NASA’s Curiosity rover has been a busy bunny on Mars. Currently still parked in the “Pahrump Hills” terrain on the lower slopes of “Mount Sharp”, the Mars Science Laboratory (MSL) rover has now completed its latest drilling activity, collecting samples from a rock dubbed “Mojave 2”.
This isn’t actually the rock from which the science team had originally hoped to gather samples. That rock, dubbed “Mojave” broke apart as a result of the percussive action of the rover’s drill during a “mini-drill” test. As a result, the rock was ruled out as a sample gathering target. “Mojave” was of particularly interest to scientists as Curiosity had images tiny, rice-grain sized crystalline minerals that might have resulted from evaporation of a drying lake, thus presenting the science team with a further insight into environmental conditions within Gale Crater.
To counter this loss, the team relocated Curiosity to “Mojave 2”, another rock within the same outcrop as “Mojave”, and which exhibits similar crystalline features. In doing so, the team were able to bring into play software improvements only recently uploaded to the rover as a part of an overall systems upgrade, which was deployed to one of the rover’s two computer systems at the end of January.
The software improvements for the drill are the result of investigations into the fracturing of a rock during a previous attempt to obtain samples prior to the rover arriving on “Mount Sharp”. Like an Earth-based hammer drill, the rover’s drill uses a percussive action, so that as well as drilling into a rock, the drill bit effectively hammers its way into the rock. In all, there are six settings governing the amount of percussive energy used during drilling, which range from a gentle tapping (level 1) through to hammering at the rate of 30 times a second with a 20-fold increase in energy imparted (level 6).
During early drilling operations the software monitoring these percussion settings “learned” that defaulting to the “level 4” setting best met the needs of gathering samples in the harder rock types the rover initially encountered. However, this was proving too forceful for the softer rocks closer to, and on, “Mount Sharp”, but the software was unable to switch down to a lower setting.
The new update causes the drill software to reset to “level 1” after each drilling operation, and then step through the levels incrementally until the ideal is found. As a result, a sample was gathered from “Mojave 2” without the drill needing to step beyond the “level 2” percussion action.
Drilling operations on “Mojave 2” took place on Sol 881 and Sol 882 (January 28th and 29th, PDT, respectively). As per standard operating procedure, the first drilling operation was a test “mini drilling” to see how the rock responded to encroachment and cutting. The second, which took the dill to a depth of around 6.5 centimetres (2.6 inches). The gathered samples were then sifted and sorted through the CHIMRA system in the rover’s turret, prior to being transferred via the surface scoop to Curiosity’s primary laboratory systems, ChemMin and SAM.
At the same time as Curiosity was carrying out its initial analysis of the “Mojave 2” rock, NASA released an image captured by the HiRise (High Resolution Imaging Science Experiment) carried aboard the orbiting Mars Reconnaissance Orbiter (MRO), which forms the mainstay of the rover’s communications with Earth. The image, which was taken on December 13th, 2014, reveals Curiosity mid-way through its “walkabouts” in “Pahrump Hills”, when it was seeking potential targets of interest for further study.
While not the first time the rover has been imaged from orbit, this is one of the clearest pictures from the rover yet capture from an altitude of around 280 kilometres (175 miles) above the surface of Mars.
Initial results from ChemMin (the Chemical and Mineralogy) instrumental has shown that the rock was likely effected by water that was much more acidic in nature than evidenced through the analysis of other rock samples obtained by the rover. The still-partial analysis shows a significant amount of jarosite, an oxidized mineral containing iron and sulphur that forms in acidic environments. This raises the question of whether the more acidic water was part of environmental conditions when sediments were being deposited to form “Mount Sharp”, or the result of fluids soaking the rocks at a later time.
ChemMin was also unable to identify a clear candidate mineral for the crystalline deposits which first attracted the science team to the outcrop; this presents the possibility that the minerals responsible for originally forming the crystals may have been leached away over time and replaced by other minerals during later periods of wet environmental conditions.
It is hoped that SAM – the Sample Analysis at Mars – suite of instruments may be able to reveal more about the nature and composition of the samples once they have completed their round of analysis. Depending on the outcome of this work, Curiosity may be ordered to gather a further rock sample from “Pahrump Hills”, or may be ordered to continue upwards and into new territory on “Mount Sharp”.
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