Phobos

A small, heavily cratered moon that orbits so close to Mars that it will eventually break apart or crash into the planet due to tidal forces.

A long-duration orbiter launched in 2003 that has spent over 19 years studying Mars's atmosphere, surface, and moons while also serving as a vital communications relay for surface missions.

The first spacecraft to visit Mercury conducted three flybys between 1974-1975, capturing over 2,800 photos and revealing previously unknown features including the planet's scarred, cratered surface and weak magnetic field.