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, thus opening the way for the development of a defense technology against killer asteroids. Ones whose fall would likely destroy 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 of great impact
The risk is not theoretical. If the Earth’s surface slowly swallows up its hundreds of millions of years old archives through the play of plate tectonics – the Earth’s crust deforms and renews itself all the time – it nevertheless bears the scars of impacts of great impact. distant past. Long debated, the collision of an asteroid or comet at least ten kilometers in diameter formed a huge crater 66 million years ago in the present-day Yucatán Peninsula, Mexico, and wiped out much 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 occurred in June 1908 in the uninhabited region of Tunguska in central Siberia, where the forest was laid down for tens of kilometers. More recently, in February 2013, a bolide about fifteen meters in diameter exploded over the Chelyabinsk region of Russia, generating a shock wave that shattered surrounding windows and injured hundreds of people.
The crash that shook the conscience is, however, extraterrestrial. In July 1994, the displacement and fall on Jupiter of comet Shoemaker-Levy 9 was carefully observed from Earth. The impacts were accompanied by intense heat release, generated massive seismic waves and left dark marks on the surface of the gas giant, thousands of kilometers long and recognizable for months. What should one wonder about the consequences of such a catastrophe on Earth.
In light of this remarkable pyrotechnic spectacle, the broken windows in Chelyabinsk seem like the lesser evil. Cosmic accident and the law of probability will sooner or later reserve more sinister troubles for the earthlings. Usually it should be late rather than early. None of the known large objects are considered to be threatening during the next century. But all those that exceed a hundred meters in diameter are not counted, far from it. Asteroids number in the millions in the solar system, which they witness from the first ages. They orbit our star and for some of them are parked in the main belt between the orbits of Mars and Jupiter.
Aim for the target of 22,000 km/h
Nothing guarantees success when 27 countries cooperate. The Dart probe, with a mass of 550 kilograms, will hit the surface of Dimorphos at about 22,000 km/h. This is the opposite of routine for space exploration programs, where ships are designed to slow down as they approach their targets. “It is very difficult to adjust the trajectory at such high speeds,” warns Simone Pirrotta, who oversees Italy’s contribution to the venture at his country’s space agency. The Italians delivered 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 last hour of its run. It will do this autonomously without intervention from Earth,” explains Nancy Chabot, an American planetary scientist who coordinates the mission. The ship has its own camera, called Draco, which transmits images until it is destroyed.
It is very difficult to adjust the trajectory at such a high speed
It will then be necessary to evaluate the farm’s reality using ground-based telescopes. If Dimorphos moves slightly, his revolution around his older brother Didymos will be modified. He achieves it in 11 hours and 25 minutes. “A few minutes more or less would be a sign of a significant change. It could be detected in a few weeks, even a few days,” said Tom Statler, the scientist overseeing the mission at NASA.
And then the Hera probe
The case will not be over yet. In two years, a European probe called Hera will pull itself off 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 shock.