GROVER, which stands for both Greenland Rover and Goddard Remotely Operated Vehicle for Exploration and Research, is an autonomous, solar-operated robot that carries a ground-penetrating radar to examine the layers of Greenland's ice sheet. Its findings will help scientists understand how the massive ice sheet gains and loses ice.

The solar-electric propulsion thruster pictured above ditches burning chemical fuel for xenon ions accelerated by an electric field generated using solar panels. This provides a steady stream of ions that can slowly nudge a spacecraft to high speeds with minimal fuel, making it a good choice for long-range missions.