On reaching Kimberley, managing communications and solving mysteries

CuriosityIt’s been a quiet time for the last three weeks as far as news from NASA’s Mars Science Laboratory is concerned. There have been a couple of reasons for this.

The primary reason is that the rover is on a slow but steady drive towards its next intended science waypoint while en route to the lower slopes of “Mount Sharp”. At the start of February, that waypoint had been around half a kilometre from the rover. However, concerns over the amount of wear and tear being suffered by the rover’s wheels as a result of traversing very rough terrain meant that Curiosity took a diversion.

While this put the rover on much smoother – comparatively speaking – terrain, it also meant the route to the waypoint had become more circuitous, requiring Curiosity cover around a kilometre in order to reach its intended stopover. In addition, engineers have been periodically checking the amount of damage to the wheel which may be accruing, further slowing daily progress, as well as continuing to test alternative driving methods to further ease the load on the wheels – such as letting the rover drive backwards towards its destination. However, the good news is that in the month since crossing Dingo Gap on February 18th, wear on Curiosity’s wheels has been around one-tenth what had been experienced per month during the months traversing the rougher terrain.

The long drive south. Murray Buttes mark the point at which Curiosity is expected to start the traverse onto the lower slopes of “Mount Sharp”, which forms a natural break in a line of dark sand dunes between the rover and the mound. “Kimberley” marks the next stop on the way (click for full size)

Additional tests using Curiosity’s test bed “twin” on Earth have revealed that the rover could sustain substantially more damage than incurred so far, including breaks in the wheel treads themselves, and still remain operational. However, given the potential duration of the mission – Curiosity’s nuclear “battery” could provide it with an operational life measured in a couple of decades barring other failures – means caution is key at this stage of the mission.

“The wheel damage rate appears to have levelled off, thanks to a combination of route selection and careful driving,” said JPL’s Richard Rainen, mechanical engineering team leader for Curiosity. “We’re optimistic that we’re doing OK now, though we know there will be challenging terrain to cross in the future.”

MRO Computer Glitch

The other break in news, although brief in nature, was caused by an unexpected issue with Curiosity’s primary communications relay between itself and Earth – the Mars Reconnaissance Orbiter (MRO) unexpectedly switched itself into a “safe” operating mode on Sunday March 9th. This immediately brought a cessation in the orbiter’s communications relay function for both Curiosity and Opportunity on the surface of the planet, although it did not put either rover entirely out of communications with Earth.

An artist's impression of the Mars Reconnaissance Orbiter orbiting the planet
An artist’s impression of the Mars Reconnaissance Orbiter orbiting the planet

While MRO forms the primary means of communications between the surface of Mars and mission control at NASA’s Jet Propulsion Laboratory facility at the California Institute of Technology, the rovers on Mars can also use NASA’s Mars Odyssey as a relay – and, should it be required, Europe’s Mars Express. However, Mars Odyssey, which has been operating around Mars for almost twelve and a half years, has much lower bandwidth and data transmission rates compared to MRO, which reduces the amount of information which can be relayed to Earth at any given time.

MRO’s issue first became apparent on March 9th, when the orbiter performed an unplanned swap between its duplicate computer systems. This is the prescribed response by a spacecraft when it detects conditions outside the range of normal expectations; the safe mode is initiated to reduce the risk of whatever caused the out-of-range event from being repeated by the second computer and potentially permanently harming the vehicle while matters are investigated. MRO has experienced unplanned computer swaps triggering safe-mode entry four times previously, most recently in November 2011, the root cause of which still hasn’t been clearly determined.

The March 9th safe mode entry also included a swap to a redundant radio transponder on the orbiter, marking the first time this has happened during the vehicle’s eight years in orbit around Mars. Whether or not the transponder issue triggered the computer swap-out is unclear. However, after carrying out a series of diagnostics on MRO from Earth, the mission team began bringing the orbiter back-up to full operational capabilities on March 11th, leaving it operating on the computer the swap-out switched to, together with the previously redundant radio transponder.

“The spacecraft is healthy, in communication and fully powered,” Mars Reconnaissance Orbiter Project Manager Dan Johnston said on March 11th. “We have stepped up the communication data rate, and we plan to have the spacecraft back to full operations within a few days.”

Charting a New Frost Channel

Since that event, MRO mission scientists have released a photo comparison showing the active nature of the Martian environment. The image shows two pictures of the same slope in the wall of crater Terra Sirenum, located in the southern highlands of Mars. There were captured some two and a half years apart (roughly equivalent to 1.2 Martian years), in November 2010 and May 2013 respectively.

Side-by-side: an image of Terra Sirenum crater walls taken in November 2010 compared with an image of the same region taken in May 2013, complete with freshly-carved gully and outflow fan (light areas)
Side-by-side: an image of Terra Sirenum crater walls taken in November 2010 compared with an image of the same region taken in May 2013, complete with freshly carved gully and outflow fan (light areas)

The right-hand (May 2013) clearly shows the creation of a new gully down the inner wall of the crater, created when material flowing down the older channel broke out to form a new channel and corresponding fantail deposit. While the material responsible for the new gully was liquid in nature, as the event occurred in the Martian winter period in the southern hemisphere, it is believed that carbon dioxide ice, and not water, played the major role in forming the new channel.

NASA had previously experimented with dry ice to see if it could be responsible for such gullies, with interesting results.


Stepping out with Kimberley

In the meantime, and as noted at the top of this article, Curiosity has been continuing towards its next immediate goal: a rocky formation where it will carry out more rock analysis and sample-gathering (including drilling) as a part of attempts to map the geology and likely history of the region of Gale Crater between “Glenelg” and “Mount Sharp”.

Previously referred to as “KMS-9″, the waypoint the rover is making for comprises three different terrain / rock types offer a relatively dust-free area, and has now been renamed “the Kimberley” after a region in north-western Australia noted for its ancient, exposed rocks.
With the slow-but-steady approach taken by the rover team, Curiosity was still some 86 metres (282 feet) from the rock formation on Monday March 24th, when the latest images returned by the rover were released, and excitement within the science team is growing.

“The orbital images didn’t tell us what those rocks are,” Deputy Project Scientist Ashwin Vasavada said in reference to the site originally being identified via images returned by MRO, “but now that Curiosity is getting closer, we’re seeing a preview. The contrasting textures and durabilities of sandstones in this area are fascinating. While superficially similar, the rocks likely formed and evolved quite differently from each other.”

The rocks that the Curiosity mission has studied most intensively so far are finer-grain mudstone, rather than sandstone. The rover found evidence for an ancient lakebed environment favourable for microbial life when it analysed sample powder drilled from mudstone last year in an area called “Yellowknife Bay.”

A white-balanced images of sandstone layers with varying resistance to erosion close to “the Kimberley”, Curiosity’s next science waypoint. Differing degrees of resistance to erosion result in a stair-stepped pattern visible here. Steeper steps result from more resistant rock, so the flat, tan surface is a weakly resistant sandstone. The small steps to the right center are a bit more resistant, and the steeper steps near the top of the scene are even more resistant. This image was captured by the left Mastcam on Sol 553 (February 25th, 2014) – click for full size

Whatever its composition, material filling the space between grains of sand in sandstone is called “cement”, and the nature of this the cement can vary greatly, depending on the environmental history that affected the rock. Sandstones with some clay-mineral cements are quite soft. Tap them with a hammer and they crumble. Sandstones with quartz cement can be very hard. Hit them with a hammer and they ring.

Michael Malin of Malin Space Science Systems and principal investigator for the rover’s Mastcam systems explained why “the Kimberley” could be of major interest. “A major issue for us now is to understand why some rocks resist erosion more than other rocks, especially when they are so close to each other and are both likely to be sandstones. The variations in cement material of sandstones could provide clues to different types of wet environmental conditions in the area’s history.”

More Evidence of Martian Microbes?

In 1996, the world got into something of a lather over excitement surrounding findings obtained from a Martian meteorite found in the Allan Hills region of Antarctica far back in 1984. At that time, studies by a team, led by David McKay, Everett Gibson and Kathie Thomas-Keprta, of the ALH84001 meteorite, appeared to suggest biogenic evidence deep within the structure of the rock.

In February 2014, members of that team (David McKay passed away in 2013), together with other researchers, published a paper indicating believe they have found structures within another Mars meteorite found on Earth which may be indicative of biogenic activity. The rock in question is a more recent discovery called Yamato 000593 (Y000593), named for the Yamato Glacier in Antarctica, where it was found in 2000.

This scanning electron microscope image of a polished thin section of a meteorite from Mars shows tunnels and curved microtunnels, possibly bogenic in origin
This scanning electron microscope image of a polished thin section of a meteorite from Mars (Y000593) shows tunnels and curved microtunnels, possibly bogenic in origin

Studies of the rock have revealed distinctive tunnel and micro-tunnel structures threaded throughout Yamato 000593. These structures display curved, undulating shapes consistent with bio-alteration textures similar in kind to those reported by researchers who study interactions of bacteria with basaltic materials on Earth. Alongside of these, nanometre- to-micrometre-sized spherules have been observed sandwiched between layers within the rock and are distinct from carbonate and the underlying silicate layer.

While the team note that they cannot rule out the possibility that the carbon-rich regions in both sets of features may be the product of purely chemical mechanisms, the textural and compositional similarities to biogenic features in terrestrial samples seem to imply the intriguing possibility that the Martian features were formed by biotic activity.

Pinnacle Rock “Mystery” Resolved

In January 2014, something of a stir was when NASA’s Opportunity rover apparently imaged a tiny rock – later dubbed “Pinnacle Island” – which mysterious appeared in shots of an area of rock where the rover was parked.

Before and after: “Pinnacle Rock” seems to pop-up from nowhere, sparking theories on its origin …

The appearance of the little stone, just 4 centimetres (1.5 inches) across, gave rise to all sorts of theories as to its origin, including claims that it somehow “grew” when the rover wasn’t looking! However, in February the proof of the matter was revealed when Opportunity executed a command to move its location.

After it had done so, it was able to survey the area and show that “Pinnacle Rock” was, as the mission’s Principal Investigator, Steve Squyres had guessed, actually the piece of a larger rock which had been broken-off by the rovers passage across it. Becoming temporarily stuck on the rover’s wheel, the stone subsequently fell to the ground after the rover had been parked, allowing it to be imaged by Opportunity’s Panoramic Cameras.

The reality: from its revised position, Opportunity reveals "Pinnacle Rock" (arrowed lower left) to have been broken-off of a small rock (top centre) by the rover's passage (note the wheel tread marks top centre), and temporarily lodged in the wheel
The reality: from its revised position, Opportunity shows “Pinnacle Rock” (arrowed lower left) to have been broken-off of a small rock (top centre) by the rover’s passage (note the wheel tread marks top centre), and temporarily lodged in the wheel prior to falling to the ground