During her trip to Mars, Curiosity experienced radiation levels that would exceed NASA's career limit for astronauts, if left unshielded. The Radiation Assessment Detector (RAD) instrument on Curiosity found that two forms of radiation pose potential health risks to astronauts in deep space. One is galactic cosmic rays (GCRs), particles caused by supernova explosions and other high-energy events outside the solar system. The other is solar energetic particles (SEPs) associated with solar flares and coronal mass ejections from the sun. NASA will use Curiosity's data to design missions to be safe for human explorers.