Strange, dark-veined meteorites rained down on Earth when a fireball exploded over Chelyabinsk, Russia, in February 2013. The origin of these unusual meteorites remained a mystery, but now planetary scientists have uncovered a possible source: a mile and a half long near-Earth asteroid.
Scientists know that the dark streaks across the Chelyabinsk Meteorites are caused by a process called shock blackout. However, only about 2% of a common type of meteorite Chondrite meteorites, dubbed chondrite meteorites, are showing signs of shock darkening, and the source of these space rocks has remained a mystery.
Now scientists have identified them Asteroid 1998 OR2 as a potential source of shock-darkened meteorites. The near-Earth asteroid was discovered in July 1998 by NASA’s Jet Propulsion Laboratory’s Near-Earth Asteroid Tracking Program. Its last close approach to Earth was in April 2020 when space was rocked Happened within 3.9 million miles (6.3 million kilometers) of our planet.
Related: Mile-long asteroid 1998 OR2 wears a ‘mask’ before flyby (Photos)
While this may not seem very close, NASA still considers 1998 OR2 to be “potentially dangerous” because changes to the asteroid’s orbit could pose a risk over the next 1,000 years Earth.
Meteorites are formed when parts of an asteroid break off and penetrate, such as 1998 OR2 earth atmosphere. The discovery that shock-eclipsed meteorites may have come from a near-Earth asteroid points to the difference in material thickness from asteroids and has implications for protecting the Earth from potential impacts, the researchers said.
“Shock darkening is a process of change caused when something impacts a planetary body so severely that temperatures partially or completely melt those rocks, changing their appearance both to the human eye and in our data,” says Adam Battle, a Ph.D. student in planetary sciences at the University of Arizona and lead author of the study, said in a expression (opens in new tab). “This process has been observed many times in meteorites, but only in one or two instances on asteroids far out in the main asteroid belt that lies in between Mars and Jupiter.”
Vishnu Reddy, a planetary scientist at the University of Arizona and co-author of the new study, who spotted shock dimming on these main-belt asteroids, said it’s a much more common phenomenon on asteroids than on meteorites. “Impacts are very common in asteroids and all solid bodies solar system because we see impact craters on these objects from spacecraft imagery,” he said in the statement.
Reddy, who co-directs the Space Domain Awareness Lab at the Lunar and Planetary Laboratory, added that finding a near-Earth asteroid dominated by this process has implications for impact risk assessments.
“Adam [Battle]The work of has shown that common chondrite asteroids can show up as carbonaceous in our classification tools when affected by shock dimming,” Reddy said. “These two materials have different physical strengths, which is important when trying to deflect a dangerous asteroid.”
Is Asteroid 1998 OR2 Chondrite or Carboniferous?
Reddy, Battle and their team used the Rapid Astronomical Pointing Telescopes for Optical Reflectance Spectroscopy (RAPTORS) on the Kuiper Space Sciences Building on the University of Arizona campus to observe asteroid 1998 OR2.
The team collected data on the surface composition of 1998 OR2, with the asteroid appearing visually as a common chondrite asteroid, a type of space rock that’s bright in color and contains the minerals olivine and pyroxene. But an asteroid classification tool found that 1998 OR2 appeared to be a carbonaceous asteroid; These space rocks are dark and featureless compared to chondrite asteroids.
The team then set about investigating the reason for this discrepancy and determining the correct classification.
“The discrepancy was one of the early things that prompted the project to explore possible causes of the discrepancy,” Battle said.
They ruled out the possibility that exposure to the space environment had caused changes on the asteroid’s surface, since this process, called space weathering, would have slightly reddened the space rock.
The team concluded that shock darkening was responsible for the differences between the two analysis methods, as the shock darkening process can obscure olivine and pyroxene while darkening the asteroid’s surface, making it look like a carbonaceous asteroid.
“The asteroid is not a mixture of ordinary chondrite and carbonaceous asteroids, but is definitely an ordinary chondrite based on its mineralogy, which has been altered – likely by the shock darkening process – to look like a carbonaceous asteroid to the classification tool,” Battle said.
Asteroid shock-eclipsing was first theorized in the late 20th century, but was not an intense area of study until the 2013 Chelyabinsk fireball peppered Earth with shock-eclipsed meteorites.
Interest in Shock Darkening grew after Reddy found asteroids affected by the process in the main asteroid belt. This new discovery, showing evidence of the process in a near-Earth asteroid, could further fuel interest in shock dimming, the team said.
The study was published on October 4th The Planetary Science Journal and presented at a conference held this week by the American Astronomical Society’s Division of Planetary Sciences.
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