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

[Shaka]

Does anyone consider it worthwhile to speculate on how we might explore Martian caves or lava tubes for the traces of life - past or present? I have not yet run across any 'official' proposals for "spelunker probes", so perhaps we could have some fun and get in on the ground floor with some feasible early designs. With the engineering and scientific expertise we have at UMSF we should be able to whittle down the possible features for such a rover to a practical core. If the planned surface scrapers and drillers don't turn up conclusive evidence to answer The Big Question, can we justify a search of the Martian Underground?

I can envisage a RTG-powered rover that enters a cave, or rappels down a skylight opening, leaving a base communication stage outside connected to it with a fiber-optic umbilical cable. Some form of laser or other illumination - in the visible and/or infrared - would presumably be required. How many of the MSL instruments could be included? What novel instruments would be appropriate? What is the optimal size and mobility design? 'Do we yet have 'hot' prospects for accessible caves? How should we choose the best candidates?

We can leave this to some JPL bright spark to develop, or we can dive right in. Any takers?

[Cugel]

Elevation is only a problem if you come in on a chute. If you have a nice powerful descent rocket you can land anywhere on Mars. I know this will do something ugly to your budget but powered EDL on Mars must be developed for manned missions anyway. So, in true Zubrinian style, let's just suppose we have that technology and somebody has payed for it.
The good thing is that the landing ellipse will now be down to a few meters or so. We can do a pinpoint landing right next to the hole in the ground.
So, maybe we don't even need a rover type lander (to get to the hole), just a big boom might be sufficient to deploy the probe. (This is the optimistic part)
Also, I don't see the cable problems nprev mentioned before. If you can lower something many miles into an ocean on Earth it surely must be possible to do that in a cave on Mars.
The whole shebang (lander + probe) can be solar powered, so accept for the EDL hardware I don't see why it would cost many billions (MSL class maybe?).

Another idea if you don't like that cable: just drop a battery powered probe into the hole and dangle an antenna which is connected to the lander a meter deep or so in the cave . That would be good enough for a radio link. With airbag technology the fall must be survivable for the probe (which could be pretty small and simple anyway).
Probably carry more than one of these probes anyway. The probes could be deployed into the hole by shooting them out of an airgun, so the lander could actually be quite some distance from the rim.