SOHO
A solar observatory that has become the greatest comet discoverer in history.
Key facts
- Agency
- European Space Agency (ESA) and NASA
- Type of mission
- Solar observatory
- Target
- The Sun (and, by chance, comets)
- Launched
- 2 December 1995
- Status
- Operating
The Solar and Heliospheric Observatory, SOHO, was launched to study the Sun from the L1 point, about 1.5 million kilometres towards the Sun. It was designed to work for two years and is still operating three decades later.
Accidental comet hunter
One of its instruments, a coronagraph, blocks the bright disc of the Sun with a small disc, like holding a thumb over the Sun, so the faint outer atmosphere around it can be seen. Comets that pass very close to the Sun show up in these images as small moving smudges.
SOHO's pictures are published online within hours, and amateur astronomers around the world look through them for comets. Volunteers have found most of the discoveries. In March 2024 the total passed 5,000 comets, making SOHO by far the most successful comet finder ever.
Sungrazers
Most of these comets belong to the Kreutz family, fragments of one giant comet that broke apart long ago. They pass within a few hundred thousand kilometres of the Sun's surface, and most are small and evaporate completely. Watching them shows how comets crumble and how much dust they release, the same process that fills space with meteoroid streams.
Why it matters to meteors
Some smaller families of comets found by SOHO are linked to each other and to meteor showers, which helps trace how one comet's break-up spreads debris into many paths over thousands of years.
Key dates
| Date | What happened |
|---|---|
| 2 December 1995 | SOHO launched on an Atlas II rocket. |
| June 1998 | Contact was lost for several months; the spacecraft was recovered. |
| March 2024 | SOHO's 5,000th comet discovery was confirmed. |
See where this mission fits among all the others in the mission timeline.
Did you know?
More than half of all comets with known orbits were discovered in SOHO images.
Many SOHO comets were found by students and other volunteers looking at the pictures at home.
Related pages
Comets connected with this mission: Comet Machholz, Comet NEOWISE, Comet Tsuchinshan–ATLAS, Comet 3I/ATLAS, Ikeya–Seki and the Kreutz sungrazers, Comet McNaught, Comet ISON. See all comets.