SOHO discovers thousands of comets
Since beginning operations in 1996, the ESA/NASA SOHO spacecraft has spent its time staring non-stop at the enormous, sizzling Sun. One of its instruments, called LASCO, is used to observe the Sun’s outer atmosphere (the corona). However, the sharp-eyed LASCO camera has also shown a wonderful ability to find the small chunks of dirty ice that we call comets. By September 2010, SOHO had found over 1,900 comets, more than all the other discoverers of comets put together. Not bad for a spacecraft that was designed to study our nearest star.
Comets are chunks of ice and dust - ‘leftovers’ from the formation of the planets 4.5 billion years ago. All comets travel around the Sun, and many of them are sungrazers, passing very close to its scorching surface. Some of the comets swinging around the Sun show up as tiny dots or streaks in SOHO’s images – though not all of them survive the fiery passage. Many of them are vaporised or plunge into the star.
Roughly 85% of SOHO’s discoveries are pieces of a once-great comet that split apart in a death plunge around the Sun, probably many centuries ago.
When it comes to comet catching, SOHO has one big advantage over everybody else: its location between the Sun and Earth. By blocking out the Sun’s glare, LASCO can see regions that would otherwise only be visible during a total solar eclipse.
Of course, LASCO itself does not make the detections. That task falls to a group of highly-skilled volunteers who scan the images as soon as they are downloaded. After SOHO transmits them to Earth, the pictures can be on the Internet and ready for analysis just 15 minutes after they are taken.