Every two years, the International Academy of Astronautics engages in a funny exercise: simulating an asteroid impact on Earth and its consequences.
Even if it is one of the least probable natural hazards, specialists know that in the long term, this catastrophic event can happen.
"It's so complex that it is better to take care of it, to be ready before you need it", explains Dr Patrick Michel, research director at the CNRS at the Côte d'Azur Observatory.
The analogy with the Covid-19 pandemic, made by the European Space Agency, is according to him “absolutely perfect”: “What is happening to us at the moment is a crazy thing, and we realize that prepare for it only when we need it, it's too late to get it right.
"
For five days at the end of April, during the International Planetary Defense Conference, the scientists therefore played out a hypothetical scenario supposed to take place over six months, the “Deep (fake) impact”, worthy of a science fiction film.
A giant role-playing game rich in lessons for the astronautics community.
The fictitious scenario
Let us first dive into this parallel reality.
On April 19, the Minor Planet Center discovers an asteroid.
He baptizes it 2021 PDC.
The next day, the American (NASA) and European (ESA) space agencies sketch several impact dates with the Earth.
The two quickly agree: there could be a collision around October 20, 2021. In six months.
At that time, the probability of an asteroid crash on Earth is a one in 2,500 chance. Its magnitude suggests an asteroid 120 meters away, but observers are in total haze: it could very well measure 35 like 700 m!
And the consequences would not be the same at all ...
Assuming it measures 150 m, the object could affect up to 86 million people, mainly because of its explosion, but also because of the burns and tsunamis it will have caused.
Every night, astronomers track him down with a magnifying glass.
On May 2 (day 2 of the simulation), they 100% confirm the asteroid's fall to Earth and the date of October 20.
The crash zone is getting thinner: in the heart of the European continent, somewhere between Norway and Greece.
But it's too late to launch a space mission that would deflect it, especially since we still don't know much about its size.
Day 3, the atmosphere is gloomy.
It's June 30, and astronomers now know that in four months the imaginary asteroid will hit central Europe, somewhere between Germany, the Czech Republic and Austria.
The only good news: the fresh measurements from a satellite indicate that the object is not as big as expected, maximum 500 m.
Six days before impact, the asteroid rushes towards Earth.
It is still more than 6 million km.
We know the precise area of the crash: the asteroid will destroy an entire cross-border region, within a perimeter between 150 and 300 km wide.
The astronomers, taken aback, could do nothing.
Exercise
A scenario like this, we invent one every two years, since 2013. As usual, it is Paul Chodas, in charge of the NEO program of NASA at JPL (Jet Propulsion Laboratory), who sticks to it.
For months, he imagined the "short one": in this scenario, scientists know at the last moment, that is to say six months before impact, that an asteroid will fall on our planet.
The participants fully play the game: "we organize ourselves every day to know who does what, we debate the best way to deflect it, we embark on a whole lot of calculation, it's very dynamic," says Dr. Patrick Michel, also responsible for the European HERA mission.
This space mission contributes to the first deviation test of a (real) asteroid with the NASA DART mission, which will be launched in November.
Experts around the world not only want to predict, but also prevent the impact.
Or at least learn to organize early enough to protect people, and in a coherent way, internationally.
"The purpose of these exercises is to test where we are in all these efforts," summarizes the researcher.
During these five days, we get ready and all aspects are considered: the UN meets, as if we were there, to decide whether or not to activate the nuclear option, for example.
We think of things that we never thought of before, and we move forward a lot.
"
For him, this simulation is a "concrete demonstration" of the need to list asteroids, their position and their size, so as not to be taken aback.
So far, scientists have never been able to avoid the impact.
The lessons to be learned
“As we did not know how to manage the problem, we can come back to it and ask ourselves: what should we have done to avoid it?
»Explains Dr. Patrick Michel.
And there, with hindsight, “it's very easy to find solutions”.
Every decision obviously has serious consequences.
For example, consider the economic cost of a large-scale evacuation.
“As we do not know whether to evacuate 10 or 100 million people, we can take the risk of evacuating a lot of people when the impact will ultimately be minor.
Remember the reproaches addressed to Roselyne Bachelot
(when she ordered too many vaccines against the H1N1 flu, Editor's note)
!
Conversely, we can underestimate the dangerousness of the object and end up with millions of deaths… ”
The challenge is also to "progress in all areas", as in that of communication.
In such a situation, who communicates?
At what moment ?
And how do you avoid panic?
With each simulation, astronomers learn lessons for subsequent times.
The International Academy of Astronautics has already made an inventory of objects over 1 km long that threaten us.
Almost all of them are known to experts, none of which will pose a problem for the next century.
“Now, the objective is to take an inventory over the next ten years of threatening objects over 140 m, because only 30% of them are known.
This will allow us to identify the danger further upstream.
This is what we lack: in six months, it is difficult to assess the size of the object and therefore its consequences ”.