Original: Huygens probe The Huygens probe , supplied by the European Space Agency ( ESA ) and named after the 17th century Dutch astronomer Christiaan Huygens , scrutinized the clouds , atmosphere , and surface of Saturn 's moon Titan in its descent on January 15 , 2005 .
Simplified: The spacecraft has two main parts : the NASA Cassini orbiter , named after the Italian-French astronomer Giovanni Domenico Cassini , and the ESA Huygens probe , named after the Dutch astronomer , mathematician , and physicist Christiaan Huygens .