This suicide mission, unprecedented in space history, has a very specific goal: to slightly deviate the trajectory of the pebble by the force of the impact, and thus open the way to the development of a defense technology once morest killer asteroids. Those whose fall would be likely to devastate entire regions, even continents. It is quite clear that this is a test. In no case does the Didymos/Dimorphos system threaten to cross the course of the Blue Planet in the more or less long term.
The Earth bears the scars of shocks with major effects
The risk is not theoretical. If the surface of the Earth is slowly swallowing up its archives, hundreds of millions of years old, through the play of plate tectonics – the earth’s crust is constantly deforming and renewing itself – it nevertheless bears the scars of shocks with major effects. in the distant past. Long discussed, the collision of an asteroid or comet at least ten kilometers in diameter formed a huge crater 66 million years ago on the current Yucatán Peninsula, Mexico, and eradicated a large part of the living world, starting with non-avian dinosaurs.
The threat will appear sooner or later
On the very short scale of human history, the disintegration of a celestial object is incriminated to explain the colossal damage that has occurred in June 1908 in the uninhabited region of Tunguska, in central Siberia, where the forest has been laid down for tens of kilometers. More recently, in February 2013, a racing car regarding fifteen meters in diameter exploded over Chelyabinsk region, Russiaand generated a shock wave that shattered the surrounding windows and injured hundreds of people.
However, the crash that shook consciences is extraterrestrial. In July 1994, the dislocation and fall on Jupiter of comet Shoemaker-Levy 9 was carefully observed from Earth. The impacts were accompanied by intense heat release, generated seismic waves galore and left dark marks on the surface of the gas giant, thousands of kilometers long and discernible for months. What to wonder regarding the consequences of such a cataclysm on Earth.
In view of this remarkable pyrotechnic spectacle, the broken windows of Chelyabinsk seem like the lesser evil. Cosmic bad luck and the law of probability will sooner or later reserve more sinister inconveniences for earthlings. Normally it should be late rather than early. None of the known large objects are considered threatening over the next century. But all those that exceed one hundred meters in diameter are not counted, far from there. Asteroids number in the millions in the solar system of which they are witnesses of the first ages. They wander in orbit around our star and are, for some of them, parked in the main belt, between the orbits of Mars and Jupiter.
Aim for the target at 22,000 km/h
Nothing guarantees success, in which 27 countries are collaborating. The Dart probe, with a mass of 550 kilos, must strike the surface of Dimorphos at some 22,000 km/h. This is quite the opposite of the routine of space exploration programs, in which ships are designed to slow down as they approach their target. “It’s very difficult to adjust the trajectory at such high speeds,” warns Simone Pirrotta, who oversees Italy’s contribution to the venture at her country’s space agency. The Italians provided a 30-pound mini-satellite that separated from Dart two weeks ago to film the impact at close range. “Dart will only be able to distinguish Dimorphos from Didymos during the final hour of his race. It will do so autonomously, without intervention from the ground,” explains Nancy Chabot, an American planetary scientist who coordinates the mission. The ship carries its own camera, called Draco, which will send images until it is destroyed.
It is very difficult to adjust the trajectory at such high speed
It will then be necessary to evaluate the reality of the feat by means of terrestrial telescopes. If Dimorphos moves a bit, his revolution around his big brother Didymos will be modified. He accomplishes it in 11 hours and 25 minutes. “A few minutes more or less would be a sign of a substantial change. It might be detected in a few weeks, even a few days,” said Tom Statler, the scientist supervising the mission at NASA.
And then the Hera probe
The case will not be over yet. In two years, a European probe called Hera must pull itself out of the ground to reach Dimorphos in 2026. It will then study the impact crater and be able to map the asteroid. We do not know its chemical composition, its density, or its resistance to shocks.
