Four sites today -- totally exhausting and finishing close to 7 PM -- but good arguments about what we would want to do with this billion dollar piece of hardware...
The second day of the landing site workshop got off to a rip-roaring start, as the top site from the first two landing site workshops was presented with several detailed talks by Jack Mustard (the main proponent), Nicola Mangold, Bethany Ehlmann, and Dave Des Marais. The context that Jack Mustard laid out for his presentation was the question: where would we go on Mars if any putative biology never developed photosynthesis? His argument was we would want to go somewhere where there is lots of water rock-interactions -- fluid in cracks or where fluids moved through the subsurface.
The Nili Fossae Trough site is interesting because it has diverse exposures of alteration products, especially phyllosilicates. Bethany Ehlhmann's talk also presents evidence that at least in some portions of the stratigraphy, there are also other alteration minerals, including carbonates. The basic traverse path carries the vehicle from an interesting ejecta (out of place) material into a valley or reentrant of mineralogical diversity. Jack Mustard argues that as you drive on the way to the reentrant, you get some The fact that the ellipse science is on 'float rock' is criticized by some in the audience who don't like this sort of thing and prefer rocks in their clear bedrock context.
There is a presentation of the idea that Nili saw extended fluvial episodes or 'extended wetness'. There is some pushback from the audience on this. How long and/or how episodic?
The discussion than devoloves into an argument about whether MSL would have any hope of observing supposed life in cracks (eloquently argued in the negative by Dawn Sumner). Perhaps these water-rock interactions may have provided energy gradients for life, but what's the concentration mechanism? (Crowd tension rises...) Jack and Dave Des Marais then argue that we don't really know what martian life looks like, and our presumptions might be substantially biased by terrestrial experience and photosynthetic organisms.
The second site of the day is Holden crater -- a large crater which impacted into the Udon-Ladon-M???? valley system that extends north towards the Chryse basin through a really old degraded Holden proto-basin. The region has some of the best preserved evidence for fluvial activity -- Eberswalde crater, another candidate, to be discussed shortly sits directly to Holden's north. John Grant and Ross Irwin are the lead proponents of this site -- he first emphasizes that Holden is a go-to site. The landing ellipse is on an alluvial fan, and the presenters call in Kelin Whipple to describe how examining these alluvial deposits might tell us about the environment of early Mars. Both at the edge of the alluvial fan, and in the light toned layered deposits in the 'go-to' target to the south, bedding, meter-scale subunits, and clearly discernable units are apparent. The context and local stratigraphy is well-established. Two possibilities for layered units are distal alluvial deposition or lacustrine -- the presenters argue that this does not matter much, but I am a bit skeptical (lacustrine is much sexier). One unanticipated element of the Holden ellipse is that there are clear 'bedrock' blocks available in the Holden drive site, including megabreccia and a mound with good mafic signatures and linear veins running through it. This was presented as a possible advantage vis a vis Nili, which has similar (perhaps more spectacular) veined materials.
Ralph Milliken presents the mineralogy of this site -- the main spectral signature of interest with CRISM is clay.
The third site of the day is Holden's neighbor, Eberswalde crater, and 'the best delta on Mars'. Jim Rice is the lead presenter, although the best discussion of the actual fluvial architecture is given by Kevin Lewis, who has produced spectacular elevation models of the delta. One of the cool things that comes out of this discussion is the fact that the foreset beds of Eberswalde are actually clear in new data, which is the first time these have been convincingly observed. (Earlier suggestions have all been based on observational artifacts!). All of the presenters for this site argue that the source-to-sink architecture of this site is clearly apparent, which is a positive element for understanding its context. The landing ellipse is on the putative lake beds, supported by the fact that across the ellipse Eberswalde, like Holden, has smectite clay. During the discussion of Eberwalde, the room starts to try and wrestle with whether the strength of the clay absorptions matter for how we might understand preservation potential. Bethany Ehlmann argues that stronger absorptions are better -- probably indicative of more 'good stuff' that could help preserve biosignatures. However, there are two counter-arguments raised: (1) the absorption strength in the CRISM wavelength range do not translate particularly well into abundances, and (2) Ralph Milliken and Jurgen Schieber argue that it is better to have weaker clay absorptions with a presumption about how biosignatures might actually be preserved rather than just strong absorptions alone.
The third site of the day is Holden's neighbor, Eberswalde crater, and 'the best delta on Mars'. Jim Rice is the lead presenter, although the best discussion of the actual fluvial architecture is given by Kevin Lewis, who has produced spectacular elevation models of the delta. One of the cool things that comes out of this discussion is the fact that the foreset beds of Eberswalde are actually clear in new data, which is the first time these have been convincingly observed. (Earlier suggestions have all been based on observational artifacts!). All of the presenters for this site argue that the source-to-sink architecture of this site is clearly apparent, which is a positive element for understanding its context. The landing ellipse is on the putative lake beds, supported by the fact that across the ellipse Eberswalde, like Holden, has smectite clay. During the discussion of Eberwalde, the room starts to try and wrestle with whether the strength of the clay absorptions matter for how we might understand preservation potential. Bethany Ehlmann argues that stronger absorptions are better -- probably indicative of more 'good stuff' that could help preserve biosignatures. However, there are two counter-arguments raised: (1) the absorption strength in the CRISM wavelength range do not translate particularly well into abundances, and (2) Ralph Milliken and Jurgen Schieber argue that it is better to have weaker clay absorptions with a presumption about how biosignatures might actually be preserved rather than just strong absorptions alone.
The final site of the day is Mawrth Vallis, and here my notes get particularly flaky because my laptop has long since run out of power (not enough damn power strips). JP Bibring is the lead presenter for the Mawrth site, which gets focused on one of four possible ellipses in this region "ellipse 2" (a complication which confuses the audience at various times). The main target at Mawrth is some of the best phyllosilicate absorptions on Mars, with diversity among the various clay minerals [Fe-phyllosilicates beneath Al-phyllosilicates] and considerably interesting bedding. By the end of the Mawrth discussion, the main issue seems to be that no one has any reasonable idea how the stack of clays actually ended up a stack of clays, and the whole stratigraphy of the region is a bit uncertain. One possibility is that the kaolinite (Al) bearing upper units might or might not be draped across the region (indeed, perhaps all of the clays are draped), creating some uncertainty into how the actual material gets where we observe it. Part of why I run out of power is that the Mawrth presenters (*cough, Bibring, cough*) run an hour over time -- probably not helping their case since I'm getting hungry and the rest of the audience seems like its getting punchier and punchier. I wonder if this has any influence on the ultimate decision making process...I hope not. Anyhow, more coming when I get around to summarizing the ultimate day tonight or tomorrow. Votes will be cast and one site will be presented, and then people will hopefully civilly discuss the merits of each site.
Out for now...
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