An astounding gamma-ray burst, dubbed GRB 221009A, continues to amaze even though it has been more than a year since it was detected. Scientists from Italy have recently published a study that shows how our planet’s ionosphere was impacted as a result of its high intensity and long duration.

The ionosphere is one of the Earth’s atmospheric layers, stretching from 60 km to more than 950 km in altitude. Containing electrically charged plasma, its lower half, called the bottom-side, extends until 350 km. Beyond 350 km lies the upper half, called the top-side.

Charging the top-side

According to Mirko Piersanti, who is a professor at the University of L’Aquila, gamma-ray burst effects have often been observed in the bottom-side but rarely in the top-side of the ionosphere. “That’s because the plasma density and conductivity in the top-side is much lower than the bottom-side. Also, to observe this effect, you need a satellite that can make observations, orbiting in this layer,” Piersanti said.

Such a satellite happened to orbit the Earth at an altitude of 507 km. “The China Seismo Electromagnetic Satellite (CSES), which is a Chinese–Italian mission, was in the right place at the right time, under the illumination zone of this gamma-ray burst. The satellite has an instrument that recorded a significant spike in the electric field in the top-side ionosphere,” Piersanti said.

The link between this observation and the gamma-ray burst event wasn’t evident at first. According to Piersanti, typically the ionosphere dynamics is completely driven by the Sun. “The first thing we thought was probably something coming from the Sun. But the Sun emitted flares that were not corresponding in time to what we observed. Also, at that time, we were sure that a gamma-ray burst would never be able to generate such a variation in the top-side ionosphere.”

“However, after analyzing the data from CSES as well as ESA’s Integral space telescope, we changed our opinion. Now, we think it is possible that a gamma-ray burst can produce an effect in the entire ionosphere,” he said.

Saved by the distance

While the series of events that generated GRB 221009A (supernova explosion or creation of a black hole) remains undetermined, the gamma-ray source is located almost 2 billion light-years away—quite a distance from our Milky Way galaxy.

According to Piersanti, if such a distant event can cause a significant disturbance in the relatively less conductive part of the ionosphere, an event occurring in our galaxy (which is 100,000 light-years wide) could cause damage to the Earth’s ozone layer.

“I haven’t gone through the ozone layer data, but this gamma-ray burst has the potential to disturb the ozone layer. In fact, with the help of statistical analysis, we are working on the possible effects a gamma-ray burst like GRB 221009A can induce in the ozone layer. We are also creating a table of the past gamma-ray bursts and the observations of the ozone layer and trying to see if they match,” he said.

Nature Communications, 2023.  DOI:  10.1038/s41467-023-42551-5

Dhananjay Khadilkar is a journalist based in Paris.

https://arstechnica.com/?p=1984948