HMM: Could humans be too heavy to land on Mars?

Landing a relatively light rover like the Perseverance rover is one thing, but landing craft carrying the crew of astronauts – and much of the provisions and equipment needed to keep them alive on Mars for many months – would be heavy.

And that means it needs a powerful rocket motor to touch down safely.

For the Apollo moonlandings, the descent motor mostly blasted dust horizontally away across the surface, and no visible crater was gouged out by the rocket.

This is because over billions of years, the lunar surface has become compacted, and the vacuum conditions allow the rocket exhaust to disperse.

However, the situation is very different on Mars. Its surface material is much looser, and the atmospheric pressure serves to keep the engine plume focused on one small spot, allowing it to blast much deeper.

This means, Metzger says, that the descent engine of a large Martian lander would blow loose rocks across the surface at high speeds up to a kilometre away – presenting a risk to the crew habitats or other equipment that the mission needs to touch down near.

This is where reusable spacecraft will become even more valuable, creating a more affordable way to test landing larger, heavier spacecraft.