A team of scientists from different divisions at ISRO made use of S-band radio signals from Mangalyaan to study the sun¡¯s corona.
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To the unaware, the corona is the outermost layer of the Sun's atmosphere. It is at the corona where strong magnetic fields fuse plasma and trap the turbulent solar winds, preventing them from escaping.
For the study, scientists made use of the solar conjunction event when Earth and Mars were on the opposite side of the Sun. This occurred during May-June of 2015. It occurs once every two years.?
During this event, radio signals from Mangalyaan passed through the solar corona -- around 69,57,000 kilometres from the centre of the Sun (one solar radii is about 695,700 kilometres, making this around 10 solar radii away).
Scientists discovered that the transition of solar wind from slower speeds to higher velocities occurs in a region that¡¯s 10 to 15 times the solar radii from the Sun¡¯s centre.?
What¡¯s surprising is that the Sun's surface is a few thousand degrees Kelvin whereas the outer later -- the corona -- goes up to millions of degrees Kelvin. The cause for this divide is unknown.?
Studying the corona is crucial since it passes through interplanetary spaces and is capable of affecting the space weather, which would in turn affect us on Earth.
The radio signals that passed through the plasma during the aforementioned conjunction event showed dispersive effects. The turbulence was registered at the Indian Deep Space Network for Mangalyaan as Isrtrac (Isro Telemetry, Tracking and Command Network).?
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Looking at the signals, scientists found the coronal turbulence spectrum was between four and 20 solar radii. This was the zone where solar wind experiences acceleration.
They also found that the turbulence power spectrum at a smaller distance from the Sun¡¯s centre -- less than 10 solar radii -- had shorter frequencies which corresponds to the solar wind acceleration region.?
This curve gets steeper for distances larger than 10 solar radii. Scientists further found that these findings were in line with theoretical models of solar wind turbulence.?
Moreover, the findings were also supported by the first direct observation of solar corona recently conducted by NASA¡¯s Parker Probe in the space agency¡¯s first-ever endeavour to touch the sun.??
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