Common Questions

What is SOHO and how old is it?

SOHO is a joint ESA/NASA solar observatory launched in December 1995 and still active after more than 28 years. It monitors the Sun from the L1 Lagrange point.Source: Event: Two storm forecasting models get their first live test

How is SOHO used in Artemis II?

SOHO imagery is fed alongside SDO data into the University of Michigan's ML model generating daily solar particle event probability scores for crew radiation safety.Source: Event: Two storm forecasting models get their first live test

Where is SOHO located?

SOHO orbits the L1 Lagrange point approximately 1.5 million kilometres from Earth, giving it an unobstructed upstream view of the solar wind.Source: NASA/ESA SOHO mission documentation

Background

The Solar and Heliospheric Observatory (SOHO) is a joint ESA/NASA spacecraft launched in December 1995 and still operational after more than 28 years, making it one of the longest-running solar Science missions in history. During Artemis II, SOHO imagery is being used alongside data from NASA's SDO spacecraft to power the University of Michigan's machine-learning model, which generates daily probability scores for solar particle events that could expose the crew to harmful radiation.

SOHO operates at the Lagrange point L1 between Earth and the Sun, approximately 1.5 million kilometres from Earth, giving it an unobstructed view upstream of the solar wind that arrives at Earth. Its 12 scientific instruments monitor solar activity from the deep interior (helioseismology) to the outer corona and early solar wind. SOHO is also notable for its LASCO coronagraph, which has detected more than 5,000 comets, most of them sungrazing Kreutz-group comets spotted by citizen scientists.

SOHO's longevity and its L1 vantage point make it uniquely valuable for Space weather monitoring. Unlike Earth-orbiting observatories, it provides Early Warning of solar wind structures heading directly towards Earth and the Moon. Its continued operation well beyond its design lifetime reflects the difficulty of replacing orbital solar infrastructure, and its role in Artemis II solar forecasting illustrates the extent to which ageing Science assets are being repurposed for crew safety roles.