Supernova ‘destroyed’ part of Earth’s ozone layer – 11/27/2023 – Science

On October 9, 2022, telescopes in space detected a jet of high-energy photons racing through the cosmos toward Earth, evidence of a supernova exploding 1.9 billion light-years away. These events are known as gamma-ray bursts, and astronomers who specifically studied that one called it the “brightest ever.”

Now, a team of scientists has discovered that this explosion caused a measurable change in the number of ionized particles found in Earth’s upper atmosphere, including ozone molecules, which easily absorb harmful solar radiation and form a protective shield that protects us from harmful solar radiation. .

“The ozone was partially reduced, that is, temporarily destroyed,” said Pietro Ubertini, an astronomer at the National Institute of Astrophysics in Rome who was involved in the discovery of the atmospheric event. The effect was detectable for just a few minutes before the ozone repaired itself, so it was “nothing serious,” Ubertini said. But if the supernova had occurred closer to us, he added, “it would have been a catastrophe.”

The discovery, reported on the 14th in a study published in the journal Nature Communications, demonstrates how even explosions that occur far from our solar system can affect the atmosphere, which can be used as a giant detector of extreme cosmic phenomena.

Most atmospheric ozone is concentrated in a thin layer of the stratosphere, about 16 km to 40 km above the Earth’s surface. It was in this region that researchers discovered a hole in the ozone layer above Antarctica, largely the result of the use of chemicals called chlorofluorocarbons, which were previously found in aerosol sprays and plastic foams. The ozone layer absorbs most of the Sun’s ultraviolet radiation, which can cause sunburn, skin cancer and crop damage.

Simulations have shown that a gamma-ray burst in the Milky Way could eliminate the stratospheric ozone layer for years, long enough to cause large-scale extinction.

Ozone also exists in lower concentrations in the ionosphere, a part of the atmosphere that extends from 59 km to 498 km in altitude. At these altitudes, it has some protective effect, but much less than at lower altitudes.

To study the effects of last year’s gamma-ray burst on Earth, Ubertini and his colleagues looked for signals at the top of the ionosphere using data from China’s Seismo-Electromagnetic satellite, an orbiter designed to study changes in the atmosphere during earthquakes.

They identified a sharp jump in the electric field at the top of the ionosphere, which they correlated to the gamma-ray burst signal measured by the European Space Agency’s (ESA) International Laboratory for Gamma-ray Astrophysics, a mission that was launched in 2002 to observe the radiation from distant celestial objects.

The researchers found that the electric field increased by a factor of 60 as the gamma rays ionized (essentially knocking electrons away) ozone and nitrogen molecules in the upper atmosphere. Once ionized, the molecule is unable to absorb any ultraviolet radiation, temporarily exposing the Earth to more damaging rays from the Sun.

Gamma-ray bursts have been known to ionize molecules in the lower part of the ionosphere, about 346 km above the Earth’s surface. But this is the first time scientists have proven that cosmic explosions like this can affect the entire ionosphere, according to Laura Hayes, a solar physicist at ESA who was not involved in the study.

It’s unusual for distant cosmic phenomena to cause such large atmospheric disturbances, Hayes added. “Fortunately for us, this gamma ray burst was extremely distant, making its effects more of a scientific curiosity than a threat,” she wrote in an email.

According to Ubertini, if the gamma ray burst had been 1 million times larger, it could have ionized enough ozone to weaken the protective barrier for days or months.

But the chances of that happening, he added, are low. Explosions as powerful as the one that occurred last year are rare, occurring only once every 10,000 years. And because gamma rays come out of supernovae as jets, they also have to be oriented in the right direction to reach Earth.

Still, knowing how the ionosphere responds to any cosmic phenomenon is important for threats that are closer to home. “This helps us evaluate recovery time after significant ionization, especially in scenarios involving intense solar flares from our Sun,” said Hayes.

The good news is that the ozone layer repairs itself: eventually, the released electrons are recaptured by ionized molecules in the air. In this case, part of the shield that protects Earth from the formidable dangers of space has been restored, keeping the planet and its inhabitants safe for a while longer from the deadly radiation that the Sun would otherwise send our way.