Using satellite observations, including from ESA’s International Gamma-Ray Astrophysics Laboratory (Integral) mission, and a new developed analytical model, astronomers proved that GRB 221009A — a very bright and long-lasting gamma-ray burst that occurred on October 9, 2022 — deeply impacted on the Earth’s ionospheric conductivity, causing a strong perturbation in the top-side ionosphere (at around 500 km) of our planet. The findings suggests that GRB 221009A — the result of an exploding star almost two billion light-years away — may be amongst the strongest gamma-ray bursts ever detected in the Earth’s atmosphere.
The artistic impression depicts the effect of GRB 221009A that provoked a significant disturbance in our planet’s ionosphere. Image credit: ESA / ATG Europe / CC BY-SA 3.0 IGO.
“GRB 221009A was probably the brightest gamma-ray burst we have ever detected,” said Dr. Mirko Piersanti, an astronomer at the University of L’Aquila.
“We’ve been measuring gamma-ray bursts since the 1960s, and this is the strongest ever measured,” said Dr. Pietro Ubertini, an astronomer at the National Institute for Astrophysics.
So strong in fact that its nearest rival on record is ten times weaker. Statistically, a gamma-ray burst as strong as GRB 221009A arrives at Earth only once every 10,000 years.
During the 800 seconds that the gamma rays were impacting, this event delivered enough energy to activate lightning detectors in India.
Instruments in Germany picked up signs that Earth’s ionosphere was disturbed for several hours by the blast.
This extreme amount of energy gave the team the idea to look for the burst’s effects on Earth’s ionosphere.
One of those spacecraft is the China Seismo-Electromagnetic Satellite (CSES), also known as Zhangheng, a Chinese-Italian space mission.
The authors realized that if the gamma-ray burst had created a disturbance, CSES should have seen it. But they could not be sure.
“We had looked for this effect from other gamma-ray bursts in the past but had seen nothing,” Dr. Ubertini said.
In the past, gamma-ray bursts have been spotted affecting the bottom-side ionosphere during the night, when the solar influence is removed, but never in the top side.
This had led to the belief that by the time it reached Earth, the blast from a gamma-ray burst was no longer powerful enough to produce a variation in the ionospheric conductivity leading to an electric field variation.
This time, however, when the scientists looked, their luck was different. The effect was obvious and strong.
For the first time ever, they saw an intense perturbation in the form of a strong electric field variation in the top-side ionosphere.
“It is amazing. We can see things that are happening in deep space but are also affecting Earth,” said Dr. Erik Kuulkers, a project scientist at ESA.
This particular gamma-ray burst took place in a galaxy almost 2 billion light-years away, yet it still had enough energy to affect Earth.
While the Sun is typically the primary source of radiation robust enough to affect Earth’s ionosphere, this gamma-ray burst triggered instruments generally reserved for studying solar flares.
“Notably, this disturbance impacted the very lowest layers of Earth’s ionosphere, situated just tens of kilometers above our planet’s surface, leaving an imprint comparable to that of a major solar flare,” said Dr. Laura Hayes, a solar physicist at ESA.
This imprint came in the form of an increase in ionization in the bottom-side ionosphere. It was detected in very low frequency radio signals that bounce between the ground and Earths lower ionosphere.
“Essentially, we can say that the ionosphere ‘moved’ down to lower altitudes, and we detected this in how the radio waves bounce along the ionosphere,” Dr. Hayes said.
“It reinforces the idea that a supernova in our own Galaxy might have much more serious consequences.”
“There has been a great debate about the possible consequences of a gamma-ray burst in our own Galaxy,” Dr. Piersanti said.
“In the worst case, the burst would not only affect the ionosphere, it could also damage the ozone layer, allowing dangerous ultraviolet radiation from the Sun to reach Earth’s surface.”
“Such an effect has been speculated to be a possible cause of some of the mass extinction events known to have taken place on Earth in the past. But to investigate the idea, we will need a lot more data.”
The team’s results were published in the journal Nature Communications.
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M. Piersanti et al. 2023. Evidence of an upper ionospheric electric field perturbation correlated with a gamma ray burst. Nat Commun 14, 7013; doi: 10.1038/s41467-023-42551-5
