• NASA has announced the launch of a "planetary defense mission" by sending a satellite crashing into an asteroid to cause it to deviate from its path.

  • This is the first real attempt at this technique, although no asteroid currently threatens Earth.

  • A European mission, called HERA, must then go and measure the effectiveness of the technique.

When you read the words "planetary defense mission" and "deliberately crashing into an asteroid" to make it deviate from its trajectory, you immediately had your eyes shining.

With, in the back of his mind, the image of Bruce Willis and Ben Affleck in

Armageddon

, ready to sacrifice their lives to save the Earth.

Obviously, the reality is a little less sexy, no one is going to leave for the space of five minutes after eating their croissant and come back that evening.

We tell you all about this NASA experience.

Learn to avoid a possible danger

First, no massive asteroid is heading our way to eradicate all life on the Earth's surface, let's face it. Even among “the 2,300 potentially dangerous objects identified, none has a probability greater than 1 in 10,000 of impacting us,” reassures Francis Rocard, astrophysicist in charge of the solar system exploration program at CNES. The project implemented by NASA is in fact a test, aimed at "validating a planetary defense technique", in case the situation changes.

Clearly, the US space agency is going to send the DART satellite crashing into Dimorphos, "a sort of small moon" 160 m in diameter which revolves around a larger asteroid, Didymos, with the objective of " estimate the extent to which it is deviated, ”explains Patrick Michel, CNRS research director at the Côte d'Azur observatory. To give an idea, if Dimorphos were to crash into Paris, "the city would be razed" and the region devastated, he imagines. DART is slated to launch on November 23 at 10:20 p.m. PT, for a collision ten months later.

Why such a target? First, because "the effects of deviations are easier to measure", points out Francis Rocard, given that Dimorphos revolves around Didymos in only 12 hours whereas it would be necessary to wait for a complete (and complex) revolution of "the asteroid principal ”around the Sun otherwise. The measurement being made after 100 revolutions, it was better to aim at the moon.

But also because "it is better to disturb a small pebble around another rather than a big pebble which turns around the Sun", synthesizes Patrick Michel.

This experiment is the first of its kind, and must "validate the simulations made in the laboratory" to add the satellite collision to the arsenal of weapons available (with the nuclear explosion and the gravitational traction, slower) to avoid us. an impact with a large asteroid on D-Day. "The good news is that no scenario will endanger us," he adds.

Hera, the next mission

So, inevitably, there are a lot of unknowns, starting with the composition of Dimorphos. "If the asteroid is hard, the crater will be large, if it is" soft "or made up of a pile of rubble, the impact will be low", summarizes Francis Rocard. However, this data is not always easy to predict in low gravity conditions. To assess this, the HERA mission, piloted by the European Space Agency, will arrive "at the scene of the crime" in 2026, savors Patrick Michel, scientific manager of the expedition.

“What we are trying to determine is the amount of movement transmitted,” he explains.

In other words, how much of the energy released by a 600 kg satellite speeding at 6 km / sec can be transmitted to a pebble larger than the Statue of Liberty floating in space.

If the crater is large, and material has been ejected towards where DART is coming from, then the satellite will have maximized its impact.

"It is much more revealing about the effectiveness of the mission than the change of speed of revolution" of the moon, Dimorphos being supposed to turn ten minutes faster around Didymos after the impact.

Science

Blue Origin: The complaint filed by Jeff Bezos' company against NASA rejected in court

Science

ISS: When will Thomas Pesquet return to Earth?

  • Asteroid

  • Space

  • Experience

  • Nasa

  • Science