On Sept. 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. The 3,000th comet, highlighted in this image, was originally spotted in the data by Worachate Boonplod, of Samut Songkhram, Thailand.
SOHO’s mission is to observe the sun and interplanetary space, above Earth’s atmosphere that blocks so much of the sun’s radiation. From there, SOHO watches the solar disk itself and its surrounding environment, tracking the constant outward flow of particles known as the solar wind, as well as giant explosions of escaping gas called coronal mass ejections, or CMEs. In its two decades in orbit, SOHO has opened up a new era of solar observations, dramatically extending our understanding of the star we live with.
The telescope’s comet prowess, however, was unplanned and has turned out to be an unexpected benefit. With its clear view of the sun’s surroundings, SOHO can easily spot a special kind of comet called a sungrazer, because of its close approach to the sun.
Image Credit: SOHO/ESA/NASA/NRL