Mars 2020's turret weighs that much, because it's equipped with HD cameras and a rich collection of sensors and science instruments, including a percussive drill and coring mechanism. While Martian gravity is only about 38 percent of our planet's, the ground team still made sure the arm is sturdy and strong enough to be able do its task, designing it with five electrical motors and five joints.

The rover's arm and turret have to be in sync, because they're working together on Mars. They'll be in charge of scraping, analyzing and collecting samples from interesting geological structures. Any rock or soil sample they collect will be returned to Earth by a future mission.

Dave Levine, integration engineer for Mars 2020, said:

"This was our first opportunity to watch the arm and turret move in concert with each other, making sure that everything worked as advertised -- nothing blocking or otherwise hindering smooth operation of the system. Standing there, watching the arm and turret go through their motions, you can't help but marvel that the rover will be in space in less than a year from now and performing these exact movements on Mars in less than two."

If everything goes according to plan, the rover will leave for Mars in July 2020 and will touch down in February 2021. You can watch the rover's arm test below: