Which space agency built the Huygens probe?

The European Space Agency built the Huygens probe. NASA launched it as part of the joint Cassini–Huygens mission, while ESA designed and operated the lander that descended through Titan’s atmosphere.

Huygens separated from NASA’s Cassini orbiter on December 25, 2004, then entered Titan’s atmosphere and landed on January 14, 2005. It became the first spacecraft to land on Titan and the first successful landing in the outer Solar System. The probe transmitted atmospheric and surface measurements to Cassini, which relayed them to Earth.

The wording can cause confusion because Huygens was an international project. NASA supplied and operated Cassini, and Italy’s space agency contributed major hardware, including the high-gain antenna and radar system. However, the probe itself was built and operated under ESA leadership. It was named for Dutch astronomer Christiaan Huygens, who discovered Titan in 1655.