1. Do Mars meteorites represent our best analogue to test Mars bound instruments. If so is this a relevant use for such precious samples?
2. What are the most important technologies to test in the coming decade and why?
3. What are the most minimal set of criteria for past life identification and what is your favorite biosignature (null hypothesis)?
4. If Mars had no life, is that such a bad result?
Can we consistently detect life on earth?
History would tell us the answer is no - at each point in time (and arguably the same would hold true today) - our ability to detect life is dependent on our current understanding of life's capabilities. The lesson learned is we must continually challenge our assumptions.
On Earth, astrobiology analog sites have arguably been overly focused on relatively geologically young marine systems. A broader data mining of astrobiological targets such as the terrestrial subsurface, in particular ancient terrains of comparable age to the Noachian/Hesperian; of Antarctic or arctic springs, groundwaters and lakes; might ensure Life detection tools are not limited by unintentional sampling bias
Hi Steelie, Not sure what order you wanted to proceed with for your questions – but in case you need a kickoff here is a perspective on your Q3.
While the field of biosignatures research is well-established its governing principle is identification of the signs that life (as we know it) can produce. While it continues to be enormously valuable, the limitations of this approach have also become clear as piece by piece, putative biosignatures, some isotopic, some chemical, mineralogical or morphological, have been shown to be able to also be produced by abiogenic processes under certain circumstances. Can we change the paradigm? i.e. integrate more examination of what signatures CANNOT be produced by chemical and physical processes – an under-explored but necessary corollary to biosignatures research. Or to put it another way, more reliably establish the abiotic baseline so that what is uniquely biological as a fingerprint can be identified more clearly in relation to that base?
I thin you and I have always thought the same way about this issue. Set a chemistry baseline and look to see how unique and non abiotic chemistry perturbs that baseline. Trouble is, as you point out, that chemical baseline is in itself a challenge to set and one that is allowing us to understand some very fundamental processes that have not been seen before.
How do you think multiple isotope systematics will unlock this given our lack of knowledge about martian stable isotopes.
That's a tough but important question. As we've chatted about before perhaps the only way to address it is to understand that the baseline isotopic signatures will be different - and hence absolute isotopic signatures will be less important than looking at relationships between products and reactants (feedstocks); focusing on measuring multiple compounds in reaction series to understand processes; integrating multiple lines of evidnece and ensuring context as Abby Allwood always emphasizes so well.
For all technologies, to my mind, the most important challenge to address over the coming decade will be the need to reduce sample size requirements.
I agree in some ways. Sample preparation is also an issue.
I would also like to see more emphasis on minaturisation of instrumentation without the loss of instrument performance usually associated with such endeavours.
Going back to the earlier point, context is key to understanding any chemical bacground signal. Multiple and mutually supporting lines of evidence are also key. Life detection will be done by community consensus.
.. and probably to develop technology for the sample return mission. If we are looking for multiple lines of evidence to detect undoubtful biosignatures (which is diffucult to do even for terrestrial samples) the best chance we may get is if we bring samples back and analyze them using the best available instrumentation.
IMO in-situ missions and sample return are two tools in our box to apply to the problem. Both have advantages and are essential in the long term. I do not think that the community will be 100% convinced either way without sample return, but we need to explore the distribution of possible biosignatures through in-situ missions configured to look for them.
Absolutely - rapid instrumentation development is critical - for in situ measurements on Mars with miniaturization with minimal loss in sensitivity; and increased sensitivity (and decreased sample size requirements) for earth-based measurements to reduce sample size requirements for MSR. A program of instrumentation development along these lines is a critical corollary to analog research programs. New ones could be tested out in the trickiest terrestrial systems. Can we find locations on earth that are more analogous to the Mars problem i.e. a dominantly abiotic baseline where life, if present, is a biotic needle in the dominantly abiotic haystack?
That is a fabulous question. I would say a fresh lava field during and after cooling before primary colonization and then over time as colonization of the degassing and drying basalt would be great to study for that context. Any ideas where we can find one of these? Would be fun to do.
A great example of a fresh lava field is Eyjafjallajokull in Iceland, which erupted in 2011. Many parts of the lava field are still too hot to colonise, whilst other areas have cooled enough to allow initial microbial colonisation. Additionally the whole area is surrounded by glacial ice, so has very little influence from external complex biology. This would provide an ideal geochemical 'baseline' from which to identify increasingly complex biosignatures over time.
Besides active volcanos there are also excellent field sites in Antarctica, Atacama, US southwest ... also we should look into geologically old/ancient rocks because fossilization process is the best way to depleat bio-materials.
Steve Squyers has also talked about that in last week discussion
Mihaela,
Do you think that one or many such sites are the best targets at this point.
Like multiple lines of evidence to detect a biosignature do you need multiple analogue sites to completely ground truth instruments?
Multiple lines always. In terms of such sites you know I gravitate to the idea of going deep for exactly that reason. Subsurface sites, in certain settings where the water geochemistries indicate the systems have been isolated from the surface water cycle for geologically long time periods, provide us with settings in which we can investigate systems along gradients of biotic and abiotic control. In other words, I have always advocated that the subsurface is important to analog research not simply because signs of extinct or extant life on Mars may be preserved there, but because on Earth, the ultradeep subsurface may provide the best approximation of the Mars challenge. The Earth's surface has been hopelessly overprinted by life. In the deep and ancient waters where the water chemistries indicate dominance of abiotic water-rock interaction, the search for life and testing of life detection tools may be more analogous to the Mars challenge.
I have mentioned multiple types of samples as different samples/locations may be used as analogs to different places on Mars. Since we are not focussing on any particular location on Mars, I suggested more than one type of analogs.
Also, I mentioned more than one type of locations to keep in line with Barbara's response to post #2 ... multiple locations should be used to test/characterize biosignatures.
Are you suggesting analogie sites based on science or technical questions that need to be addressed or are they inseparable?
Desert Southwest has too much life. Atacama, Dry Valleys, and this fresh lava field suggestion would get my vote in terms of astrobiological significance. Also, going deep to paleowater is very important.
Hi Cynthia,
In the context of atacama and the dry valleys, what non-life processes would you consider to be the most useful to test the context and perhaps develop a non-biological biosignature baseline from?
Endoliths from the Atacama Desert could work great. There rocks, from calcite, to gypsum, to ignimbrite are colonized right under the surface - the communities are photosynthetic-based - and the whole interior of the rock is organisms free.
Hi Jocelyn,
Agreed that would be a great set to look at. Do you get much leaching of organic acids in that system and if so do traces of their effects remain in the minerals?
We have just been looking at microbial communities using molecular tools and microscopy. I don't think it is something that anyone has looked at. We have an idea of a project with Tom Zega (Univ Arizona) to use his FIB-SEM method on colonized and non-colonized zone. It is also possible to find rocks with ancient colonization that would be the middle step.
HI Jocelyn, It would be great to know if ancient traces of microbe mienral interactions are in these rocks. I remember Bill Schopf had an abstract about this at an Abscicon a few years back but I am not sure if he published that work. Mihaela has also been working on some aspects of this but I am unsure of her latest findings on that issue. Mihaela?
HI all,
Will sign off for now. Its been a great start to the discussion, I look forward to keeping the discussion going over the coming weeks.
Best
Steelie
All sorts of tools can be used when samples come back -- while before that, a sample selection has to be made at the surface, i.e., in situ. What are the creteria for THAT?
Purely from the angle of instrument detection and mission operation, I would look for the signature of carbon, in situ, -- it can be abiotic as Steele's paper said, but would be a good starting point.
To some lower probability, I would look for so-called bio-markers, in situ also -- the chem compunds that have the records of survival through long-geo-history/harsh-process on Earth.
In a big picture, I would look for the "right" geo/min/chem environments, they tell us if those precious "hot spots" can be preserved for a long time. In a way, these geo/min/chem are the richest heystack -- e.g., if I will see a salt with high degrees of hydration or a phyllo with enough H2O (not only OH, but H2O), I will do a full set of in situ analyses to assiss its bio-signature-bearing potentiality :-).
Two cents from the eyes of mineralogy/spectroscopy.
HI Alian,
Sample selection is an issue that deserves serious scientific and technical development.
I concur with your other thoughts, although it is the nature of possible biosaignatures from an unknown organism that has been the sticking point for a long time. I think it all points towards trial and error and therefore a long term commitment to the exploration of Mars.
I think the search for life ought to be based on the search for biochemsitry. A high risk, high reward approach. I would propose the following standard protocol to search for biochemistry (extinct or extant) in extraterrestrial samples. This would be the analyses necessary to establish whether a sample contains evidence of life, beyond doubt:
1-Estimation of Total Organic Carbon: This ought to be the baseline analysis to select a sample for further analysis in situ, or for return to Earth. A postive result would justify analyese 2 through 4.
2-Detection of lipids (and their possible decay products): Lipids are necessary to separate water-based life from the abiotic environment. Lipids are resistant to decay.
3-Detection and characterization of complex polymeric organic molecules: Biopolymers are the most conclusive evidence of life. Finding a polymer of amino acids, sugars or nucleotides would be a definitive proof of life.
4-Chiral excess in basic building blocks (amino acids, sugars…): Necessary to distinguish a second genesis of life
This is a very simpliefied post for the sake of space. In the case of Mars, the success of this approach would largely depend on selecting the right landing site. Work in analogue environments (Atacama, Antarctica) can help decide what consititues the right landing site.
HI Alfonso,
Thanks for your comments. I agree with 1 and 2.
3 and 4 are indicative of extant rather than extinct life given the labile nature of amino acids sugars and nucleotides. Chiral excesses of amino acid and sugars racemize over time, although models of this published by Kminek show that the excess may last much longer than the million or so years that it disappears in terrestrial environments.
I also agree that analogue sites can inform site selection on Mars. BAsed on the Atacam and Antarctica examples do you have a favourite landing spot on Mars?
Hi Andrew,
Favorite landing sites for extant or extinct life? For extant life (while ignoring pesky engineering details like trafficability), I say the seasonally recurring slope flows in the mid- and high-latitudes... I started a thread on this a few days ago, but it hasn't seen much traffic yet.
Andrew
You are right, it is commonly assumed that labile organics do not last long in the environment and therefore they are indicative of extant life only. This is indeed the case in most environments on Earth. However, I am not ceratin we can make the same assumption for Mars (at least not with the available data). Temperature is perhaps the key parameter controling the decay of labile organics, because it determines the rate of biological activity (which is the main process of decomposition), and chemical decay (i.e hydrolysis). In environments where biological activity is very limited like soils in the Atacama Desert (because they are very dry) or permafrost in the Dry Valleys (becuase they are very cold), labile organics do accumulate over time. Amino acids have been extracted from Atacama soils and based on their degree of racemization it is estimated that they are c.a. 10kyrs old. Relic PLFAs have also been found. There are whole cells and plenty of biomass (100s of ppm) in ground ice in the dry valleys, which can be >100kyr old. We know virtually nothing about the composition of that frozen biomass. I personally think it might be rich in relic labile organics, because nobody is consuming them, and chemistry is exceedinly slow. We are in the process of characterizing those compounds, but it is not easy.
I actually have two favoutite landing spots on Mars. One is based on our work in Atacama, and are salt flats in the southern highlnads which look a lot like ancient evaporites. In the driest parts of the Atacama, this kind of evaporites are the only ones that can still sustain life (due to the deliquescence of the salt). The second spot would be the ice-rich permafrost at the Phoenix landing site. This is based on our work in the Dry Valleys. During the last obliquity cycle that permafrost might have witnessed conditions similar to those on the Dry Valleys today.
The two examples above represent the last habitable substrates in the driest and coldest deserts on Earth. By extrapolation, they could have been the last habitable substrates on Mars, and therefore the most likely places to find a well preserved, extinct, biochemistry. Both salts and ice are very good at preserving organics, even labile ones.
sorry for the long post!
On Mars, perhaps the diurnal temperature cycle releases water from hydrated salts (chlorates ?).
On Earth in the Atacama ,the changes in the vertical distribution and chemical composition of the fluid inclusions in halite (that also may form water films in pore spaces) should be studied as an inorganic background.
James,
In the Atacama ancient NaCl evaporites (c.a. 5 Myr old) are colonized by a distinct community of cyanobacteria and associated heterotrophs and archaea. This endolithic community takes advantage of the deliquescence of the halite when the RH raises above a threshold value. This occurs in regions where rainfall does not happen in decadeas, and where even fog an dew are very rare. Deliquescence, however, results in liquid water inside the halite crusts for >60% of the time in the year. Deliquescence-based photosynthesis is the only solution we know for life in extreme dryness, so far.
The Atacama is particularly relevant for Mars because there we find a dramatic rainfall gradient, with precipitation falling from 50-60 mm/yr to <1mm/yr within 300-400 km. The change in microbial communities and their adaptative strategies along the gradient are remarkable. If we follow the Atacama rainfall gradient we can learn how life adapts to an increasingly dry environment. The most important thing that happens is that microorganisms stop being ubiquitous (i.e soil microorganisms dicrease rapidly), and tend to concetrate in specific niches that we call oasis of life. These oasis are typically lithic substrates, and the deliquescent halite crusts mentioned above represent the extreme case, the last oasis. We think that the Atacama rainfall gradient can help us re-trace the possible sequence of event that lead to the disappearence of life on Mars (if it ever existed). We can speculate that some of the adaptations we see towards the dry end of the gradient in the Atacama (such as colonizing the interior of deliquescent substrates) could have occurred on Mars. One possible strategy to search for life on Mars (extinct or extant) would be to identify these last possible oasis, and look for preserved biomarkers (and even labile organic compounds?)
Most in situ instruments would sample both unconsolidate sediment and rock on Mars, so shouldn't we assess instruments with compositional analogs of both? Martian meteorites alone may not suffice, given outstanding questions on the degree to which they sample the compositional diversity of the Martian crust [e.g., McSween et al., 2009 http://dx.doi.org/10.1126/science.1165871]. Meteorites may represent minor compositional components of Martian sediment even less effectively, such as the hydrous Fe-sulfate rich sub-surface "soil" that Alian and others have examined [e.g., Wang et al., 2013 doi: 10.1016/j.icarus.2013.07.020].
Would a meta-review of the literature distill the myriad analog site categories examined on Earth (lava tubes, cave environments, hydrothermal vents, playas, deep biosphere etc.) to a level sufficient to compare with recommendations by the workshop participants? Perhaps this may even complement the consensus that emerges from the workshop and even identify specific locales that need closer examination.
Much of the Martian exploration focuses on the surface, with few areas sampled deeper than decimeter scale even by in situ missions. Gamma photon spectroscopy offers several decimeter depth sampling, but only a regional perspective. Radar sounding provides km scale sampling, but with limited compositional detail. Even though technological constraints may prevent deeper sampling for the next decade beyond what a mission like InSight offers, should the workshop also consider Earth's deep biosphere [e.g., Edwards et al., 2012 10.1146/annurev-earth-042711-105500] as a suitable analog? Could some of the instrumentation methods used to examine Earth's deep biosphere allow us to increase the sampling depth on Mars?
Does Earth's biosphere pervade our range of sampling so much that even relatively lifeless areas may not provide an abiotic baseline? Can we meaningfully consider locations on Earth as not exposed to biology? Our atmosphere contains biogenic oxygen, biogenic volatiles, and suspended microbial spores, which may affect the alteration processes of even the fresh Eyjafjallajokull lava flows that Claire mentioned. The terrestrial biosphere may extend deeper than we can sample at present. How might this affect Barbara's thought on sampling isolated aquifers?