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Valerie Fox

8th Mars Report: Martian habitability

Posted by Valerie Fox

30-07-2014 13:22 CDT

Topics: Mars 2020, Opportunity, Mars Exploration Rovers, ExoMars, Mars, Curiosity (Mars Science Laboratory), conference report

The 8th International Conference on Mars was, as head convener David Beaty put it, "the largest gathering of Martians in the 4.5 billion year history of the Earth." However, when the largest gathering of Martians in the history of Mars happened -- if ever -- remains uncertain. In many ways, our space program has been driven by the search for extraterrestrial life, and Mars has been a particularly popular hunting ground. The conference provided an opportunity for the community to reflect on what we've learned so far.

While conditions on the red planet's surface are certainly inhospitable today, Martian geology hints at a more promising past. The evidence for flowing water on our neighboring planet is plentiful, meaning that surface temperatures and pressures would have been higher and early Mars may have more closely resembled Earth. And since life has an obvious stronghold here, Mars has a good case for being a likely place to discover how life might have come about early in our solar system's history.

Mars during the 2003 opposition

NASA, J. Bell (Cornell University), and M. Wolff (Space Science Institute)

Mars during the 2003 opposition
This photo was captured by the Hubble Space Telescope during Mars' closest approach to Earth in over 60,000 years, on August 27, 2003.

Finding life elsewhere in our solar system requires hard thought about just what exactly we are looking for. David Des Marais, of NASA Ames Research Center, started off the July 16 session about rover-scale geology (PDF) by discussing life in the context of Mars. Before starting to define or look for habitable environments, tasks both current and future missions are charged with, we need a working definition for life and an appreciation for how life on another planet might be similar or different from on Earth.

The requirements for life might be boiled down to four main elements: the raw materials required in chemical reactions, a solvent to promote said reactions, an active metabolism to maintain its disequilibrium state, and the capability for adaptive response to changes in its environment and promote its own survival. Each of these criteria might manifest somewhat differently from on Earth, but we have to start somewhere. Firstly, what is life made of? The most common elements found in the solar system—carbon, hydrogen, oxygen, nitrogen, potassium and silicon—are likely candidates, due to a combination of their abundance and how they bond with other atoms. Carbon, in particular, with its versatile bonding capabilities, seems a logical building block for life beyond Earth, as carbon can form a vast number of complex molecules. This structural versatility means that life would have a wide variety of forms at its disposal for building cellular structures. Silicon is another commonly imagined fundamental block, but the rigidity of its bonds and its preference for forming tetrahedrally coordinated structures limit its versatility, leaving carbon at the forefront of likely foundational elements. Assuming carbon-based life forms on Mars, and elsewhere in our solar system, is likely a safe bet.

We also assume that water will be a necessary component for life on Mars and other Earth-like planets, again based on water's role in Earth's organic material and water's chemical properties. Water is another versatile molecule that can promote complex chemical structures and reactions. Without some sort of solvent, the ongoing chemical reactions necessary to create and repair biological molecules are limited. Water is also a relatively common material, and is liquid at the usual temperature range assumed to be advantageous for life. There are other potential liquid solvents—methane on Titan, for example—but they are typically only liquids at much colder temperatures, perhaps limiting life as we know it. In the context of life on Mars, the evidence for plentiful liquid water early in the planet’s history is therefore encouraging.

Of course, life is more than just the presence of complex molecules. In order to be alive, the organism has to be able to control its self-repair and create copies of itself to pass on its aliveness. On earth we have DNA and a complex chemistry designed to copy the encoded "how-to" manuals, and something similar would be expected on Mars. Further, this copying method should probably include some means of improvement, perhaps via Darwinian evolution, because if an organism's environment changes but the organism doesn't, it's likely that the organism will lose its "alive" status.

These last two criteria may be the most difficult aspect of characterizing past life on another planet. We may be able to find organic molecules that may indicate the presence of life, but concluding that they unambiguously mean that there was life may still be a stretch. Given that there are components of the geologic record on Earth whose biological implications are still contested, it might be presumptuous to assume that organic molecules equal life. Finding fossils of macroscopic organisms would of course be a whole different ball game, but no one is really holding their breath. We'll likely have to make do with the organic chemistry for now.

The last element to consider with regards to finding life on Mars is the preservation potential of the habitat and the biological signatures for which we search. It is generally agreed that if Mars was ever inhabited, it would have been early in the planet’s history when conditions were more amenable, meaning that any evidence for life must have survived billions of years. The greatest threat to biological markers on Mars is likely the radiation environment at the surface. High-energy rays—in the form of cosmic, gamma and UV radiation—can rapidly break down complex organic molecules and erase unambiguous clues about life on the red planet. Therefore, we need to look where it is both old and new; that is, where the rock deposits were formed in the early, wet periods of Mars' history, but where these rocks have been buried for most of their history and are only recently (in geologic terms) exposed at the surface by erosion, such that they have been protected from surface radiation and weathering.

Both rovers currently driving around on Mars, Opportunity and Curiosity, have reported finding potentially habitable environments, the clues contained in the ancient rock record. The final session of the conference (PDF) focused on exciting science to come, including updates on the next generation of rovers, which intend to take the next steps towards detecting biological material and identifying life.

In 2018, the European Space Agency, along with collaboration with Russia and NASA, intend to send a rover capable of drilling deep into the Martian surface (where deep is up to 2 meters) and exploring the subsurface. A deep drill might penetrate below the radiation-cauterized horizon to where organic traces have been protected and preserved, therefore skirting the issue of preservation in landing site selection. This mission, called ExoMars, is a two-stage endeavor, with an orbiter to study trace gases in the atmosphere, along with the descent probe intended as a technology demonstration to prove that landing on the surface is possible, in 2016, and the rover/landing platform following two years later. The rover will be about the size of Curiosity and carry, in addition to its drilling platform, a substantial science payload to examine surface rocks, probe the subsurface remotely, and analyze samples, providing a well-rounded laboratory designed to detect and characterize signs of life. Despite the rover's subsurface capabilities, choosing the landing site is still a complicated task. To make the most of its time on the surface, the rover is not planned to stray more than a kilometer or so from the landing location, and will instead very thoroughly characterize the nearby landscape. Operations on the surface of Mars take a long time; if a part malfunctions, there is no hardware store to run to, so every movement of the robotic arm, every drive, and certainly every drill will need to be thoroughly vetted for risks. Given the time, effort and expense required for every operation, having considerable geologic variation with the rover’s range is highly desirable, and selecting the landing site will be an exciting prospect in the next few years. [Note: It now appears ExoMars may be delayed to 2020. --Ed.]

Artist's Concept of Mars 2020 Rover, Annotated

NASA/JPL-Caltech

Artist's Concept of Mars 2020 Rover, Annotated
Planning for NASA's 2020 Mars rover envisions a basic structure that capitalizes on re-using the design and engineering work done for the NASA rover Curiosity, which landed on Mars in 2012, but with new science instruments selected through competition for accomplishing different science objectives with the 2020 mission.

NASA will also have to think about the destination for its next robotic exploration on Mars. This mission, planned for 2020 (and creatively called Mars 2020) will expand on the current directive to find and characterize habitable environments, and is planned to actually collect and store promising samples for return to Earth sometime in the future. Laboratories here on Earth can perform investigations on Martian samples unrivaled by anything we can send to Mars, and returning pristine samples to Earth would advance our understanding of our neighbor planet by leaps perhaps comparable to Neil Armstrong's step on the moon. At the very least it would be a spectacular return on investment. Again, the choice of a landing site, still in the early stages, will require balancing geologic and safety considerations to pick the juiciest location. The instrument payload will be announced this month. [In fact, it's expected to be announced tomorrow. --Ed.]

The planetary science community is going to have to rally in order to make the sample return mission a reality, but in the mean time, mission designers are gearing up to collect and study the best samples possible. The 8th Mars conference was a valuable opportunity for the Martian community to synthesize the big advancements in the past 7 years and develop overall goals and broad themes that will guide the next few years of Mars planetary science. Understanding habitable environments and the potential for life on the red planet is certainly one of the big ones.

References: 

Des Marais, D., Concepts of Life in the Context of Mars. (2014) Eighth International Conference on Mars, abstract #1467.

Grotzinger, J. (2014) Habitablility, Organic Taphonomy, and the Sedimentary Record of Mars. Eighth International Conference on Mars, abstract #1175.

Vago J. L., Rodionov D. S., Witasse O., Kminek G., Lorenzoni L., the Landing Site Selection Working Group and the ExoMars Team. (2014) ExoMars Status and Landing Site Selection. Eighth International Conference on Mars, abstract #1105.

Farley K., and Schulte M. Update on the Mars 2020 Mission. Eighth International Conference on Mars, invited talk.

 
See other posts from July 2014

 

Or read more blog entries about: Mars 2020, Opportunity, Mars Exploration Rovers, ExoMars, Mars, Curiosity (Mars Science Laboratory), conference report

Comments:

Bob Ware: 07/30/2014 08:58 CDT

How would the Southern hemisphere ocean that ESA has found factor in? They believe (last I read) that there is enough water to cover the entire planet under several meters. MER A & B water related findings, acidic and neutral, plus signs of neutral water at MSL site(s) recently, may provide an underground shore line close enough to the surface, somewhere, that we could drill through. This would (I think) give a large enough zone so that we could have many areas to search. We Since the rover is not intended to rove far from touchdown, perhaps it could carry a shovel/blade so the rover could "strip mine" to a so called communication depth limit and then drill. This would get us deeper down. AI (Artificial Intelligence) would have to monitor for subsurface "leaks" so we don't "break the pipe" catastrophically, so to speak. To advance as we desire we must do things at a higher level. I'm sure Chris Kraft would have wanted to say to President Kennedy that his idea of 'landing a man on the moon and returning him safely to the Earth...' was insane. Especially so since we were still trying to figure out how to get off of the planet in the first place at that time! Let's do this on a future mission too. Of course maybe we'll get lucky and we won't have to with our current plans. For the record, I doubt it.

Enzo: 07/31/2014 03:22 CDT

Part 1 I find the conclusions of this article strangely at odds with its content. It states (my comments after "-") : 1) "In many ways, our space program has been driven by the search for extraterrestrial life" 2) "While conditions on the red planet's surface are certainly inhospitable today, Martian geology hints at a more promising past" 3) Life is difficult to define, so let's stick to life-as-we-know "Assuming carbon-based life forms on Mars, and elsewhere in our solar system, is likely a safe bet." - ok, I agree 4) " it might be presumptuous to assume that organic molecules equal life. Finding fossils of macroscopic organisms would of course be a whole different ball game, but no one is really holding their breath. We'll likely have to make do with the organic chemistry for now." - So far three probes (Viking 1-2, Phoenix) and 1 rover (Curiosity) have found none. 5) Unfortunately it looks like the surface of Mars is hostile to the preservation of organic molecules "biological markers on Mars is likely the radiation environment at the surface. High-energy rays—in the form of cosmic, gamma and UV radiation—can rapidly break down complex organic molecules and erase unambiguous clues about life on the red planet" 6) So maybe we need to dig underground - Except that we are not doing that and we have no plan to (except, maybe, ESA, see below) After all this, the author calls for Mars Sample Return ! You spend the whole article about how important is looking for life even in the form of simple organics (and by the look of it we are not even plan to look in the right place) to then conclude with how great will be MSR that does not meet the objective of the whole article (simply because we have not found any organics on Mars and therefore any samples containing the to return) ? That sound very convincing (NOT) and contradictory. At its astronomical cost, I do hope that "the planetary science community is going to have to rally" AGAINST it.

Enzo: 07/31/2014 03:33 CDT

Part 2 The problem I have with MSR is its astronomical cost (I heard ~$6B) and the damage it will do to all other potential missions. And yes it will, money spent on Mars is money not spent somewhere else. Regarding ESA and ExoMars 2018, there are many doubts that it will land working on Mars. This is because NASA was supposed to provide a sky crane-like system to ESA. Citing funding problems, NASA withdrew and basically left ESA in the lurch (only to announce their very own rover, MSL-2, soon afterwards :-) ) ESA has then approached the Russians to provide the landing system. Since the Russians have a terrible track record recently with problems even reaching Mars orbit, let alone land anything, there are serious doubts about ExoMars.

Enzo: 07/31/2014 03:54 CDT

And by the way, if it is true that "In many ways, our space program has been driven by the search for extraterrestrial life" and water and organic molecules are really that important, why lobbying for a sample return from a place where BOTH organics and water have already been found , like Enceladus ? Why Mars where we can find neither ?

Doug Currie: 07/31/2014 01:29 CDT

The search for life on Mars is certainly an interesting topic. However one thing I would still like some answers from is why Mars Express found methane in Mars' atmosphere in 2003 and 2006 and not since then and also that earth based telescopes found methane there but I don't know if they have found it recently. Also I heard that the bottom of Gale Crater wasn't a good place to look for methane because of its low elevation so will the upcoming European Mars missions or NASA's Mars 2020 land at higher elevations where detection of methane or perhaps other organic chemicals might be easier. Also I think the Viking results could have indicated the presence of some organic chemicals but how much is Mars Curiosity looking for methane or other organic chemicals in the soil as that is something that could change with location rather than sampling the atmosphere that might not change as much as long as Curiosity is still at a low elevation. The presence of neutral water at some Curiosity sites and a thicker atmosphere could certainly have supported life but how seriously is NASA looking for fossilized larger scale life with all those cameras and other instruments present on Curiosity or will we have to wait for probes from Mars One to look more seriously?

Bob Ware: 07/31/2014 09:15 CDT

Hi - Regarding methane, I heard that it is from geologic/chemistry reactions. I wish I could recall where I heard/learned that and the reason for it. Sorry Doug. As for MSR, that mission would need to dig deep and return UNSTERILIZED samples in a dark container to keep sunlight out so as to not sterilize the samples.

Torbj??rn Larsson: 08/04/2014 05:06 CDT

Too bad about the ExoMars rover trouble. But the 2020 US rover is exciting, without or with sample return (increased capability to find organics)! @Enzo: Water and, tentatively, organics _have_ been found on Mars. In the latter case the origin is still open, but it doesn't seem to be contaminants. (E.g. impactors produce organics too.) There is no reason to criticize the Mars research, which is faster in terms of turnaround (closer body) and fruitful. Neither is there reason to chose one particular habitable environment when we can investigate several. @Doug, Currie: Methane is unlikely to be produced in massive amounts by life (but can appear from impact events at times): "On 19 September 2013, NASA scientists used further measurements from Curiosity to report a non-detection of atmospheric methane with a measured value of 0.18±0.67 ppbv corresponding to an upper limit of only 1.3 ppbv (95% confidence limit). As a result, they conclude that current methanogenic microbial activity on Mars is extremely unlikely.[57][58][59]" [ http://en.wikipedia.org/wiki/Atmosphere_of_Mars#Methane ] See the link for a history of methane on Mars.

Enzo: 08/04/2014 06:06 CDT

@Torbj, For water, I mean liquid water, not ice. There might be some hints that it is possible somewhere but I don't think it has been found (maybe some droplets on Phoenix ?). For the organics, I found two articles on JPL page. The first : http://mars.jpl.nasa.gov/msl/blogs/index.cfm?FuseAction=ShowBlogs&BlogsID=272 It says : "Mahaffy detailed SAM’s detection of a perchlorate-like substance – single carbon organics that raise more questions than they answer. “We have no definitive detection yet of martian organics,” emphasized " The other : http://mars.jpl.nasa.gov/msl/blogs/index.cfm?FuseAction=ShowBlogs&BlogsID=283 is very long, but I couldn't say that they definitely found organic molecules, more like a maybe. And, if it was otherwise, there would be a gigantic article about it. The main problem I had was not so much with Mars research but with the article above. It spends 80% of the time discussing how important are organic molecules to Mars research, never mentions they they have never really been found and concludes on how important will be Mars Sample Return that does not even meet the very objective of the article ! If organics are so important, then how is spending $6B (or whatever) on MSR going to help to return something you haven't found ? Also, if we think that there are organic-destroying processes on the surface, how sending another rover without drilling capabilities is going to help this famously important objective ? By the way, besides ice from liquid water frozen as it is sprayed, Enceladus' plumes also contain complex organic molecules, not just "maybe" precursors : http://www.nasa.gov/mission_pages/cassini/multimedia/pia10356.html A sample return to Enceladus should be relatively easy (aereogel-like material through the plumes). Main problems would be the lenght of the mission and preserving the samples as it enters the inner solar system.

Enzo: 08/04/2014 06:08 CDT

Just to clarify, for "article above" I mean the article on this blog we are commenting now, not the second JPL article.

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