An asteroid skimmed past Earth last week just 3,000 kilometers from the planet’s surface, but no one noticed until after the fact, as NASA data points out.
Nicknamed 2021 UA1, the asteroid, which skimmed past Antarctica last Sunday, was very small: it was only about 2 meters in diameter, which is about the size of a golf cart. As such, it is unlikely that it would have caused any damage if it had impacted the planet, as it would likely have burned up in the atmosphere.
But while the damage it could have caused if it had impacted was minimal, the real danger is that an asteroid got so close to the planet that no one noticed until after the fact.
2021 UA1 flew very close to the planet, and is estimated to be the third closest asteroid flyby ever recorded without impact, after 2020 QG in August 2020 and 2020 VT4 in November 2020.
With a distance of just 3,000 kilometers, 2021 UA1 was much closer to Earth than it was to the Moon, which orbits at a distance of 384,400 kilometers from the planet. A simulation shows how close it was.
– Tony Dunn (@ tony873004) October 27, 2021
2021 UA1 is not as close to Earth as the International Space Station, which has an average altitude of 408 kilometers. However, it is much closer to the planet than many of Earth’s communication satellites, most of which are orbiting at a distance of around 35,785 kilometers.
Asteroid impacts are one of the biggest possible disasters that could affect the planet, which is why space agencies around the world monitor many of these asteroids, calculate their size, distance, orbits and whether they could hit the planet.
So why didn’t scientists detect 2021 UA1 before it passed the planet?
This is because it came from a blind spot.
Most of the asteroids detected by agencies like NASA come to Earth from the “front”, which means they come from the direction facing the inner solar system, toward Earth and the Sun.
But there are asteroids coming from “behind,” heading toward Earth from the direction of the Sun, and heading outward.
Therefore, it is very difficult to see these objects when they approach Earth, especially since they often tend to zoom in during the day when visibility is low due to glare from the sun.
Generally, the best time to detect these objects is during twilight. This is the case for all objects in space between the Earth and the Sun, such as the planets Mercury and Venus.
This is not the first time that an asteroid of this type has passed the planet without anyone noticing: on September 16, 2021, SG, an asteroid with a diameter of between 42 and 94 meters, flew past the planet approximately half the distance between the Earth and the Moon, and no one noticed until a day later.
With its large size and a speed of 85.748 km / h (about 23.8 km per second), the asteroid could certainly have had an impact if it struck.
The last known significant impact of an asteroid was on February 15, 2013, when an asteroid exploded in midair over Chelyabinsk, Russia. This asteroid was 17 meters wide and, while it did not cause casualties, the shock wave from the explosion shattered windows in six different Russian cities and caused 1,500 people to require medical attention.
This asteroid also came from “behind”.
The destructive nature of asteroids, even small ones, is well known to experts, with space agencies around the world monitoring potential catastrophic impacts, as well as investigating possible means to stop them.
One method of possibly stopping an asteroid impact is by using deflection, which would mean launching something to slightly alter an asteroid’s trajectory. The most prominent of these efforts is the Double Asteroid Redirection Test Mission (DART), which will launch in November, as a result of efforts by NASA and the Applied Physics Laboratory.
In simple terms, it means hitting an asteroid with a rocket with enough speed to change its direction by a fraction of a percentage.
However, this method has its flaws, especially the timing. The spacecraft used in the DART mission has required a considerable amount of time and resources to develop and launch. In the event of an asteroid impact that seems so sudden, that kind of weather could be a luxury the planet cannot afford.
This is especially true with asteroids coming from “behind” as they are much more difficult to track.
In fact, NASA currently has no means of accurately detecting the asteroids closest to the Sun.
However, this may change soon. NASA is building a new space telescope that would help with this effort. Called the Near-Earth Object (NEO) space telescope, it is scheduled to launch in 2026 and will be in orbit between Earth and the Sun, allowing it to better detect these objects. NEO Surveyor is expected to help find about 90% of near-Earth asteroids with a width of 140 meters or more, a size that could destroy a city if they hit.
In March, NASA had announced that the planet had little to no risk of an asteroid impact over the next century, following astronomers’ calculations that 9942 Apophis, a massive 340-meter asteroid, will safely pass the planet. at a distance of less than 32,000 km. on April 13, 2029.
However, as incidents like the close 2021 UA1 flyby show, the risk of unexpected asteroids closer to the Sun remains a potential threat.