This week’s discovery of an Earth-impacting asteroid just hours before it exploded over the English Channel was a stark reminder that objects in outer space are far from being “out there” and could even pose a threat to us here on Earth.
What was the event on the 13th of February 2023?
A small asteroid, originally called Sar2667 but now known as 2023 CX1, entered the Earth’s atmosphere in the early hours of the 13th of February 2023, where it broke up due to the friction of the air and exploded before hitting the ground.
For only the seventh time, an asteroid was observed to be on collision path with Earth and its approximate impact point was worked out just prior to its arrival. This meant there were lots of folks observing in England and France and videoing the spectacular event.
How was this asteroid detected?
The asteroid was first observed only a few hours before it hit the Earth by prolific asteroid hunter, Hungarian astronomer Krisztián Sárneczky. He first imaged it using a 600mm Schmidt telescope when the asteroid was just two thirds of the distance from the Earth to the Moon late in the evening of the 12th of February 2023. He realised it was a near Earth object but didn’t know it was headed straight for us until he imaged it again about half an hour later. He immediately sent out notifications and 2023 CX1 was observed by other astronomers.
Only a few hours elapsed between the first observation of 2023 CX1 and its arrival at Earth. A piece of the asteroid was found a few days later by 18 year old Loïs Leblanc and other members of volunteer meteor hunting team Vigie-Ciel.
Why was it found only a short time before impact?
Astronomers constantly scan the sky looking for changes. This means they take images one night and compare them to images taken on previous nights. If something is in one image and not the other, it means there’s something moving against the background stars. This can be done manually by visually comparing two or more images, although it more likely will be done with software.
The reason 2023 CX1 wasn’t discovered earlier is simply because it was fairly small and there’s a vast number of solid chunks of rock whizzing around the Solar System. 2023 CX1 needed to get reasonably close to us before it could be confirmed. One bright spot on the horizon is that of the seven meteors detected before hitting the Earth, three have been discovered in the last 12 months. It means detection systems and analysis procedures are getting better!
How many objects are whizzing around in the Solar System?
When I looked just now, the Minor Planet Center has a count of some 1,264,694 asteroids, 31,325 near Earth asteroids and 4,449 comets known to us. (If you’re reading this after the 17th of February 2023, this number is likely to go up. Also, don’t stress about the number of near-Earth asteroids. This is simply the number of those that orbit the Sun in our general vicinity. None are on a confirmed collision course with the Earth.)
What would happen if the asteroid was much bigger?
If 2023 CX1 was much larger it stood a chance of being seen earlier. While the scans of our skies are comprehensive, they don’t give perfect, 100% coverage and detection of all incoming objects. If 2032 CX1 was larger or travelling faster, the amount of energy in the impact event would also have been much greater. The impact the other night was spectacular, but no damage was caused, nor anyone was injured.
The Chelyabinsk meteor that exploded in the air over Russia in 2013 was much bigger – about 20m across and weighed over 9,000 tonnes. The energy it carried was equivalent to approx. 400–500 kilotons of TNT. Most of the energy was absorbed by the atmosphere and this in turn produced a series of shock waves. Damage was widespread. About 7,200 buildings were damaged and some 1,500 people were injured, many by flying glass from broken windows. Despite some initial claims, the Chelyabinsk meteor was not discovered prior to impacting the Earth.
In 1908, a meteor about 50-60 metres exploded in the air over a remote region of Russia in what became known as the Tunguska event. This is the largest meteor impact confirmed and recorded in history. A vast area was impacted by the explosion which estimates put in the range of 20–30 megatons. Outside of a one-off Russian special demonstration gizmo, this is larger than most hydrogen bomb tests. Had it happened a couple of hours later, London or Paris would have simply ceased to exist. Several other major impact events have occurred during the last several thousand years, but it’s hard to separate legend from fact in many cases.
How often do serious meteor impacts occur?
It’s been suggested that impacts in the Tunguska-sized range happen about every thousand years. Air burst events at around the 5-kiloton level are estimated to happen annually. As with all events, whether they’re meteor impacts, dice rolls or poker machine spins, nothing is “due” to happen based on prior events. Just because Tunguska happened about 100 years ago, it doesn’t mean we wont have another one for 900 years. It could still happen at any time. Bear in mind that much of the Earth’s surface is covered by water where impacts or events might not be readily observed.
The Earth has also been hit by even larger bodies in the distant past, such as the Chicxulub meteor which is estimated to have been about 14km across, and a major reason why non flying dinosaurs are in short supply today.
What happens when something really dangerous is found?
At the moment, if something that could cause serious damage to life and property on Earth was found we would have big problems! There have been several concepts about how large space rocks could be steered away from an impact, but there’s nothing that is fully operational. NASA successfully tested an asteroid deflection mission last year and ESA is about to carry out further testing with its HERA program. Read more in this BINTEL article here.
Why are there chunks of rocks flying around the Solar System?
The Earth and most of the other planets were initially formed by a process called accretion. This is when matter is attracted and clumps together due to gravity. As more and more matter is collected, the total gravity is even greater and in turn, collects even more matter. During this time, the new planet generally “sweeps” up all the matter in its orbital path around the Sun. Collisions between some of these earlier planets resulted in larger bodies, but likely further spread dust, rocks and other bits of material through the Solar System. The Earth-Moon system was confirmed by rocks brought back by the Apollo missions to be the result of a large ancient collision between the Earth and another large body that threw out enough material for the Moon to form.
We sometimes tend to think of the Solar System as being an ordered place – in fact it’s somewhat chaotic with much to be discovered.
Finally – who is looking out for incoming objects and can amateur astronomers help?
There are multiple programs for finding objects from space that might impact the Earth. For example –
CNEOS is NASA’s centre for studying near Earth objects, calculating their orbits and the chances of them impacting us.
The Minor Planet Center contains an up-to-date list of objects that have been found in the Solar System:
Here’s an example of one of the more successful asteroid sleuths –
Another option is the Planetary Defense program for amateur astronomers run as part of the Unistellar Network:
As always, this is a very complex and fascinating topic that I’ve just only scratched the surface of. Additions or comments are welcome!