InSight engineers sent up the commands to the spacecraft on Tuesday, and the seismometer was gently placed onto the ground by the arm in front of the lander on Wednesday, according to the team.

"Seismometer deployment is as important as landing InSight on Mars," said InSight Principal Investigator Bruce Banerdt.

"The seismometer is the highest-priority instrument on InSight. We need it in order to complete about three-quarters of our science objectives," he said.

The seismometer allows scientists to peer into the Martian interior by studying ground motion, also known as marsquakes. By analyzing how seismic waves pass through the layers of the planet, scientists can deduce the depth and composition of these layers.

In the coming days, the InSight team will work on leveling the seismometer. The first seismometer science data will flow back to Earth after the seismometer is in the right position, said the team.

The heat probe is scheduled to be placed onto the Martian surface by late January, on the east side of the lander's work space, according to the team.

InSight landed safely on Mars on Nov 26, kicking off a two-year mission to explore the deep interior of the Red Planet.