Planetary defense: HERA took off to study the asteroid Dimorphos

The HERA probe, which will study the asteroid Dimorphos, took off Monday from Cape Canaveral, Florida, aboard a SpaceX Falcon 9 launcher, according to a live broadcast from the European Space Agency (ESA).

The mission is due to arrive at the end of 2026 near this asteroid, hit two years ago by a NASA vessel to deviate its trajectory during an unprecedented test of planetary defense.

The launch was preceded by several days of uncertainty. SpaceX, whose Falcon 9 had suffered from an anomaly on its previous flight, only obtained the green light from the American authorities on Sunday.

In addition, weather conditions were uncertain as Hurricane Milton approached the coast of Florida (southeastern United States).

Milton, which strengthened into a Category 4 hurricane on Monday, has already led to the postponement of the launch, initially scheduled for next Thursday, of Europa Clipper, a NASA mission which is to study an icy moon of Jupiter to find out if its ocean underground can shelter life.

The HERA probe must meet Dimorphos, a small body only 160 meters in diameter, which is the moon of a larger asteroid, Didymos.

In 2022, in a scenario worthy of a science fiction novel, NASA’s DART (Double Asteroid Redirection Test) probe deliberately crashed on its surface.

Protect the Earth

The objective of this unique test of planetary defense was to assess whether it was possible to deflect an asteroid’s trajectory and use this technique if, in the future, an asteroid threatened to hit Earth.

It is estimated that every 500,000 years, a one kilometer object crashes into the Earth (triggering a global catastrophe like the extinction of the dinosaurs), and that a 140 m asteroid (the threshold for a regional catastrophe ) does the same every 20,000 years.

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.

It is therefore a natural risk among the least likelymore on a the advantage of being able to take actions to protect yourselfindicated during a press briefing Patrick Michel, scientific manager of the HERA mission of theESA.

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, which is 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 the impact.

However, if the DART experiment 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.

Two nanosatellites

Numerical simulations suggest that Dimorphos is an agglomerate of rocks linked together by gravity, a body with very little resistance in which we sink like in sand without cohesionsays Mr. Michel.

The consequence is that instead of making a craterDart would have completely deformed Dimorphos, he adds.

But there is other possibilitiesscientists still have difficulty understanding these bodies with very low gravity, whose behavior defies intuitionaccording to Mr. Michel.

Costing $544 million and equipped with 12 instruments, HERA will carry two nanosatellites, Juventas and 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.

At the end of the HERA mission, its managers already hope to offer the probe an end comparable to that of its ancestor Rosetta – which explored the Tchourioumov-Guérassimenko comet between 2014 and 2016 – by delicately placing it on Dimorphos or Didymos before ‘she goes out.