Martian Cave Probe?, Designs for the DEEP Search for Life Options

[Shaka]

"navigate back" Wow, you don't want much! I definitely saw Shelob on a one-way trip. Without her umbilical, how would she get back up all those precipices and skylights? If she finds a community of organisms 10 meters inside, a followup sampler probe would be in the cards, but I wouldn't want the sample brought back to my planet! (Sorry, I watched the Alien movies too many times.)
I prefer the fantasy that all the alphabet soup of instruments have been nanosized into that shoebox in the spider's thorax. No return required.
Choosing what to include as instruments can start with what's going into MSL. I like all that stuff. But maybe the chemcam laser should have a "lethal" setting. Just in case we have to fight for Shelob's life.

P.S. My marine biology career was on the opposite side of planet earth from WHOI, but some of the 'oldtimers' would be known to us both.

[Shaka]

Expanding further on the subject of Shelob's instrumentation: In contrast to MSL's equipment for identifying organic carbon, we would send an underground probe in the hope that Martian life was surviving there and not just fossilized, so tools to describe living organisms should be a priority. Microscopic unicells would be most probable, so nutrient broths to grow a range of primitive earthly organisms should be offered to rock scrapings, with appropriate chemical and visual sensors to detect metabolism. I use earthly archaea, bacteria and eukaryotes as models, because the most parsimonious assumption is that the evolution of life follows predictable paths in likely environments. The real possibility that Martian life employs a totally 'exotic' alien chemistry opens up a can of worms with too many possibilities to be handled by a first-generation probe. If Shelob Model I produces negative results, Model II may include more exotic chemical broths. (Too many broths spoil the cook! sorry).

I would like to include in Model I tools for the inspection of macroscopic tissue, in the hope that larger organisms are surviving on the tiny stuff. But how to do histology in a crowded shoebox is fairly daunting. Maybe a tool to 'smear' a tissue sample and put it under our microscope would be feasible. Of course at the ambient temperatures underground, things might be frozen solid. Then we would need a nanotech 'cryomicrotome'.
Get to work on that, nprev!

[nprev]

All over it, Boss! Gonna stick to my guns on Shelob going home, though; these advanced (and delicate) instruments you cite would have a far greater probabilty of surviving long enough to function if they remain on the surface vehicle & the spider comes back. Certainly there should be some in situ instruments: an imager (duh), a light source, a microscope, and maybe a mini-mini-TES. I see the balance of the Shelob payload as collection machinery, though.

EDIT: Just to be perfectly clear: when I say the spider should go home, I mean it should return to the surface & deliver its samples to the rover/lander where all the advanced analytical instrumentation would be. Nohow, no way am I suggesting returning living Martian organisms to the Earth (if found); we got enough trouble in the US with kudzu alone...

Couple of thoughts on ingress/egress methods as well. I can't see Shelob walking up to the edge of a hole & just jumping in (AAAaaahhhhh....splat...or, whack, whack, bang, bang against the sides on the way down...or, even worse, snagged on a projection on the side of the wall, helpless. Crawling down the wall would seem safest, but don't forget that there probably would be some discontinuity in the descent, and gravity sucks...) Seems like you'd have to get the rover VERY close to the rim, extend a good-sized boom, and carefully lower the descent platform with our intrepid spider perched thereupon. Depending on the depth of the hole, you might get a moment arm significant enough to topple the rover...game over. Therefore, the rover would almost certainly have to have some heavy-duty pyro-fired soil anchors to prevent this (added benefit: we could put some chemo or seismo sensors in the anchors!)

A design heuristic emerges: the lighter the spider, the longer the boom, and therefore the better the chance that we can get a straight drop down...

[tanjent]

Getting any hardware to Mars is going to be expensive for a long time yet. It is hard to visualize a one-shot mission that puts this precious spider-robot into an unscouted hole in the ground. But if the caves are clustered on the flanks of the volcanos, could a lander with MARSIS-type radar be put in a surface location from which it could map several of them at once? Or could a balloon make the rounds, taking snapshots into the cave mouths, and perhaps lowering some kind of radar device on a tether into the entry chambers? Then at least you would have some idea of where your spider would have the best chance to survive and discover something interesting.

[Shaka]

Scouting is good. Expensive is bad. But good and bad are subjective, and infinitely malleable, so you always have to specify: "Compared to what?"
Scouting from orbit can be very cheap compared to scouting close to the ground, so if possible we scout from orbit. We should be able to see openings to the Underworld bigger than a breadbox, but what else can we scout? Probably not detailed isotopic composition of gases at the opening. For that we need to get closer; a surface rover takes too long to scout more than one opening, and why not send it into the opening? A flyer could visit multiple openings, but how will it fare down low in Mars' atmospheric roller coaster? (I don't like to even think about a balloon!) If we don't scout up any marked gaseous clues, does that rule out life in the caves? What if Martian beasties don't belch out methane? What can subsurface radar tell you about micro-organisms clinging to the walls of a cave?

Scouting is good, but it's not necessarily cheap or easy, nor can it guarantee success. We can select more promising caves on the basis of elevation, probable depth and extent, proximity to geothermal warmth, etc., but in the end we still have to roll the dice and send Shelob on her mission of exploration.