NASA confirms successful test to deflect asteroid

Now it’s official: humanity has for the first time demonstrated the ability to deflect an asteroid from its trajectory, crucial technology to save Earth from a future impact when the need arises. The announcement was made at a press conference by NASA, this Tuesday (11).

The American space agency presented, among other data, the fruits of two weeks of observation of the asteroid Dimorpho and its parent star, Didymus, after the spectacular impact of the Dart probe (acronym for Double Asteroid Redirection Test, or double asteroid redirection test). , on the last day 26.

Prior to the collision, Dimorph completed a loop around Didymus every 11 hours and 55 minutes. The new measurements show that the trajectory has been shortened, accompanied by a reduction in the period, which is now 11 hours and 23 minutes. So we’re talking about a 32-minute change in orbital period.

“The result was consistent with our simulations, but more towards the upper end of the margin,” said Lori Glaze, director of NASA’s planetary science division.

There was, it is true, great uncertainty about how big the change in the orbital period would be. This is because the effect of the hit, performed at a speed of approximately 22,500 km/h, would depend on parameters such as the shape and internal consistency of the asteroid. If it were denser, like a single giant 170-meter boulder, the change would be less than if it were a large collection of boulders loosely aggregated by gravity.

Dart images of Dimorph’s surface just before impact revealed that it appeared to be more like a pile of pebbles, quite porous. Post-impact observations, made both by space telescopes and by the Italian spacecraft LICIACube, which traveled along with Dart, showed large ejection of material, also consistent with this.

To proclaim success in changing the asteroid’s trajectory, NASA expected to measure a change of at least 73 seconds in the orbital period. It ended up with 32 minutes, about 25 times longer. In practice, this means that the planetary defense strategy involving the kinetic impact technique – simply colliding a high-speed spacecraft with an asteroid to change its course – is efficient in deflecting at least stars with a size and consistency similar to Dimorph.

It was a very significant 4% change, especially since the general expectation of astronomers and planetary scientists is that when the time comes to have to deflect such a star, we will have years, possibly decades, of notice. The key to this is to catalog as many space rocks as possible roaming the Earth’s surroundings, so that you can predict a potential impact in advance. The sooner an intervention is made in orbit, the greater the chance that it will “miss” the planet in the future.

The most dangerous asteroids, with 1 km or more, which in theory would be capable of promoting mass extinctions, comparable to the one that wiped out the dinosaurs 65.5 million years ago, are practically all cataloged, and none of them pose a risk to Earth. in the near future. For those smaller than that, however, especially in the range of 140 meters and below (comparable to Dimorpho), there are thousands yet to be discovered. It is against these, capable of potential local damage, that an action such as that carried out by Dart would prove most effective.

CONFIRMATION

According to Nancy Chabot, from the Johns Hopkins University Applied Physics Laboratory (APL), the body responsible for managing and executing the Dart mission for NASA, the determination of the orbital period change was made by two different methods.

Telescopes in Chile and South Africa monitored eclipses of Dimorpho every time the asteroid-light passed under Didymus’ shadow, and two independent groups came to the same conclusion: the period changed to 11:23 am. The margin of uncertainty for the measurement is two minutes, plus or minus.

In parallel, radio telescopes made radar imaging of the Didymus-Dimorpho system, capable of recording the relative position of the stars, one in relation to the other, and confirmed that Didymus was not in the position that would be expected if the orbit was the same as before the impact. . Instead, the observation also corroborated a 32-minute reduction in period — which is to say the star is now making a slightly tighter loop around Didymus than it did before impact.

Studies are now continuing to determine exactly what happened to the material ejected from the surface after the impact and what other changes to the system (such as the degree of flattening of the orbit or the asteroid’s rotation) may have taken place. It is worth remembering that all this happened 11 million km from Earth, and the Didymus-Dimorpho duo, before or after the blow, offers zero risk to our planet. It was just the “victim” of a historic test: for the first time, the inhabitants of the third planet from the Sun are no longer completely defenseless if an asteroid tries to get in their way.