The Curiosity rover has found and analysed the first definitively identified piece of organic matter on the surface of Mars.
These organic molecules, consisting primarily of carbon, hydrogen and oxygen atoms, are the building blocks of all life on Earth. However, it is important to note that these molecules may not have come from life forms on Mars -- organic molecules can be created from chemical processes that do not involve life, NASA said. At this stage, there is not enough evidence to determine the provenance of the molecules -- but either way, their presence has meaning.
The team responsible for Curiosity's Sample Analysis at Mars instrument suite have several hypotheses. The first is, of course, a biological process. Others include chemical reactions in water at ancient hot springs on the Red Planet, or arrival from off-planet via dust, meteorites, asteroids or comets.
Recently, Curiosity found evidence of dry river and lake beds on Mars -- of surface water on the planet -- such as minerals that can only form in the presence of liquid water, and erosion patterns formed by sediment deposited by water flows. This indicates that, billions of years ago, conditions on Mars could have supported life.
The molecules -- which seem to confirm recent findings that a Martian meteorite contained extraterrestrial organic matter -- were found in a drilled sample in the Sheepbed mudstone of the Gale crater -- the location of Curiosity's exploration. The mudstone on the crater floor is consistent with the clay found on Earth from dried-up lakes, formed from sediment on the lake floor -- presenting optimum conditions for the preservation of organic matter.
"We think life began on Earth around 3.8 billion years ago, and our result shows that places on Mars had the same conditions at that time -- liquid water, a warm environment, and organic matter," said Caroline Freissinet of NASA's Goddard Space Flight Center in Greenbelt, Maryland. "So if life emerged on Earth in these conditions, why not on Mars as well?"
The samples were analysed by the SAM laboratory heating the molecules to a temperature of 875 degrees Celsius (1,600 Fahrenheit), and then monitoring the volatiles released through a quadrupole mass spectrometer and Gas Chromotograph Mass Spectrometer Mode, which separates volatiles based on the amount of time they take to travel through a glass tube.
Other atoms present in the molecules identified by the SAM team include chlorine atoms: chlorobenzene, and dichloroalkanes such as dichloroethane, dichloropropane and dichlorobutane; the most abundant is the chlorobenzene, which is used for manufacturing pesticides, herbicides, adhesives, paints and rubber, and does not occur naturally on Earth. Dichloropropane, used as an industrial solvent in paint strippers, is carcinogenic.
While these could have been present in the mudstone, it is more likely that they formed when the molecules were heated for analysis inside the SAM instrument. Perchlorate -- chlorine bound to oxygen -- is abundant in the Martian atmosphere. As the molecules were heated, these perchlorates could have bound to the organic molecules to produce the atoms found by the SAM team.
"The search for organics on Mars has been extremely challenging for the team," said study co-author Daniel Glavin of NASA Goddard.
"First, we need to identify environments in Gale crater that would have enabled the concentration of organics in sediments. Then they need to survive the conversion of sediment to rock, where pore fluids and dissolved substances may oxidize and destroy organics. Organics can then be destroyed during exposure of rocks at the surface of Mars to intense ionising radiation and oxidants. Finally, to identify any organic compounds that have survived, we have to deal with oxychlorine compounds and possibly other strong oxidants in the sample which will react with and combust organic compounds to carbon dioxide and chlorinated hydrocarbons when the samples are heated by SAM."