Unraveling ‘dance of electrons’! CLASS instrument of #Chandrayaan2 to detect charged particles in geotail

News Bharati    04-Oct-2019
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Bangalore, October 4: ISRO revealed few days ago that all orbiter Payloads of Chandrayan-2 are showing satisfactory performance and the orbiter continues to perform scheduled science experiments to complete satisfaction. One of the orbiter Payloads named CLASS is expected to detect charged particles and it’s intensity variations during its first passage through the geotail during September.

This is how charged particles form magnetic envelope around earth:
Our Sun emits a continuous outflowing stream of electrons and protons into the solar system, called the solar wind. The solar wind plasma which has charged particles embedded in the extended magnetic field of the Sun, moves at speeds of a few hundred km per second. It interacts with solar system bodies including Earth and its moon. Since the Earth has a global magnetic field, it obstructs the solar wind plasma and this interaction results in the formation of a magnetic envelope around Earth, called the magnetosphere.
What is Geotail? 
The Earth’s magnetosphere is compressed into a region approximately three to four times the Earth radius (~22000 km above the surface) on the side facing the Sun. However, it is stretched into a long tail which is called as ‘geotail’. It lies on the opposite side of the sun that goes beyond the orbit of Moon. It is also called as ‘Magnetotail’. Approximately, once every 29 days, Moon traverses the geotail for about 6 days centered around full moon. During the crossing, the moon comes in contact with a gigantic 'plasma sheet' of hot charged particles trapped in the tail. The lightest and most mobile of these particles, electrons, pepper the moon’s surface and give the moon a negative charge. The solar wind drags out the night-side magnetosphere to possibly 1000 times Earth's radius.

How Chandrayaan-2 will unravel movement of charged particles:
Chandrayaan-2 also crosses this geotail and its instruments can study properties of geotail at a few hundred thousand kilometers from Earth. The CLASS instrument on Chandrayaan-2 is designed to detect direct signatures of elements present in the lunar soil. This is best observed when a solar flare on the Sun provides a rich source of x-rays to illuminate the lunar surface; secondary x-ray emission resulting from this can be detected by CLASS to directly detect the presence of key elements like Na, Ca, Al, Si, Ti and Fe.
While this kind of flash photography requires one to await an opportune time for Sun to be active, CLASS in its first few days of observation, could detect charged particles and its intensity variations during its first passage through the geotail during September.