What is the surface of a comet like? That's one of the main questions that motivated Philae's mission to the surface of comet 67P/Churyumov-Gerasimenko. We now know the comet has a rigid crust about 10 to 50 centimeters thick, below which the comet is much more fluffy.
MarCO or Mars Cube One is an experimental mission that is sending two tiny spacecraft along with InSight to Mars. If successful, they will relay real-time telemetry from InSight to Earth during the landing.