Two tiny satellites that just launched on a historic mission to Mars have phoned home for the first time.

The Mars Cube One duo, officially known as MarCO-A and MarCO-B, lifted off early Saturday morning (May 5), rising into skies above California's Vandenberg Air Force Base along with NASA's InSight Mars lander. They are the first cubesats ever launched to another planet.

Radio signals from the cubesats, each of which is about the size of a briefcase, were received on Saturday afternoon, NASA officials said. [Launch Photos: See NASA's InSight Soar Toward Mars]

"Both MarCO-A and B say 'Polo!'" MarCO mission chief engineer Andy Klesh, of NASA's Jet Propulsion Laboratory in Pasadena, California, said in a statement. "It's a sign that the little sats are alive and well."

An artist's illustration of the twin Mars Cube One (MarCO) spacecraft deep space. The MarCOs are the first cubesats attempting to fly to another planet. (Image credit: NASA/JPL-Caltech )

If all goes according to plan, MarCO-A and MarCO-B will fly by Mars on Nov. 26, the same day that InSight is scheduled to land. In fact, the cubesats will attempt to beam data to Earth from InSight during the lander's harrowing "7 minutes of terror" entry, descent and landing sequence. (The duo's contribution here isn't crucial; NASA's Mars Reconnaissance Orbiter will also perform this communications-relay work.)

But the main purpose of the $18.5 million MarCO mission is to show that cubesats, which to date have been restricted to Earth orbit, can explore interplanetary space. MarCO-A and MarCO-B are demonstrating a number of cubesat technologies during their nearly 7-month cruise to Mars, including a folding high-gain antenna and a cold-gas propulsion system.

This gas is compressed R236FA, which is commonly found in fire extinguishers. For this reason, the mission team have dubbed the cubesats Wall-E and Eva, two robots from the 2008 Pixar film "Wall-E." In the movie, the trash-compacting robot Wall-E flies around space using a fire extinguisher for propulsion.

"We're nervous but excited," MarCO project manager Joel Krajewski, also of JPL, said in the same statement. "A lot of work went into designing and testing these components so that they could survive the trip to Mars and relay data during InSight's landing. But our broader goal is to learn more about how to adapt cubesat technologies for future deep-space missions."

The MarCO mission will come to an end shortly after the cubesats' planned Mars flyby, mission scientists have said.

The main purpose of Saturday's launch, which involved a United Launch Alliance Atlas V rocket, was to get InSight on its way to Mars. The lander will probe the interior structure and dynamics of Mars, using a supersensitive seismometer and a heat probe, which will hammer itself up to 16 feet (4.9 meters) beneath the planet's surface.

Mission scientists will also note tiny wobbles in Mars' axis of rotation by tracking InSight's location precisely. This information will reveal insights about the planet's core, NASA officials have said.

JPL built the MarCO spacecraft. InSight — which is short for Interior Exploration using Seismic Investigations, Geodesy and Heat Transport — was built by aerospace company Lockheed Martin.

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