Editorial Feature

Materials Testing on Mars

Image Credit: NASA/JPL-Caltech/MSSS

Mystery surrounds Mars but progress is being made to understand its environment. The National Aeronautics and Space Administration (NASA) has sent a series of rovers to inspect land samples on the planet, which is half the size of earth and known to have seasons and structures like mountains. Microorganisms have already been found in the samples, indicating signs of life.

Although no liquid water is believed to exist on the planet's surface, water is thought to be in its soil and clouds.

Mars Rovers: Curiosity Opportunity and Spirit

Helping us understand the soil on Mars are Curiosity and Opportunity, rovers that landed in 2012 and 2004, respectively.Curiosity is the size of a car, and Opportunity was smaller at just 5 feet in length and height and 384 pounds.

Opportunity is in the Meridiani Planum part of Mars, and it identified smectite clay minerals that form in the presence of water in rocks on the rim of what is called the Endeavour Crater. Scientists theorize that the rocks precede the crater, whose rim itself dates back more than 3.7 billion years ago.

Having spent time on the Gale Crater, Curiosity discovered a groundwater system that may of existed for millions of years. The smectite clay minerals there indicate a moderate to neutral pH as a lack of sulfate minerals suggests no acidic environment.

In an area called Yellowknife Bay, rocks were discovered with evidence of sustained water. Aging tests measure the material to be 4.2 billion years old.  

Another American rover called Spirit landed in January 2004, on the opposite side of the planet. Before it got stuck in soft soil resulted in the end of its mission, Spirit also saw evidence of water, possibly in the form of snow melt, that had flowed into a subsurface continuously.

Image Credit: NASA/JPL-Caltech/MSSS

Sample Analysis at Mars

The suite of instruments analyzing the samples on Mars are collectively known as SAM (Sample Analysis at Mars), and they consist of three items: a Quadrupole Mass Spectrometer (QMS), a Gas Chromatograph (GC), and a Tunable Laser Spectrometer (TLS).

The QMS and the GC can operate together in a GCMS mode for separation and definitive identification of organic compounds, while the TLS obtains precise isotope ratios for C and O in carbon dioxide, and measures trace levels of methane and its carbon isotope.

Materials Found on Mars

To date, organic molecules found by NASA have chlorine atoms, and include chlorobenzene and several dichloroalkanes, such as dichloroethane, dichloropropane (dichloropropane is a carcinogen and used on earth as a paint stripper and varnish) and dichlorobutane with chlorobenzenes being the most abundant at concentrations between 150 and 300 parts-per-billion.

Not found naturally on Earth, chlorobenzene is manufactured for pesticides (insecticide DDT), herbicides, adhesives, paints and rubber. Similarly, dichloropropane is a carcinogen and used on earth as a paint stripper and varnish.

How did they get on Mars? NASA theorizes that the precursor organic molecules were those found in the mudstone, and that the chlorinated organics actually formed from reactions inside the SAM instrument as the sample was heated for analysis.

So what is thought is that perchlorates, a chlorine atom bound to four oxygen atoms that are abundant on the surface of Mars, were heated so that the chlorine from it combined with fragments from precursor organic molecules in the mudstone to produce the chlorinated organic molecules detected by SAM.

Back in 1976, similar evidence on Mars was found. A Gas Chromatograph Mass Spectrometer instrument on NASA’s Viking landers detected chloromethane and dichloromethane, or two simple chlorinated hydrocarbons, after heating Martian soils for analysis. However they were not able to rule out that the compounds were derived from the instrument itself, according to the team. While sources within the SAM instrument also produced chlorinated hydrocarbons, they don't make more than 22 parts-per-billion of chlorobenzene, far below the amounts detected in the mudstone sample, giving the team confidence that organic molecules really are present on Mars.

More information on Mars’ soil is coming. NASA is planning to launch another Curiosity-sized rover in 2020, which could collect samples that later missions may return to Earth.

References and Further Reading

NASA: 2 Places on Mars Could Have Been Habitable

NASA's Bolden: Mars Mission is 'Closer Than Ever'

Mars Science Laboratory/Curiosity

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