No crew, no return trip. A space probe is an unmanned spacecraft built to explore distant targets, send back data, and often continue operating far beyond its designed lifetime.

Probes range from small flyby spacecraft to complex orbiters with dozens of instruments. They visit planets, moons, asteroids, and comets, and a few have left the solar system entirely. Communication delays stretch from minutes to hours, which means probes must handle problems on their own.

Notable probes

• Voyager 1 and 2, launched in 1977
• New Horizons, which flew past Pluto
• Rosetta, which landed on a comet
• Parker Solar Probe, studying the Sun's corona

Power is a constant constraint. Solar panels work near the Sun but fade at distance. Radioisotope thermoelectric generators provide decades of electricity for missions to the outer planets.