Asteroid Bennu Ejecting Particles

This view of asteroid Bennu ejecting particles from its floor on January 6, 2019, was created by combining two pictures taken by the NavCam 1 imager onboard NASA’s OSIRIS-REx spacecraft: a brief publicity picture (1.Four ms), which reveals the asteroid clearly, and an extended publicity picture (5 sec), which reveals the particles clearly. Different picture processing methods have been additionally utilized, resembling cropping and adjusting the brightness and distinction of every layer. Credit score: NASA/Goddard/College of Arizona/Lockheed Martin

Shortly after NASA’s OSIRIS-REx spacecraft arrived at asteroid Bennu, an surprising discovery by the mission’s science workforce revealed that the asteroid may very well be energetic, or constantly discharging particles into area. The continued examination of Bennu – and its pattern that can finally be returned to Earth – might doubtlessly make clear why this intriguing phenomenon is happening.

The OSIRIS-REx workforce first noticed a particle ejection occasion in pictures captured by the spacecraft’s navigation cameras taken on January 6, 2019, only a week after the spacecraft entered its first orbit round Bennu. At first look, the particles gave the impression to be stars behind the asteroid, however on nearer examination, the workforce realized that the asteroid was ejecting materials from its floor. After concluding that these particles didn’t compromise the spacecraft’s security, the mission started devoted observations with a purpose to totally doc the exercise.

“Among Bennu’s many surprises, the particle ejections sparked our curiosity, and we’ve spent the last several months investigating this mystery,” mentioned Dante Lauretta, OSIRIS-REx principal investigator on the College of Arizona, Tucson. “This is a great opportunity to expand our knowledge of how asteroids behave.”

After finding out the outcomes of the observations, the mission workforce launched their findings in a Science paper that can be revealed December 6. The workforce noticed the three largest particle ejection occasions on January 6 and 19, and February 11, and concluded that the occasions originated from totally different areas on Bennu’s floor. The primary occasion originated within the southern hemisphere, and the second and third occasions occurred close to the equator. All three occasions came about within the late afternoon on Bennu.

This animation illustrates the modeled trajectories of particles that have been ejected from Bennu’s floor on January 19, 2019. After ejecting from the asteroid’s floor, the particles both briefly orbited Bennu and fell again to its floor or escaped away from Bennu and into area. Credit score: NASA/Goddard/College of Arizona/Lauretta & Hergenrother et al., Science 10.1126

The workforce discovered that, after ejection from the asteroid’s floor, the particles both briefly orbited Bennu and fell again to its floor or escaped from Bennu into area. The noticed particles traveled as much as 10 ft (Three meters) per second, and measured from smaller than an inch as much as Four inches (10 cm) in measurement. Roughly 200 particles have been noticed in the course of the largest occasion, which came about on January 6, 2019.

The workforce investigated all kinds of attainable mechanisms that will have induced the ejection occasions, and narrowed the record to a few candidates: meteoroid impacts, thermal stress fracturing, and launched of water vapor.

Meteoroid impacts are frequent within the deep area neighborhood of Bennu, and it’s attainable that these small fragments of area rock may very well be hitting Bennu the place OSIRIS-REx just isn’t observing it, shaking free particles with the momentum of their impression.

The workforce additionally decided that thermal fracturing is one other affordable rationalization. Bennu’s floor temperatures fluctuate drastically over its 4.3-hour rotation interval. Though this can be very chilly in the course of the evening hours, the asteroid’s floor warms considerably within the mid-afternoon, which is when the three main occasions occurred. Because of this temperature change, rocks might start to crack and break down, and finally particles may very well be ejected from the floor. This cycle is called thermal stress fracturing.

Water launch might also clarify the asteroid’s exercise. When Bennu’s water-locked clays are heated, the water might start to launch and create strain. It’s attainable that as strain builds in cracks and pores in boulders the place absorbed water is launched, the floor might turn out to be agitated, inflicting particles to erupt.

However nature doesn’t all the time permit for easy explanations. “It could be that more than one of these possible mechanisms are at play,” mentioned Steve Chesley, an creator on the paper and Senior Analysis Scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. “For example, thermal fracturing could be chopping the surface material into small pieces, making it far easier for meteoroid impacts to launch pebbles into space.”

If thermal fracturing, meteoroid impacts, or each, are in actual fact the causes of those ejection occasions, then this phenomenon is probably going taking place on all small asteroids, as all of them expertise these mechanisms. Nevertheless, if water launch is the reason for these ejection occasions, then this phenomenon could be particular to asteroids that comprise water-bearing minerals, like Bennu.

Bennu’s exercise presents bigger alternatives as soon as a pattern is collected and returned to Earth for research. Lots of the ejected particles are sufficiently small to be collected by the spacecraft’s sampling mechanism, that means that the returned pattern might presumably comprise some materials that was ejected and returned to Bennu’s floor. Figuring out {that a} specific particle had been ejected and returned to Bennu is likely to be a scientific feat much like discovering a needle in a haystack. The fabric returned to Earth from Bennu, nevertheless, will nearly actually improve our understanding of asteroids and the methods they’re each totally different and comparable, even because the particle ejection phenomenon continues to be a thriller whose clues we’ll additionally return residence with within the type of information and additional materials for research.

Pattern assortment is scheduled for summer time 2020, and the pattern can be delivered to Earth in September 2023.

NASA’s Goddard House Flight Middle in Greenbelt, Maryland supplies total mission administration, programs engineering, and the protection and mission assurance for OSIRIS-REx. Dante Lauretta of the College of Arizona, Tucson, is the principal investigator, and the College of Arizona additionally leads the science workforce and the mission’s science remark planning and information processing. Lockheed Martin House in Denver constructed the spacecraft and is offering flight operations. Goddard and KinetX Aerospace are chargeable for navigating the OSIRIS-REx spacecraft. OSIRIS-REx is the third mission in NASA’s New Frontiers Program, which is managed by NASA’s Marshall House Flight Middle in Huntsville, Alabama, for the company’s Science Mission Directorate in Washington.



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