A sun-observing spacecraft discovers its 3,000th comet.
On September 13, 2015, the Solar and Heliospheric Observatory—a joint project of the European Space Agency and NASA—discovered its 3,000th comet, cementing its standing as the greatest comet finder of all time. Prior to the 1995 launch of the observatory, commonly known as SOHO, only a dozen or so comets had ever even been discovered from space, while some 900 had been discovered from the ground. Comets are essentially a clump of frozen gases mixed with dust. They circle the sun on various trajectories and are often pristine relics that can hold clues about the very formation of our solar system. SOHO's comet prowess, however, was unplanned, as its mission is to observe the sun and interplanetary space. Scientists say in its two decades in orbit it has opened up a new era of solar observations, dramatically extending our understanding of the star we live with. Watch the video to learn more.