For the first time, two CubeSats have gone interplanetary

The first CubeSats launched in 2003, and in less than a decade, more than 100 had reached orbit. The aerospace industry has debated whether the 2kg to 15kg microsatellites are a fad, a toy, or a disruptive technology that will change they way we ultimately observe and study Earth and the rest of the Solar System.
However, what is now beyond doubt is that the first CubeSats have gone interplanetary.
On Saturday, after the launch of the InSight probe to Mars, NASA received signals from the Mars Cube One, or MarCO-A and -B satellites. The signals indicated that the twin spacecraft had retained enough charge in their batteries to deploy their own solar arrays, stabilize themselves, pivot toward the Sun, and turn on their radios.
The twin MarCO satellites are not critical to the success of the InSight lander, they instead have their own separate mission to test the feasibility of CubeSats in deep space. They will follow InSight on its interplanetary trajectory to Mars and attempt to track the larger spacecraft’s descent and landing on Mars in November.

"We’re nervous but excited," said Joel Krajewski of NASA’s Jet Propulsion Laboratory and MarCO’s project manager. "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."
Scientists are eager to see how well the CubeSats work because they have the potential to revolutionize how we study the Solar System. Larger satellites, weighing hundreds of kilograms to several tons, are more complex and cost exponentially more to build than CubeSats. With their much greater mass, they also require larger, more powerful rockets to reach their intended targets—and they also cost more.
If CubeSats can perform significant amounts of science, they could be launched in swarms to planets in the outer Solar System to gather intelligence. Moreover, if one or two failed out of that swarm, they would be relatively inexpensive to replace.
By comparison, NASA is developing a six-ton "Clipper" satellite that will launch to Jupiter’s Moon of Europa as early as 2022. This mission will cost as much as $3 billion and includes eight different science instruments. If the MarCo satellites work at Mars, scientists will be able to begin to consider how much of that science could be done with smaller, much cheaper options.