Curiosity is continuing its exploration and ascent of “Mount Sharp”, the huge mountain-like mound of deposited material occupying the centre of Gale Crater, which has been the rover’s home since it arrived on Mars in August 2012. And it is continuing to find curious and enigmatic hints about the past conditions in the crater, and about Mars as a whole.
The rover’s most recent discoveries come from an area of rock dubbed “Garden City”, which contains areas of two-tone mineral veins quite unlike anything so far encountered in the rover’s travels.
The veins appear as a network of ridges left standing above the now eroded-away bedrock in which they formed. Individual ridges range up to about 6 centimetres (2.5 inches) high and half that in width, and they bear both bright and dark material. They are strongly suggestive of multiple episodes of fluid movement which occurred much later than the wet environmental conditions that formed lake-bed deposits which gave rise to “Mount Sharp’s” formation.
“Some of [the veins] look like ice-cream sandwiches: dark on both edges and white in the middle,” said Linda Kah, a Curiosity science-team member at the University of Tennessee, Knoxville. “These materials tell us about secondary fluids that were transported through the region after the host rock formed.”
On Earth, veins of this kind form as a result of fluids moving through move through cracked rock, depositing minerals in the fractures which often affect the chemistry of the surrounding rock. Curiosity has found bright veins composed of calcium sulfate visible on the surface of rocks at several other locations, which appears to be the same with the lighter material found as “Garden City”, but the dark material suggest something else.
“At least two secondary fluids have left evidence here,” Kah said. “We want to understand the chemistry of the different fluids that were here and the sequence of events. How have later fluids affected the host rock?”
While there are no plans to gather any samples form “Garden City”, analysis of the three sets of samples gathered from within “Pahrump Hills” reveal that mineral deposits within the area vary according to elevation, revealing a complex process may have been responsible for the formation of the area. Samples taken from the lowest elevation of the area revealed themselves to be rich in clays and hematite, both of which commonly form under wet conditions.
However, at just a 5 metre higher elevation, jarosite, an oxidized mineral containing iron and sulfur that forms in acidic conditions, was the dominant mineral, while towards the top of the area, at an elevation of 10 metres, clay minerals and hematite were almost non-existent, and traces of jarosite were greatly reduced, while the samples – from “Telegraph Peak” – were rich in cristobalite and quartz, both of which are mineral forms of silica.
Quite what the process may have been that gave rise to this spread of deposits is unclear – the science team have several options to choose from, and are continuing their investigation.
Sometimes, All I Need is the Air That I Breathe (and to Analyse It)
As well as examining the rocks under its wheels, Curiosity has been sniffing the air around it in an attempt to better understand the chemical composition of the Martian atmosphere and the processes at work within it.
A planetary atmosphere is made up of different gases, which are in turn made up of variants of the same chemical element called isotopes. When a planet loses its atmosphere, that process can affect the ratios of remaining isotopes. In particular, Curiosity has been using the Sample Analysis at Mars (SAM) instruments carried within it to analyse the Martian atmosphere for xenon, a heavy noble gas.
One of the theories for how Mars lost its atmosphere is that it was gradually stripped away, almost layer by layer by the solar wind. One way to see if this may have been the case is to study the ratio of the different isotopes of a given gas present in the atmosphere; if the ratio is biased towards heavier isotopes than lighter ones, then it is probably because the lighter ones have been lost through the process of the upper reaches of the atmosphere being stripped away over the millennia.
Previously, SAM had studied isotopes of argon, which exists in two forms in the Martian atmosphere, and found the heavier isotope to be much more abundant, pointing towards the lighter isotope having been stripped away. Xenon allows for a more granular study, as it naturally exists in nine different isotopes of different atomic masses.
The results of the SAM studies strong suggest that there was a very early period in the history of Mars when a vigorous atmospheric escape process was pulling away even the heavy xenon gas. The lighter isotopes were escaping just a bit faster than the heavy isotopes, further adding weight to this particular theory as to the loss of the Martian atmosphere.
Targets of (or for) Opportunity
Half a world away from Curiosity, little solar-powered Opportunity continues to explore the region around Endeavour Crater, and recently had some assistance in its work – from the Expedition 43 crew aboard the International Space Station.
NASA astronaut Terry Virts, the station’s commander, and his cremates cosmonaut, Anton Shkaplerov, and the European Space Agency’s Samantha Cristoforetti used some of their dinner time to look over images taken of Opportunity’s surroundings both by the rover and from overflights of the Mars Reconnaissance Orbiter in order to select potential areas for further study – what in military and science parlance are often called “targets of opportunity”, which seemed doubly appropriate in this case.
The idea to connect the station crew with Mars photos was sparked by astro-geologist, James Rice, Jr., Mars Exploration Rover (MER) Geology Team Leader and Senior Scientist at the Planetary Science Institute. In particular, he wanted feedback from Astronauts on images taken by the rover itself, the idea being to better gauge how things might appear to an astronaut “on the ground” – what they might see which might attract them to points of interest which might otherwise be missed.
While it might sound an esoteric exercise, the study was not without foundation – when it comes to exploring Mars, astronauts will be the eyes on site, as such, they’ve often be making calls on exploration targets outside of pre-determined mission parameters.
As it turned out the ISS crew quickly identified a location that has been puzzling members of Opportunity’s science team, as a primary target for investigation. A tiny crater, just 35 by 27 metres across and dubbed “Spirit of St Louis” appears to be too small to have been an impact crater, and might possibly be the result of ancient volcanic or hydrothermal origins. As a result of the crew’s work and discussions, “Oppy” is about to start an investigation of the crater.