With the understanding that the 2020 mission is not necessarily relevant to this subject matter, I still wish to address polar to mid-latitude, seasonally recurring slope features, such as the polar dark dune spot seepage features, changes occurring within dune gullies, and recurrent slope lineae on crater walls. These remain compelling sites for understanding the potential current habitability of Mars yet, due to topography, are not easily accessed through traditional landed and roving missions.
1. What terrestrial analog studies of related features might be pursued on Earth to best prepare for (perhaps far-)future missions to these seasonally recurring features on Mars?
2. What could a Mars mission to seasonally recurring slope features consist of, both in terms of (a) accessibility (e.g., locomotion) and (b) science?
3. What are the best terrestrial analogs to seasonally recurrent slope features?
We don't know what time of day RSLs are active. Unless that changes, any landed mission should pack a flashlight and a power source that allows doing science in the very early morning (or night). Joe Levy's Antarctic Dry Valleys water tracks are the best terrestrial analogs that I'm aware of (Icarus, 2012).
Edwin, yes, Dry Valleys water tracks for the RSL, but what about polar dune seepage features? Are debris flows known to occur on dunes in Antarctica?
Thanks for the shout-out, Edwin!
Cynthia, in my experience, dry debris avalanches are very common in seasonally thawed sediments in Antarctica. Mostly, permafrost in the Dry Valleys is dry frozen (<1% water by mass in the upper 50 cm or so). When these slopes are destablized by rock fall or wind, lobes of dry sand and pebbles can cascade down hill to form lobate features. In my experience, wet debris flows really only occur in the Dry valleys at ice-cored moraines, moraines at glacier termini, or in areas where melting ice is buried by sediments. Without these big, melting ice sources, there's not enough water to saturate sediments to generate sediment/water debris flows that move as a single phase. In water tracks, the slopes are too shallow and the water content is too low to generate overland flow or debris flows. The famous sand dunes in Victoria Valley have intermixed ice and snow in them, but I don't know of cases where wet debris flows have been observed emanating from them. I don't know if there's melt out of the buried ice and wicking of water to the surface in these dunes (like in a water track or an RSL), but my sense is that most of the buried ice/snow is below the ice table, so it doesn't seasonally thaw.
Hi Joe,
I suspect that if alluvial debris flows are forming on the Victoria Valley sand dune slipfaces, it is very early in the season when noone is out there to observe them. I would expect there to be a seasonally frozen/thawed layer at the surface of the dunes with requisite volatile fluxes, just as in arctic and subarctic dune systems. It does not require much water to form alluvial debris flows nor air temperatures greater than the thaw point as we've seen in Alaska.
On (3), we need to remember that morphological similarity may not necessarily constrain the composition. For example, following Joe Levy's (2012) cautious approach to brines, alternatives to the CaCl2 enriched brines seen at the strongest analogs to RSL at DJP (Dickson et al. 2013) may work as effectively on Mars. Low eutectic and deliquescent minerals (e.g., Levy et al., 2012 GRL) such as hydrous Fe-sulfates (my personal favorite at regional scales) and perchlorates would be examples. Chevrier et al.'s (2012) and Gough et al.'s (2011) approach may exemplify the laboratory work that should accompany analog field expeditions. :)
On (2, a), locomotion, as Lujendra Ojha told me recently, the DuAxel instrument design concept by Issa Nesnas (http://www.youtube.com/watch?v=Ijjo1nW94tY) holds promise. The same may apply for Paul Schenker's CliffBot rover developed since 2001 (http://www.jpl.nasa.gov/video/index.php?id=51) and tested in the Svalbards by Steve Squyres and others. As Edwin noted initially, any rover may need its own light source, though terrestrial water tracks occur during sun-lit times.