Should We Be Concerned About Asteroid 2024 YR4’s Potential Impact on Earth?

The asteroid 2024 YR4 was discovered on December 27, 2024 by American researchers from the University of Hawaii posted in Chile for research operations for geocroisters asteroids – small celestial bodies whose orbit crosses that of the earth.

[Article issu de The Conversation, écrit par Patrick Michel, Astrophysicien, Directeur de Recherche au CNRS, Responsable Scientifique de la mission spatiale Hera (ESA), Observatoire de la Côte d’Azur, Laboratoire Lagrange, Université Côte d’Azur]

Following this discovery, telescopes around the world detected this object, the diameter of which is estimated between 40 and 90 meters, and carried out detailed monitoring. Images dating from the day before and the day before (December 25 and 26, 2024) were also found.

Until then, nothing very original, since we are currently detecting about 3,000 geocroisters asteroids per year … until the probability of this asteroid impact calculations with the earth give a non-zero probability for December 22, 2032.

In the first days following its discovery, this probability was extremely low, of the order of 0.3 %. Then, the accuracy of the asteroid trajectory improved with new observations, and the probability of impact increased until January 27, the three independent calculation centers dedicated to its estimate (that of NASA, that of ESA and the Neodys system of the University of Pisa, supported by ESA), each using their own calculation method, converge with the value of 1 %. As of February 11, 2025, it was even 2 %.

But for the moment, this probability is very uncertain, because we do not know the trajectory of the asteroid 2024 YR4. Determining this trajectory is the whole issue of the coming months.

In comparison, in 2004, an asteroid 340 meters in diameter called Apophis had first had a probability of calculated impact of 2.7 % (for 2029), but the calculations of the following days had determined that the probability of collision was Finally zero. Feeling us, we had then realized that a work was necessary to put a coordinated response on an international scale, this risk concerning all of humanity, allowing to have a well -defined process to move from prediction to 'Information, then to an action if necessary. Today, such a process is established.

An alert threshold and uncertainties

Since we started to set up an international coordinated response, the 1 % threshold had never been reached. However, it is precisely this threshold which was defined to issue a notification by the steering committee of the international asteroid alert network which, under the aegis of the UN, is responsible for assessing the risks of impact (the iAwn or International Asteroid Network).

Thus, on January 28, NASA brought together the IAWN Visioconferencing IAWN steering committee, which shows the reactivity and efficiency of the international coordination implemented to deal with the risk of impact. Following this meeting, the steering committee-of which I am a part-sent a notification to the member states of the United Nations and to the working group devoted to the “planetary defense” (that is to say at the risk of impact of asteroids), bringing together the space agencies which participate in the planetary defense (the SMPAG for Space Mission Planning Advisory Group).

It should be noted that this 1 % criterion is very low, but high enough for a notification to be issued, allowing to prepare well upstream in the event that the probability is maintained or increases as the observations of this object . Moreover, since she exceeded this symbolic threshold, the probability continued to increase, then it decreased very slightly, reaching 2 %, on February 11, 2025. This is neither abnormal nor necessarily disturbing (knowing that 'A probability of collision of 2 % corresponds to 98 % chance that nothing happens).

Indeed, each new observation improves our knowledge of the current trajectory of 2024 YR4, and therefore to reduce uncertainties on its future trajectory.

There are uncertainties in our picy forecasts We know badly the current positions and speed of the asteroid, which determine its future positions and speeds. A possible analogy is that of a football ball: depending on the exact position of the foot when it hits, the ball leaves in order or next. If we do not know exactly the position of the foot at the start, the calculations can predict a goal … or an outing of the frame.

One can also imagine a cloud of starting points. The larger this cloud (the greater the error on speed and position), the more possible departure points and therefore possible developments. As the observations progresses, the cloud of initial conditions (speed and position) possible, reduces the uncertainties on its future trajectory.

Today, because of our ignorance of the current conditions, the area of ​​uncertainty in 2032 is much greater than the distance of the earth to the moon (it is currently of more than a million kilometers) – it is To say the current uncertainties, for this body whose dimensions are estimated 40 to 90 meters wide.

Here, it should therefore be noted that the current probability should not be taken as acquired, because there are many efforts to reduce uncertainties. We can therefore hope that, among all possible trajectories, we will soon be able to eliminate those leading to a collision with the earth.

What are the next steps?

If amateur astronomers were able to participate in the observation of 2024 YR4, it is now the telescopes of more than 4 meters, then those of more than 8 meters, which will observe 2024 YR4 until April. These measures will make it possible to specify these probability of impact calculations. After April, the asteroid will be too far from us so that we can distinguish it from the earth, until June 2028.

But good news arrived on February 10: the Observation Time Awarding Committee of the Spatial Webb Telescope approved the proposal submitted to observe 2024 YR4 with this telescope. This will make it possible to carry out the latest measures of its trajectory and to estimate its diameter with a precision of 10 %. Indeed, knowing if it measures 40 or 90 meters would be very useful, in particular to estimate more precisely the damage than an impact on earth would produce and to design a mission which would aim to deviate it.

Today, according to a statistical analysis of the evolution of this probability, we believe that it is very likely that the probability of impact will be canceled in the coming weeks. But this probability of impact could also remain non -zero and, by extrapolating its evolution until April, in the worst case, it can potentially reach 20 % – we should live with that until the next passage of the 'Asteroid 2024 YR4 in three years.

Finally, if a non -zero probability were to be confirmed in 2028, there will only be four years left to act. Defining a mode of action will then be the role of the SMPAG, which will meet first to take stock of the situation next April. But it is far too early to talk about this scenario and whatever happens, there is no reason to worry because the planetary defense community is at the front and takes care of this object with all the necessary attention . Nothing is overlooked and everything is communicated with transparency.

What damage could cause this asteroid if he had to collide with the earth?

The last question often asked is: what damage could cause this asteroid if it should collide with the earth? It all depends on its exact mass, which depends on its density and its volume, and therefore on its diameter.

If he measures 40 meters in diameter, he will produce at least damage such as those caused by the explosion of an object of the same size eight kilometers above the Toungouska forest in Siberia. June 30, 1908 (this is why June 30 is the UN day of asteroids): two thousand square kilometers were sprayed. A capital or a big city would pass there, if it happened above one of them; But it should not be forgotten that the earth is mostly covered with water and deserts. Statistically, it is therefore more likely that a local event occurs above an uninhabited area without other long-term consequences, as in the case of Toungouska.

If the asteroid 2024 YR4 measures 90 meters, the damage could be spread over a region. Naturally, the exact consequences, in particular the fraction of mass lost in the atmosphere and the impact energy, depend on the mass of the object and its structure that we do not know.

We must first wait to see how the probability of impact will evolve by April and specify which terrestrial regions would be affected if it should be reached. According to current data, if the impact of 2024 YR4 should occur in 2032, it would be somewhere on a strip surrounding the earthly sphere, called “uncertainty corridor”, ranging from the eastern part of the Pacific Ocean Up to South Asia, passing through the northern part of South America, the Atlantic Ocean, part of Africa and the Arabian Sea. It is too early to know where precisely an impact or an explosion in the atmosphere would occur in this band.

If the probability remains non -zero, this will be the subject of IAWN and SMPAG meetings to decide on the actions to be carried out.

To conclude, we must be delighted with our reactivity and the extraordinary efficiency of international coordination that we have established in the last ten years in the face of this first case which exceeds the alert criterion that we have defined. At the time of Apophis, twenty years ago, we had none of this.

In parallel, the inventory of these objects must continue and their characterization from soil and space too, in order to increase our knowledge on their properties. Deviation tests must be carried out, such as that offered by the Dart missions of NASA and Hera de l'ESA. We are continuing our efforts to prepare for the different scenarios that this risk can confront us. And I allow myself to say that I am proud to be able to modestly represent France in several bodies and the spatial missions devoted to it, as well as in the community of French scientists who are involved to protect the land from the arrival of 'A celestial body, which is not impossible and what the dinosaurs did not know how to do …