Nasa is sending a robotic geologist to Mars to dig deeper than ever before to take the planet's temperature.

The Mars InSight spacecraft, set to launch this weekend, will also take the planet's pulse by making the first measurements of "marsquakes", and to check its reflexes, scientists will track the wobbly rotation of Mars on its axis to better understand the size and make-up of its core.

The lander's instruments will allow scientists "to stare down deep into the planet", said the mission's chief scientist, Bruce Banerdt of Nasa's Jet Propulsion Laboratory.

"Beauty's not just skin deep here," he said.

The billion-dollar (£734 million) US-European mission is the first dedicated to studying the innards of Mars.

Scientists hope to better understand how the red planet - and any rocky planet, including our own - formed 4.5 billion years ago.

Mars is smaller and geologically less active than Earth, where plate tectonics and other processes have obscured our planet's original make-up. As a result, Mars has retained the "fingerprints" of early evolution, said Mr Banerdt.

In another first for the mission, a pair of briefcase-sized satellites will launch aboard InSight, break free after liftoff, then follow the spacecraft for six months all the way to Mars.

They will not stop at Mars, just fly past. The point is to test the two CubeSats as a potential communication link with InSight as it descends to the red planet on November 26.

These Mars-bound cubes are nicknamed Wall-E and Eve after the animated movie characters, because they are equipped with the same type of propulsion used in fire extinguishers to expel foam.

In the 2008 movie, Wall-E used a fire extinguisher to propel through space.

InSight is scheduled to rocket away from central California's Vandenberg Air Force Base early on Saturday, in Nasa's first interplanetary mission launched from somewhere other than Florida's Cape Canaveral.