On the edge of a (yellow)knife

For the self-portrait, the VSTB used an engineering model of MAHLI which allowed mission planners to carefully plot the moves required to capture sufficient images which could then be put together to produce the mosaic of the rover, a “close-up” version of which focusing on Curiosity itself was released in early November. In all 50 arm movements were required in order to ensure MAHLI would be correctly placed to capture the required images, and on December 11th,2012, NASA released a video animation showing how the commands were used to capture the core part of the self-portrait made on October 31st.

Onwards to Yellowknife Bay

Since my last update Curiosity has been busy. While parked above “Point Lake”, where it halted after leaving “Rocknest”, the rover passed the last remnants of a soil sample gathered at “Rocknest” to SAM – the Sample Analysis at Mars instrument – for tailored analysis based on feedback sent to the rover following Earthside studies of the initial data on the soil sample returned by SAM in November.

Following this, Curiosity resumed its trek towards “Mount Sharp”, driving through the region dubbed “Glenelg”, which had initially been determined as an intermediary way-point for the mission where the rover’s drill mechanism – the last of the major items of equipment on the Curiosity to be tested – could be put through its initial paces. Glenelg had originally been selected as an area for study because images captured from orbit showed it to be the meeting point of three terrain types. However, after leaving “Rocknest”, the rover proceeded to a point above a depression dubbed “Point Lake”. From here, images of a region bordering Glenelg proper and dubbed “Yellowknife Bay” suggested it might be a more suitable candidate for drilling.

Since that time, and up to Sol 123 (December 11th) the rover has completed four consecutive days of driving, moving southward into Glenelg and around the depression of “Point Lake”, before once again heading eastwards towards “Yellowknife Bay”. The four days of driving saw the rover cover  79 metres (260 feet), with the total distance covered on Mars standing at that time at just a shade under 600 metres (598 metres in fact, or 0.78 miles).

Along the way, Curiosity stopped at a rocky outcrop dubbed “Shaler”, which showed strong evidence of cross-bedding. This is a geological process in which the original depositional layering is tilted, and the tilting is not a result of post-depositional deformation. Cross-bedding forms during deposition on the inclined surfaces of bedforms such as ripples and dunes, and indicates that the depositional environment contained a flowing fluid – typically water or wind.

“Shaler” imaged by Curiosity’s Mastcam on Sol 120 (December 7th), showing the outcrop’s striking pattern of cross-bedding, suggesting the depositional environment had been subject to either wind action or that of free-flowing water. The image shows an area some 90 centimetres (3 feet across), an is shown as it would appear to the naked eye if standing on the surface of Mars – it has not been “white-balanced” for Earth levels of sunlight.

“Shaler” was subjected to intense study using the rover’s Mastcam system and ChemCam to assess the rock’s layering and composition. As very strong evidence for Gale Crater once having been subject to the impact of free-flowing water has already been found, determining the possible causes for the cross-bedding effects at Shaler might help in further characterising how water influenced the formation of the region – if water was responsible for the cross-bedding.

In order to reach “Yellowknife Bay”, Curiosity has to negotiate different terrain types to those so far encountered on the mission and see its way over a half-metre (roughly 20 inch) “lip”. While the latter is well within the rover’s capabilities, the former did bring an unexpected halt to progress on the 10th December, when Curiosity stopped itself after completing only 30% of the planned drive for that day. This was due to the rover’s main computer system detecting a slight difference in two calculations of its angle of tilt.

While there was no danger of the rover toppling over, a safety routine kicked-in to stop forward progress in order to allow those Earthside to assess matters. “The rover is traversing across terrain different from where it has driven earlier, and responding differently,” said Rick Welch, MSL mission manager commented on the stop, “We’re making progress, though we’re still in the learning phase with this rover, going a little slower on this terrain than we might wish we could.”

The rover’s traverse map up to Sol 123 (December 11th). The inset shows Curiosity’s progress through Glenelg, skirting the depression of “Point Lake” ( click to enlarge)

Drill Fears

Once at “Yellowknife Bay”, Curiosity will seek a location suitable for testing and commissioning the last of its mission systems – the hammer drill mounted on the turret of the robot arm. While there have already been opportunities to test the drill mechanism, the mission team has held off doing so as there are concerns as to how well – and how long – the drill may in fact operate before potentially breaking down and possibly threatening the entire rover.

Like many DIY drills used at home, Curiosity’s drill works on a percussive action as well as screw / drill action. This means that the drill head is vibrated at high-speed, “hammering” the bit into rock as it drills. The problem – which was discovered a little over a month prior to Curiosity’s launch and thus too late in the day to carry out a redesign – is that the percussive action of the drill might at some point break a bond in the drill mechanism and cause an electrical short.

Close-up of Curiosity's drill in action (simulation)
Close-up of Curiosity’s drill in action (simulation)

Concerns where heightened when it was realised the potential short could in turn threaten the rover’s entire electrical system. Describing the issue, Rob Manning, veteran lead engineer on all of NASA’s Mars rovers, commented, “It’s almost like the drill grabs the rover and shakes the whole thing electronically.”

To try and avoid this latter event, engineers installed additional wiring on the rover shortly before it was due to be shipped for launch in 2011. The hope is that should the drill’s hammering cause the bonding to break, andy resultant short can be limited in scope. “So if this short happens on the spacecraft, it doesn’t rattle around everybody,” Manning said. “We’ve been testing all that — to see what’s going on, to make sure it all works properly.”

While the issue has been reported in some quarters in something of a sensational manner (see comments at the head of this article), it is nevertheless believed the drill should at least see out the two years of Curiosity’s primary mission – the concerns are more that over time, and with repeated use, the bonding in the drill mechanism will eventually break. But the emphasis is on “eventually”.

In the meantime, it is anticipated that the first drill tests and possible sample acquisition will take place before Christmas.

Meanwhile “Oppy” Makes Another Discovery

Part way round the planet from Gale Crater, NASA’s surviving Mars Exploration Rover, Opportunity is also exploring a crater – the 22 kilometre (14 mile) wide Endeavour crater, a site it has been exploring since Curiosity blasted off from Earth on the start of its mission.

Curiosity's "little cousin" Opportunity, active on Mars since January 2004
Curiosity’s “little cousin” Opportunity, active on Mars since January 2004

Opportunity arrived on Mars in January 2004 at what was expected to be a mission measured in days (both of the MER rovers, Opportunity and Spirit, had initial primary mission periods of just 90 days, which were initially only extended in 90-day segments, such were the thoughts within NASA that the rovers wouldn’t survive much beyond a year). Now, just over a month shy of its ninth anniversary on the Red Planet, Opportunity appears to have made another interesting discovery.

Speaking at the 2012 Fall Conference of the American Geophysical Union (AGU), MER’s Principal Investigator, Professor Steve Squyres revealed that in investigating a hill named for Jacob Matijevic, a NASA engineer who worked on all three generations of NASA’s Mars rovers an who passed away earlier this year, the rover has been trundling over what mission personnel believe to be clay-bearing rocks.

Clays are water-altered minerals and are actually not in themselves a new phenomenon on Mars – both Opportunity and Spirit encountered them on their travels. However, what is unusual about the deposits “Oppy” has come across is their look and consistency, coupled with the discovery of a new kind of “Martian blueberry”.

The clays examined by both Spirit and Opportunity in the past have tended to show very high levels of sulphates, indicating the water involved in their creation was very acidic, which would have made it very challenging for life to have evolved. However, “There’s water and there’s water,” Squyres commented at the AGU – and the clay Opportunity will be examining in an outcrop dubbed “Whitewater Lake” may have a  different chemical composition to previous clays discovered by the rover. The thinking behind this is not only does the outcrop appear different to previous clay deposits examined by Opportunity, the rover has recently been examining a nearby outcrop, called “Kirkwood”, which has significant amounts of spherical concretions.

Such concretions have been encountered by both Opportunity and Spirit almost since their first day on Mars. Haematite-rich and formed by action of mineral-laden water inside rocks (again evidence of a wet environment on early Mars), the spheres have been previously nicknamed “Martian blueberries”. However, the spheroids discovered at Kirkwood appear to be of an entirely different composition, prompting Squyres to dub them “newberries” when first discussing them back in October.

The “spheres that don’t taste like blueberries” as seen through the Microscopic Imager on NASA’s Mars Exploration Rover Opportunity (image courtesy of NASA/JPL-Caltech/Cornell Univ./ USGS/Modesto Junior College)

As it is, Opportunity is still in the earliest stages of investigation both “Kirkwood” and “Whitewater Lake”, and Squyres is hopeful that the rover will produce interesting results as further work is carried out; work which not only involves examining the outcrops themselves, but also understanding how they were formed. Where they a result of the impact which created Endeavour Crater, do they pre-date it, or were they created after the crater was formed? Answers to such questions could further increase our understanding of Mars’ past and the role once apparently played by water in its evolution.

One thing is clear from “Oppy’s” discovery – it hasn’t finished with Mars yet, and the planet isn’t done with surprising scientists.

MSL progress reports in this blog

All images courtesy of NASA/JPL unless indicated otherwise

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