MarCO, also known as the Mars Cube One, have fallen silent, according to NASA, and mission engineers are not expecting to hear from it again.

A few months after arriving at the red planet, the pair of briefcase-sized spacecraft worth $18.5 million has been unable to communicate to ground control since January. The U.S. space agency does not know why, but they have some theories.

NASA Loses Contact With WALL-E, EVE

According to a blog post published on Tuesday, Feb. 5, WALL-E and EVE (named after Pixar's Oscar-winning 2008 animated movie) are more than 1 million and almost 2 million miles past Mars respectively. They are in orbit around the sun and the farther they are, the more difficult it would be to contact them.

NASA said that the pair will not begin moving toward the sun until this summer. At that point, the space agency will again attempt to contact the mini-spacecraft duo, but the mission team is not sure whether the batteries and other parts will last until then.

The mission team fears that the pair of spacecraft has attitude-control issues that are preventing them from communicating with Earth. They also shared that the brightness sensors, which stay pointed at the Sun and recharge the batteries, could be another factor why the twins have gone silent for so long.

Mission Success

While losing the MarCO spacecraft too early would be unfortunate, NASA said that they consider the mission a success.

"This mission was always about pushing the limits of miniaturized technology and seeing just how far it could take us," stated Andy Klesh, the mission's chief engineer at the Jet Propulsion Lab. "We've put a stake in the ground. Future CubeSats might go even farther."

WALL-E and EVE are the first interplanetary mission to use CubeSats, a class of mini-spacecraft. They were launched alongside the stationary lander InSight on May 5, 2018. They arrived at Mars in November.

The duo participated during the entry and touchdown of InSight on the surface of the Red Planet by relaying information to Earth.

According to NASA, the goal of the MarCO mission is to demonstrate the CubeSats' capabilities for interplanetary exploration. The success of the mission could lead to "many other applications" to study the Solar System.

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