ESA's Integral space telescope has detected an unprecedented gamma-ray burst from the explosion of a distant star, causing severe disruptions to the Earth's ionosphere. The event was the brightest and most powerful of its kind ever recorded, leading researchers to explore potential links to mass extinctions throughout Earth's history.
ESA's Integral space telescope has detected a massive gamma ray burst hitting Earth. The explosion caused severe disturbances in our planet's ionosphere. Such disturbances are usually associated with high-energy particle events on the Sun, but this time they were the result of the explosion of a star nearly 2 billion light-years away. Analyzing the impact of the explosion can provide information about mass extinctions in Earth's history.
At 15:21 Central European Time on October 9, 2022, many high-energy satellites in orbit close to the Earth, including ESA's Integral mission, detected an extremely bright and persistent gamma-ray burst (GRB).
The International Laboratory for Gamma-Ray Astrophysics (Integral) was launched by ESA in 2002 and has been detecting gamma-ray bursts almost every day since then. However, this gamma-ray burst, named GRB221009A, is anything but ordinary. "This is probably the brightest gamma-ray burst we have ever detected," said Mirko Piersanti of the University of L'Aquila in Italy.
Gamma-ray bursts were once mysterious events, but are now recognized as bursts of energy from stellar explosions called supernovae, or the collision of two ultra-dense neutron stars.
Co-author Pietro Ubertini of the National Institute of Astrophysics in Rome, Italy, said: "We have been measuring gamma-ray bursts since the 1960s, and this is the strongest gamma-ray burst ever measured. In fact, it is so strong that the closest record is ten times weaker. According to statistics, a GRB as strong as GRB221009A only occurs once every 10,000 years."
Impact on the Earth’s ionosphere
Within 800 seconds of the gamma rays hitting Earth, the burst produced enough energy to activate lightning detectors in India. German instruments captured signs that the Earth's ionosphere was disturbed by the explosion for several hours. This extreme energy gave the research team the idea of looking for the impact of the explosion on the Earth's ionosphere.
The ionosphere is the layer in Earth's upper atmosphere that contains electrically charged gases called plasma. Its height ranges from 50 kilometers to 950 kilometers. Researchers call this the topside ionosphere above 350 kilometers and the bottom ionosphere below 350 kilometers. The ionosphere is very fragile, and spacecraft can maintain orbit in most of it.
One of them is the China Seismological and Electromagnetic Satellite (CSES), also known as "Zhang Heng", a space mission jointly conducted by China and Italy. Launched in 2018, it monitors changes in the electromagnetic behavior of the top surface of the ionosphere. Its main task is to study possible links 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.
In the past, GRBs affecting the bottom side ionosphere have been found at night, when the Sun's influence has disappeared, but GRBs affecting the top side have never been found. This leads people to believe that by the time it reaches the Earth, the GRB's explosive power is no longer powerful enough to produce changes in the conductivity of the ionosphere, leading to changes in the electric field.
This time, however, when the scientists looked, their luck was different. The effect is clear and strong. For the first time ever, they saw strong disturbances in the form of strong electric field changes on the top side of the ionosphere.
The far-reaching impact of gamma-ray bursts
This particular gamma-ray burst occurred in a galaxy nearly 2 billion light-years away, so 2 billion years ago, but it still had enough energy to affect Earth. While the Sun is usually the primary source of radiation large enough to affect Earth's ionosphere, this GRB triggered instruments typically used to study giant explosions in the Sun's atmosphere, known as solar flares. ESA researcher and solar physicist Laura Hayes said: "It is worth noting that this disturbance affected the lowest layer of the Earth's ionosphere, only tens of kilometers away from the Earth's surface, leaving an imprint comparable to a large solar flare."
This imprint takes the form of increased ionization in the bottom side ionosphere. The phenomenon was detected in extremely low-frequency radio signals bouncing between the ground and Earth's lower ionosphere. "Essentially, we can say that the ionosphere has 'moved' to a lower altitude," explains Laura. "We detect this in the way radio waves bounce along the ionosphere."
Laura published these results in 2022. "This reinforces our idea that supernovae in the Milky Way may have more severe consequences," she explained. There has been intense debate about the possible consequences of gamma-ray bursts in the Milky Way.
In the worst-case scenario, gamma-ray bursts not only affect the ionosphere but could also damage the ozone layer, allowing dangerous ultraviolet radiation from the sun to reach the Earth's surface. It is speculated that this effect may be one of the causes of some of the mass extinction events that have occurred on Earth in the past. But to study this idea, we need more data.
Now that they know what to look for, the team has begun going back through the data collected by CSES and connecting it to other gamma-ray bursts seen by Integral. While they can only go back to the launch of CSES in 2018, follow-up missions are already planned, ensuring that this fascinating new window will continue to open into the way Earth interacts with the very distant universe.