“It’s normal to make mistakes in science”: NASA didn’t expect asteroid Dimorphos to be so disruptive

"It's normal to make mistakes in science": NASA didn't expect asteroid Dimorphos to be so disruptive

DART hits an asteroid to change its orbit. NASA predicted a change of just one minute in the time it takes the object to orbit its parent body. The result of the test is different: why?

For the first time in human history succeeded in deliberately deflecting the trajectory of an asteroid in space. We learned that on October 11, 2022 The DART mission Its main objective was successfully accomplished: to disrupt orbit The asteroid, Dimorphos, crashed into the spacecraft at the end of September. It’s all an exercise:Asteroid Does not represent any known hazard.

Dimorphos orbits the large asteroid Didymos. After Impact of DART, scientists scanned the sky with powerful telescopes. Their conclusion: Dimorphos’ orbit around Didymos was shortened by 32 minutes. In other words, the smaller of the two asteroids will take less time to go around the larger one. However, this is much longer than NASA expected: the space agency predicted that Dimorphos would spend only 1 minute and 13 seconds in orbit. Why such a deviation from predictions?

Scientists studying these asteroids made 2 mistakes

There are two reasons for this, explains Numerama Stephanie Lizi-Destrus, teacher-researcher at ISAE-SUPAERO: ” Uncertainties about the mass of the main body Didymos and error about the composition of Dimorphos – The second reason is the bigger “wrong” of the two.

To better understand these asteroids, scientists work with models. Here an asteroid is orbiting another in a binary system. The models used are comparable to those used in the study of movement the moon, which orbits the Earth. ” We can approach distance and period (number of laps performed in a given time) by physical properties. Specifically, the mass of each object “, continues Stephanie Lisi-Destrus.

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Representation of Didymos and Dimorphos. // Source: YouTube screenshot ESA

However, unless an exploratory mission is launched to an asteroid to get a closer look, determining its mass is complicated. ” We get information from light. Let us calculate the mass [d’un astéroïde] Depending on the received light, it gives an impression of its structure. As these calculations remain approximate, error is possible. This is what happened to the large asteroid of the pair. ” Didymos’ mace was not right. However, it plays on the mass of Dimorphos. As we change the mass of the earth, the moon will have another movement. This is the first uncertainty we have. »

“Mistakes are common in science”

What happened to another parameter, the structure of dimorphos? ” It was supposed to be very sturdy, but the footage revealed that it was made of a lot of dustSummarizing the scientist with numerama. This meant it had a large volume but a small mass.. When DART crashed into Dimorphos, a large amount of mass was ejected from it. ” What is left? [de Dimorphos] So it was small. Also, because this nucleus was smaller than we estimated, the deviation was larger than we expected.. »

These errors in the predictions do not question the success of the DART mission. ” It’s natural to make mistakes in science, that’s how we learnsays Stéphanie Lizy-Destrez. It’s pretty much guaranteed: the whole principle of deflecting an asteroid by a probe that hits it works. We have seen it work. Then, we can improve the accuracy of the obtained result. But it is unusual for us to be able to touch an object so far from Earth. »

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Dimorphoses after DART trauma.  // Source: OBS E. Guido, M. Rocchetto, G. Savini, S. Fossey (cropped image)

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