Rock fragments left over from the creation of our Solar System are asteroids. The Sun is orbited by over 500 million asteroids larger than four meters in diameter, which move through our Solar System at velocities up to 30 km/s, or roughly the same as Earth.
Asteroids are undoubtedly effective at piqueing public interest. This comes after numerous Hollywood productions that depict the havoc they could bring if one of them collides with Earth.
Online headlines depicting asteroids the size of a “bus,” “truck,” “vending machine,” “half the size of a giraffe,” or even an entire giraffe, appear almost every week. The words “city killer,” “planet killer,” and “God of Chaos” have also appeared in headlines.
Of course, asteroids provide a concern. Famously, life on Earth was likely brought to its knees approximately 65 million years ago by the impact of a large asteroid, which wiped off the majority of the dinosaurs. Even an object that is four meters tall and moving at a relative speed of up to 60 miles per second will be able to deliver a blow.
But what actual threats exist outside of the media labels? How many asteroids hit Earth each year, and how many are likely to go right by us?
What is the threat of a direct hit?
The NASA image below summarizes the general hazards of asteroids impacting Earth and its effects.
Small asteroids are significantly more common than giant asteroids, and they also cause a lot less damage.
NASA
As a result, Earth frequently encounters small asteroids with little impact and rarely encounters large asteroids with great impact. The smaller asteroids typically don’t even reach the surface because they are mostly destroyed when they enter Earth’s atmosphere.
A stunning “fireball” is created when a small asteroid or meteoroid, an object smaller than an asteroid, collides with Earth’s atmosphere. This fireball is a very long-lasting and brilliant variant of a shooting star, or meteor.
The remnants of the item are known as meteorites if they fall to Earth. The atmosphere burns up the majority of the object.
How many asteroids fly right past Earth?
You may get an idea of how many asteroids you might anticipate to approach our planet using a very simplistic computation.
The figures in the previous graph represent the yearly potential number of asteroids that could strike Earth. Let’s now consider the situation of four-meter asteroids. A four-meter asteroid will generally cross Earth’s surface once a year.
You would get two per year if you quadrupled that surface area. 6,400 km is the size of the Earth. The radius of a sphere with a surface area twice as large is 9,000 km. A four-meter asteroid will therefore pass by the Earth’s surface every year at a rate of once every 2,600km (the distance between 9,000km and 6,400km).
Within 6,400 kilometers of the surface of the Earth, you could expect two per year if you double the surface area once more, and so on. This fits recent records of close approaches quite well.
For objects a few meters in size, a few thousand kilometers is a relatively huge distance, but the majority of asteroids highlighted in the media are traveling at much, much greater distances.
Anything that comes within 300,000 km of the Moon is referred to as a “close approach” by astronomers. For an astronomer, “close” is typically not what the average person would consider to be “close.”
We had 126 near approaches in 2022, and 50 so far in 2023.
Consider asteroids that are over one kilometer in diameter now. It is possible to use the same incredibly simple logic as above.
We could anticipate thousands of close calls (closer than the Moon) over the course of a half million years for every such impact that could endanger civilisation.
This will happen in 2029, when asteroid 153814 (2001 WN5) passes Earth at a distance of 248,700 kilometers.
How do we assess threats and what can we do about it?
According to estimates, 95% of asteroids larger than one kilometer in size have already been found, and the other 5% are constantly being sought for in the heavens. Astronomers conduct in-depth observations to evaluate any threat to Earth when a new one is discovered.
The Torino Scale, which ranges from 0 (no hazard) to 10 (certain collision with massive object), classifies threats that are anticipated to occur up to 100 years in the future.
All currently identified objects are rated as zero. No known object has received a grade higher than 4 (a close approach deserving astronomers’ attention).
Therefore, what we actually want to know from the media is the ranking an asteroid has on the Torino Scale rather than hearing about giraffes, vending machines, or trucks.
Finally, technology has developed to the point where we might be able to take action if the Torino Scale ever rises significantly. A spacecraft’s course recently changed as a result of a collision with an asteroid during the DART mission.
It is conceivable that such an activity may assist shield Earth from impact in the future with appropriate forewarning.
Steven Tingay, John Curtin Distinguished Professor (Radio Astronomy), Curtin University
This article is republished from The Conversation under a Creative Commons license. Read the original article.
