SPACE

Asteroids: what danger for the Earth?

This undated image made available by NASA shows the asteroid Bennu from the OSIRIS-REx spacecraft.

© NASA/Goddard/University of Arizona/CSA/York/MDA via AP

Text by: Nenad Tomic

7 mins

These large stray rocks in the solar system are of great interest to scientists and astronomy lovers.

Studying the composition of asteroids and their movements can provide many answers as to the origin of the universe, but also helps to guard against a fall that would represent a great threat to humanity.

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What is an asteroid?

Asteroids are more or less large rocks that are mainly located between Mars and Jupiter.

But a non-negligible quantity crosses the Earth's orbit, they are called “near-Earth cruisers”.

It is these asteroids that have the possibility of colliding with our planet.

Even if the risks of collision are very low, they are very real.

Scientists are almost unanimous on the theory of the disappearance of the dinosaurs.

66 million years ago, an asteroid about 12 kilometers in diameter fell near the town of Chicxulub, Mexico, causing a pile of dust and soot.

As the Earth's atmosphere cooled considerably, the dinosaurs could not survive.

Illustration of the Chicxulub crater, shortly after its formation.

This crater was formed 66 million years ago, off the coast of present-day Mexico, following the impact of an asteroid 10 to 14 kilometers in diameter.

It is widely believed that the asteroid caused the extinction of dinosaurs and other species around this time.

© GettyImages/Mark Garlick/Science Photo Library

danger from heaven

Aware of the danger that such a collision would represent for humanity, space agencies (in particular NASA and the European agency ESA) closely monitor these large celestial bodies and often discover new ones never observed before.

Some trajectories are monitored very closely to possibly anticipate a collision.

Specialists point the finger in particular at the asteroid Apophis which will graze the Earth very closely in 2029, or even the asteroid Bennu.

For the moment, their trajectories do not seem very worrying, but different criteria such as the gravity of the planets can modify their orbit and lead them straight towards us.

Since 2004, the year of the discovery of Apophis, astronomers have observed that its orbit is gradually approaching Earth's orbit.

Even if NASA ensures that there is no danger that Apophis will fall from the sky, the concern is real: the asteroid measures 350 meters and weighs around 27 million tons.

In 2021, it has already passed close to Earth, approaching 17 million kilometers from our planet (44 times the Earth-Moon distance).

During this passage, he did not pose a threat.

On the other hand, its approach in 2029 will be almost visible to the naked eye: Apophis will graze the Earth at only 32,000 kilometers.

It is one tenth of the distance between our planet and the Moon.

This large rock will therefore pass between the Earth and certain geostationary satellites!

it has already passed close to the Earth, approaching 17 million kilometers from our planet (44 times the Earth-Moon distance).

During this passage, he did not pose a threat.

On the other hand, its approach in 2029 will be almost visible to the naked eye: Apophis will graze the Earth at only 32,000 kilometers.

It is one tenth of the distance between our planet and the Moon.

This large rock will therefore pass between the Earth and certain geostationary satellites!

it has already passed close to the Earth, approaching 17 million kilometers from our planet (44 times the Earth-Moon distance).

During this passage, he did not pose a threat.

On the other hand, its approach in 2029 will be almost visible to the naked eye: Apophis will graze the Earth at only 32,000 kilometers.

It is one tenth of the distance between our planet and the Moon.

This large rock will therefore pass between the Earth and certain geostationary satellites!

Mission: prepare the defense

For some years now, NASA and ESA scientists have been working on solutions to consider if, in the more or less near future, a near-Earth asteroid poses a risk to humanity.

Constant observations and modern technologies (powerful telescopes, satellites, computers that allow precise calculations, etc.) make it possible to predict the orbits of the most dangerous asteroids.

In the event of a proven risk, the space agencies must be able to develop the best solutions to anticipate and avoid a potential danger for the planet.

Among the solutions devised, one seems to be giving convincing results with NASA's recent DART (Double Asteroid Redirection Test) mission.

It is above all a question of anticipating and improving physical models in order to be ready in case of need.

Conceived in 2017, the DART mission aims to reach an asteroid with a ship to try to change its trajectory.

Thanks to the Falcon 9 rocket, the DART probe takes off in November 2021. Destination: Dimorphos, an asteroid about 160 meters in diameter and moving at a speed of 6.6 km/s.

Ten months later, on September 26, 2022, the DART probe has traveled almost 11 million kilometers and, with all its weight (610 kilograms), crashes into Dimorphos with a speed of 34,000 km/h.

A scenario worthy of the film Armageddon, but without a human crew: cause the impact that will deflect the rock from its orbit.

Because the objective of the mission is to develop a technique which makes it possible to avoid the collision of a large asteroid which, one day, would threaten to strike the Earth.

Once the DART probe hits the asteroid,

whose filmed images are impressive, several days later, it is the absolute suspense.

It is necessary to wait for the information to arrive to know if the operation is a success or a failure.

Then, on October 12, 2022, NASA announced that the mission was more than a success.

Indeed, the ship was to deviate the trajectory of the asteroid by 11 minutes, but the result showed almost triple: 32 minutes, which represents a very significant deviation from its orbit.

Clearly, if this object as large as half the Eiffel Tower was heading towards Earth, its trajectory would be kept at a good safe distance for us!

This is'"

Then, on October 12, 2022, NASA announced that the mission was more than a success.

Indeed, the ship was to deviate the trajectory of the asteroid by 11 minutes, but the result showed almost triple: 32 minutes, which represents a very significant deviation from its orbit.

Clearly, if this object as large as half the Eiffel Tower was heading towards Earth, its trajectory would be kept at a good safe distance for us!

This is'"

Then, on October 12, 2022, NASA announced that the mission was more than a success.

Indeed, the ship was to deviate the trajectory of the asteroid by 11 minutes, but the result showed almost triple: 32 minutes, which represents a very significant deviation from its orbit.

Clearly, if this object as large as half the Eiffel Tower was heading towards Earth, its trajectory would be kept at a good safe distance for us!

This is'"

its trajectory would be held at a good safe distance for us!

This is'"

its trajectory would be held at a good safe distance for us!

This is'"

”, welcomed the head of NASA, Bill Nelson during the press conference.

NASA confirms that the impact of the DART mission changed the movement of the asteroid in space.

© NASA/ESA/STScI/Hubble

But the research does not stop there.

The European Space Agency is due to launch the HERA mission in a few years, the purpose of which is to calculate and prospect all the changes in orbit of Dimorphos and its large companion, Didymos, another asteroid.

These latest results are reassuring, as there are more than 1,300,000 recorded asteroids of all sizes, and around 30,000 near-Earth objects are now known to be over a kilometer in diameter.

And none are likely to fall on our heads in the next hundred years.

But the problem is not with large asteroids.

Only 40% of small asteroids over 140 meters in diameter are spotted.

The others are sometimes invisible or spotted at the last moment, often too late to launch such a mission as DART when a pebble of this size can devastate an entire region, even a country.

Hence the importance of developing telescopes and permanent sky monitoring systems.

What other scientific interests?

Apart from preventing a catastrophe, studying asteroids is mainly used to understand the formation of the solar system.

One of the first missions of this kind was Rosetta, launched by an Ariane 5 rocket on March 2, 2004 towards comet Tchourioumov-Guérassimenko, known as Tchouri.

During its journey, the probe crossed the asteroid Lutèce in July 2010, then succeeded in landing the Philae lander on the comet.

This small device collects valuable information on the structure and composition of Tchouri.

Since then, other missions have targeted carbonaceous asteroids, considered as witnesses of the formation of our galaxy, but also of the beginnings of life on Earth, which the asteroids could have brought.

Studying celestial bodies obviously presents many scientific interests, in particular asteroids, which are at the origin of the multiplication of space missions.

Especially since their cost is not very high compared to manned missions to the ISS or the next return of man to the Moon.

The very rapid evolution of technologies thus makes it possible to envisage even more distant exploration missions towards other asteroids or even comets.

Finally, the probability of seeing a large asteroid endanger our humanity is rather low, but it cannot be completely ruled out.

Thanks to current technologies, man has tools that can be used to prevent or prevent a collision.

But we are never safe from an object that would pass without being detected by observation systems.

Hence the importance of strengthening international cooperation in this field of action in order to develop appropriate and effective actions if, one day, we are confronted with such a problem and urgent action is required.

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