Chandrayaan-2 Orbiter detects solar proton events, says ISRO

A Large Area Soft X-ray Spectrometer (CLASS), a payload on-board Chandrayaan-2 Orbiter, has detected solar proton events (SPEs) which significantly increase radiation exposure to humans in space, the Indian Space Research Organisation (ISRO) said on Wednesday.

The instrument on January 18 also recorded coronal mass ejections (CMEs), a powerful stream of ionised material and magnetic fields, which reach the Earth a few days later, leading to geomagnetic storms and lighting up the polar sky with auroras, it said. Such multi-point observations help us understand the propagation and its impact on different planetary systems, the ISRO said. When the 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, the space agency said.

Many intense solar flares are accompanied by CMEs, a powerful stream of ionised material and magnetic fields, which reach the 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 more intense than C-class flare and 100 times intense than B-class flare, the ISRO said. Within each letter class there is a finer scale from 1 to 9 - 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), the space agency said. The 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, the ISRO said. The CLASS instrument also detected a CME event as it passed through the moon due to an M1.5 class solar flare that occurred on January 18, it added.

CME travels at a speed of about 1000 km/s and it takes about 2-3 days to reach the Earth.

The signature of this event is missed by the GOES satellite, as Earth's magnetic field provides shielding from such events. However, the event was recorded by Chandrayaan-2, the ISRO said. The CLASS payload on Chandrayaan-2 saw both the SPE and CME events pass by from two intense flares on the Sun, it added.

Planned to land on the South Pole of the Moon, Chandrayaan-2 was launched on July 22, 2019. However, the lander Vikram hard-landed on September 7, 2019, crashing India's dream to become the first nation to successfully land on the lunar surface in its maiden attempt. The ISRO had then said the mission had achieved 98 per cent of the success as the orbiter continues to share data with the ground station.