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A few more days and the Dart probe will crash into the Dimorphosthe small asteroid chosen as the target to study if, and how, we could stop one of the asteroids dangerous directed towards our planet, in case of need. A historical event, if we think that with all the advances made by science in the last century, at the moment we are still completely powerless in the face of the dangers that come from space. And if it is true that the NASA And Esa have been cataloging for some time the potentially dangerous objects that pass near our planet, and none of those known represent a risk at least for the whole century in progress, it is also true that currently we only know the 40% of the existing ones. And that the close passages (so to speak, of course) are really on the agenda. A few examples? Here are some of the most dangerous asteroids that roam around our planet.
Potentially dangerous items
To begin, it is worth pointing out that if our Solar System probably hosts millions of asteroids of all shapes and sizes, not all of them obviously represent a danger to our planet. What scares us are those who move in an orbit that brings them close enough to the Earth to make one collision at least possible, and of sufficient size to do real damage once they enter our atmosphere. In English they are defined Potentially Hazardous Object (Pho), o potentially dangerous objectsand their formal definition speaks of asteroids or comets with a diameter of at least 150 meters and an orbit with a minimum distance from Earth of less than 0.05 astronomical unitsequal to seven and a half million of kilometers, or about 19 and a half times the distance that separates us from the Moon. Such an object has a sufficient chance of being able to collide with our planet in the future, and in the event of an impact it would cause damage to an extent never recorded in human history.
Currently only 20 potentially dangerous objects are known with a non-zero probability of impact with the earth (albeit minimal), and none for which the Rendez Vous it could arrive within the next century. As we said, however currently NASA estimates to have just identified the 40% of potentially dangerous objects that lurk in Space, and even if new ones are now being discovered at the rate of about 500 a yearhe reckons that others will be needed 30 years to catalog the 90%a goal set for the 2020but which evidently proved to be much more difficult than expected.
The comet
Moving on to our parade of dangerous asteroids, let’s start with an exceptional post. It is not in fact an asteroid, and it has not even passed near the Earth. There Shoemaker-Levy 9 however it was still the protagonist of one of the most catastrophic and spectacular celestial collisions of our days, crashing into Jupiter in the July 1994, with such power to leave a hole the size of our planet in the clouds of the gas giant for months. The event, recorded by many observatories and by the Hubble Space Telescope, had an incredible resonance, opening the eyes of the world to the dangers of a close encounter with a space giant. For NASA, the event meant an important increase in funding for the research of Near Earth Object (i.e. the objects orbiting near the Earth), with the initial goal of mapping the 90% of those above the kilometer in diameter (easily reached within the allotted time) and then to do the same with those above 140 meters (an objective which, however, as we have seen, for now continues to remain elusive). For Hollywood, however, the period of catastrophic space-based blockbusters began, with the release of two colossals, “Armageddon” And “Deep Impact“, In the solo 1998. Self Dart it is flying towards its destination, however, it is also thanks to the comet Shoemaker-Levy 9.
Tunguska
Returning to Earth, the most powerful impact of a meteorite on our planet that we have witnessed was the so-called Tunguska eventcaused in 1908 from the fall of a meteorite of about 60-80 meters in diameter in a remote area of the Siberia Central. The explosion of the asteroid, which occurred several kilometers above the ground, generated a glow that was perceived beyond 700 kilometers away, and a shock wave powerful enough to knock down all the trees in an area of over two thousand square kilometers. If something similar happened in an inhabited area, the consequences would clearly be dramatic. However, it is estimated that events of this magnitude occur about once every 300 yearsand therefore statistics in hand, we should be safe at least for another couple of generations.
Apophis
So we come to the truly terrifying encounters. 99942 Apophis is an asteroid of approx 340 meters in diameter discovered in 2004, which for years was thought to be on a collision course with our planet. The most recent calculations and observations have made it possible to exclude the possibility, at least during this century, but it remains destined for a truly close passage with the Earth: the April 13, 2029 it will touch our planet at a distance of just 31 thousand kilometres from the surface. For comparison, the Moon is about 350 thousand kilometers, and geostationary telecommunications satellites are normally placed in orbit at approx 36 thousand kilometers.
Bennu
We wrote about it in the past when it was joined by NASA’s Osiris Rex mission, the first mission that collected samples of an asteroid directly at the source. Bennu however, it has also been talked about for other reasons: in the next few centuries it will pass dangerously close to our planet, and on several occasions. Fortunately for us, the (minimal) risks of an impact on Earth are concentrated in the last decades of 2100 and early 2200when the probability of a collision will reach on average 0.05%. If it ever really does happen, the consequences could still be devastating: with an average diameter of 500 metersthe resulting explosion would reach about i 1,200 megatons of power. We hope that by that day, also thanks to the Dart mission, humanity will be able to defend itself.
2019 OK
We conclude with an asteroid that reminded us of the unpredictability of the Universe. 2019 OK the July 24, 2019 just one and a half million kilometers from Earth, and just one day from the moment when it would have reached the minimum distance from our planet. The July 25at one twenty-two (UTC) in the morning, he just missed us 70 thousand kilometers, whizzing about 88,500 kilometers per second. An extremely rare event, given that asteroids of its size are usually detected with greater warning, and rarely pass so close to our planet; but not for this – evidently – impossible. The diameter of 2919 OK is estimated between 50 and 100 metersand an impact with the surface would therefore have potentially devastating consequences if it had occurred in an inhabited area.
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