It is a small harmless body about 160 meters in length, currently located 11 million kilometers from Earth.
However, in a little less than three days, Dimorphos will be violently rammed by a probe and all of humanity will be able to witness the impact.
Objective: to test the full-scale deflection of an asteroid, like Dimorphos, or a comet, to be ready the day such an object threatens our planet.
The first operation of its kind.
The impact will take place on the night of Monday 26 to Tuesday 27, at 1:14 a.m., Paris time zone.
“The time is not perfect for Europe but it is almost prime time in the United States,” jokes Nancy Chabot, planetary scientist at Johns Hopkins University in Maryland.
Before finishing its race on the big "pebble", the DART probe (for Double Asteroid Redirection Test) will have time to deliver detailed images, which NASA, responsible for the project, will broadcast live.
The mission scientists are expecting a great show, full of surprises, including for them.
“We know the size but not the shape of this asteroid.
These small bodies of the solar system are crazy, they are small geophysical worlds that we still have trouble understanding.
What DART will see, we don't know.
We are going to discover it with the general public and together share the excitement of encountering a new territory,” enthuses Patrick Michel, astrophysicist at the Côte d'Azur Observatory and member of DART.
LP / Infographic
An hour before the crash, viewers will be able to distinguish Dimorphos from another asteroid around which it orbits, Didymos.
From then on, DART will autonomously navigate to its target.
“The last minutes should be extremely exciting.
The last details will be a few tens of centimeters, giving the impression of holding part of the asteroid in your hand, ”predicts Tom Statler, researcher in NASA's scientific missions directorate.
And then, three seconds before impact, as the asteroid's surface fills the entire screen, the transmission will stop.
Like when the end credits appear at the cinema.
Dozens of pointed telescopes
Will the story end there?
On the contrary: this is where it all begins.
About ten days before the fateful moment, LICIACube, a satellite of the Italian space agency, dissociated itself from DART to be able to capture the images of the first seconds after the shock.
Two other satellites, Milani and Juventas, will be dropped about thirty kilometers from Dimorphos to capture data and more than 30 telescopes on Earth, as well as the James Webb Space Telescope, will also follow the impact.
However, since the gravity there is extremely low, the dust will take a long time to settle on the floor of Dimorphos.
Too long for the nano-satellites currently approaching the asteroid.
Another mission is necessary to examine the consequences of the collision.
It is called HERA, is piloted by the European Space Agency (HESA), will be launched in 2024 and will begin operations on site in January 2027. What it will find, no one knows.
“A lot of things can happen: a crater or a total deformation of the object,” says Patrick Michel.
Read alsoDART probe against asteroid: how space agencies anticipate the risk of collision with Earth
Only 15% of asteroids are double, like the Didymos-Dimorphos couple.
Why did you choose this type of object?
Because, precisely, we are trying to calculate how the impact will disturb it.
Dimorphos revolves around Didymos in 11 hours and 55 minutes.
“We expect that to change by a few minutes,” said Tom Statler.
But to find out, you will have to be patient.
“We wouldn't be surprised if it takes several months before there is an effect.
Launched on November 24, DART has already taken 200,000 images during its journey.
Interviewed a few days ago, Nancy Chabot wore a big smile: “Everything is normal, on the right track!