Why we need to see inside Mars

NASA's latest Mars mission, the InSight lander, will be the first robotic explorer to look deep inside the red planet. It will provide a picture of the inner geological workings and compare that to Earth, but it is also the type of activity we need to do more if we are going to find life.

Mars has been invaded by more spaceships from Earth than any other planet. That's because it is the only planet in our solar system humans have a chance of exploring. All the others are too hot, made of gas or too far away. So we've been sending a fleet of robotic probes there since the 1960s to survey the planet with orbiters mapping the surface, landers sampling the soils and rovers driving around exploring the terrain. In fact, we know the surface of Mars better than the surface of the Earth because our planet is mostly covered in water.

Throughout this survey there has always been the hope that we would find signs of life on our neighbouring world. After all, Mars is famous for once being thought of as a planet covered in canals that bring water to cities built by a civilization of little green men who invade Earth in their flying saucers. Alas, when we arrived with our invading fleet, not a single canal, city or alien was to be found. But there are signs of ancient rivers and lakes that once covered the surface billions of years ago, so there was a time when Mars was warm and wet like Earth.

Did life evolve on Mars then?

That question is still wide open because no positive signs of life have been found in the soil (yet) and no fossils have been discovered. Mars changed from a blue planet where life could have thrived, to a cold, dry, dusty, red one today that is quite hostile to life. Cold temperatures that seldom rise above freezing and a thin atmosphere lacking an ozone layer to filter ultraviolet light from the sun make the surface quite inhospitable to life today.

But there could be life inside Mars.

The InSight mission, designed to look inside Mars, will put an ear to the ground with a seismometer to listen for "Marsquakes," a temperature probe to measure the heat flowing out from the core and a way to watch the planet wobble as it spins, all to check Mars's "vital signs" and to determine whether it's soft or hard on the inside.

We know the Earth is active on the inside thanks to earthquake waves that travel right through the globe and act as x-rays to show a molten liquid core, surrounded by a hot mantle and crust, that is broken into large plates that shift around on the surface producing more earthquakes and erupting volcanoes.

Mars also has volcanoes, in fact one of them, Olympus Mons, is the largest in the solar system, standing more than two-and-a-half-times the height of Mount Everest. But no eruptions have been seen, suggesting the planet has lost some of its internal heat. That makes sense because Mars is a smaller planet.

So the question remains, how much quickly did Mars cool down and how much heat is left inside Mars today? Is there enough to provide energy for life underground? Could there be hot springs or underground streams where life could still thrive?

That is for future missions to find out.

The InSight mission is designed to provide fundamental information on how rocky planets form, evolve and cool off, which is useful to know because the Earth is also cooling down, so eventually our volcanoes will go quiet, our atmosphere will slowly leak off into space and one day we could end up looking like Mars does today.  

Who knows, perhaps if anyone or anything comes looking for life on Earth in the future, they might have to dig inside our planet to find it.