This week, a “robotic explorer” left Earth on its way to Mars.

It should get there next September. Mars is more than 700 million kilometres away.

The explorer is going to Mars to try to solve some of the planet’s mysteries.

For instance, why is Mars now a cold, dry planet when it started out warm and wet?

The Associated Press reports that “the early Martian atmosphere was thick enough to hold water and possibly support microbial life.”

Scientists at NASA want to know what happened to change that.