Superflare
Since superflares can occur on stars apparently equivalent in every way to the Sun, it is natural to ask if they can occur on the Sun itself. An estimate based on the original Kepler photometric studies suggested a frequency on solar-type stars (early G-type and rotation period more than 10 days) of once every 800 years for an energy of 10 erg and every 5000 years at 10 erg. One-minute sampling provided statistics for less energetic flares and gave a frequency of one flare of energy 10 erg every 5–600 years for a star rotating as slowly as the Sun; this would be rated as X100 on the solar flare scale. This is based on a straightforward comparison of the number of stars studied with the number of flares observed. An extrapolation of the empirical statistics for solar flares to an energy of 10 erg suggests a frequency of one in 10,000 years.
Neutron monitor
Approximately 10-15 times per decade, the Sun emits particles of sufficient energy and intensity to raise radiation levels on Earth's surface. The official list of GLEs is kept by the International GLE database. The largest of these events, termed a "ground level enhancement" (GLE) was observed on February 23, 1956. The most recent GLE, (#72) occurred on September 10, 2017 as a result of an X-class flare and was measured on the surface of both the Earth (by Neutron Monitors) and Mars (by the Radiation Assessment Detector on the Mars Science Laboratory's Curiosity Rover).