[mabbo]

Simple answer from a space nerd: Rovers are small, light, and have very little energy. So what we can't do is anything that requires a large or heavy device or anything that requires significant energy. They break/fail. They take forever to make happen.

Want to burn 20kg of soil to see if there's any trace of specific elements? You'll need a furnace. Those are both heavy and high-energy. You could do a smaller scale test on a rover of 2g perhaps, but what if the traces are very, very small? Plus, whatever analysis tools you would use now have to also be extremely small and light, which means less capabilities.

Also, rovers have limited size: we can only do a small number of tests per rover because the rover's utility belt of tools is only so large. If your experiment is really easy to do but it's not a high enough priority, it won't happen.

Lastly, rovers die. You might spend 5 years building a tool, 2 years sending it on the next rover to Mars, only to have it crash or die before it's time to run your experiment.

But if we sent 300kg of soil back from Mars, we could do every test we can think of, carefully, with the best tools humanity can make and as much energy as we need.

Edit: +1 to what Something1234 said too! You can't clean out apparatuses easily after an experiment!

[valuearb]

These are all reasons why sending humans is so important. They will explore more of Mars in a week than rivers have in 50 years. They will arrive with a testing lab and do all sorts of tests immediately.

If Starship meets its performance targets, it’s first missions will bring hundreds of scientists to a Mars, with thousands of tons of equipment and supplies. In-orbit and in-situ refueling are game changing technologies that will literally reduce the cost of deep space manned missions by a thousandfold.

[freeopinion]

> Anything that requires significant energy

So instead of sending a rover with 4x or 10x energy, the answer is a mission that requires enough energy to launch the samples all the way back to Earth? This makes me smile.

I do agree though. We can expend 1000x the energy of the return trip once the samples are back on earth. And we also have the luxury of unlimited time to invent new tests and new tech to apply to whatever is left of the samples.

[jerf]

"So instead of sending a rover with 4x or 10x energy"

The rocket equation is a real jerk. You're likely thinking "that sounds linearly harder" when you should be thinking it's exponentially harder.

[marcosdumay]

At that point, adding weight to the rover or to the return system is an equivalent cost.

[jerf]

No, rover is easier; return system has to fly all of its mass back to Earth, rover never leaves Mars.

In which case you might be asking what the advantage of a return system is in the first place, the answer being for much the same reason that we have "stages" of rockets. The return system gets a fresh exponential curve to work with. If you tried to ship both at once it would be a nightmare. Plus there are all the advantages of shipping things back, regardless of what the rocket equation says. Science via a rover is great but it just can't match numerous full laboratories with humans in them.

The part that disappoints me a bit is that I still don't see us launching fuel into space for space refueling very often. Rocket equation bites no matter what you do, but launching a Falcon fuel of nothing but fuel (to the extent possible) shrinks the solar system a lot. It's still pretty big after that, but it's a different place, even with conventional chemical rockets. I hope we'll see it soon. I'm not sure it'll be quite as simple as "SpaceX will have a Mars Starship there before the mission can get there", but there is a real prospect of making it so space missions takes weeks instead of years if we can get space refueling figured out. A lot of other things come into reach as well, like satellite reclamation.

[jessriedel]

I think the GP wanted to know what the actual tests an analyses are.