Chandrayaan instrument helps unravel the mysteries of solar corona

An instrument on board India’s Chandrayaan-2 mission has offered excellent science outcomes on the solar corona and heliophysics, the Indian Space Research Organisation (ISRO) mentioned.

Though we’ve got a reasonably good understanding of the origin of vitality and different numerous points of the Sun, a number of doubtlessly life-changing phenomena nonetheless stay a thriller, notes the Bengaluru-headquartered area company.

Some of these mysteries are associated to the scorching outer environment of the Sun, often called corona, which emits profusely in ultra-violet and X-ray wavelengths of the electromagnetic spectrum.

It is understood that the corona consists of ionised fuel at temperatures exceeding a million Kelvin, which is way increased than photospheric temperature of 6000K, the seen floor temperature of the Sun.

However, this remark is towards the pure expectation that the temperatures ought to scale back as we go away from the supply of vitality, and this is called the ‘coronal heating problem.’ From observations, resembling the presence of even hotter corona, known as energetic areas above the Sunspots (darkish patches seen in seen photos of the Sun) the place the magnetic fields are recognized to be stronger, it’s urged that the magnetic fields have an vital position in the coronal heating, based on the ISRO.

While there are totally different theories relating to the precise mechanism, one of these depends on the prevalence of a big quantity of small solar flares known as nanoflares.

Another puzzling remark about the corona is that sure components are discovered to have abundances three to 4 occasions increased in energetic areas than in the photosphere.

This occurs for components that are simpler to ionise, or require lesser vitality to ionise. In extra technical phrases, these components have their First Ionisation Potential (FIP) decrease than 10 eV, and therefore this phenomenon is mostly termed as FIP bias.

The actual cause behind the FIP bias and its origin stays an open query. A group of scientists from Ahmedabad-based Physical Research Laboratory (PRL), a unit of Department of Space, used observations of the Sun in delicate X-rays with Solar X-ray Monitor (XSM) on board ISRO’s Chandrayaan-2 mission throughout the deepest solar minimal of the previous hundred years to study thrilling particulars about the solar corona, an replace on the ISRO web site mentioned.

“For the first time, absolute abundances of elemental Mg, Al, Si in the quiet solar corona are derived. The team discovered and characterised around 100 sub-A class microflares in the quiet corona providing new insight into coronal heating puzzle”, it mentioned.

The XSM, designed and developed by PRL with assist from numerous ISRO centres, offers measurement of delicate X-ray (1- 15 keV) spectrum of the Sun.

The XSM additionally helps the quantitative measurements of elemental abundances of the lunar floor utilizing 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 floor.

At current, XSM is the solely instrument that gives delicate X-ray spectral measurements of the Sun, i.e., measures the depth of X-ray in numerous energies over the 1 to fifteen keV.

More importantly, XSM offers such measurements with superb vitality decision at each second, the highest cadence for any instrument up to now, the ISRO replace mentioned.

XSM began observations of the Sun in September 2019, throughout the interval of solar minimal when sometimes there have been only a few Sunspots and energetic areas on the Sun.

The solar minimal of 2019-2020 was much more peculiar as the Sun was extraordinarily quiet, and its exercise was at the lowest stage over the previous century, the area company mentioned.

This offered a novel alternative for XSM to watch the quiet corona with out energetic areas for lengthy intervals.

The solar X-ray flux was noticed by the XSM throughout this era when no energetic areas had been current on the solar disk.

A exceptional and shocking remark is the detection of a big quantity (98) of extraordinarily small flares in the quiet corona.

These flares are so small that their depth is effectively beneath the commonplace scale to categorise solar flares (i.e. A, B, C, M, and X class flares, the place every class is 10 occasions extra intense than earlier), and therefore these are termed as sub-A category microflares.

Using the X-ray spectra of these microflares obtained with the XSM and modern photos in Extreme Ultra-violet obtained with the Atmospheric Imaging Assembly (AIA) of NASA’s Solar Dynamics Observatory (SDO), the vitality content material of these flares could possibly be estimated, ISRO mentioned.

“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,” the replace mentioned.

The X-ray emission over these 76 days, excluding the durations of the microflares, is unusually fixed.

This is the lowest depth of X-ray emission noticed from the Sun since space-borne observations started, the ISRO mentioned.

Analysis of the XSM spectra of the quiet Sun, excluding the microflares, offered the measurement of abundances of numerous components.

The abundances of the low FIP components Mg, Al, and Si had been estimated and located to be decrease than the abundances seen in energetic area corona however increased than that in the photosphere.

“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 ISRO mentioned.

These excellent science outcomes on the solar corona and heliophysics obtained throughout a novel solar extraordinarily quiet interval utilizing a delicate instrument XSM aboard Chandryayaan-2 observations are revealed in two companion papers in the May situation of the Astrophysical Journal Letters.

“Both the Chandrayaan-2 orbiter and the XSM instrument are performing extremely well, and expected to provide many more exciting and new results”, the replace added.