Mars missions ... why not on the ice caps?

Mars Phoenix just landed on the permafrost of the Martian arctic circle. The scientists “expect” and “hope” that there will be water below the surface here. Um, why have no Mars missions landed on the giant icecaps of the planet? There’s probably water there, it being frozen water and all. (Yes, and CO2.) Is it just me, or are we tiptoeing around the obvious place to find large quantities of water on Mars?

We want more than just water. (And CO2, which forms part of the icecaps.)
The icecaps are the same as Earth’s: the water is all from precipitate that froze. Subsoil permafrosts will have (we think) other nutrients handy, and there’s a far greater likelihood that the water becomes liquid from time to time, being mixed with other stuff and all. “Molal Freezing Point Depression” it’s called.

well there is the whole landing with rocket engines burning thing. It would suck to melt the ground out from under the lander just as it was trying to touch down…
I know that there isn’t enough energy in the rockets to melt much ice, but even a little bit might endanger the lander orientation. But mostly what the other reply mentioned.

Why not use a parachute and airbag instead?

You can’t touch down larger probes with airbags. Plus, NASA needs to get the thruster landing thing down if men are ever to land there.

In answer to the OP: permafrost has a nice quality in that it has been around a long time. Therefore, one can hope that, trapped within its ice are things that have been there a long time. This is not true of the frozen gasses at the poles, which melt and reform each season, for the most part.

For parachutes alone, there’s just not enough atmosphere to reliably slow down a package for a relatively gentle landing. Even with the usual generous definition of gentle for space probes.

As well, those Martian ice caps aren’t stable in time; they grown and shrink over the course of the Martian year, and so the ice the probe sits on could disappear into thin air.

It also occurs to me that high-latitude landing sites might be harder to get to in terms of fuel required, and have low insolation, meaning less power is available for the lander.

This is a real problem for a manned landing. Dropping a probe that weighed 600 LBS or Viking at 1200 lbs is one thing but a manned mission lander would weigh a dozen tons or more. The sad fact is no known method can soft land large masses on the Martian surface. The atmosphere is too thin for parachutes to slow it enough for a soft landing and using rockets requires so much fuel it is difficult to have a really large craft, it is a real engineering corundum.

the kind of problem that just wears you down?

A sort of WAG, but I imagine a polar landing would require more energy to de-orbit than an equatorial landing. I imagine the probe in question would be coming more-or-less from an equatorial direction (give or take a couple of dozen degrees relative to Mars’ equator). I also imagine that to land a probe on Mars’ poles, not only do you have to shed a lot of speed to bring it to the ground, you have to also burn some energy to change your flight vector to bring it into a safe and stable de-orbit around the poles. It’s just cheaper to land at lower latitudes.

Wait till someone much better-versed in physics comes along and shred my WAG-fest to bits…

Or possibly worse - the thin air around the probe could turn to ice - encrusting and embedding it.

A proper grind, I’m sure.

This is quite a big deal - after all, its the reason the poles are colder than the equator. We wouldn’t build a solar power station in Earth’s Arctic Circle, because the energy yield would be so poor - operating a probe near Mars’ cold poles is going to be difficult for the same reasons.

And I thought he meant carborundum (SiC)