- October 27, 2021 - Planétarium Rio Tinto Alcan : Astronomical News
NASA is getting ready to launch a spatial probe with an unusual mission: deflecting an asteroid! This mission will make it possible to test a planetary defense scenario devised to protect the Earth in case of possible collision with an asteroid.
The danger of a collision in the skies
In the 1990s, astronomers grew aware that our planet could be the site of an important cosmic collision. Since then, there’ve been a number of programs designed to catalogue near-Earth asteroids orbiting close to our planet. The estimate is that over 95 percent of the most threatening asteroids measuring at least one kilometer in diameter have been recorded this way. But a number of asteroids measuring a few hundred meters remain to be discovered. These can also cause significant damage around the point of impact.
Thus, several governments and space agencies have looked into defenses for protecting us from these collisions.
The DART probe
A promising scenario is one involving the deflection of the threatening asteroid by striking it with an important mass. It was to verify the feasibility of this scenario that NASA established the mission called DART (Double Asteroid Redirection Test).
The DART probe, 2.6 meters high and weighing close to 700 kilograms, will be equipped with just one instrument, a high-resolution camera. It will be used for navigation and for targeting the impact site on the asteroid. Steering corrections will be possible up to two minutes before impact.
It’s also transporting a small satellite on its side, LICIACube, manufactured by the Italian Space Agency. LICIACube will be released 10 days ahead of impact in order to change its direction and avoid it crashing into the asteroid. It’s equipped with two cameras (LUKE and LEIA, a sly allusion to the movie Star Wars) that will allow it to take pictures of the ejecta and impact crater. It will even have to carry out a flyover of the asteroid in the minutes following the collision.
A carefully chosen target
The choice of target was crucial for this mission. Impact speed will be a relatively slow 6.6 km/s, or 24,000 km/h. Orbital changes in the trajectory of a single asteroid would have been slight and difficult to measure before several years have passed. In the case of a double asteroid, changes will be perceptible in several weeks, or at most a few months.
It was finally the binary asteroid Didymos that was selected for the DART mission. This asteroid, with a diameter of 780 meters and rotating once every two hours and 15 minutes, has a 160-meter moonlet called Dimorphos. This moon takes 11 hours and 55 minutes to complete an orbit around Didymos. The probe is to crash into Dimorphos. We’ll then be able to observe the orbital changes that the collision has caused on the binary asteroid system.
These asteroids don’t represent a danger of collision with our planet, and the DART’s impact shouldn’t significantly alter their trajectory, because the changes will be too slight.
Representation of the effects of the DART collision on the trajectory of the Dimorphos asteroid.
Observing the long-term effects
The binary system will pass 11 million kilometers from the Earth in the fall of 2022. It’s at that moment that DART should collide with Dimorphos. Telescopes on Earth will be able to track the evolution of the binary system and gauge the orbital changes over the long term.
The European Space Agency, ESA, is also to launch its probe, Hera, in 2024, which will be observing the binary system in 2026. It will be able to measure more accurately the changes brought about by the collision.
All these observations will allow us to verify whether it’s possible to protect ourselves from an eventual cosmic collision by deflecting the threatening asteroid – without calling on the Bruce Willis character from the apocalyptic film Armageddon!