NASA’s record-setting astronaut Scott Kelly is getting his gold watch. The veteran who spent a year on the International Space Station retired from the agency today after two decades.

But he is not free just yet. Tests on Kelly will continue, with the aim of expanding knowledge of how the human body fares in space over the long term to enable crewed missions to Mars. Initial assessment has concluded that a year is not the limit. That’s great news for NASA – and the private companies eager to send people to Mars in the coming decades.

For some, though, Kelly’s achievements are a fillip for much bigger ambitions – colonising the Red Planet as a bolthole for humanity. Should we even think about doing this?

The idea that we can flee messy, complicated Earth and start again somewhere else has long been popular. If we had colonies elsewhere, the argument goes, we could if necessary evacuate a dying Earth to make a fresh start. On this view, becoming a multi-planet species is a rational response to the threat posed by the environmental crisis of climate change.

This is a dangerous fantasy. It is a fantasy because nowhere in our solar system is anywhere near so hospitable as the harshest places on Earth. The top of Everest, the driest deserts and the South Pole are all far more conducive to human settlement than anywhere in space.

The challenges of moving people – even a handful, let alone a whole civilisation – to Mars, our nearest neighbour, and then establishing a viable habitat would be enormous. To turn a barren, freezing, airless rock millions of miles away into a place we could call home would take vastly more resources than tackling problems here.

Absolutely. To read more, click here.