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Mars 2020 landing site - Expert Reaction


NASA has announced the landing site for its Mars 2020 rover, which is due to touch down in February 2021 in a mission to search for signs of ancient life.

A giant impact basin known as the Jezero Crater was the winning site from four final contenders - chosen for its geographically rich terrain, with landforms up to 3.6 billion years old which NASA hopes will shed insight into the planet's ability to sustain life.

The mission will see scientists use the Mars 2020 rover to collect rock and soil samples that will be stored for potential return to Earth in a future mission.

Next week, NASA's InSight mission is scheduled to land on the Red Planet, which will investigate the planet's crust, mantle and core.

The SMC asked experts to comment on the decision. Please feel free to use these comments in your reporting.

Dr Duncan Steel, Centre for Space Science Technology, Alexandra, comments:

"Where to land on Mars is by no means a random choice: a vast amount of thought and debate has gone into this decision.

"There is, in general, a trade-off between where the engineers would choose, and where the scientists would like to go: the engineers’ job is to get the mission landed without a mishap, whereas the scientists want to go to the most interesting places – and ‘interesting’ generally means ‘dangerous’. That’s why the Apollo landers on the Moon mostly went to the ‘boring’ flat areas, and it was only the final mission – Apollo 17 – that landed in the lunar highlands: there was a greater chance of a disaster, but the geologists really wanted to get samples from somewhere different.

"The reality, even the scientists acknowledge, is that the most interesting places on Mars – say, at the foot of steep scarps where water is seen to be seeping out from underground – are simply too dangerous to attempt a landing. The risk of losing the mission, costing over US$2 billion, is too high. But Jezero Crater has been intensely surveyed from orbit, and it looks like there are enough flat areas that the Mars 2020 rover can be successfully landed and deployed there.

"Why this crater? It’s an ancient part of Mars - the 45-kilometre crater having been formed perhaps 3.6 billion years ago, at 80 per cent of the full age of the planet. Over the billions of years since then, Jezero has had a river delta formed within it, the waters have long since dried up, but the sediments that were carried there from many different places will contain an array of different rock types.

"In essence, the rover will be able to inspect rocks of many varieties, from a wide area, without travelling too far. On top of that, these sediments may well contain evidence of microbial life on Mars, if it ever existed.

"Even from orbit, scientists are able to tell broadly what sorts of rocks are there, and there is evidence for carbonates and clays, among other types. All in all this makes Jezero a playground for the geologists, and the astrobiologists who look for evidence of life.

"It happens that I have a little bit of Mars: a tiny fragment, less than a centimetre across, of a Martian meteorite, blasted off the planet aeons ago by an asteroid impact, which eventually found its way to Earth. But it’s made of basalt, a volcanic rock – it was that which alerted meteoriticists to the fact that it’s a piece of the planet Mars – and volcanic rocks are unlikely to contain evidence of life. The sedimentary rocks laid down by flowing water in Jezero Crater, though... That’s a great place to be looking for evidence of life, even if it is long-since extinct."

No conflict of interest in that I am not directly involved with this mission. However, I am a visiting space scientist with NASA-Ames Research Center in California, and have been involved in the past in various aspects of Mars mission planning.

Professor Kathy Campbell, Astrobiologist, University of Auckland, comments:

"I was a proponent and team member of the Columbia Hills landing site proposal for the Mars 2020 rover mission. So, of course, this means I am biased in my opinion as to which landing site NASA could / should have selected. Having presented in this capacity at both the 3rd and 4th landing site meetings in California over the past couple of years, I have witnessed the hard work and dedication that scientists and engineers from within NASA and other organisations around the world have put into furthering our understanding of the final landing site candidates in order to be able to help advise NASA administrators as to the best location for the next mission.

"This mission uniquely has had, at its core, a major objective of searching for signs of past life rather than simply establishing habitability or the indicators of ancient surface water. While each proposed Mars 2020 landing site has its pros and cons, of which we were all aware, I am still of the opinion that the Columbia Hills locale is the best place we know of so far on Mars for a chance to find fossil microbes entombed – in situ – in very old (>3 billion years) rocks. Here I will briefly lay out the reasons, and compare to the Jezero crater site that has just been chosen by NASA for their 2020 mission to Mars.

"With respect to Columbia Hills, the Home Plate area preserves odd finger-like silica deposits that are hydrothermal (hot water) in origin and almost certainly formed in an ancient hot spring. On Earth these same types of features are found in many places today, from the high Andes to Rotorua, New Zealand. They are invariably located in the outflow channels of hot springs and are replete with microbial life trapped in the silica. This silica is carried dissolved in the thermal waters until they exit as hot springs at the land surface, upon which an opal mineral deposits around the spring vent outflow area due to cooling and evaporation of the waters. This natural process effectively entombs the ‘extremophile’ microbes (i.e. adapted to extreme conditions – like the kind of organisms scientists think might have once existed on Mars) in place, and in a durable mineral mausoleum that has been shown on Earth to stand the test of ‘Deep Time’ (in this case, billions of years).

"At Home Plate the silica there was likely covered by ash, which has more recently eroded to expose the apparently pristine features for Spirit Rover to have discovered in the 2000s. Spirit got stuck in a sand dune and was unable to explore further, including a locale nearby that is likely a fossilised spring vent mound (the hot-spring source itself) which, again, on Earth preserves microbes specially adapted to living in hot water. Over time, the spring-derived silica and the microbes interact to build up finely layered, organic-sedimentary deposits known as stromatolites. Stromatolites on early Earth are one of the reasons we have oxygen in our atmosphere today. Similar silica features on Earth, specifically in rocks of Western Australia, go back ~3.5 billion years – around the same time on Mars that surface water and volcanoes were active (i.e., prime conditions for forming hot springs on the land surface).

"A new 2020 rover mission could have studied these features in detail – including whether organic carbon is present – and would have cached samples for a future, as yet unfunded, mission to bring them back to Earth for unprecedented study to help determine if life ever could have arisen more than once in our Solar System. Either way, the answer – yay or nay – would be one of the greatest discoveries of Humankind, finally answering the age-old question: “Are We Alone in the Universe?” If life arose twice in our Solar System (but didn’t make it for long on Mars because of its different history to Earth), then that finding would imply life should be abundant in the Universe. So this explains why the Columbia Hills team was so keen to go back to Home Plate to study and sample the silica to look for potential organic biosignatures to go along with the known and very compelling mineral and rock outcrop evidence that a perfect locale exists on Mars for preserving the kind of extreme life we would expect near the time of life’s origin on Earth and potentially Mars.

"But this was not to be. From the beginning, many people were clear they did not want to go back to a place already explored by a rover. Missions are expensive and each a precious opportunity to learn of the history of Mars and how it came to be so different from Earth when they both started out kind of similar. Our group was clear that it is essential to go back if you find something compelling, especially if it might answer the main objective of your next rover mission. As a geologist, each time I go on an expedition to the hot springs and their deposits in Rotorua, or somewhere else in the world, I glean new information to further strengthen our understanding of life in extreme environments and how it comes to pass that these microbes turn to stone and stand the test of time to tell us something about early life on Earth. Some people have complained about the dust at Columbia Hills, or the lack of novelty of other new things to discover, but Spirit did find cool stuff despite the dust, and the Columbia Hills team did present some good targets for an extended mission that likely would have paid dividends in a better understanding of the global history (e.g., climate, volcanism, another possible delta, formation of regional rock bodies, etc.) of Mars as a planet. A worried official asked our team leader, Steve Ruff of Arizona State University: “What if you’re wrong?” (i.e., about the origin of the silica, and they are not stromatolites?). Steve’s spine-tingling question in response always is this – “What if we’re right?”

"Regarding Jezero crater. It is beautiful in its form as seen from orbit – a classic delta shape that emptied into a lake that had filled the crater. But as we already know from the Curiosity mission that has studied an old lake bed at Gale Crater on Mars, it is very difficult to pinpoint the source of the organic carbon that was identified in mudstone at this locale. From space? From Mars? But from where? Deltas transport materials from far and wide, which will also be the case at Jezero. This is great for sampling different rock types from different places, but not so great if one is trying to sort out the source of that carbon. In a hot spring environment, the silica that comes out of the spring vent preserves heaps of biology in the place where the organisms once lived.

"Another issue with Jezero is that recent studies have shown that catastrophic floods carved river valleys on Mars, including that of Jezero, over a period of months instead of thousands of years, which would be terrible conditions for accumulating a concentration of biosignatures in the delta. Also some have questioned the age of the Jezero delta, suggesting it is too young to have been in the right time window for life to have evolved on the Red Planet. While I am very sure that excellent science will come out of the Mars 2020 mission to Jezero crater, I still very much doubt that the best location has been chosen to probe for fossil biosignatures, which in my view (and that of the public) is the most exciting part of the mission. Hopefully one day a mission – maybe even humans – will go back to Columbia Hills and pick up some of that silica, bring it back home to Earth, and determine if life ever existed on Mars."

Conflict of interest statement: I am a member of the Columbia Hills proposed landing site team.


ends

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