Asteroide Apophis

No, the asteroid Apophis will not hit the Earth in 2029: here’s what the studies really say

These days we are talking about again 99942 Apophisthe “potentially dangerous” asteroid (Potentially Hazardous AsteroidPHA) of 320 meters which will have a close pass with the Earth April 13, 2029 alone 37,000 km away from our planet, close enough to be seen even with the naked eye in some areas of Europe, Africa and Asia. It is an asteroid near-Earth composed mainly of silicates, iron and nickel, which caused alarm after its discovery in 2004 due to its probability of colliding with the Earth, later excluded by subsequent observations. These days we are talking about Apophis again and we read various contents according to which if a celestial body, even a small one, were to impact Apophis, the trajectory of the latter could be deviated enough to significantly increase the probability of a collision with the Earth in 2029, and that a solution would be anuclear explosion. However these articles tend to confuse different studies and what’s more they have Definitely clickbait titles. Let us therefore try to clarify and explain in detail what the latest studies say about Apophis.

Apophis trajectory
Trajectory of Apophis’ flyby with Earth in April 2029. Credit: NASA/JPL–Caltech

It’s worth starting with a little context. The asteroid Apophis has been the victim of a certain type of hasty and sensationalist journalism for twenty years, that is, since it was discovered in 2004. From the first observations of the celestial body – therefore still with too little data to accurately determine its orbit – a 2.7% chance of impactapproximately 1 in 37, therefore very high considering the considerable size of the asteroid, capable of releasing an energy greater than that of the Zar bomb – the most powerful nuclear device ever exploded in history – and of causing destruction on a regional scale.
Subsequent observations they then excluded the possibility of impact for the entire century starting from 2013, but for some reason the reputation of the “bad asteroid” remained attached to Apophis. Of course, in 2029 it will pass at a small distance from us, but the data collected clearly tell us that there will be no risk of collision. In fact, let us remember that “potentially dangerous asteroid” does not necessarily mean that the celestial body poses a concrete danger: by definition, a PHA is an object larger than 140 meters with an orbit capable of taking it to less than 7.5 million km from Earth.

Ok, so where do these new studies reviewing impact probabilities come from? Actually there is no study that presents collision probabilities greater than 0. And the reason is simple: the asteroid has not been visible since 2021 (it is above the horizon only during daylight hours) and will not be visible until 2027, so no one has new data which can change predictions about its orbit. Simply, the Canadian astronomer Paul Wieger he discovered together with his colleague Ben Hyatt That if – I underline “if” – Apophis were to impact another celestial body, its orbit could be deviated enough to cause it to crash into Earth. According to Wieger and Hyatt’s study, this possibility can essentially be ruled out: Apophis’s only close encounter between now and 2029 will be with the asteroid 4544 Xanthus1300 meters wide, but there will not be a collision.

However, there is another “if”: if Xanthus were accompanied by a bevy of smaller fragments – but this is something we have no evidence of – then the scenario of the disturbance in the orbit of Apophis could arise again. Wieger then pursued the topic further with another study, in which he concludes that the probability of Apophis being deflected enough to impact Earth in 2029 is one in a billion. That is, it is practically impossible. The odds of the catastrophic scenario occurring in post-2029 close encounters rise to one in a milliona thousand times higher but still negligible. In the study, Wieger himself is keen to point out that:

The probability of a small asteroid colliding with another asteroid over the course of a few years or decades is minuscule and can for all intents and purposes be considered negligible in almost all other cases. It is only the unusual trajectory of this asteroid (Apophis, Ed.) and the possible risk it poses to our planet that pushes us to examine this scenario in detail.

In other words, Wieger investigated this possibility only for a right scruple due to precautionary principle. The fact is that we will not be able to 100% exclude any possibility that the asteroid was deflected until 2027, when Apophis will be visible again in the night sky. Wieger calculates that an unlikely deflection of its orbit would most likely be more than visible with our telescopes (specifically Wieger talks about tens of arcseconds), so we will be able to discover the crime two years early. And we remember, currently it is an almost science fiction scenario, but this is where the discussion ofnuclear explosion.

This discussion comes from a completely different study, led by Nathan Moore of the Sandia National Laboratories in Albuquerque, which does not concern Apophis specifically and which demonstrates, through small-scale asteroid models, that diverting the orbit of large asteroids on a collision course with Earth through nuclear explosions it would be possible in principle beyond science fiction style Armageddon. In the famous film by Michael Bay with Bruce Willis, a device was installed directly in the asteroid to destroy it, but according to the analysis of Moore and colleagues it would be enough for the celestial body to be hit by X-rays produced by the explosion to be deflected sufficiently: the surface of the celestial body heats up to the point of vaporizing, dispersing into space thus changing the speed and direction of the celestial body. This study is very interesting because it opens the way to a new possible planetary defense technique (so far only the kinetic impact technique has been successfully tested with the Dart mission) but It’s not about Apophis and is not directly related to Wieger’s studies.