Region 4409

Solar Region 4409 is an active sunspot complex on the Sun's disc that NOAA's Space Weather Prediction Center identified as carrying a 20% daily probability of producing an X-class flare during the Artemis II flyby window. A major flare during closest lunar approach on 6 April 2026 could not be excluded, though NOAA did not forecast it as probable.

Active sunspot regions are numbered sequentially by NOAA and persist for days to weeks as they rotate across the solar disc. Region 4409 is ephemeral: its relevance is specific to the Artemis II flyby period. An X-class flare is the highest category on the solar flare scale, associated with intense bursts of X-ray and ultraviolet radiation and, if accompanied by a coronal mass ejection, a potential radiation dose increase for crew in deep space. The Orion capsule and the crew's dosimetry equipment are designed to handle the radiation environment beyond the Earth's magnetosphere.

A 20% daily probability is modest but non-trivial for mission planning. Flight controllers monitor active regions continuously and can adjust EVA or high-exposure activity windows accordingly. For Artemis II, the lunar flyby itself carries no EVA, so the primary concern is accumulated dose rather than acute exposure from a direct-path particle event.