One of NASA's rovers will land on Mars later, to start searching for traces of life.
Perseverance - which is about the size of a car - launched in July, and will be bringing back around 30 samples of rocks and soil in the early 2030s.
Nicholas Booth worked at NASA's Jet Propulsion Laboratory.
He says things will have to go just right in order for this to work.
"Tonight when Perseverence comes in to land it's got this way of looking for exactly the precise spot for where it has to land.
"There is a debate whether it will all fit together in one go - Mars is a terribly hostile environment to explore."
