Fireball over France sparks concerns over Earth's asteroid defences
An asteroid which exploded above France creating a 'fireball' in 2023 has just uncovered a new impact risk here on Earth.
Asteroid 2023 CX1, as it has been named, broke apart abruptly and disintegrated almost instantly at an altitude of around 28 kilometres, ripping across the sky above northern France.
This is rather unusual behaviour for an asteroid, which would ordinarily start to break apart much earlier and fall into the Earth's atmosphere in little crumbles. Instead, 2023 CX1 held together until the very last minute, releasing 98 percent of its total energy in one single explosion, causing the fireball.
According to calculations from NASA's Ames Research Center, the meteor released a dynamic pressure of 4 MPa, which created a zone of high overpressures around four times bigger than expected for an asteroid of this particular size.
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This is particularly significant as it hugely raised the risk of damage at ground level because the blast happened much lower in the atmosphere.
Two years later, after an in-depth study of the fireball, published in Nature Astronomy, scientists have revealed a new vulnerability in our planet's asteroid defences.
Planetary defence planners are now being forced to reassess what they might consider to be a 'safe' small impact going forward.
What is an asteroid?
An asteroid is essentially a chunk of rock dating back to the early formation of the solar system. Asteroids mostly tend to orbit the Sun in the asteroid belt between Mars and Jupiter, however, they can stray as far as Earth.
When an asteroid does enter Earth's atmosphere, it becomes a meteor, otherwise known as a shooting star, and when any pieces reach the ground, they're known as meteoroids.
An increased risk to Earth
While 2023 CX1 fortunately didn't cause any harm, if a larger asteroid behaved in a similar manner in terms of its delayed disintegration, it could have a very different impact.
Auriane Egal, who conducted the research at the University of Western Ontario in Canada, compared the meteor to a bomb, explaining it was a 'single blow that generated one spherical shockwave, not multiple detonations all along its trajectory'.
Therefore, if a larger asteroid released all of its energy in one single burst, the shock to the surface of our atmosphere would be significantly stronger.
“This kind of fragmentation is more dangerous,” Egal continued. “If you have a larger asteroid, its effects are going to be amplified. Maybe we need to evacuate a larger area near the predicted impact location.”
In terms of why 2023 CX1 held together for so long, the team believes it may be because the object, known as an L chondrite, has come from a battered parent in the inner asteroid belt where many collisions could have 'toughened' it up.
“We have multiple shock veins in the meteorite that are witnesses [to] lots of impacts,” she said.
“Maybe this network of veins glued the rock together, and that’s why it holds better than other typical meteorites.”
She added: “It’s a very common meteorite type, so this is the biggest worry. These L chondrites could cause more damage than expected.”
Emma Rosemurgey