What is geotail?

NEW DELHI: The advanced scientific instruments on board Chandrayaan-2 's orbiter, circling the Moon at 100km altitude, have started making new findings. While the high-resolution camera on board the orbiter has provided some sharp images of a lunar crater named after a German astronomer, its X-ray spectrometer has detected charged particles of solar wind plasma.Indian Space Research Organisation (Isro) on Friday made public some images captured by the orbiter high resolution camera (OHRC) of Boguslawsky E crater (14 km diameter and 3km depth) and its surroundings, which lies in the south polar region of Moon.The crater has been named after German astronomer Palon H Ludwig von Boguslawsky. The images also showed some small craters of 5 m diameter and boulders of height 1 to 2 metre. These findings from the orbiter have been released for the first time by the space agency after the Vikram lander made a "hardlanding" on the lunar surface on September 7. However, no image of the lander has been made public.Isro also said that the orbiter's camera, with which the images have been taken, has a spatial resolution of 25 cm (means two stones or objects lying at a distance of 25 cm can be distinctly identified), can cover a swath of 3km and operates in the visible panchromatic band of 450-800mm. The agency's statement that the camera has 25 cm resolution is an acknowledgement of the fact that this is the best-ever high-resolution camera ever used by Isro in any space mission. Even the cameras used in the country's surveillance or spy satellites do not have such high resolution and their resolution power is limited to 50 cm.In another important findings, Chandaryaan-2 large area soft X-ray spectrometer (CLASS), in its first few days of observation, could detect charged particles. CLASS is designed to detect signs of key elements like sodium (Na), calcium (Ca), aluminum (Al), silicon (Si), titanium (Ti) and iron (Fe) 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 and its secondary X-ray emission can be detected by CLASS to detect presence of the elements.This kind of “flash photography” requires one to wait for the right time for Sun to be active. However, CLASS could detect charged particles and its intensity variations during its first passage through the geotail during the month of September.The 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. Earth’s magnetosphere is compressed into a region approximately three to four times the Earth radius (22,000 km above the surface) on the side facing the Sun, but is stretched into a long tail (geotail) on the opposite side that goes beyond the orbit of Moon. Approximately, once every 29 days, Moon traverses the geotail for about six days centered around full moon.Thus Chandrayaan-2 also crossed this geotail and its instruments can study properties of geotail at a few hundred thousand kilometers from Earth, which in turn, will help turn spotlight on our planet’s extended magnetosphere (geotail) plasma around Moon.