CNN  — 

When NASA’s InSight lander was on its seven-month trip to Mars, it wasn’t alone. Two suitcase-size spacecraft, called MarCO, followed InSight on its journey. They were the first cube satellites to fly into deep space. And now, they’ve fallen silent.

During InSight’s entry, descent and landing on November 26, the MarCO satellites received and transmitted communication from the lander to let NASA know that InSight was safely on the surface of the Red Planet. They were nicknamed EVE and WALL-E, for the robots from the 2008 Pixar film.

They were the great experiment accompanying the InSight mission, and their success was measured by survival, according to NASA. The fact that the tiny satellites made it to Mars, flying behind InSight through space, excited engineers.

But the experiment has come to an end.

After InSight was safely on Mars, MarCO kept on flying. At the time, the MarCO team collected data from each satellite to determine how much fuel they had left and took a deeper look at how they performed.

Engineer Joel Steinkraus uses sunlight to test the solar arrays on one of the MarCO spacecraft.

“WALL-E and EVE performed just as we expected them to,” MarCO chief engineer Andy Klesh at NASA’s Jet Propulsion Laboratory said at the time. “They were an excellent test of how CubeSats can serve as ‘tag-alongs’ on future missions, giving engineers up-to-the-minute feedback during a landing.”

Engineers last heard from WALL-E on December 29 and EVE on January 4, the agency said. They estimate that EVE is now 2 million miles past Mars, and WALL-E is more than 1 million miles past Mars.