By David A. Ord
…… studying Mars is throwing up some real surprises
It seems that although it is probably the most studied rock in the Solar System; Mars is still providing scientists with some surprises. Most people have this image of Mars as a red and brown-hued surface with rocky landscapes peppered with craters – but the Red Planet isn’t always so red. This recent image of the planet has been described by NASA as “Smooth cream-coloured plateaus surrounded by cocoa-dusted ridges interspersed with caramel-hued streaks creating a scene reminiscent of a cosmic cappuccino.”
Sounds like something created by M&S. The bright white region of this image shows the icy cap that covers the South Pole of Mars; composed of frozen water and carbon dioxide. While it looks smooth in this image, at close quarters the cap is a layered mix of peaks, troughs and flat plains.
The southern cap reaches some 3 km thick in places, and is around 350 km in diameter. This icy region is permanent; in the Martian winter another, thinner ice cap forms over the top of it, stretching further out across the planet and disappearing again when the weather warms up. The Mars ice-cap is on the bucket-list of things to see of most amateur astronomers.
Further detracting from the stereotypical ‘benign, dead rock’ image of Mars has been the appearance of plumes rising some 250Km from the surface. On two separate occasions in March and April 2012, amateur astronomers had spotted the plumes.
A search through the archives of Mars images over the last 20 years revealed that shorter plumes up to a height of 100 Km. had occasionally occurred before and the Hubble archive contained an image from 1997 showing a plume of similar height to the one in 2012.
None of the spacecraft orbiting Mars saw the plumes due to the viewing geometry of their orbits or the illumination conditions at the time.
The plume features developed in less than 10 hours, covering an area of 1,000 x 500 Km and 250 Km high. They remained visible for about 10 days and continually changed their structure.
Scientists at the Universidad del Pais Vasco in Spain studied the images of the plumes and have published some suggestions in the 16th Feb. 2015 issue of the journal Nature.
One idea is that the features are caused by a reflective cloud of water-ice, carbon dioxide-ice or dust particles, but this would require exceptional deviations from standard atmospheric circulation models to explain cloud formations at such high altitudes.
It is also possible that the plumes are somehow caused by Martian auroras. These brilliant light displays are known on Earth as the northern and southern lights, and are caused by the interaction of high- energy particles and a planet’s magnetic field.
Indeed, Martian auroras have been previously observed at these locations, linked to a known region on the surface where there is a large anomaly in the crustal magnetic field.
Mostly the observations are inconclusive as to the cause and the nature of these Martian plumes and it may require the arrival of the ESA ExoMars Trace Gas Orbiter probe in 2016 before further insights can be gleaned.
The ExoMars Trace Gas Orbiter will determine the best location to land the ESA Mars rover in 2018 in its quest for ‘evidence of Life on Mars’ (as opposed to the NASA Curiosity mission to find the ‘evidence of the conditions for life on Mars’). It will also act as the ESA rover’s dedicated data relay satellite rather than share the communication capacity of ESA’s Mars Express and NASA’s Mars Reconnaissance orbiters. Financial crisis? What crisis?
Meanwhile, on Mars surface, the rover Curiosity is coming up with a few surprises of its own. It turns out that the planet is prone to bouts of out gassing methane. The issue is not so much the presence of the gas but the fact that it begins quite suddenly and stops with similar alacrity – analogous to ‘burping’ methane (and you may appreciate I could have gone another way with the analogy).
Now, methane is particularly interesting because on Earth at least, 95% of methane is sourced from microbial organisms. On Mars, there seems to be a consistent background level of about 0.7 parts per billion (ppb). This would suggest some 5,000 tonnes in the Martian atmosphere, which had to come from somewhere.
This compares to Earth where the methane background is around 1,800 parts per billion (ppb) and 500 million tonnes in our atmosphere.
What has been seen by Curiosity is that on four occasions in a 2 month period, the level of methane increased from its background level of 0.7 ppb to 7-9 ppb; more than ten fold.
There are only 3 ways in which methane can be produced on the planet. Firstly, by the reaction of sunlight (UV) with organic chemicals on the surface; Secondly by a geological process of the mineral olivine interacting with water and thirdly from Martian bugs.
Both of the latter could have taken place (or indeed still is) below the surface and then stored in porous substrates called clathrates. From time to time, these underground stores could be disturbed and the methane gas released. Hence the ‘burping’ characteristic observed by Curiosity.
It is actually possible to differentiate methane generated from micro organisms by determining the carbon isotope ratio. On Earth, a high Carbon-12 to Carbon-13 ratio is used to indicate biological activity, which has existed on Earth for 4 Billion years.
It is thought that 4 billion years ago, the two planets were not so dissimilar, so there is some merit in the expectation of biological activity on Mars too.
Unfortunately, the methane concentrations on Mars are insufficient for the analysers on Curiosity to determine the carbon isotope ratio. Otherwise, it could have been a startling revelation.
However, there is encouragement in the discovery of abundant organic compounds in surface and sub-surface materials. The first to be confirmed by Curiosity was chlorobenzene in powdered rock from mudstone called ‘Cumberland’.
The other intriguing parameter that Earth had in its favour for the evolution of life was stability over a long period of time. Now, data from Curiosity suggests that its current location, called Gale Crater, could have been a lake and that it appears to have dried and been replenished several times over. This process could suggest that favourable conditions were to be had for a much longer period than was once thought. Maybe just enough time for some biological activity to establish!
Images of the rocks show evidence of layering; alternating between lake, river and wind deposits.