In the song The War of the Worlds there is the line
The chances of anything coming from Mars are a million to one.
But it turns out that’s wrong according to the latest findings from NASA’s Curiosity rover.
In September and October 2013, the Jet Propulsion Laboratory (JPL) announced some interesting results from the roving laboratory. The first is that only trace amounts of methane exist on Mars. The findings go against theories that microbial methane production by subsurface bacteria may be occurring on the red planet.
The second observation of note is that some meteorites that have dropped to Earth really are from Mars.
Minimal Martian methane
Curiosity performed extensive air sampling from October 2012–June 2013 to search for traces of methane and reportedly detected none. A press release from the JPL said, “Given the sensitivity of the instrument [Tunable Laser Spectrometer] used and not detecting the gas, scientists calculate the amount of methane in the Martian atmosphere today must be no more than 1.3 parts per billion. That is about one-sixth as much as some earlier estimates.”
“This important result will help direct our efforts to examine the possibility of life on Mars,” says Dr Michael Meyer, NASA’s lead scientist for Mars exploration. “It reduces the probability of current methane-producing Martian microbes, but this addresses only one type of microbial metabolism. As we know, there are many types of terrestrial microbes that don’t generate methane.”
Methane is persistent
Methane, the most abundant hydrocarbon in our Solar System, has 1 carbon atom bound to 4 hydrogen atoms in each molecule. Previous reports of localised methane concentrations up to 45 parts per billion on Mars, as measured from Earth and from orbit around Mars, sparked interest in the possibility of a biological source on the planet. However, the earlier observations were probably wrong, as the researchers working on the methane data say there is no known way for methane to disappear quickly from the atmosphere.
“Methane is persistent. It would last for hundreds of years in the Martian atmosphere. Without a way to take it out of the atmosphere quicker, our measurements indicate there cannot be much methane being put into the atmosphere by any mechanism, whether biologygeology or by ultraviolet degradation of organics delivered by the fall of meteorites or interplanetary dust particles,” says Professor Sushil Atreya, one of the methane research team from the University of Michigan.
Details of the methane findings were published online on 19 September 2013 and then printed in the 18 October 2013 edition of Science magazine.
Martian meteorites invaded Earth
The JPL announced in October 2013 that a key new measurement of the inert gas argon in the Martian atmosphere provides evidence of the origin of Mars meteorites found on Earth while at the same time providing a way to rule out Martian origin of other meteorites. In addition, the measurements will help scientists understand how the once warm, water-rich planet, similar to our own, lost much of its atmosphere and became the drier, colder and less-hospitable desert planet it is today.
“The new measurement is a high-precision count of two forms of argon – argon-36 and argon-38 – accomplished by the Sample Analysis at Mars (SAM) instrument inside the rover. These lighter and heavier forms, or isotopes, of argon exist naturally throughout the Solar System. On Mars, the ratio of light to heavy argon is skewed because much of that planet’s original atmosphere was lost to space. The lighter form of argon was taken away more readily because it rises to the top of the atmosphere more easily and requires less energy to escape. That left the Martian atmosphere relatively enriched in the heavier isotope, argon-38.”
The analysis by SAM pins down the Martian argon ratio at 4:2. This can be matched with analysis of gas bubbles trapped inside what are thought to be Martian meteorites, confirming or rejecting the identification.
“We really nailed it,” says Professor Atreya. “This direct reading from Mars settles the case with all Martian meteorites.”
Argon – the key measurement
A press release from the American Geophysical Union (publishers of Geophysical Research Letters) explains that, had Mars held onto all of its atmosphere and its original argon, its ratio of the gas would be the same as that of the Sun and Jupiter. “Those bodies have so much gravity that isotopes can’t preferentially escape, so their argon ratio – which is 5:5 – represents that of the primordial Solar System.”
“Other isotopes measured by SAM on Curiosity also support the loss of atmosphere, but none so directly as argon,” says Professor Atreya. “Argon is the clearest signature of atmospheric loss because it’s chemically inert and does not interact or exchange with the Martian surface or the interior. This was a key measurement that we wanted to carry out on SAM.”
Details of the argon findings were published on 16 October 2013 in Geophysical Research Letters.
Curiosity landed inside Gale Crater on Mars in August 2012 and is investigating evidence about habitable environments there. JPL manages the mission and built the rover for NASA’s Science Mission Directorate.
Learn more about the Sample Analysis at Mars (SAM) instrument here.
Scientists in this article discuss measuring methane in parts per billion. Your students can get some idea of how small this is by exploring parts per million in this activity, Exploring small doses
Go to the NASA website for more information about the Curiosity mission.