In recent weeks, asteroid 2024 YR4 has become a popular “guest” in the headlines of various media. And this is not surprising, because it became the first object in many years, which has, although small, but different from zero probability of collision with the Earth in the coming years. It could happen on December 22, 2032.
On this occasion, the editors of Universe Space Tech would like to talk about how astronomers find asteroids, how their danger level is determined, and whether 2024 YR4 threatens our planet.
Near-Earth and potentially dangerous
Let’s start with a little terminology. When we talk about near-Earth asteroids, many people paint a picture in their minds of huge rocks threatening Earth and about to destroy our civilization. But that’s not the case. Near-Earth objects are bodies whose perihelion orbit is less than 1.3 a.u. The vast majority of them (99.7%) are asteroids. At the moment astronomers know 37 thousand near-Earth asteroids.
But near-Earth is not at all synonymous with the word dangerous. For an asteroid to be considered potentially dangerous, it must meet several criteria. First, it must approach the Earth’s orbit at a distance of less than 0.05 a.u. (about 19.5 times the distance from the Earth to the Moon). The second criterion is that its diameter must exceed 140 meters. The fall of an object of this size would cause serious destruction. At the same time, the wording “potentially dangerous” does not mean that the asteroid will necessarily collide with the Earth soon. It is just that he should pay increased attention. As of the end of 2022, astronomers knew 2300 potentially dangerous objects.
Thus, in terms of formal criteria 2024 YR4 is not considered a potentially dangerous asteroid, because its diameter does not exceed 100 meters. However, this does not mean that its possible collision with the Earth does not carry any risks.
How near-Earth asteroids are found
Astronomers once searched for asteroids by hand. But now this task has almost entirely been taken over by automation. 2024 YR4 was discovered using the automated telescopes of the ATLAS system, whose main task is precisely to search for potentially dangerous bodies. Other similar systems are Pan-STARRS and the Catalina Digital Survey. They are responsible for detecting the vast majority of near-Earth asteroids known to us.
At the same time, in the coming years, the ability of astronomers to detect small bodies in the vicinity of the Earth will seriously increase. Great hopes are pinned on the Vera Rubin Observatory, which will begin operations this year, as well as on the NEO Surveyor space telescope, whose launch is scheduled by NASA for 2028.
The problem of long-term forecasting
As of February 7, the probability of 2024 YR4 colliding with Earth was estimated at 2.3%. Although this is not much, it is almost twice as high as in late January, when the public first learned of its existence. At the moment, the danger level of 2024 YR4 on the so-called Torino scale is estimated at 3 points out of a possible 12. No other asteroid known to us now has a score higher than 1.
You’ve probably already asked the logical question – why do astronomers even talk about percentages? After all, if they know the object’s orbit, they should know for sure whether the asteroid will fall to Earth or warm up with it.
But it’s not that simple. Observations are needed to accurately determine the orbit of a newly discovered celestial body – the longer they last, the more accurate the prediction. But 2024 YR4 was found less than a month and a half ago. And the current arc of observations is still not enough to calculate its trajectory with absolute accuracy, which creates an element of uncertainty.
Another point worth noting is that, unlike planets, the orbits of small asteroids are generally not characterized by long-term stability. Under the influence of the gravity of the Sun and the planets, they can change quite rapidly. That is why it is difficult enough for astronomers to make any long-term predictions about potentially dangerous asteroids for at least a couple hundred years ahead. After all, during this time their orbit can change significantly.
Why the probability of 2024 YR4 colliding with Earth is increasing
As for 2024 YR4, as observations continue, the uncertainty about where it will be in 2032 will decrease. At the same time, it is possible, at first glance, a paradoxical scenario that it will increase for some time (which is happening now), and then sharply decrease to zero.
This is because as new information becomes available, the uncertainty about the area through which the asteroid will pass in December 2032 is gradually decreasing. But since it initially still has Earth in it, it will occupy an increasing portion of the reduced area and the estimate of the probability of impact will increase accordingly. This is usually a temporary phenomenon. Most likely, in the course of further observations, the Earth will move out of the uncertainty area, after which the probability of impact will decrease to zero.
It is also worth noting that in 2028, 2024 YR4 will fly at a distance of 8 million kilometers from Earth. This rapprochement will provide astronomers with the opportunity to determine its orbital characteristics and physical parameters much more accurately. The final answer about the danger of 2024 YR4 may be received only then.
Consequences of the fall of 2024 YR4
Suppose things go to the most unfavorable scenario and 2024 YR4 does fall to Earth. What would happen in that case?
As banal as it may sound, so far scientists do not have enough data to make an accurate prediction. They need to know the following things. First, the diameter and composition of the asteroid. At the moment, the diameter of 2024 YR4 is estimated to be between 40 and 100 meters. Anyone can check the difference with the help of an online calculator of the consequences of the fall of celestial bodies. When a rock asteroid with a diameter of 40 meters falls, it will release energy equivalent to about 3 megatons of TNT. But if its diameter is 100 meters, it will release 47 megatons.
NASA’s prediction, based on a conservative estimate that the asteroid has a rocky composition and is 55 meters in diameter, says that the effects will be similar to the fall of the Tunguska meteorite, which in 1908 devastated about 2,000 km2 of taiga. 2024 YR4 will explode in the atmosphere with the release of about 8 megatons of energy in TNT equivalent. In this case, the most favorable scenario would be an explosion somewhere over the ocean. An explosion of 2024 YR4 in a populated area would cause significant destruction and could devastate a major city.
However, NASA’s calculations are based on the premise that the 2024 YR4 is indeed a rocky object. And most likely, this is indeed true, because its spectrum is similar to the spectra of L and S-type asteroids. But if it does turn out that 2024 YR4 has a metallic composition, the energy of the fall will be much greater and it will not explode in the atmosphere, but will reach the surface. If the asteroid falls on land, it will form a crater, if in the ocean – it will lead to a tsunami.
Source: wikipedia
As for the potential 2024 YR4 fall corridor, it runs through the Pacific Ocean, northern South America, the Atlantic Ocean, central Africa, and northern India.
Can the Earth be protected from an asteroid
Are we capable of deflecting an object like 2024 YR4 away from Earth with current technology? In general, the answer to this question is yes. And it doesn’t require an Armageddon-style nuke. In 2022, the DART probe crashed into the asteroid Dimorphos and successfully changed its orbit, showing that the space ram is quite workable.
Source: NASA/ESA/STScI/Hubble
Of course, such an interceptor can’t be built and launched in a day. But fortunately for us, it will not have to be equipped with any complex scientific instruments or systems. The key is a precise guidance system and the right calculations. In the case of the 2024 YR4, we have a fairly comfortable margin of safety. And even if, against all odds, the asteroid falls to Earth, there will always be an option to evacuate the population from dangerous areas in advance.
But once again we emphasize that at the moment all this is rather general reasoning, which is good for loud headlines, but which lacks specificity. To talk about something definite, we need to know the exact orbital parameters and physical characteristics of 2024 YR4. And that’s going to take some time.
At the same time, we should not forget that although 2024 YR4 will almost certainly not collide with Earth in 2032, sooner or later there will be an asteroid that does threaten our planet. So the situation with 2024 YR4 is in some ways even useful, for it reminds us all of the potential celestial threats and that humanity must be prepared to deal with them if necessary.
