The Solar and Heliospheric Observatory (SOHO) is celebrating its 30th anniversary, a remarkable feat in space exploration. Since its launch on December 2, 1995, SOHO has been a beacon of innovation and collaboration, providing invaluable insights into the Sun's behavior. This mission, initially planned for just two years, has now spanned nearly three 11-year solar cycles, thanks to its engineers' and scientists' ingenuity. Prof. Carole Mundell, ESA Director of Science, praises the mission's success, highlighting its ability to overcome challenges and become one of the longest-operating space missions. The partnership between NASA and ESA has been instrumental in this achievement, as noted by Nicky Fox, associate administrator at NASA Headquarters. But SOHO's journey hasn't been without its dramatic moments. Two years after launch, the spacecraft encountered a critical error, losing contact with Earth. An international rescue team worked tirelessly to recover it, and by February 1999, new software enabled the spacecraft to fly without gyroscopes, revolutionizing solar science ever since. SOHO's impact extends far beyond its technical achievements. It has pioneered helioseismology, a field akin to studying Earth's seismic activity, revealing the Sun's inner workings. The data from SOHO has solved a long-standing mystery about plasma flows, showing that they follow a single loop in each hemisphere, taking 22 years to complete. This discovery aligns with the Sun's magnetic cycle, offering insights into sunspot emergence. SOHO's data also provides a steady stream of energy output measurements, crucial for understanding solar heating's impact on Earth's atmosphere and climate. The mission's influence is so significant that it was enshrined in US law in 2020, mandating real-time space weather monitoring. SOHO's coronagraph, LASCO, has been instrumental in this, allowing us to predict solar storms up to three days in advance. One of SOHO's most unexpected achievements is its role as a comet hunter. It has discovered over 5,000 comets, including sungrazers, which approach the Sun at incredibly close distances. These discoveries have provided valuable data on comet movement, composition, and dust production, thanks to citizen scientists worldwide. SOHO's success has set a standard for future solar observatories, influencing their technology and scientific objectives. It has also been a role model for open data policies and international collaboration. The mission's legacy is evident in projects like the Solar Orbiter and Solar Dynamics Observatory, which carry on SOHO's work in full-disc imaging and helioseismology. Looking ahead, ESA's Proba-3 and Vigil missions will further enhance our understanding of the Sun, opening up new vistas and improving our ability to predict solar storms. SOHO's 30-year legacy is a testament to its enduring value and relevance, shaping the future of solar science and inspiring generations of scientists.
