In what has been something of a surprise to scientists around the world, findings from the Mars Science Laboratory (MSL) suggest the amounts of methane present in the Martian atmosphere, at least at near-ground levels, are at best negligible.
While it can be produced by non-organic, as well as organic means, methane has long been regarded as one of the tell-tale signs that life may have once existed on Mars – or even may still exist somewhere beneath the planet’s arid surface.
Using the highly sensitive Tunable Laser Spectrometer, a part of the Sample Analysis at Mars (SAM) science package aboard Curiosity, MSL has subjected six samples of the atmosphere gathered between October 2012 and June 2013 to analysis – and failed to detect any signs of methane, trace or otherwise.
This has come as a surprise because previous data gathered by US and international scientists via a range of means have suggested that while not present in abundant amounts, methane is very detectable within the Martian atmosphere. So much so that some of those involved in MSL were extremely confident ahead of the mission that the rover would find clear evidence of the gas as a part of its analysis of atmospheric samples.
Europe’s Mars Express, for example, which started on-orbit operations in 2004, and is still functioning today, found strong evidence for methane within the atmosphere of Mars. Not long after this, NASA’s own Mars Global Surveyor (the precursor to the Mars Reconnaissance Orbiter which relays communications between Curiosity and Earth today), which operated in Mars orbit from September 1997 through to November 2006, also detected methane to a point where scientists where able to map its annual ebb and flow.
On Earth, methane (CH4) is largely the by-product of two distinct activities: geological, such as through volcanic eruptions – and Mars certainly has a fair few volcanoes, some of the largest in the solar system in fact; and via organic means. Either way, it tends to break down relatively quickly, so even trace amounts of it within Mars’ atmosphere suggest that it is being renewed somehow. Given that an erupting volcano on Mars is a tad hard to miss (see “some of the largest in the solar system”, above), a renewable source of methane has seen as evidence that either there is some as yet unknown chemical reaction going-on to create methane – or it may just be the result of outgassing from Martian microbes.
The amount of methane in the Martian atmosphere has never been particularly high; even the best analyses over the years have placed it at a peak of around 70 parts per billion, However, the TLS on Curiosity is a very sensitive piece of equipment. So sensitive that any trace amounts of methane in the Martian atmosphere must be below 1.3 parts per billion (around 10,000 tonnes in total throughout the atmosphere) in order for the TLS to miss it.
Responding to the findings, published on Thursday September 19th in Science Express, NASA has pointed out that the chances of future missions finding evidence of microbial life on Mars, past or present, aren’t entirely dashed. “This important result will help direct our efforts to examine the possibility of life on Mars,” Michael Meyer, NASA’s lead scientist for Mars exploration, said in a press release accompanying the report’s publication. “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.”
Even so, that the TLS has failed to find significant evidence of methane in the air around Curiosity has left scientists facing something of a conundrum. Just how is it that less sensitive instruments aboard space craft like the Mars Global Surveyor and Mars detected methane in the Martian atmosphere of sufficient density for it to even register with them?
One possible explanation might lie in ongoing research by the team managing Europe’s Mars Express orbiter. These studies appear to point to the peak concentrations of methane in the Martian atmosphere actually occurring relatively high-up, around 25-40 kilometres (12 to 25 miles) above the surface of Mars.
Interestingly, the highest concentrations of methane previously recorded on Mars have been located in the northern hemisphere of the planet, which has a much higher average elevation than the southern hemisphere in which Curiosity is located. These concentrations have also been localised around two areas which were once extremely volcanic in nature – the Tharsis Bulge (straddled by the largest volcanoes in the solar system) and Elysium, with a third concentration on the upland plains of Arabia Terrae, which is thought to have a subsurface aquifer of frozen water.
Certainly, Curiosity’s findings do not mean the search for methane is over. The next few years will see further studies into the whole question of methane on Mars, as India is due to launch Mangalyaan probe there later in 2013, which includes the ability to detect methane. Then, in 2016, Europe plans to launch the Trace Gas Orbiter to Mars, which will able to carry out a detailed search for trace gases in the Martian atmosphere, including methane. Curiosity itself will continue the search at ground level; an “enrichment” process will shortly be used within the TLS which should increase its sensitivity, allowing it to detect concentrations of the gas as low as 50 parts per trillion.
Taking a Break from Driving
As previously reported, Curiosity is currently en route to the entry point mission controllers have selected for it to start its explorations of “Mount Sharp”. The drive is expected to take a few months, even allowing for the rover’s improved “self-drive” capabilities, and a few stop-over “waypoints” have been selected at areas of potential interest spotted from orbit, where the rover will pause in its journey and carry out local studies.
On September 5th (Sol 385) the rover completed its longest single drive of the mission to date, covering some 141 metres (464 feet), using both guided driving from Earth and autonav driving. This brought the rover onto a rise dubbed “Panorama Point” from which it was able to survey the first of the planned waypoints, a light-coloured area of rock dubbed “Darwin”.
Following this, on Sols 386 and 387, Curiosity spent time surveying the area and gathering images, prior to completing a further drive on Sol 388 to the reach the top of “Panorama Rise” to undertake a further survey of “Waypoint 1”, after which it drove the remaining 75 metres (245 feet) to reach “Darwin” in preparation to undertake “contact science” work on and around the rock.
“Darwin” is if interest as on-orbit imaging had suggested it appears to be exposed layers of rock that could reveal the inner makeup and history of the plains on the floor of Gale Crater, including any flows of water that laid these materials down in the past. So analysis of “Darwin” may provide further evidence of whether and how water played a role in the history of Gale Crater.
Studies of the rock began in earnest on Sol 390 (September 10th), using the rover’s Mastcam systems and also the turret-mounted Mars Hand Lens Imager (MAHLI), attached to the rover’s robot arm. At the same time, the Mastcam systems have been used in further night-time studies of Mars’ two tiny moons, Phobos and Deimos.
The images of “Darwin” returned by Curiosity have given rise to some excitement among the science team, although a formal press-release has yet to be made about the work. As it is, the stop-over had originally been scheduled for “a few days” but has already extended some 10 days.
Commenting on the work Curiosity will be carrying-out at each of the waypoints, mission project scientist John Grotzinger said, “We want to know how the rocks at Yellowknife Bay are related to what we’ll see at Mount Sharp. That’s what we intend to get from the waypoints between them. We’ll use them to stitch together a timeline — which layers are older, which are younger.”
Take On Mars
If you’re interested in undertaking your own mission to Mars using a robotic explorer – or even tracing Curiosity’s wheel tracks, you might want to have a look at Take On Mars, a new, in-development game being produced by Bohemia Interactive.
Take on Mars “places you in the seat of a Rover Operator, allowing you to control the various, fully simulated mobile Rovers and stationary Landers. With this scientific arsenal at your disposal, you will work your way through the numerous Science Missions in each location, unlocking the secrets of Mars’ distant past.” It allows you to explore Mars from the perspective of a science-driven space agency programme, or leap straight to the surface of Mars and carry out rover / lander-based missions.
The Curiosity missions, for example, can take you through the “seven minutes of terror” of EDL, complete with skycrane set-down, before getting you busy with various science objectives. You can operate in “game time” or “real-time” (when the time of the game is mapped to real-time for the region of Mars you’re exploring), and more.
The game is currently available through the Steam Early Access programme. I’m even tempted myself!
All images courtesy of NASA JPL, unless otherwise indicated