There's a lower success rate landing on Mars than on Venus, the moon, the earth, even

Saturn's moon Titan.

And in large part, this is because Mars's atmosphere is in the perfect goldilocks zone

of being a total headache.

On the moon (or an asteroid) you can use lightweight spacecraft made essentially out of tinfoil

because there's no air to cause drag or pressure or heat.

Essentially, you save weight not having heat shields or thick walls, but need to use rockets

to land in what's called a “powered descent.”

On earth, or Venus, or Titan, there's enough air that you can land largely unpowered, first

by slowing down with a heat shield and atmospheric drag, and then with parachutes.

So you use a lot of weight for heat shields and walls and parachutes, but don't need

big rockets or lots of fuel to land.

However, the air on Mars is literally the worst of both worlds – thick enough that

you actually have to deal with it with heat shields and walls, but thin enough that it

doesn't help you slow down much and you also need to use rockets.

Mars is simply a challenging place to land a spacecraft, which is why we've tried so

many different and crazy techniques for landing there: we've landed landers and rovers using

retrorockets, in inflatable bouncy airbags, by being lowered from a hovering sky crane

– all of which ALSO used heat shields and parachutes and rocket powered descent before

the last stage of landing.

And space agencies are testing other crazy things like giant supersonic parachutes and

inflatable innertubes around landers to increase their surface area and help them slow down

more in the thin air before landing (probably still with rockets, or sky cranes).

Yes, you heard that right – it's possible that when the first humans land on Mars, we

may do so in an inflatable donut.

Or we'll just skim at a really low angle past the tops of mountains for a really long

time to slow down enough...