NASA's nervous moment - the Mars mission faces its biggest test

Video report by ITV News Correspondent Robert Moore

Cross your fingers at about 8.48pm UK-time today and keep them crossed for the following seven minutes.

There's a spacecraft and a rover about 200 million kilometres (124m/miles) away from Earth that needs all the help it can get at that time.

At that moment today, NASA's Perseverance rover will be beginning the sequence of moves known as the "seven minutes of terror".

The rocket for the Mars mission left Earth seven months ago. Credit: NASA

That's the period of time that the rover will be entering the ultra-thin Martian atmosphere and attempting a series of high-stakes manoeuvres that has to slow the craft down from 13,000mph to 1mph, allowing it to touch down gently on the surface of the red planet. If anything goes even slightly wrong, it can all end in disaster.

Assistant Professor Melissa Rice, a planetary scientist, who is part of this Mars mission, has described to ITV News the huge challenges.

Perseverance is the size of a large car. It's the most sophisticated rover ever to explore the planet. Most exciting, it's being landed in the Jezero crater, an area near Mars' equator that was an ancient river delta.

That gives the rover a clear science mission: To find signs of ancient microbial life and to prove - if at all possible - that life has existed beyond Earth.

It is unlikely that Perseverance can do that forensic science by itself. So - as you might expect from the smart folk at NASA - there's a back-up plan.

The most interesting and promising rocks that are found by the rover are going to be collected and carefully stored.

Then a future mission - perhaps in 2026 - will land on the surface of Mars and retrieve those samples. A third mission will bring them back to Earth for a close examination in a laboratory. NASA is hopeful that a rock from Mars could be in the hands of scientists by 2031 or so.

This a long-term mission with thrilling scientific goals. And it reaches the most perilous stage this afternoon.

There is one other exciting experiment aboard the rover - a mini-helicopter, known as Ingenuity.

This will attempt the first-ever controlled flight of an aircraft on the surface of another planet. It's so experimental that NASA is comparing this part of the mission to the Wright Brothers taking to the air in 1903 in North Carolina and becoming the first true aviators.

So if you enjoy space or science or have ever asked the oldest question of all - has life ever existed out there in the universe? - then wish Perseverance a safe landing.

It's the robot that will provide some tantalising clues. Perhaps even, if we are really fortunate, some answers.