For three decades, a spacecraft has been relentlessly staring at the sun, and the images are absolutely breathtaking! On December 2, 1995, the Solar and Heliospheric Observatory (SOHO), a joint project between NASA and the European Space Agency, embarked on a mission to unravel the mysteries of our nearest star. Positioned at the sun-Earth L1 Lagrange point, roughly 932,000 miles (or 1.5 million km) closer to the sun than Earth, SOHO enjoys an almost uninterrupted view. This vantage point allows it to capture stunning composite images, offering a unique perspective on the sun's activity over time. But what exactly is SOHO, and why is it so important? Let's dive in!
What is SOHO, and what does it do?
Equipped with 12 different instruments, SOHO was designed to study the sun's internal structure and dynamic processes. It does this by observing the sound waves that ripple through the sun's interior. SOHO also focuses on the sun's corona, the outermost layer of its atmosphere, which is surprisingly hotter than the sun's surface – a scientific puzzle that continues to intrigue researchers. But here's where it gets controversial... Some scientists suggest that the corona's extreme heat is due to the sun's magnetic field, but others have different theories!
SOHO has also been instrumental in capturing solar flares and coronal mass ejections (CMEs). These events have significant impacts on space weather, potentially disrupting communications and causing stunning auroras on Earth. And this is the part most people miss... SOHO has witnessed nearly three full cycles of the sun's approximately 11-year solar cycle, providing invaluable data on the sun's natural rhythms.
Where is SOHO located?
This incredible image was taken from the L1 Lagrange point, where SOHO is strategically positioned.
Why is SOHO so amazing?
Despite initial success, SOHO's journey hasn't always been smooth sailing. In 1998, the spacecraft experienced a series of setbacks, including a loss of contact and a potential freeze in space. However, engineers, through their expertise, were able to locate and correct the errors, saving the mission.
Over its 30 years of operation, SOHO has revolutionized the field of helioseismology and provided scientists with the first detailed look at the sun's corona. Although its original mission was planned for only three years, SOHO's mission has been extended repeatedly and remains active today.
But that's not all! SOHO has also become an unexpected comet hunter. Thanks to its LASCO coronagraph, which blocks the sun's bright disk to reveal its faint corona, SOHO had discovered over 5,000 comets by early 2025, surpassing any other observatory in history.
Professor Carole Mundell, ESA Director of Science, noted that "SOHO has overcome nail-biting challenges to become one of the longest-operating space missions of all time."
Want to learn more?
You can explore SOHO's mission and the sun's solar cycle to deepen your understanding.
What do you think? Are you amazed by SOHO's discoveries? Share your thoughts in the comments below! Do you find the sun's corona mystery as intriguing as scientists do? Let's discuss!
Kenna Hughes-Castleberry is the Content Manager at Space.com. Formerly, she was the Science Communicator at JILA, a physics research institute. Kenna is also a freelance science journalist. Her beats include quantum technology, AI, animal intelligence, corvids, and cephalopods.
