Chandrayaan-2 detected solar proton events due to high intensity solar flares in January 2022.

When Sun is active, spectacular eruptions called solar flares occur that sometimes also spew out energetic particles (called Solar Proton Events or SPEs) into interplanetary space. Most of these are high energy protons that impact space systems and significantly increase radiation exposure to humans in space. They can cause ionisation on large scales in Earth’s middle atmosphere.  Many intense solar flares are accompanied by coronal mass ejections (CMEs), a powerful stream of ionised material and magnetic fields, which reach Earth a few days later, leading to geomagnetic storms and lighting up the polar sky with auroras.

Solar flares are classified according to their strength.  The smallest ones are A-class, followed by B, C, M and X. Each letter represents a 10-fold increase in energy output.  This means that an M class flare is ten times intense than C-class flare and 100 times intense than B-class flare. Within each letter class there is a finer scale from 1 to 9 i.e a M2 flare is twice the strength of M1 flare.

Recently, there were two M-class solar flares. One flare (M5.5) spewed out energetic particles into interplanetary space and the other flare (M1.5) was accompanied by a Coronal Mass Ejection (CME). SPE event was seen by NASA’s Geostationary Operational Environmental Satellite (GOES) satellite orbiting around Earth. However, the CME event was not detected by GOES.

Chandrayaan-2 Large Area Soft X-ray Spectrometer (CLASS) on-board Chandrayaan-2 Orbiter detected SPE due to an M5.5 class solar flare that occurred on January 20, 2022 (blue curve). The red curve shows the proton counts due to SPE recorded by GOES satellite operated by NOAA.