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The two asteroids, which have the same darkness as coal and are shaped like spinning tops, have the distinction of having both been visited by spaceships in recent years.
The Japanese spacecraft Hayabusa2 visited and collected samples from Ryugu, and those samples are Currently on the way to Earth. NASA’s OSIRIS-REx mission has been orbiting Bennu since December 2018 and will collect samples from the surface later this year to also return to Earth.
“We have a great opportunity for two space missions to visit two early Near Earth asteroids at almost the same time, allowing us to discover two new small worlds,” said Patrick Michel, co-author of the study and director of research at the National Center for France. for scientific research in Paris.
“What really fascinated us when we saw the first images is the striking similarity of the two objects, before more detailed observations brought up the differences. This is truly fascinating because these asteroids were chosen entirely independently from mission to mission. ”
Dual space missions are shedding light on the nuances of these asteroids that would have been impossible to know from Earth.
Close flybys of these spacecraft by asteroids have revealed how similar they are. Both are carbonaceous-type asteroids, which means that their composition includes a large amount of carbon. Ryugu and Bennu are debris-pile asteroids, meaning they are clusters of rocks held together by gravity rather than individual objects. And both have large impact craters on their equators.
This led researchers to believe that these asteroids were larger asteroid remains and that “they could have originated from the same ‘asteroid family,'” said Ronald Ballouz, author of the study and a postdoctoral research associate at the Lunar and Planetary Laboratory. from the University of Arizona, in An email to CNN.
For tens of millions of years, near-Earth asteroids collide with Earth or are sent toward the sun when they interact with Earth’s gravity, Ballouz said.
The near-Earth asteroid population is replenished with fragments from larger asteroid collisions, about 62 miles in size each, in the main asteroid belt between Mars and Jupiter.
“These little pieces are ejected, but because they follow each other, their mutual attraction is high enough for them to re-accumulate and form a family of aggregated asteroids after a few hours,” said Michel. “This is how families of asteroids form in the belt.”
The fragments of the largest asteroid, and what remains of the parent’s body, form what astronomers call a “family of asteroids.” These fragments, which become asteroids, “can be placed on unstable trajectories that change their orbit from a circular to an elongated one that causes it to cross Earth’s orbit,” Michel said.
Similar Bennu and Ryugu orbits date back to the same region in the asteroid belt.
But when the two spacecraft reached Ryugu and Bennu, the researchers noticed some key differences. The biggest difference is that Ryugu was much drier than Bennu, which made astronomers wonder if they were, in fact, twin asteroids from the same family.
However, the latest investigation by the teams investigating both asteroids has revealed two different scenarios that could be responsible for the varied water content in the asteroids. The study published this week in the journal Nature Communications.
‘Shared history’, different scenarios
Based on their simulations, the researchers theorized that an asteroid between 4.3 and 8 miles in diameter collided with The asteroid from the body of Bennu and Ryugu’s parents, which was probably 62 miles wide. This impact occurred in the main asteroid belt, possibly between 60 million and 1.4 billion years ago.
In one scenario, the material, both near and far from the point of impact, may escape to become asteroids, Ballouz said. If that’s the case, Ryugu was close to impact and the intense heat caused dehydration, while Bennu was further away and didn’t suffer any thermal disturbance.
In the second scenario, the material for Ryugu came from inside the main body, which was heated and compacted by the impact, while Bennu came from surface material that escaped from intense heating and compaction.
“The returned sample and further observational analysis of the surface of both asteroids will help us get a better idea of the shared history of these two asteroids, and which of these scenarios could be more favorable,” Ballouz said.
Brian May, astrophysicist and guitarist for Queen, was also a co-author of the study and provided stereo images for the simulations.
“The shapes of asteroids and their level of hydration can serve as real tracers of their origin and history,” May said in a statement. “During a collision, it is possible to form an aggregate like Bennu, which experienced little impact heating, and another with more heated material, like Ryugu.”
Both scenarios explain the fact that a difference in asteroid hydration is not a signature of a different origin, Michel said. “For me, this is yet another demonstration that collisions play a critical role in the history of the solar system and its solid bodies.”
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