The long trek and looking to the next decade

CuriosityCuriosity has started on the long trek to Aeolis Mons, which NASA unofficially refers to as “Mount Sharp”. With some eight kilometres (5 miles) between the rover an its initial destination among the lower slopes of the mound, the drive is liable to take several months to complete. Nevertheless, the drive marks the start of the core part of the mission.

The journey started on July 4th, when Curiosity departed the sedimentary rock target NASA had dubbed “Shaler” within the “Glenelg” region of Gale Crater between “Yellowknife Bay”, where the rover had been carrying out drilling and other tasks, and the landing zone at Bradbury Landing. “Shaler” had actually been passed b the rover on its way to “Yellowknife Bay” and had, along with another location in “Glenelg” which had been dubbed “Point Lake”, been identified as a “target of interest” for the rover as it backtracked through “Glenelg” in order to start the long trip to “Mount Sharp”.

“Point Lake” became a target of interest to MSL scientists as Curiosity passed it while en route to “Yellowknife Bay”, and remained of interest even as the rover carried out various science operations in “Yellowknife Bay”. This image was captured by the Mastcam telephoto lens on  Sol193 (February 20th, 2013) when Curiosity was engaged in the “John Klein” rock drilling operations. It show the cliff-like face of the outcrop. At the time the image was captured, it was unclear if the outcrop might be sedimentary or volcanic in origin. This image has been white-balanced so the rocks appear as they would under Earth-type atmospheric and lighting conditions

Point Lake first caught the interest of Curiosity’s science team in October and November of 2012. It caught the attention of mission scientists for two reasons: it forms a small cliff, and geologists love cliffs because they offer a sense of how a rock unit differs from bottom to top; plus images captured by the rover as it passed relatively close to the outcrop while en route to “Yellowknife Bay” revealed it to be full of holes. Why holes form in rocks can be due to diverse mechanisms, and Identifying which mechanism in particular is responsible can provide a greater understanding about the rock and its history.

The rover returned to “Point Lake” on Sol 301 / 302 (June 11th and 12th, 2013) and captured a further series of images using the Mastcam systems, some of which were then put together to create a mosaic.

A 20-shot mosaic of “Point Lake” captured by the telephoto lens of Curiosity’s Mastcam system on Sol 302 (June 12th, 2013) (click to see the full size image)

The mosaic clearly shows that the upper and lower portions of the outcrop differ in composition, with the upper part having more holes while being more resistant to weathering. The holes themselves range in size from about that of a garden pea through to some larger than a golf ball’s diameter. Some additionally have raised rims, as if the material immediately around a hole is slightly more resistant than material farther from the hole. A number of smaller rock fragments towards the right-hand end of the mosaic look as if they might have fallen out of some of the holes, and some of these exhibit colour banding suggestive of material which could have coated the interior of a hole.

The science tem are still studying the images captured by the Mastcam system and by the rover’s Mars Hand Lens Imager (MAHLI), mounted on the turret at the end of Curiosity’s robot arm. Taken from a distance of just 4cm, the MAHLI images reveal pebble-like deposits within many of the holes covering “Point Lake”, and which have made the identification of the processes responsible for forming the holes somewhat harder, as both sedimentary and igneous processes could account for the “pebbles”.

The Mars Hand Lens Imager (MAHLI) mounted on Curiosity’s robot arm captured this close-up of the holes in the “Point Lake” rock outcrop, in which the “pebbles” cxan be seen to be nestling

Following the stop at “Point Lake”, Curiosity continued retracing its route back through “Glenelg”, reaching the vicinity of “Shaler” around Sol 313, where it remained for several days taking further images and manoeuvring in the area immediately adjacent to the rock formation. Then on July 4th, the rover started on the drive to “Mount Sharp” in earnest, initially travelling  back towards “Rocknest”, which it visited in September 2012, prior to skirting around it in a drive of some 36 metres (118 feet) between July 5th and July 8th (Sol 327).

Why “Mount Sharp”?

“Mount Sharp” – so dubbed by NASA in memory of American geologist Robert P. Sharp, but officially called Aeolis Mons – is a huge sedimentary mound rising an average of five kilometres (three miles) above the surrounding crater floor and which covers the central mound of the crater. It is thought that the sediments in the mound may have been laid down over an interval of 2 billion years and may have even once completely filled Gale Crater. How the layers in the mound formed is subject to extensive debate, with the upper layers of the mound exhibiting cross-bedding of strata which suggests æolian (wind) processes have affected their formation, while the lower layers are suggestive of having been deposited on a lake bed.

A comparsion between Aeolis Mons and a number of mountains on Earth (image courtesy of Wikipedia)

Given the possible nature of the mound’s composition, coupled with the very strong evidence of water playing a significant part in the history of Gale Crater, it is seen as a prime target for MSL’s core mission objective: to find evidence of conditions on Mars which might have been conducive to the development of living organism.

The reason the mound has two names is twofold: while NASA may dub surface features like mountains, craters and so on, they do not have the authority to officially name them – that lies with the International Astronomical Union. Secondly, it is traditional to name large Martian mountains after the Classical albedo feature in which they are located. The IAU therefore officially named the mound at the centre of Gale Crater “Aeolis Mons” in May 2012, some two months after NASA had first dubbed it “Mount Sharp”. As the IAU traditionally names large craters on Mars after scientists, a crater 150 kilometres (93 miles) in diameter and some 260 kilometres (160 miles) west of Gale Crater was named Robert Sharp in honour of the American geologist.

Looking to the Future

The success of the MSL mission has already led to talk of a follow-on mission, possibly in 2020 and using a rover vehicle which employs much of Curiosity’s design. On July 9th, 2013, NASA hosted a teleconference to discuss these plans.

A conceptual drawing of the Mars 2020 rover, which draws strongly on the Curiosity rover design

One of the major critiques of the MSL mission has lain in the fact that for all its science capabilities, Curiosity is unable to look for evidence of past life on Mars; it can only confirm whether or not past environmental conditions on Mars might have supported living microbes.

While it may sound like a minor point, it’s actually a very important distinction and points to the Achilles’ heel of the MSL mission. While Curiosity may well find evidence that environmental conditions on Mars might once have been right for microbial life to arise, it cannot go on to look for signs that microbes actually did arise. The could only be done by a future mission, and under the assumption the budget would be made available for such a mission.

As well as looking for evidence of past microbial life on Mars, the 2020 mission additionally offers the potential for a sample return mission as well, with the rover vehicle caching up to 31 different samples gathered through the course of the mission while might then be returned to Earth for more detailed analysis at some point in the future by another robot mission.

A possible design for a “sample cache” to be carried aboard the Mars 2020 rover, which would allow 31 samples to be collected on Mars, stored and subsequently returned to Earth by a “future mission” for even more detailed analysis

A further key component of the Mars 2020 mission would be directly focused on future human missions to Mars. This would include more detailed studies of the dust suspended in the Martian atmosphere and the effects it may have on the human body as a result of direct / indirect contact (such as inhaling the dust as a result of a living environment becoming slightly contaminated by it following an EVA, for example). It’s also proposed that the Mars 2020 mission be used to test the concept of using the Martian atmosphere to create fuel to power surface vehicles (and quite possibly even the craft used to start a crew on their return to Earth).

This latter idea isn’t as crazy as it sounds and is actually something which could dramatically reduce the need for a human mission to carry expensive and heavy consumables all the way to Mars or relying purely on solar-produced electrical energy or deal with nuclear power sources while on the surface of Mars. What’s more the technology required to produce fuel from the Martian air isn’t in any way exotic – it is based purely on a reaction first developed in the era of the gas lamp.

Called the Sabatier reaction, the process involves the reaction of hydrogen (which would need to be transported to Mars) with carbon dioxide (the key component of the Martian atmosphere) at elevated temperatures (optimal 300-400 °C) and pressures in the presence of a nickel catalyst to produce methane and water, which can be expressed thus:

CO2 + 4H2 → CH4 + 2H2O

The methane could then be stored as fuel, and the water further electrolysed to produce oxygen (for use as the fuel’s oxidser) and hydrogen (which could be fed back into the Sabatier reaction.

This reaction formed a central part of the “Mars Direct” mission profile, first developed in the 1990s by Drs. Robert Zubrin and David Baker, and which has since revised several times. In its original format, it called for two vehicles to be used in a human mission to Mars. The “Earth Return Vehicle” would fly to Mars two years ahead of the first crew, and would carry just six tonnes of hydrogen in its tanks for the return trip. Once on Mars, the vehicle would use the Sabatier reaction (referred to as “in-situ resource utilisation”, or ISRU) over a 10-month period to leverage that 6 tonnes of hydrogen into 112 tonnes of usable fuel – 96 of which would be needed for the return trip.

The crew would fly to Mars about a “habitat” vehicle, which would double as their living and working space during a 500-day stay on Mars, before they transfer to the “Earth Return Vehicle” for the trip home. And if they arrived on Mars to find their waiting taxi broken, a second “Earth Return Vehicle”, launched at the same time as the crew departed Earth, would follow them to Mars where it could generate the fuel for the trip home under human supervision. If the vehicle wasn’t needed by the first crew, it would land elsewhere and become the taxi home for the next crew, two years later.

The Mars Direct proposal calls for two vehicles to be used. An "Earth Return Vehicle" (l), and a "Mars Hab" (r), used to fly a crew to Mars be form their living / working space for a 500-day mission on the surface. The "Earth Return Vehicle" would fly to Mars ahead of the crew and fuel itself for the return trip using the Sabatier reaction

The Mars Direct proposal calls for two vehicles to be used. An “Earth Return Vehicle” (l), and a “Mars Hab” (r), used to fly a crew to Mars and be their living / working space for a 500-day mission on the surface. The “Earth Return Vehicle” would fly to Mars ahead of the crew and fuel itself for the return trip using the Sabatier reaction (Images courtesy Orange Dot Productions)

Later variants of this idea saw some revisions to the plan – the fuel would be used at the end of a human mission to Mars to launch the crew into Mars orbit in a more modest launch vehicle, where they’d rendezvous with a much bigger (and fully fueled) vehicle waiting to return them to Earth, which became an approach NASA adopted with a series of mission concepts they proposed under the banner title of “Mars Design Reference Missions” through to 2012.

So the idea of creating fuel on Mars is still very much under consideration, and the Mars 2020 mission could give engineers the opportunity to test the feasibility of producing and storing fuel remotely on Mars well ahead of any human mission.

Related Links

All images coutesy of NASA / JPL, unless otherwise indicated.

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