(Paris) Hit by a NASA vessel to deviate its trajectory, the asteroid Dimorphos will now be studied by the European probe Herascheduled to launch on Monday to learn how to protect humanity from a possible future threat.
Published at 12:25 p.m.
Bénédicte REY
Agence France-Presse
In a scenario worthy of Hollywood, the Dart mission ship deliberately crashed in 2022 on the asteroid Dimorphos, the “Moon” of a larger asteroid named Didymos.
This unique “planetary defense” test mission was to see if it was possible to deviate its trajectory, in the event that an asteroid one day threatened to hit the Earth.
It is estimated that a one-kilometer object – triggering a global catastrophe like the extinction of the dinosaurs – crashes into Earth every 500,000 years, and a 140 m asteroid – the threshold for a regional catastrophe – every 20,000 years old.
Among these near-Earth objects – most of which come from the asteroid belt between Mars and Jupiter – almost all those of one kilometer are known and none threaten the Earth in the coming century.
No direct threat has been identified for those of 140 m either. But only 40% of them have been identified.
If it is therefore a natural risk “among the least probable”, we have “the advantage of being able to take actions to protect ourselves from it”, indicated during a press briefing, Patrick Michel, scientific manager of the Hera mission of the European Space Agency (ESA).
Dimorphos, located some 11 million kilometers from Earth at the time of impact, measured approximately 160 m in diameter and posed no danger to our planet.
By hitting it, the NASA device – the size of a large refrigerator – managed to move it by reducing its orbit by 33 minutes.
But we don’t know what effects the impact had on the small asteroid, or even what its internal structure was before it.
However, if the Dart experiment (Double Asteroid Redirection Test) made it possible to demonstrate the feasibility of the technique, we need to know more to validate it and be able to determine what energy would be necessary, if necessary, to effectively deflect a threatening asteroid.
Nanosatellites
Numerical simulations suggest that Dimorphos is an agglomerate of rocks linked together by gravity, a body with very little resistance into which “we sink like in cohesionless sand,” says Mr. Michel.
“The consequence is that instead of making a crater”, Dart would have “completely deformed” Dimorphos, he adds.
But there are “other possibilities”, scientists still having difficulty understanding these bodies with very low gravity, “whose behavior defies intuition”, according to Mr. Michel.
Costing 363 million euros and equipped with 12 instruments, Hera will take with it two nanosatellites, The youth et Milani.
The first will try to land on Dimorphos, a first on such a small object. It is equipped with a low-frequency radar and a gravimeter to probe the asteroid’s structure and measure its gravity field.
The second will study the composition of Dimorphos using a multispectral camera and a dust detector.
The probe should normally be launched on Monday from Cape Canaveral (United States), in the fairing of a rocket Falcon 9. But an anomaly recently detected on the SpaceX launcher could force this launch to be postponed. The ESA hopes for a green light from the American authorities by Sunday.
The shooting window runs until October 27. After a flyby of Mars next year, Hera will arrive near Dimorphos in December 2026, for an initial duration of six months.
At the end of its mission, those responsible for Hera already hope to offer the probe an end comparable to that of its ancestor Rosettawho explored the Tchourioumov-Guérassimenko comet between 2014 and 2016, delicately landing it on Dimorphos or Didymos before it went out.
