The launch of Chandrayaan, India’s very own moon mission raised India’s expectations from its own apparently beleaguered Technology sector along with world’s great powers’ eyebrows regarding India’s unsevered attempts to space.
And hence we launched Chandrayaan-2.
It was supposed to be the first space mission to make a soft landing on the South Pole of the moon but a last-minute glitch in the guidance software, led the Vikram lander for Chandrayaan-2 mission to crash on unintended location.
This finds place in an internal report presented to the Space Commission. It remains a matter of debate as to Chandrayaan-2 failed or not. We are contented that a third of the series is being planned.
Despite this, according to ISRO, an instrument aboard India’s Chandrayaan-2 mission has provided outstanding science results on the solar corona and heliophysics, that every Space scientist yearns to know more of.
The curious case of Solar corona, puzzling enough?
The coronal plasma continually expands outwards of the Sun along with solar magnetic field, emitting profusely in ultra-violet and X-ray wavelengths of the electromagnetic spectrum.
This is also called solar wind, reaching speeds of hundreds of kilometers per second and enthralling entire solar system.
The space carved by it defines the heliosphere and is important to know how the stars get rid of stressed magnetic fields and various physical processes operating throughout the universe.
That is, the solar wind is a medium through which larger space weather events propagate.
Additionally, this solar wind depending on Solar activity bombards Earth’s magnetic field and plasma environment, driving another dynamic called space weather. Understanding solar wind is therefore a key for understanding the space environment surrounding our planet.
Corona is composed of ionized gas at temperatures exceeding one million Kelvin, much higher than core temperature of the Sun ranging 6000K, probably due to solar flares called nanoflares. This anomaly is known as the ‘coronal heating problem.’
As this happening is against the natural expectation that the temperatures should reduce as we go away from the source of energy production.
There are other suggestions for this behavior including magnetic fields influencing the coronal heating or the relevance that certain elements are found in abundance three to four times in coronal space, even higher than in the photosphere.
Most of these elements like Mg, Al, and Si, found are those easier to ionize, or require lesser energy to ionize i.e., their First Ionization Potential (FIP) is lower than 10 eV but this FIP bias and its origin remains a mystery.
Chandrayaan2 revelations: Elements, flares and beyond
Ahmedabad-based Physical Research Laboratory (PRL) under the Department of Space analyzed the Sun using soft X-rays with Solar X-ray Monitor (XSM) on board ISRO’s Chandrayaan-2 mission to learn exciting details about the solar corona.
“For the first time, absolute abundances of elemental Mg, Al, Si in the quiet solar corona are derived. The team discovered and characterized around 100 sub-A class microflares in the quiet corona providing new insight into coronal heating puzzle”.
A large number (98) of extremely small flares were detected in Solar corona. These were small enough to not even classify under solar flares (i.e. A, B, C, M, and X class flares) and hence, were termed as sub-A class microflares.
According to ISRO, the energy content of these flares could be estimated using their X-ray spectra with the XSM and contemporary images in Extreme Ultra-violet obtained with the Atmospheric Imaging Assembly (AIA) of NASA’s Solar Dynamics Observatory (SDO).
“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”.
How does this become possible to be detected?
“This is the first report of measurement of abundances as well as reduced FIP bias in the quiet Sun.
Our observations of FIP bias in the quiet Sun provides significant inputs towards understanding the FIP bias and suggests that it arises due to the presence of Alfvn waves in the closed magnetic loops”.
The clarity in the observations could be attributed to both: a unique solar extremely quiet period and the extremely-sensitive instrument XSM aboard Chandryayaan-2.
About XSM: difficult made possible
ISRO update read: “Both the Chandrayaan-2 orbiter and the XSM instrument are performing extremely well, and expected to provide many more exciting and new results”.
The XSM, designed and developed by PRL and ISRO, provides measurement of soft X-ray (1- 15 keV) spectrum of the Sun, making it the only instrument providing soft X-ray spectral measurements of the Sun
It supports the quantitative measurements of elements on lunar surface using another payload CLASS (Chandrayaan-2 Large Area Soft X-ray Spectrometer) developed by URSC (U R Rao Satellite Centre) that efficiently measures the X-ray fluorescence spectrum.
Most importantly, XSM gives these measurements with very good energy resolution at every second, the highest cadence for any instrument so far, as per ISRO.
Also, like every entity’s own cycle, Sun has 11-year cycle of its own. The solar minimum of 2019-2020 proved crucial as the Sun was extremely quiet, and its activity was at the lowest level over the past century.
It worked in the agency’s favor as the solar X-ray flux got observed by the XSM during a period when no active regions were present on the solar disk to hamper clarity.