Since the Martian poles are water ice caps, belong to the most likely locations on Mars to host life, and the north pole being the most likely place for a crewed mission, it seems reasonable that one should send a lander to one of the polar caps. However there were never missions to the polar caps. Closest were the Phoenix lander which landed close to but not on the north polar ice cap, and two failed probes that crashed near the south pole. What's the reason there are no probes being sent to the polar caps? Is it due to orbital issues? Is one afraid that the probes might sink in Martian snow or due to other possible weather conditions there? As per Wikipedia there's currently no planned polar lander.
$\begingroup$ Well, how many tries do you take, before giving up with something? Also there are more interesting places and less dangerous for rovers than the polar caps. $\endgroup$– AtmosphericPrisonEscapeJun 4, 2020 at 15:35
$\begingroup$ @AtmosphericPrisonEscape I'm talking of a stationary lander rather than a rover. Rovers would obviously have hard time driving through the snow. Before the 2024 crewed SpaceX mission one should probably send a probe to the landing site first. And that might be the North Pole. All Martian landers and rovers landed on red Martian soil, no probe on the snow/ice of the poles ever. $\endgroup$– LoveForChristJun 4, 2020 at 15:43
The polar ice caps of Mars are more challenging for a number of reasons. Mars has a similar tilt to Earth, which means that the polar regions have some of the same problems. The two main problems are extreme cold and very long nights over the winters. These together mean that there is a limited time when such missions could take place.
For the last 20 years, most of the US landers have been rovers, with the exception of two missions. One of these explored the northern areas, and the other explored the ground beneath. Sending a rover to the poles is pretty much pointless, it would only survive a few months, defeating the point of a rover.
No crew mission will be sent to the poles, at least for the early missions. The maximum latitude for a human settlement is around 40 degrees before the Martian winters become a huge challenge. The most likely sites are those with ice just below the surface, as the Phoenix mission had.
Bottom line, the poles force a short term mission, and there isn't a compelling enough reason to visit them at this time.
2$\begingroup$ It is said that the poles are more likely to be the first crew's landing destinations. I think the north pole is most likely because its ice cap is larger, the air pressure there is within the triple point of water (meaning the ice can be melt into actual liquid water) and the gravity, like on Earth, is strongest on the poles (0.381g on the Martian poles). And as you say, the day is very long there, so astronauts don't have to bother over the longer Mars day. What do you think will/might be SpaceX's crewed landing location? $\endgroup$ Jun 4, 2020 at 16:26
1$\begingroup$ The poles are likely to be a lunar landing spot, but not on Mars. The most likely spot for SpaceX's first landing is Arcadia Planitia, futurism.com/spacex-starship-mars-landing-site $\endgroup$– PearsonArtPhoto ♦Jun 4, 2020 at 17:11
$\begingroup$ Very interesting, in the far north-west of the world map. $\endgroup$ Jun 4, 2020 at 18:00
Mars special regions as defined by The Committee on Space Research (COSPAR) means that planetary protection is the main reason that the US and China have/will avoid the polar regions. If forward contamination occurred, it could wipe out any indigenous organism under the mixed ice surfaces. How we proceed in the investigation of these locations without cross contamination is not yet known, but the interim protocol is defined as being If a hard landing risks biological contamination of a special region, then the whole lander system must be sterilized to COSPAR category IVc.
NB I think it will eventually be imperative to visit the poles, but at present the risks seem too great to take. Also the curious phenomenon of seasonal Martian geysers coming from large spiderlike features, apparently spewing sediment that give rise to dark dune spots, have been proposed by some researchers as a sign of biological activity. https://en.wikipedia.org/wiki/Geysers_on_Mars#Hypothetical_biological_origin
For some good pictures of these dunes see, https://www.npr.org/sections/krulwich/2012/10/02/162147810/are-those-spidery-black-things-on-mars-dangerous-yup?t=1619264032435
See NASA planetary protection web page. https://sma.nasa.gov/sma-disciplines/planetary-protection/
Also see COSPAR policy regarding space probes and landers. https://cosparhq.cnes.fr/assets/uploads/2019/12/PPPolicyDecember-2017.pdf
1$\begingroup$ Hi uhoh Thanks for the suggestion. I've added some links, although not exhaustive, they should allow people to start investigating the dangers of not only forward contamination but more importantly backward contamination (sample return missions) that could have drastic implications for human health. $\endgroup$ Apr 24, 2021 at 11:50
1$\begingroup$ This is excellent, thanks! It's great when a new user really digs in and adds a well-sourced answer to an older question. Fyi re sample return: What precautions are planned to prevent samples returned from Mars crashing and releasing organisms on Earth? $\endgroup$– uhohApr 24, 2021 at 11:57
The poles are very cold, so thermal protection requirements are greater.
The poles reduce the potential utility of solar power, thus effectively forcing the lander to use non-solar power, which is heavier and more expensive.
But most of all: The poles are surfaced in various ices.
Ices that accumulate, and sublimate away, and accumulate again. The surface texture, and structure, and loadbearing ability are all unknown and virtually unknowable without extensive testing.
There is a similar climate on Earth, where ice falls as snow, compacts, and then sublimates away without ever melting to liquid water. The Penitentes, in the high Andes mountains of Chile.
Would you like to design the lander, and program the software, to allow for safe landing on a surface like this?
$\begingroup$ It's also worth pointing out that CO2 ice accumulation likely tore the solar panels off the Phoenix lander during its first winter, so even if you can land there you haven't solved the problem. $\endgroup$ Nov 13, 2021 at 18:15
$\begingroup$ @ChristopherJamesHuff the fix for that is to not use solar (which sucks at the poles, in any case), but rather a RTG. Its excess heat will help sublimate the co2 ices from your lander. $\endgroup$ Nov 13, 2021 at 19:47
$\begingroup$ The materials for RTGs are expensive and in very limited supply. What just keeps a lander alive over a polar winter could greatly increase the mobility and instrumentation of a rover at more temperate latitudes, or power a flagship class outer system probe. $\endgroup$ Nov 14, 2021 at 3:21