Hunt for the Sun's superflares

On March 10, 1989, solar astronomers observed an intense brightening on the Sun followed by a massive explosion that hurled a billion tonnes of hot ionised gas into space. These were tell-tale signs of a solar flare, a magnetised plasma storm that rushes out of the Sun at speeds of thousands of kilometres per second.

A few days later on March 13, 1989, the Quebec power grid tripped, blanketing large parts of Canada in darkness and shutting down the Montreal metro network. Out in space, satellites started malfunctioning, radio communications broke down and radars got jammed. Spectacular auroras — which are normally confined to the polar region — lit up the night sky in countries situated much further down south. The space storm had hit home — planet Earth was right on its path.

Solar flares originate from strongly magnetised regions known as sunspots on the Sun’s surface and can release energy far exceeding that of a billion nuclear explosions. Although solar flares have never caused large scale havoc on our civilisation, their potential to do so is feared. In their attempt to understand these flares, scientists are asking questions like: Are even stronger magnetic storms or superflares possible? Or did the young Sun unleash devastating flares when life was just forming on Earth?

Evidence, finally

In March 2019, two Indian scientists, Ritesh Kumar Mishra and Kuljeet Kaur Marhas, working at Ruprecht-Karls-Universität Heidelberg and Physical Research Laboratory, Ahmedabad, respectively, published their analysis of a meteorite sample. Buried in their meteorite sample, they claim, was evidence of a massive superflare from the Sun when it was only about 500 million years old and the solar system was in its infancy. Finally, evidence of a superflare from the Sun had been found.

The research work that led Kuljeet and Ritesh to this discovery of a solar superflare is a great piece of detective work combining experimental analysis, modelling and deductive reasoning based on studies of a meteorite called Efremovka. The Efremovka meteorite fell from the sky in a region called Pavlodar in present-day Kazakhstan in the year 1962 and it brought to us hidden clues from the ancient solar system.

Processes related to the formation of the solar system, its chemical environment, and the early Sun’s activity all conspired together to determine the elemental composition of the first solid materials that formed in the solar system. These solid materials known as calcium-aluminium-rich inclusions lay encapsulated in the heart of rocks in space known as asteroids, mostly to be found today in the asteroid belt. The Efremovka meteorite which managed to find its way to Earth is a fragment of one of these asteroids.

Utilising a sophisticated instrument called the secondary ion mass spectrometer, Kuljeet and Ritesh analysed a sample of the Efremovka meteorite which was in the collection of the Physical Research Laboratory. The instrument uses a ray of energetic ions to bombard the sample and tease out abundances of radioactive isotopes of elements encapsulated in the meteorite. These radioisotopes are unstable combinations of neutrons and protons which naturally form through energetic processes in the Universe. These radioisotopes decay with a characteristic half-life to stable atomic nuclei, or other relatively more stable radioisotopes which survive for longer times than the original ones.

Kuljeet and Ritesh found an unexpected overabundance of Lithium 7 radioisotope in their sample, which is produced from the decay of the very unstable Beryllium 7 isotope that is now extinct. Analysis of the abundance of Lithium 7 in their sample led the Indian team to deduce the original abundance of Beryllium 7 which existed 4.5 billion years ago when the Sun was just a half a million-year-old star.

Although an extremely energetic phenomena such as supernova explosions can trigger the formation of similar radioisotopes such as Beryllium 10 over a long period of time, the very short half-life of Beryllium 7 of about 53 days led the authors to conclude this could only have formed by rapid, repeated doses of very high energy particles bombarding the ancient solar system, possible only during solar flares.

The team then calculated the flare energy necessary to produce the required amount of overabundance of the radioisotope observed in their sample. They inferred that the flares that occurred 4.5 billion years back in the ancient solar system had energies which were about ten thousand to a million times stronger than a typical present-day solar flare. Evidence of superflares in the Sun had finally been found!

Flux of energy

Life as we know it today evolved from primordial life forms. The earliest evidence of such life forms is about 3.7 billion years old. The possibility of the existence of superflares on the young Sun implies that throughout the early evolutionary history of life, storms from the Sun would have sustained an extreme environment bombarding Earth with a much larger flux of high energy radiation and particles. What impact could it have had on the synthesis of early lifeforms and building blocks of life such as RNAs and nucleic acids? Is it possible that superflares could occur even today on the Sun? Are we living on a chance that our star, the Sun, has become uniquely benign and we shall not have to face the consequences of a present-day superflare?

Many space agencies have satellites dedicated to observing the Sun. Indian Space Research Organisation plans to launch the Aditya-L1 satellite next year to add to the eyes looking out for solar storms. There is hope that we shall be able to understand and predict strong flares from the Sun and protect ourselves. There is hope that we shall one day figure out the intimate relationship that the living world on Earth shares with the star that is both a life-giver and a source of violent storms in space.

(The writer is a Professor at the Department of Physical Sciences and Centre of Excellence in Space Sciences India, IISER Kolkata)

This article was first published on thelifeofscience.com and republished here by arrangement with TLoS.