectrometer (TLS) on MSL is sufficiently sensitive to provide a definitive answer to the question of the presence of methane at the parts per billion or below mixing ratio by volume in the Mars atmosphere. If there is enough methane the TLS will determine the ratio of heavy to light carbon in methane. This could be a clue as to the source of methane but would not be a definitive measurement with regard to its possible production by microbes.”

Curiosity comes equipped with its own pair of eyes – two cameras capable of capturing HD video and high resolution pictures, called Mastcam. Curiosity’s eyes even have their own sunglasses in the form of a filter allowing the cameras to look directly at the Sun. This allows the rover to measure the quantity of dust in the Martian atmosphere. Other cameras aboard include the Mars Hand Lens Imager (MAHLI) for close up, magnified views and the Mars Descent Imager (MARDI, which will video the descent of Curiosity.

The Dynamic Albedo of Neutrons experiment, or DAN, shoots neutrons at the ground and measures the energies of the reflected neutrons. This enables it to seek out any hydrogen, which usually implies water ice, up to half a metre below the ground. The weather will be recorded by the Rover Environmental Monitoring Station (REMS) and the radiation on the planet is monitored by the Radiation Assessment Detector (RAD). RAD will also monitor the radiation levels on the way to Mars, gathering potentially useful information for any possible future human missions.

Gale Crater, with the landing ellipse outlined. Also evident is the 5km mountain in the centre of the crater, the reason for the site’s selection. Image: NASA/JPL-Caltech/ASU/UA.

Curiosity can determine elements in rocks and soil with the Chemistry and Camera suite, known as ChemCam, and the Alpha Particle X-Ray Spectrometer (APXS). ChemCam will zap rocks with a laser which produces a measurable spark encoded with information about the elements in the rock. APXS identifies elements by bombarding a sample with radiation until it emits X-rays characteristic of that element. A similar device was used on Spirit and Opportunity but Curiosity has one up on its predecessors; it isn’t solely a night owl. The chip that detects the X-rays needs to remain cold, so Spirit and Opportunity could only use this at night. However Curiosity has its own cooling system allowing the spectrometer to be used during daylight hours. APXS is also speedier and more sensitive than its previous instruments.

CheMin, which is the Chemistry and Mineralogy experiment, can look at minerals in order to peek into aspects of Mars’ environmental history, such as temperature, pressure and chemistry. It is the first Mars mission to use X-ray diffraction, which can detect how X-rays are scattered from a sample and thus identify minerals. When minerals are formed they capture information about the environmental conditions, which could reveal if the Gale Crater was once a good place for life.

MSL's landing ellipse spans just 25 by 20 kilometres, and it will be the first Martian rover ever to have the capability to explore outside its landing ellipse. “The guided entry technique will land Curiosity within around 10 km of the centre of the ellipse,” MSL deputy project scientist Ashwin Vasavada tells Astronomy Now. “The rover is designed to drive at least 20 km. These design specs allowed many more sites to be considered than in previous missions. First, the smaller ellipse ‘fit’ in more places within Mars' topography. Second, it allowed sites to be considered that had the primary science target outside of the ellipse, on terrain too hazardous to land upon. Gale Crater is such a site. The ellipse contains interesting scientific targets, but the real prize is the mountain of layered rock just outside of the ellipse.”?

Over sixty potential landing sites were originally suggested, and but only Gale Crater cut the final grade. Observations from the Mars Reconnaissance Orbiter have shown that Gale used to be wet, by observing clay minerals which are known to form when water is present. “Gale Crater was chosen because orbital imagery has revealed a 5-km mountain of layered rock in the centre of the crater,” explains Vasavada. “The layering indicates that the mountain did not form during the impact itself, but over time as sediment accumulated (and eroded at times) after being transported by wind and/or water. Orbital data indicate that the layers change in composition and structure in the lower part of the mound. The lower layers contain clay minerals, which form in the presence of water, with sulphate salts above. Curiosity will investigate whether these layers have captured a record of changing environmental conditions in early Mars history. Curiosity will investigate these ancient environments for their habitability, their capability to support life.”

To find out more about the mission pick up a copy of the December issue of Astronomy Now magazine or order it online here!

Stay tuned to Spaceflight Now over the weekend for live streaming updates and launch coverage.

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