On Friday night, people from across the world were treated to a rare spectacle: vivid aurorae hanging like curtains of light in the sky. They appeared even in places where aurorae aren’t usually visible. For instance, people at the Indian Astronomical Observatory spotted an aurora over Hanle in Ladakh — far away from places near the poles, where they are a more common sight.

“I haven’t seen anything like this in the last 20 years,” says Dibyendu Nandi, a space physicist at the Indian Institute of Scientific Education and Research (IISER), Kolkata.

Beautiful though the aurorae are, the events on the Sun that produce them can trigger blackouts on the earth, knock out satellites in space, endanger the lives of astronauts, and affect space weather throughout the Solar System. Studying, understanding, and, in future, predicting them is thus a key goal of solar physics research.

Approaching the peak

Aurorae like these are created when some violent events on the Sun’s surface throw up a mass of charged particles into space. A geomagnetic storm happens on the earth when these particles become trapped in the planet’s magnetic field and interact with atoms in the upper atmosphere. These interactions finally produce aurorae.

These storms are rare, occurring around once in a few decades. The last time charged particles from the Sun blew into the earth with similar energy and intensity was in 2003. And both events happened as the Sun was nearing the peak of its solar cycle — an 11-year period during which the star’s magnetic field flips.

The peak is when the flip actually happens, creating magnetically active patches on the star’s surface called sunspots. These sunspots grow and shrink as solar cycles begin and end. The charged particles that struck the earth on May 10 are rooted in events at these sunspots. 

Surging currents

“This is definitely a sign that the Sun is ‘waking up’ and is becoming more active, especially compared to the last solar cycle,” Jonathon Eastwood, a space physicist at Imperial College London, the UK, said.

In the last solar cycle, which spanned the 2010s, no sunspot gave rise to a geomagnetic storm that matched the intensity of that on Friday.

Since early May, scientists have been monitoring the sunspot AR 3664. It was growing in size: by May 7, it was 16-times as wide as the earth and brimming with magnetic energy.

The supercharged magnetic fields in such sunspots sometimes disconnect and reconnect in fractions of a second, releasing a great burst of energy that sends plumes of charged particles called coronal mass ejections (CMEs) into space. On May 10, three CMEs struck the earth.

CMEs happen together with solar flares — powerful flashes of radiation — and all these active events are collected under the term ‘solar storms’.

Surging currents

Magnetic fields deflect charged particles, but the earth’s couldn’t prevent many of the particles from slipping through to locations close to the planet’s magnetic poles. Here, their interactions with oxygen atoms in the upper atmosphere produced vivid red light and with oxygen and nitrogen in the lower atmosphere producing green and purple light, respectively. Thus, the world had its aurorae.

On May 10, a few space-weather forecasters — including the Center of Excellence in Space Sciences India (CESSI) at IISER Kolkata — warned of potential power disruptions. The fluctuations in the earth’s magnetic field during a geomagnetic storm can send currents surging through cables, like what happened in Sweden and South Africa in 2003.

“These storms can also affect satellites in orbit on which our communication and GPS navigation networks depend,” Dr. Nandi, who also heads CESSI, said.

CESSI is the only Indian institute that provides timely updates on space weather.

Early warnings matter

This is not the worst geomagnetic storm to have ever struck the earth. In 1859, the Sun spouted a strong solar flare and triggered a super-geomagnetic storm on the earth, the most powerful in history. Telegraph wires either caught fire or were able to operate without a power supply (because they drew on the current surges produced by the storm).

Dr. Nandi said such storms — which CESSI would have categorised as ‘extreme’ — are likely to occur once every few centuries.

The May 10 geomagnetic storm was ‘severe’ on CESSI’s scale, and caused only minor power grid irregularities and GPS disruptions. In high-latitude countries such as New Zealand, power grid operators switched off local circuits to prevent outages. According to Dr. Nandi, these are some ways by which early warnings from space-weather forecasters made a difference.

He also said the solar storm that struck the earth had weakened by May 12, but that it may be too early to say the storms are subsiding altogether. For example, CESSI flagged moderate storms on May 13 as a result of an earth-bound CME that erupted on May 11.

Waiting for Aditya

Space scientists have long wanted to anticipate a solar storm before it even begins brewing. Currently, the best they can do is catch a CME and/or flares as soon as they happen. Many spacecraft that monitor the Sun for these events are parked in the L1 point in space, about 1.5 million km in the earth-Sun direction, from where they have an uninterrupted view of the star.

One of these spacecraft is Aditya-L1 of the Indian Space Research Organisation (ISRO), which reached L1 in March this year. The principal investigator of its primary instrument, the Visible Emission Line Coronagraph (VELC), told The Hindu it is still being calibrated.

Dr. Nandi, who also led the Aditya-L1 space weather monitoring and predictions plan committee and is a co-investigator of the spacecraft’s Solar Ultraviolet Imaging Telescope, said he expects other instruments to have become operational and that they would have observed the solar storms.

Indeed, in a statement on May 14, ISRO said the ASPEX payload had “captured the enhancement of the alpha particle and proton flux of the solar wind” as signatures of the solar storm. It also said the SoLEXS and HEL1OS payloads had detected “the multiple X- and M-class flares … during the last few days”. The Chandrayaan-2 orbiter around the moon also reportedly detected “signatures” of the emissions from the Sun.

Karthik Vinod is an intern with The Hindu.

On a cold winter night on March 13, 1989, the power grid in Quebec, Canada, went down without a warning, plunging the province into darkness. The underground metro railway in the city of Montreal came to a grinding halt and airport operations were disrupted. Down south in the neighbouring United States, nights lit up in beautiful bright aurorae as far south as Texas, which is not used to seeing such spectacles. Several sensors on the space shuttle Discovery started misbehaving. The broadcast of Radio Free Europe over Russia fell silent, giving rise to fears of jammed communications.

More than three decades later, in the first week of February 2022, almost an entire batch of newly launched SpaceX Starlink communication satellites fell out of their orbit unexpectedly, as if sunk by a storm.

Despite the variety of events across continents, all of them have a common cause: bad space weather.

Sun, meet Aditya

On September 2 this year, the Indian Space Research Organisation (ISRO) launched the Aditya-L1 satellite, its first space mission to explore the activities of the sun. After swinging by the earth a few times in increasingly distant orbits, the spacecraft will be boosted towards Lagrange point L1 – a strategic location in space about 1.5 million km from the earth. From here, a spacecraft can continuously observe the sun and monitor the changing local environment, or space weather, just before the earth experiences it – giving us critical tens of minutes of advance warning.

The sun is a massive ball of fiery plasma. Energy is generated by nuclear fusion at its core, where temperatures are as high as 15 million degrees Celsius and the density more than 20-times that of iron. From the centre to the surface of the sun, the temperature drops and energy flows outwards. Inside the sun, the temperature is high enough that atoms are broken up into negatively charged electrons and positively charged ions – the state of matter called plasma. Below the sun’s surface lies the convection zone, where heated plasma rises and radiates its energy as sunlight upon reaching the surface. The light from the sun that reaches us sustains life and drives atmospheric processes that govern the earth’s climate.

After the solar plasma radiates its energy away from the surface, it cools and sinks back down, much like cyclonic convection in the earth’s atmosphere. This twisting, churning motion of plasma within the sun creates vast electric currents and, as a by-product, powerful magnetic fields. This process, known as the solar dynamo, generates dark, earth-sized blotches on the sun’s surface known as sunspots, and magnetic loops that rise up like giant arches threading the star’s outer atmosphere, the corona.

A storm in space

While the sun’s visible surface, or photosphere, is only about 6,000 degrees Celsius hot, the temperature in the sun’s corona rises to a million degrees. How does it get so hot – in apparent contradiction to the laws of thermodynamics, which state that heat energy can only flow from a region of higher to lower temperature?

We know that other novel processes, such as waves rippling along those giant coronal magnetic loops, superhot plasma jets rising from the surface to coronal layers, and a process known as magnetic reconnection, are at the heart of coronal heating. The hot magnetic corona of the sun is also responsible for the supersonic outflow of plasma wind that bathes all planets in the solar system and forms the background space weather. Sometimes that environment can be violently disturbed.

The legs of the magnetic loops in the solar corona are being constantly jostled around by turbulent plasma flows beneath the surface, where they are rooted. These loops, energised by the serpentine motion of the plasma, sustain huge electric currents, and sometimes, in the course of their frenzied dance, they cross each other’s path. When the conditions are right, this results in a magnetic reconnection event that destroys the loops. The magnetic energy they shed is harnessed to create the most violent events we witness in our star: a solar flare, with an energy yield that can surpass a 100 billion nuclear bombs.

The energy released in such a solar storm heats the solar atmosphere even further, generating intense X-ray radiation and accelerating charged particles to a nontrivial fraction of the speed of light. The most energetic events can hurl magnetised coronal plasma material into outer space at speeds exceeding a few million kilometres an hour, giving rise to a coronal mass ejection – a space storm that, when directed at the earth, severely perturbs our own space environment.

A new infrastructure dependence

Severe space weather can give rise to geomagnetic storms that create beautiful aurorae on the one hand and cause power-grid failures in high-latitude regions, disrupt communications and GPS navigational networks, affect air-traffic over polar routes, and jam radar signals on the other. They can fry sensitive electronics of satellites and sometimes precipitate catastrophic orbital decays, as in the loss of the Starlink satellites in 2022.

With our increasing dependence on space-based infrastructure, a catastrophic solar storm could result in a trillion-dollar adverse economic impact. Yet we don’t yet have the means to accurately forecast severe space weather.

ISRO’s Aditya-L1 mission will explore how magnetic fields result in variations in the sun’s ultraviolet radiation, which plays a critical role in governing the earth’s atmosphere and climate dynamics. It will observe the flow of energy in the sun’s outer atmosphere to test competing theories for the heating of the sun’s corona. By analysing X-ray radiation, it will seek to understand how violent solar storms are born. Aditya-L1 will also track the early motion of magnetic storms near the sun and monitor the local space environment in its vicinity at Lagrange point L1, the environment that eventually affects the earth.

A national collaboration

Aditya-L1 was originally envisaged as a mission of purely fundamental scientific enquiry. In 2020, ISRO constituted a committee to explore how mission data could be used to extract relevant information for space-weather monitoring and predictions. I chaired that committee; it drafted a set of specific recommendations on onboard intelligence for space weather alerts and supporting data analytics and computational modelling initiatives to create value-added space weather knowledge.

More than 60 scientists from about 20 academic organisations participated in that exercise, and many more scientists, engineers, and students contributed to the mission – exemplifying the national collaborative effort that produced Aditya-L1.

If the mission succeeds, it will be a resounding vindication of India’s investment in space science research, which can on the one hand spur fundamental enquiry of our cosmos and on the other generate knowledge of strong societal relevance. Today, we wake up to the weather forecast. The day is not far when we will wake up to space weather forecasts. Not since our first sounding rocket screamed over a remote beach in Thumba have the people of India been so excited about space.

Dr. Dibyendu Nandi is professor of physics and head of the Centre of Excellence in Space Sciences India at IISER Kolkata. He specialises in understanding and predicting space weather.