In the past, GRBs 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 GRB 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,” says Erik Kuulkers, ESA Project Scientist for Integral.

This particular GRB took place in a galaxy almost 2 billion light-years away – hence two billion years ago – 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 GRB triggered instruments generally reserved for studying the immense explosions in the Sun's atmosphere known as solar flares. “Notably, this disturbance impacted the very lowest layers of Earth's ionosphere, situated just tens of kilometres above our planet's surface, leaving an imprint comparable to that of a major solar flare," says Laura Hayes, research fellows and solar physicist at ESA.

This imprint came in the form of an increase in ionisation 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,” explains Laura, who published these results in 2022.

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,” says Mirko.

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.

Now that they know exactly what to search for, the team has already started looking back into the data collected by CSES and correlating it with the other gamma-ray bursts seen by Integral. And while they can only go back to 2018, when CSES was launched, a follow-up mission has already been planned, ensuring that this fascinating new window into the way Earth interacts with even the very distant Universe will now remain open.