A huge burst of gamma rays detected by the European Space Agency’s Integral space telescope has hit Earth. The explosion caused significant disturbances in the ionosphere of our planet. Such disturbances are usually associated with events involving energetic particles on the Sun, but this event was the result of the explosion of a star nearly two billion light years away. Analysis of the explosion’s aftermath could provide information about mass extinctions in Earth’s history, the European Space Agency said.
On October 9, 2022, an extremely bright and long-lasting gamma-ray burst (GRB) was detected by many high-energy satellites in orbit near Earth, including ESA’s Integral mission.
“We’ve been measuring gamma-ray bursts since the 1960s, and these are the strongest ever measured,” says co-author Pietro Ubertini of the National Institute of Astrophysics, Rome, Italy, and principal investigator of Intergral’s IBIS instrument. So strong that its closest competitor is ten times weaker. Statistically, a gamma-ray burst as strong as GRB 221009A reaches Earth only once every 10,000 years.
Within 800 seconds of exposure to the gamma rays, the burst generated enough energy to activate lightning detectors in India. Instruments in Germany recorded signs that the Earth’s ionosphere was disrupted by the explosion for several hours. This extreme amount of energy gave the team the idea to study the impact of the burst on Earth’s ionosphere.
The ionosphere is a layer of the Earth’s upper atmosphere containing an electrically charged gas called plasma. It extends to an altitude of 50 to 950 km. Researchers call it the upper ionosphere at altitudes above 350 km, and the lower ionosphere below. The ionosphere is so thin that spacecraft can maintain orbits in most of the ionosphere.
One such spacecraft is the China Seismic Electromagnetic Satellite (CSES), also known as Zhangheng, a Sino-Italian space mission. It was launched in 2018 and monitors the upper part of the ionosphere for changes in its electromagnetic behavior. Its main purpose is to study possible connections between changes in the ionosphere and the occurrence of seismic events such as earthquakes, but it can also study the impact of solar activity on the ionosphere.
Both Mirko and Pietro are members of the CSES science team, and they realized that if the GRB created the disturbance, CSES should have seen it. But they couldn’t be sure. “We previously looked for this effect in other gamma-ray bursts, but saw nothing,” says Pietro.
In the past, gamma-ray bursts have been seen affecting the lower part of the ionosphere at night when solar influence is removed, but never the upper part. This led to the belief that by the time it reached Earth, the GRB explosion was no longer powerful enough to cause a change in ionospheric conductivity leading to a change in the electric field.
However, this time when the scientists looked, their conclusion was different. The effect was obvious and strong. For the first time, they saw an intense disturbance in the form of a strong change in the electric field in the upper part of the ionosphere. “It’s amazing. We can see things that happen in deep space that also affect Earth,” says Erik Kuulkers, ESA project scientist.
This particular GRB occurred in a galaxy almost 2 billion light years away (that is, two billion years ago), but it still had enough energy to affect Earth. While the Sun is usually the primary source of radiation strong enough to impact Earth’s ionosphere, this gamma-ray burst triggers instruments typically designed to study huge explosions in the Sun’s atmosphere, known as solar flares. “Remarkably, this disturbance affected the lowest layers of the Earth’s ionosphere, located just tens of kilometers above the surface of our planet, leaving an imprint comparable to that of a large solar flare,” says Laura Hayes, a scientist and solar physicist at ESA.
This imprint manifested itself in the form of increased ionization in the lower part of the ionosphere. It has been detected in very low frequency radio signals that bounce between the ground and the Earth’s lower ionosphere. “Essentially, we can say that the ionosphere has ‘sank’ to lower altitudes, and we detected this by the way radio waves are reflected along the ionosphere,” explains Laura, who published these results in 2022.
This reinforces the idea that a supernova in our galaxy could have much more serious consequences. “There has been a lot of debate about the possible consequences of a gamma-ray burst in our galaxy,” says Mirko.