A team of scientists from Physical Research Laboratory (PRL), a unit of Department of Space, used observations of the Sun in soft X-rays with Solar X-ray Monitor (XSM) on board ISRO’s Chandrayaan-2 mission during the deepest solar minimum of the past hundred years to learn exciting details about the solar corona.
About Solar X-ray Monitor
- The Solar X-ray Monitor XSM, designed and developed by PRL with support from various ISRO centres, provides measurement of soft X-ray (1- 15 keV) spectrum of the Sun.
- The XSM also supports the quantitative measurements of elemental abundances of the lunar surface using the companion payload CLASS (Chandrayaan-2 Large Area Soft X-ray Spectrometer) developed by URSC (U R Rao Satellite Centre), an ISRO centre, which measures the X-ray fluorescence spectrum from the lunar surface.
- At present, Solar X-ray Monitor (XSM) is the only instrument that provides soft X-ray spectral measurements of the Sun, i.e., measures the intensity of X-ray in different energies over the 1 to 15 keV.
- More importantly, XSM provides such measurements with very good energy resolution at every second, the highest cadence for any instrument so far.
- Using the X-ray spectra of these microflares obtained with the XSM and contemporary images in Extreme Ultra-violet obtained with the Atmospheric Imaging Assembly (AIA) of NASA’s Solar Dynamics Observatory (SDO), the energy content of these flares could be estimated.
About the Study
- The XSM instrument on board India’s Chandrayaan-2 mission has provided outstanding science results on the solar corona and heliophysics.
- Some of these mysteries are related to the hot outer atmosphere of the Sun, known as corona, which emits profusely in ultra-violet and X-ray wavelengths of the electromagnetic spectrum.
- It is known that the corona consists of ionised gas at temperatures exceeding one million Kelvin, which is much higher than photospheric temperature of 6000K, the visible surface temperature of the Sun.
- However, this observation is against the natural expectation that the temperatures should reduce as we go away from the source of energy, and this is known as the ‘coronal heating problem.’
- From observations, such as the presence of even hotter corona, called active regions above the Sunspots (dark patches seen in visible images of the Sun) where the magnetic fields are known to be stronger, it is suggested that the magnetic fields have an important role in the coronal heating.
- This was the first observation and statistical study of such a large sample of microflares in the quiet Sun, supporting the hypothesis of the presence of even smaller scale flares everywhere on the solar corona that could be responsible for the coronal heating.
- Analysis of the XSM spectra of the quiet Sun, excluding the microflares, provided the measurement of abundances of various elements.
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