In September 2019, NASA started the second half of an epic game of Marco Polo ; early this month the agency declared it over for good.

On Feb. 2, NASA formally ended the Mars Cube One mission. MarCO, as it was known, consisted of two tiny cubesats that hitchhiked along with the agency's InSight lander that reached the Red Planet in November 2018. The twin MarCO satellites were the first cubesats to leave Earth orbit, and they aced their goal of reporting on InSight's perilous landing to scientists on Earth.

"WALL-E and EVE performed just as we expected them to," MarCO chief engineer Andy Klesh, of NASA's Jet Propulsion Laboratory in California, said in a statement at the time , referring to the cubesats by their nicknames taken from the 2008 film "WALL-E." "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."

Related: How the tiny exoplanet-hunting ASTERIA satellite showed scientists what cubesats can do

As NASA expected, the MarCO satellites fell silent in January 2019 because of how far their orbits carried them from the sun. There was a chance that the agency would be able to reestablish communications with the plucky twins in the second half of 2019. But attempts to do so, which began in September 2019, were unsuccessful, according to a new NASA statement .

NASA will be releasing data from the twin cubesats over the next year, the agency added. That data should help future interplanetary cubesat designers to tap into MarCO's success. Among the earliest of those successors will be launching on NASA's first Artemis mission , an uncrewed flight orbiting the moon.

One such cubesat, dubbed Lunar Flashlight , is designed to contribute to lunar science by identifying ice in craters at the moon's south pole that never receive sunlight. That's the same region where the culminating Artemis mission will land astronauts in 2024, according to NASA plans.