Massive asteroids can sneak up on Earth by appearing slower - study

In 2019, a 100-meter asteroid skimmed past the Earth, and we only noticed it 24 hours in advance. Now, scientists think they know why.

 An asteroid is seen heading towards the planet in this artistic rendition. (photo credit: PIXABAY)
An asteroid is seen heading towards the planet in this artistic rendition.
(photo credit: PIXABAY)

Asteroids heading for Earth may have a small blind spot they can sneak through nearly completely undetected due to a slow speed, making it difficult for astronomers to spot them in time, according to a NASA-funded academic study.

The study in question, led by the University of Hawaii's Prof. Richard Wainscoat, was published in the peer-reviewed academic journal Icarus.

NASA and other space agencies and institutions around the world have created a vast network of telescopes and other monitoring systems to detect asteroids around space, specifically ones that approach the planet, which are known as Near-Earth Objects (NEOs). Most of these NEOs are asteroids, and the ones that approach very closely and have a diameter of at least 140 meters can often be declared potentially hazardous. 

Fortunately, due to technological advancements and the size of these asteroids, most of these asteroids are detected far in advance. But according to this study, there exists a "danger zone" of sorts that lets some asteroids essentially sneak up on the planet.

The gap in asteroid detection

When in this dangerous gap in our systems, the objects can slip past our detection systems and are only noticed right before or right after they pass the planet.

 An asteroid is seen heading towards the planet in this artistic rendition. (credit: PIXABAY) An asteroid is seen heading towards the planet in this artistic rendition. (credit: PIXABAY)

This study was prompted by one such incident in 2019. 

On July 25, 2019, an asteroid known as 2019 OK skimmed past Earth at a distance of just around 70,000 kilometers. For comparison, the distance between the Earth and the Moon is just around 384,000 kilometers, making it a far closer brush.

This asteroid was around 100 meters in diameter, the largest known object to ever have such a close brush with Earth since the Tunguska impact incident in 1908, and thankfully did not impact the planet. But the worrying part is that scientists only noticed it around 24 hours before its close approach.

So how did the asteroids sneak up on us?

It should be noted that it is not unprecedented for asteroids to go undetected despite a close flyby being imminent. In fact, this is exactly what happened in 2013 during the last known significant asteroid impact. 

At the time, the 17-meter asteroid exploded over the city of Chelyabinsk in Russia. The reason it had gone undetected is that it had approached Earth from the direction of the Sun, unlike other asteroids which approach Earth as they head towards the Sun. This is because the glare from the Sun makes it difficult to spot asteroids heading our way. 

This is not an isolated incident either. In September, asteroid 2021 SG passed by the Earth and we didn't even see it before it had already passed by at a very close distance.

But this is not the reason 2019 OK had gone undetected until 24 hours before its close flyby.

Rather, this was due to a combination of several factors, such as speed, timing and the Earth's orbit.

To put it as simply as possible, 2019 OK seemed much slower than it actually was. 

A new problem for asteroid detection

When an asteroid approaches the Earth from part of the eastern sky that, to oversimplify it, can be seen at a specific hour when looking up, the asteroid might appear stationary due to Earth's orbit around the Sun and its own spin on its axis. 

This phenomenon is what made it so hard to spot 2019 OK. In fact, if it hadn't been for this, it could have been spotted around four weeks in advance. 

It isn't isolated either. According to the study, as many as 50% of asteroids heading from the east could experience this phenomenon too. 

As such, it is imperative that scientists work hard to identify these slow-moving objects so we can be better prepared.

NASA develops countermeasures

Currently, NASA estimates that the Earth is free of asteroid impacts for the next century. However, scientists are well aware of the dangers of a possible impact event and have taken steps in this direction to not only catalog the many asteroids in the solar system but possibly find means of stopping these impacts.

The most promising of these methods is deflection, which would see a specially-designed spacecraft launched at an asteroid to slam into it, slightly altering its trajectory to avert an impact.

In layman's terms: Punching it so it moves out of the way.

NASA's Double Asteroid Redirection Test (DART) Mission seeks to do exactly that. It was launched back in November towards the Didymos asteroid system where its deflection capabilities will be tested.