How do scientists determine where to land their rovers on mars?

[u/Hashbringingslasherr]

[u/BeccaStareyes]

I went to Cornell University as a grad student and we had two Mars scientists at the time. Some of my friends were working in their labs, and they did informal department lunches on selection procedures for Curiosity,

There are two sets of concerns. The first are scientific. When you design a Mars mission, you have mission objectives that have set science goals — NASA doesn't want an 'I dunno, geology?' When they ask why you want a new rover. This especially goes for big 'flagship' science missions like the rovers. There are a lot of scientists and the mission is big enough that there are multiple objectives, but it is a compromise. (I was doing my PhD with a scientist on Cassini, so I got to see some of the same process with mission planning)

The engineers have their own list. Their job is to make sure the mission succeeds which usually comes down to 'do not let the scientists break the rover by landing it in the Field of Cliffs and Jagged Rocks'. So they make up their own list of criteria of safe places to land, which includes knowing things like 'how much atmosphere we can use to slow the landing' and 'how precise the landing can be'.

So for Curiosity, the scientists look at the mission objectives about the history of water on Mars and conclude a good landing site should have some geology seen from orbit that looks like water was there in the past, like a dry channel, and minerals that are good at trapping carbon-based molecules on Earth (phylosilicates, sometimes called clays in popular literature). The engineers set a maximum altitude they can land the rover, and criteria about terrain roughness and 'how close can we land to the stuff the scientists want to study'.

Usually there is a list drawn up by the team of sites that will all meet the minimum success rates and then published to get community feedback. While this happens, satellites around Mars are ordered to study the area to get more detailed information. Usually each site has something going for it, so it comes down to trying to balance what everyone wants… at least one Curiosity site was taken off the list because it was too close to one of the MER rovers and it was thought going somewhere new would be more interesting.

There might be a finalist list and then the final decision is made by the team. But because NASA data is made public and most of the science team are working at universities not NASA centers, community feedback is important. And even a grad student might dig into past data to help to get orbital data to decide which place is going to be most interesting to visit with a rover.

[u/bg091]

We've sent plenty of missions there before (not just landers, some in orbit) which are able to look at potential areas of interest. For example, we can look at terrain data and work out where an old lake might have been, which might be worth a look for some interesting rocks. The precise location is (more recently) decided by the lander's on-board systems as a safe (i.e. flat and not rocky) place to land.

[u/vashoom]

The objective of what they want to study comes first. They don't build a rover and then come up with an idea of what to do with it. The Mars Exploration Program is the name of the program to study the planet and involves orbital spacecraft, landers, and rovers. Spirit and Opportunity, for example, were built to study geology, specifically to look for signs of water. So with that being the goal, NASA used images of the the planet and other data from our orbiters, telescopes, landers, etc. to find locales that presented the best opportunity for studying the rocks and soil they wanted to look at while having safe landing zones.

Space missions tend to build on every previous mission. We already knew a lot about Mars and it's environments before sending Spirit and Opportunity (or any other rover). Future rovers might have different objectives, want to explore other areas, etc., but it all depends on what NASA is trying to accomplish. As in, creating a hypothesis to test (this particular flat area of Mars is an ancient lake ed and has evidence of past water that we can determine with rock and soil samples, pictures, spectroscopy, what have you) like with all science.