That’s the question a new mission from NASA is hoping to answer when it lands on the red planet later today (Monday).

While other Mars probes have been looking for water and signs of life on the red planet, the robotic lander InSight is very different. It is looking find out how warm and geologically-active the planet is.

“The key question is to explore the interior of another Earth-like planet other than the Earth — or another rocky planet — in order to be able to compare that planet with the Earth. It’s a comparison that we are aiming at,” said Tilman Spohn, director of the Institute of Planetary Research at German Aerospace Centre.

That comparison is what is fascinating scientists.

Lu Pan, a planetary geologist at the University of Lyon, said we really don’t know much about what is beneath the surface.

“We do you have some guesses from our understanding of the Earth interior. We think Mars, as a terrestrial planet, was formed more-or-less the same way as the Earth. So we think it has a core, mantle and a crust. We know that Earth’s outer-liquid core is the reason we have a magnetic field and because we don’t observe these magnetic fields on Mars, we think it probably doesn’t have a liquid outer core.”