Getting back to work and an Opportunity for comparisons

CuriosityThe Mars Science Laboratory rover Curiosity resumed full science operations on March 23rd, with the delivery of a second portion of cuttings to the Sample Analysis at Mars (SAM) instruments inside the rover. Earlier, on March 21st, Curiosity resumed continuous environmental monitoring of the “Yellowknife Bay” area of Gale Crater.

Full-scale operations with the rover had been halted following the discovery of a computer glitch in the primary computer system the so-called “A-side” computer, which prompted mission controllers to order the rover to switch to the redundant “B-side” computer.

Since then, engineers and scientists on Earth have been working to both recover the “A-side” computer while simultaneously working to transfer all relevant data and command sets to the “B-side” computer and run Curiosity through a series of tests in order to ensure the “B-side” computer can increasingly take over day-to-day operations on the rover.

The “A-side” problem was traced to the unit’s memory module which acts as the “table of contents” for accessing the computer’s memory, preventing data and instructions from being accessed and causing the computer to enter into an “endless loop”. The computer has now been fully recovered and is available as a back-up once more, should it be required.

Recovery to the “B-side” computer was drawn-out due to the need for the computer to “understand” various aspects of the rover’s condition, including the placement of the robot arm, so that it could correctly take-on command and control. This involved a series of tests carried out early in March. More recently, engineers had to confirm the “engineering camera” sets, were functioning correctly.

In all, Curiosity uses some seventeen camera systems. Of these, 12 are paired sets of “engineering cameras” comprising the black-and-white Navigation Cameras (Navcams) mounted on the rover’s mast, the black-and-white front Hazard Avoidance Cameras (Hazcams) mounted at the front of the rover’s body, and the rear black-and-white Hazcams. Of these cameras, three pairs (of Navcams and front/rear Hazcams) are hard-wired to the “A-side” computer, and three pairs are hard-wired to the “B-side” computer.

The last time the “B-side” engineering cameras had been used was in April 2012, when the Mars Science Laboratory was still en route to Mars (the “B-side” computer was used to “look after” the rover and its ancilliary systems during the long flight from Earth to Mars). As the rover was switched-over to the “A-side” computer shortly after arrival on the surface of Mars, the “B-side” cameras had never been actively used on the planet, and thus needed to be run through a similar set of commissioning tests and check-outs which marked Curiosity’s initial activities back in August 2012.

Looking at Curiosity’s left-front and left-centre wheels and tread marks, using the left Navcam on the rover’s mast, which is hard-wired directly to the “B-side” computer. Captured on March 22nd, 2013, or Sol 223 of the mission, this image marks the first time the “B-side” engineering cameras have been used in more than six months – and the first time they have been used by the rover on the surface of Mars. For reference, the wheels are 50 cm (20 in) in diameter.

Bringing the “B-side” computer up to a point where it could take over all on-board operations  was further delayed when it also suffered a glitch on March 16th which, although relatively minor in scope, caused engineers on Earth to order Curiosity back into a “safe mode” of operations while the glitch was investigated, diagnosed and corrected.

The cuttings delivered to SAM on the 23rd March is from the same sample obtained from the “John Klein” rock on February 28th. The cutting will now be subjected to more targeted analysis by SAM’s various instruments, the initial analysis results having been extensively studied on Earth in the meantime, and which are believed to further confirm Mars did indeed have wetter periods in its history which may have been benign enough for life to have arisen on the planet.

With an upcoming moratorium on transmitting commands to the rover due to commence on April 4th, and which will run through until May 1st as a result of the first period of Solar conjunction between Earth and Mars in the MSL’s primary mission, work will shortly begin on uploading a set of commands which are designed to enable the rover to largely “self-manage” itself through the four weeks of the moratorium.

In the meantime, and half a world away, Curiosity’s elder and smaller cousin, Opportunity continues to explore the region around Endeavour crater, some nine years into a mission which had originally been planned to last just 90 days after it arrived on Mars at the start of 2004. In doing so, it has come across an area of rock which appears to have striking similarities to the bedrock Curiosity has been examining at “Yellowknife Bay”.

Comparative rover sizes. Foreground: Mars Pathfinder (1997); left: Mars Exploration Rover (2003-present); right: MSL
Comparative rover sizes. On the left, the MER-class of rover (Opportunity), on the right the MSL-class (Curiosity), and in the foreground, the tiny Mars Pathfinder class (Sojourner) from 1997

Opportunity was directed to Endeavour Crater – which represented a huge trek for the solar-powered rover which can only travel at a fraction of the speed of Curiosity (at an average of just 0.036 k/ph or 0.022 mph) – as a result of evidence gathered by Nasa’s Mars Reconnaissance Orbiter (MRO) suggesting the presence of phyllosilicates (clay-bearing rocks) along the crater’s rim.

Since resuming operations in the region after the long Martian winter, Opportunity has been focused on examining a couple of rocky outcrops which represent the oldest rock on Mars it has yet been able to study, one of which – dubbed “Whitewater Lake”- shows very similar features to those discovered by Curiosity at “Yellowknife Bay” and which coincide closely with the signature of smectite clays which have been found within the rock cuttings obtained by Curiosity’s drilling operations at the “John Klein” rock.

The “Whitewater Lake” outcrop exhibits similar, light-toned veins to those imaged by Curiosity at “Yellowknife Bay”, and which appear to be filled with calcium sulphate. As with the veins at “Yellowknife Bay”, they are believed to be the direct result of water flowing through fractures in the rocks after the impact that carved out Endeavour Crater.

A false-colour image of the “Whitewater Lake” rock captured by Opportunity at Endeavour Crater on the 3,064th Sol (September 6, 2012) of Opportunity’s mission. The rock itself exhibits many similar features to those found in rocks at “Yellowknife Bay” by Curiosity, including veins of calcium sulphate and evidence of smectite clays within the rock surfaces, as well as other indications of aqueous activity at a near-neutral pH which mirror those more recently discovered at “Yellowknife Bay”.

There are also numerous rounded structures called “spherules” embedded in the rock. Opportunity has seen similar small structures out on Mars’ Meridiani plains, which the rover team nicknamed “blueberries”. However, the “blueberries” around “Whitewater Lake” are significantly different to those discovered by both Opportunity and its now defunct twin, Spirit, during their past explorations on Mars. Instead, they appear to have more in common with similar spherules imaged by Curiosity within “Yellowknife Bay”.

Commenting on Opportunity’s findings, Professor Steve Squyres, the mission’s Principal investigator, drew direct comparisons between the findings at “Whitewater Lake” and those from Curiosity, adding, “These Whitewater Lake materials are the oldest rocks yet explored by the Opportunity rover. They record an epoch before the Endeavour impact when there was aqueous activity at a near-neutral pH. They therefore represent the most habitable palaeo-environment found [by Opportunity].”

The team managing Opportunity is unable to put an exact age on the outcrop, but they believe it could date to more than three billion years ago, when Mars was a wetter place. In comparing the two sites at Endeavour Crater and Gale Crater, Professor Squyres said, “Mars is telling us something. I’m not sure what it is because it’s speaking Martian. But it’s telling us something.”

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All images and video courtesy of NASA / JPL