M7.5 solar flare

An M7.5-class solar flare erupted from Active Region 4409 on 4 April 2026, during the Artemis II lunar transit. The event caused an R2 (moderate) high-frequency radio blackout on the sunlit side of Earth. At the time of the flare, Orion and its four crew members were in deep space between the Earth and Moon, placing them outside the most intense particle-flux zones. NASA did not disclose the crew's radiation dose during or after the event .

M-class flares are the second-highest category on the NOAA scale (below X-class). An M7.5 is near the top of that band, producing elevated proton flux and geomagnetic effects but not at the level of a major radiation emergency. Region 4409 remained active through the mission: a second flare from the same region on 9 April also produced geomagnetic effects during the final approach and re-entry phase .

The 4 April flare sits within the nine-day dose record that NASA has withheld since splashdown, alongside the G3 geomagnetic storm on Day 4 and the R3 radio blackout on Day 9. Independent scientists cannot verify whether accumulated doses across these events approached or breached NASA career limits, because the agency has directed dose data to the research-solicitation process rather than operational release.