La Croix: What is the risk of an asteroid colliding with the Earth?
Sylvain Boulet: There is not the slightest threat of collision asteroid 2012 TC4, which should fly in close range with the Earth this Thursday. This object, about twenty meters in diameter, was discovered in 2012 and we have been observing its orbit ever since. However, the last time I made the same predictions on February 15, 2013 for another asteroid that actually posed no risk, another unidentified object exploded on the same day in Chelyabinsk, Russia. Thousands of people were injured from the shock wave that smashed windows and shop windows.
Two or three times a century, the Earth collides with objects about twenty meters in diameter, enough to form a crater. But these falls most often occur in desert areas or oceans. About five meteorites of very small sizes fall on the territory of France every year. Most of them have never been found: in the 20th century, only nine out of 500 possible were discovered!
What damage can meteorites cause?
- If the object is millimeter in size, it will burn up in the atmosphere and turn into a shooting star that does not pose any danger. If the size of a celestial body is 10 to 20 cm in diameter, it will fall apart in the atmosphere. The fall of the debris will slow down and the stones that have fallen to the Earth will not have enough energy to form a crater. Crater formation occurs much less frequently than meteorite falls.
Celestial bodies larger than 10 meters in diameter have enough mass to pass through the atmosphere and form an impact crater. A meteorite, about 20 meters in diameter, forms a crater from 300 to 400 meters, depending on the rate of fall and the composition of the rock. If the meteorite reaches a kilometer in diameter, the damage from its fall will be measured nationwide.
NASA plans to launch a rocket in 2022 to try to change the trajectory of the asteroid …
- This project is called DART and is part of a wider program. The essence of the project is to detonate a rocket on the surface of Didymoon, an asteroid 170 meters in size, the twin of the even larger asteroid Didymos. Even if this impact deflects the asteroid by only a few millimeters, this difference will increase over time and change its trajectory. This involves fundraising and building interceptor missiles. To do this, we first need to improve detection systems. Today we are well aware of asteroids more than 1 kilometer in diameter, but we know practically nothing about those whose dimensions are several meters.
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Are there other ways to change the trajectory of asteroids?
- Rocket strike is the easiest way, because it is the most studied. But in order not to come to the explosion of the atomic bomb, as in the movie "Armageddon", there are other possibilities. For example, use a "gravitational tractor": either the probe will be "put" on an asteroid and it will push it with the help of a powerful motor, or the probe will hover near the asteroid and its attraction will affect the trajectory of a celestial body.
There is one more comic, but not stupid way: to spray a coloring substance on the surface of an asteroid to change its color. For the trajectory of an asteroid depends, among other things, on how it rotates around its axis, and the latter depends on the albedo, the reflecting force of the surface. Roughly speaking, "repainting" the asteroid black or white will change its trajectory.
Audrey Dufour