Earth has been hit by a huge burst of gamma rays originating from a star nearly 2 billion lightyears away, according to the European Space Agency.
The gamma ray burst caused a disturbance in Earth's ionosphere and was detected by mutliple high-energy satellites in Earth orbit, including the European Integral mission.
The detections occurred at 14:21 BST / 15:21 CEST on 9 October 2022.
Disturbances like this can be caused by high energy activity from the Sun, but this time the source was an exploding star.
Astronomers say analysing the effects of the gamma ray blast could reveal information about mass extinction events throughout Earth's history.
Strongest gamma-ray burst ever measured
Gamma-ray bursts are thought to be caused by exploding stars - supernovae - or the collision of neutron stars.
The International Gamma-Ray Astrophysics Laboratory (Integral) was launched in 2002 with the aim of detecting gamma-ray bursts.
The burst that hit Earth is known as GRB 221009A.
“It was probably the brightest gamma-ray burst we have ever detected,” says Mirko Piersanti, University of L’Aquila, Italy, and lead author of the team behind the study.
“We’ve been measuring gamma-ray bursts since the 1960s, and this is the strongest ever measured,” says co-author Pietro Ubertini, National Institute for Astrophysics, Rome, Italy, and the principal investigator for Intergral’s IBIS instrument.
What happened?
Statistically, a gamma-ray burst as strong as GRB 221009A hits Earth only once every 10,000 years.
The gamma rays impacted Earth over a period of 800 seconds, delivering enough energy to be detected by lighting detectors in India.
Meanwhile in Germany, instruments recorded that Earth's ionosphere was affected for several hours.
The ionosphere is a layer of Earth’s upper atmosphere stretching from about 50-950km in altitude that contains electrically charged gases called plasma.
The ionosphere is so tenuous, spacecraft are able to hold orbits in most of the ionosphere.
One such spacecraft is the China Seismo-Electromagnetic Satellite (CSES), which was launched in 2018 and monitors the top of the ionosphere.
The CSES looks for possible links between changes in Earth's ionosphere and seismic events like earthquakes.
It can also study the impact of solar activity on Earth's ionosphere.
Mirko and Pietro are part of the science team for CSES. They deduced that any disturbance created by the gamma-ray burst should have been detected by CSES.
"We had looked for this effect from other GRBs in the past but had seen nothing," says Pietro.
But this time, they were able to detect a strong signal from the burst, including a strong electric field variation in the top-side ionosphere.
That's even though the gamma-ray burst happened 2 billion years ago, 2 billion lightyears away.
"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.
In a worst-case scenario, the science team say a strong gamma-ray burst could damage the ozone layer, allowing ultraviolet radiation from the Sun to reach Earth's surface.
This may have been the cause of mass extinction events in Earth's history.
Now the team are going back to look at older CSES data and correlate it with other gamma-ray bursts seen by Integral.
And a follow-up mission has been planned to further study the effects of gamma-ray bursts on Earth.
The paper 'First Evidence of Earth’s top-side ionospheric electric field variation triggered by impulsive cosmic photons' by Piersanti et al. is published in Nature Communications. DOI 10.1038/s41467-023-42551-5
