How pop-science got us closer to solving a big solar mystery

Murthy O V S N and Piyali Chatterjee on how a young girl’s observation sparked off an unusual discovery around spicules — jets of plasma ejected from the sun’s surface


One year back, an unusual scientific discovery was announced by one of the world’s top journals. Unusual because of how it connected two wildly disparate phenomena, and also unusual because it was sparked off by an observation made by a young girl watching a popular YouTube video. 

Mama, these look like your spicules”

The evening it all began, astrophysicist Piyali Chatterjee and her eight-year-old daughter Samiksha were watching a video on a wildly popular YouTube channel, The Slow Mo Guys. The hosts Gavin Free and Dan Gruchy were crouched in their garden with an old bass speaker, powerful cameras and bottles of paint. They poured multi-coloured paint on the speaker and recorded in slow motion (12,500 frames per second!) what happened when it was turned on.

The mesmerising sight of paint globs shooting up in straight jets, swirling, spiralling and stretching into long dancing threads that eventually detach into irregular globules before falling back down felt strangely familiar to Piyali. She turned to her daughter to ask her what she thought. Mama,” said Samiksha, they look like your spicules.”

Spicules aren’t part of a typical primary schooler’s vocabulary. They are jets of plasma ejected from the sun’s surface, rising up to great heights and speeds. Their origin, behaviour and ubiquity (millions of spicules are shooting up from the Sun at any given instance, hence earning the term forest of spicules’) have intrigued astronomers ever since they were first discovered by an Italian priest in 1877.

The science of spicules could help make sense of several solar enigmas such as coronal heating and solar wind.

The first images of the chromosphere – the area of the Sun’s atmosphere above the surface – taken with the Daniel K Inouye Solar Telescope on 3 June 2022

[Credit: US National Science Foundation] 

While some astronomers study spicules with the help of data from telescopes, satellites and solar probes, others like Piyali build and use computer simulations. Samiksha was used to seeing videos of spicule simulations playing on her mother’s laptop all day, and she couldn’t help but be reminded of them when she saw the slow motion footage of the paint jets that day.

A screenshot from the video of solar spicules from 2007, taken by the Solar Optical Telescope on board the Hinode satellite

Spicules aren’t part of a typical primary schooler’s vocabulary. They are jets of plasma ejected from the sun’s surface, rising up to great heights and speeds. Their origin, behaviour and ubiquity (millions of spicules are shooting up from the Sun at any given instance, hence earning the term forest of spicules’) have intrigued astronomers ever since they were first discovered by an Italian priest in 1877.

Hearing her daughter’s comment, Piyali’s heart raced. Somehow, she did not feel like brushing it off as a child’s flippant comment, and so she related the incident to her physicist-husband when he got home. Used to engaging with young people at the Azim Premji University he teaches at, Murthy O V S N was immediately enthusiastic about exploring Samiksha’s observation. 

How simple physics connected two unconnected phenomena

At that point, all the duo knew was that there was some visual similarity. It could definitely just be a coincidence. But when they performed some preliminary calculations comparing the ratio of accelerations of the paint jets to the jets on the sun, they found similarities there too. 

That really excited us. When you see very simple physics connecting two seemingly unconnected phenomena… I mean, that’s the kind of thing that we all like to run after,” said Murthy.

Over the coming months, Piyali and Murthy proceeded to investigate this idea further. In his laboratory at Azim Premji University, Murthy was able to recreate the paint-on-speaker experiment using a polymer fluid. 

He also managed to record high-quality footage using a 1000-frames-per-second Sony RX-10 camera. With the help of Piyali’s student Sahel Dey — who is the first author of the paper — as well as instruments and computers, the trio analysed the behaviour of the paint jets.

While the country went into lockdown, Murthy performed the experiments at home Picture Credit: Murthy O V S N

Meanwhile, Piyali and Sahel prepared a numerical simulation of the solar atmosphere. Such simulations are invaluable to astronomers who are studying difficult-to-observe objects such as the sun. Her simulations allowed them to predict the behaviour of solar surface plasma under conditions comparable to the paint on Murthy’s speakers.

Through the course of the study, there was a lot of to and fro between us,” recalled Murthy. I would see something in the polymer system, and ask her if we can get something like that in the simulation, and then she would do something in simulations, and we would check if the polymer system can show similar behaviour.” 

Plasma spicules enacting paint jets on a speaker

Soon enough, their notes started to reveal that there was more to Samiksha’s casual observation than meets the eye. The analyses were confirming their hunch that plasma spicules on the sun were somehow originating and behaving very much like paint jets on a speaker.

If they could prove this, then it may indicate that similar triggers are behind the origin of spicules on the sun. This would be a groundbreaking claim, Murthy and Piyali knew very well, and so they roped in scientists in the UK who would test the idea using another approach — examining the actual sun. 

Solar spicule simulation (left) and the paint-on-speaker experiment (right) created for this study

Among the UK-based scientists who joined the Indian scientists was space plasma physicist Robertus Erdélyi, who in 2004 had made a landmark hypothesis about the origin of spicules. They had been working on spicules for a much longer time than me, so I knew they would have a better idea of the existing literature on the topic, or whether what our experiment is producing are actually spicules,” remarked Piyali.

Erdelyi and the other scientists analysed data from a solar satellite called Interface Region Imaging Spectrograph (IRIS). They had the tools to process that data, and they also used these tools to analyse our numerical simulations,” said Piyali.

Eventually, all the analyses confirmed the same thing: these two very different phenomena seem to be operating under the same underlying physics. In their paper published in 2022 by Nature Physics, the co-authors say: We find an intriguing parallel between the simulated spicular forest in a solar-like atmosphere and the numerous jets of polymeric fluids (paint) when both are subjected to harmonic forcing… The jets thus produced [via simulation] match remarkably well with the forests of spicules detected in observations of the Sun.” 

The group proposed that only four ingredients were needed to produce a forest of jets: one, a fluid system; two, gravity; three, a strong enough and somewhat periodic force; and four, an anisotropic system (one in which the properties vary with the direction). 

(from left) Murthy O V S N, Piyali Chatterjee and Sahel Dey, the Indian scientists involved in this study

The mystery of spicules is far from fully solved. Piyali and Sahel are already exploring ways to extend their model further, in a way that could reveal even more about coronal heating and solar winds. 

For Murthy, this study was particularly satisfying because it renewed his faith in the power of simple science. They were able to achieve something that had been incredibly challenging even with much more complex physics and expensive infrastructure. 

The experiments themselves are pretty straightforward, and any well-funded high school laboratory can actually replicate them!” he said, adding, It’s not a major new discovery or anything like that, because all this physics is already well known. What we did, thanks to Samiksha, was to make a connection.”

About Murthy O V S N

Murthy O V S N is a faculty member at Azim Premji University. He may be contacted at murthy.​ovsn@​apu.​edu.​in

About the author

Nandita Jayaraj is a science writer and communications consultant at Azim Premji University. She may be contacted at nandita.​jayaraj@​apu.​edu.​in

Published on 31 May 2023