Hoppend ruimtestof en nieuwsgierige asteroïde-verrassingen

Stof Elektrostatische Lofting

Timelapse-beeld van stofkorrels die “elektrostatische lofting” ondergaan in een vacuümkamer. Krediet: IMPACT Lab/LASP

Volgens een nieuwe studie van natuurkundigen aan de Universiteit van Colorado in Boulder (CU Boulder) kunnen kleine stofkorrels rondspringen op het oppervlak van asteroïden zoals maïskorrels die in een koekenpan knallen.

Dat popcornachtige effect kan zelfs helpen om kleinere asteroïden op te ruimen, waardoor ze stof verliezen en er daardoor ruig en ruig uitzien vanuit de ruimte.

Deze nieuwe bevindingen kunnen wetenschappers helpen beter te begrijpen hoe asteroïden in de loop van de tijd van vorm veranderen – en hoe deze lichamen door de ruimte migreren, waardoor ze soms gevaarlijk dicht bij de aarde komen, zei Hsiang-Wen (Sean) Hsu, co-hoofdauteur van het onderzoek. De onderzoekers publiceerden hun resultaten in het tijdschrift Natuurastronomie op 11 juli

“Hoe fijner materiaal, of regoliet, deze asteroïden verliezen, hoe sneller ze migreren”, zegt Hsu, een onderzoeksmedewerker bij het Laboratory for Atmospheric and Space Physics (LASP) aan CU Boulder.

Het onderzoek begon met een paar curieuze foto’s.

Planetoïde Bennu Global Mozaïek

Deze afbeelding toont vier aanzichten van asteroïde Bennu samen met een bijbehorend globaal mozaïek. De beelden werden op 2 december 2018 gemaakt door de PolyCam-camera van het OSIRIS-REx-ruimtevaartuig, die deel uitmaakt van de OCAMS-instrumentensuite die is ontworpen door wetenschappers en ingenieurs van de Universiteit van Arizona. Krediet: NASA/Goddard/Universiteit van Arizona

In 2018, een[{” attribute=””>NASA spacecraft named OSIRIS-REx rendezvoused with the asteroid (191055) Bennu, after traveling more than 1 billion miles. But when the spacecraft arrived at Bennu, which is about as tall as the Empire State Building, scientists didn’t find what they were expecting. Researchers had predicted the asteroid’s surface to be smooth and dusty, but instead, it looked like rough sandpaper. There were even boulders the size of trucks scattered over its exterior.

Hsu and his colleagues are now investigating that mystery using computer simulations, or models, and laboratory experiments. He suggested that smaller dust grains, some of which are no larger than a single bacterium, may be being ejected off the asteroid and into space by static electricity-like forces, leaving only larger rocks behind.

Bennu isn’t alone in this regard, said study co-author Mihály Horányi.

“We’re realizing these same physics are occurring on other airless bodies like the moon and even the rings of

This is why, before

“No one had ever considered this process on the surface of an asteroid before,” said Wang, a research associate at LASP.

Small asteroid, big asteroid

To do that, the researchers, including former CU Boulder undergraduate students Anthony Carroll and Noah Hood, ran a series of calculations examining the physics of regolith on two hypothetical asteroids. They tracked how dust might form, then hop around over hundreds of thousands of years. One of those faux asteroids was about a half-mile across (similar in size to Ryugu) and the second several miles wide (closer in diameter to giant asteroids like Eros). 

That size made a difference. According to the team’s estimates, when grains of dust jumped on the bigger asteroid, they couldn’t gain enough speed to break free of its gravity. The same wasn’t true on the smaller, Ryugu-like asteroid.

“The gravity on the smaller asteroid is so weak that it can’t hold back the escape,” Hsu said. “The fine-grained regolith will be lost.”

That loss, in turn, will expose the surface of the asteroids to even more erosion, leading to a boulder-rich scenery like scientists found on Ryugu and Bennu. Within several million years, in fact, the smaller asteroid was almost completely swept clean of fine dust. The Eros-like asteroid, however, stayed dusty. 

Hsu noted that this scrubbing effect could help to give the orbits of small asteroids a nudge. He explained that asteroids migrate because the sun’s radiation pushes on them slowly over time. Based on previous research by other scientists, he suspects that asteroids covered in boulders may move faster than those with a dustier appearance.

He and his colleagues may soon get more proof to back up their calculations. In less than three months, a NASA mission called the Double Asteroid Redirection Test (DART) will visit a pair of smaller asteroids—and Hsu will be watching to see how dusty they are. 

“We will have new surface images to test our theory,” he said. “It’s nice for us, but also a little nerve-wracking.”

Reference: “Fine-grained regolith loss on sub-km asteroids” by Hsiang-Wen Hsu, Xu Wang, Anthony Carroll, Noah Hood and Mihály Horányi, 11 July 2022, Nature Astronomy.
DOI: 10.1038/s41550-022-01717-9

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