Findings From Sample-Collecting Mission Reveal Asteroid’s Complex History

This Nov. 16, 2018, image provide by NASA shows the asteroid Bennu. After a two-year chase, a NASA spacecraft arrived at the ancient asteroid Bennu, its first visitor in billions of years. The robotic explorer Osiris-Rex pulled within 12 miles of the diamond-shaped space rock Monday, Dec. 3, 2018. The image, which was taken by the PolyCam camera, shows Bennu at 300 pixels and has been stretched to increase contrast between highlights and shadows. (NASA/Goddard/University of Arizona via AP)

(CN) — Samples taken from an asteroid rotating like a child’s top across our solar system will be collected by a NASA spacecraft later this month and will arrive on Earth in 2023. The asteroid, cosmically speaking, may not be far behind, and could collide with our planet within 200 years.

In the meantime, six studies on the near-Earth asteroid Bennu published Thursday provide a plethora of information on the heavenly object’s boulder-pocked surface and the bright veins that may have been formed at one point by flowing water when the asteroid was part of a larger planetoid or protoplanet.

Named after the mythological bird from ancient Egypt that is associated with the sun god Ra, Bennu was first discovered in 1999 by the Lincoln Near-Earth Asteroid Research (LINEAR) project from NASA, MIT’s Lincoln Laboratory and the U.S. Air Force.

According to a logarithmic scale to rate possible connection between Earth and asteroids, Bennu has a high risk of hitting Earth in the late 22nd century, according to a 2014 study.

The NASA spacecraft OSIRIS-Rex has been orbiting the asteroid since December 2018 and has taken images of its surface, providing a closeup view of the asteroid’s widespread iron ore, clay minerals and large boulders.

Scientist Daniella DellaGiustina from the University of Arizona’s Lunar & Planetary Laboratory and her co-authors detail in a study published in Science Advances the likelihood the asteroid was once part of a larger body that had flowing water. This is most evident by veins worn into the surface.

“We interpret these veins as most likely originating in the same aqueous system that is responsible for the overall level of hydration observed on Bennu,” the study authors wrote.

“Fluid flow on Bennu’s parent body would have taken place over distances of kilometers for thousands to millions of years.”

Senior scientist Amy Simon with the solar system exploration division of NASA’s Goddard Space Flight Center and co-authors measured carbon-bearing materials that are most concentrated on boulders.

Carbonate rock formation, like what’s found in a cave system on Earth, would have formed while the asteroid was still part of the larger parent body. They would have formed around 95 degrees Fahrenheit and under extreme pressure, according to the study.

Global map of Bennu, spanning +/- 80 degrees of latitude and 360 degrees of latitude, showing the absorption attributable to carbon-bearing material. Blue corresponds to little absorption, red to deeper absorption features. (Photo courtesy Simon et al. / Science)

In another study published in Science Advances, Ben Rozitis from The Open University and his colleagues provides insight into the asteroid’s weak boulder makeup based on thermal imaging.

Many samples taken from the asteroid by the NASA spacecraft on Oct. 20 would likely not be able to survive reentry into Earth’s atmosphere according to the study authors, but other samples are hypothesized to be able to survive the trip.

“We therefore expect OSIRIS-REx to return for analysis material that is not currently in Earth’s meteoritic collections,” according to the study authors.

In another study published in Science Advances orofessor Daniel Scheeres from the University of Colorado and his co-authors measured the uneven distribution of pebble-sized particles from the asteroid’s surface. The asteroid’s gravity field gave the study authors a firm understanding of how those pebbles fly off the spherical asteroid as it spins like a top.

The rotation may have been changed by the scattering of solar radiation off its surface and its own thermal radiation emission, which is referred to as the Yarkovsky-O’Keefe-Radzievskii-Paddack or YORP effect.

The asteroid’s bulge-like shape at its equator might be explained by something that happened recently, but that does not account for the total size of the bulge or the under-dense region, which could have happened during a period of rapid rotation when the asteroid was in the main asteroid belt between Mars and Jupiter.

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