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Astronomers were surprised when NASA’s Lucy mission flew by an asteroid named Dinkinesh in November and spotted a contact binary – two smaller space rocks that touch each other – orbiting the moon-like asteroid.
This was the first discovery of a contact binary orbiting an asteroid.
Now, researchers have had the opportunity to study Lucy’s observations, and the results, published on Wednesday in the journal Nature, show that “Dinky” and its contact binary, now called Selam, are even more complex than previously thought. expected
The complexities of the two space rocks could change the way astronomers understand how asteroids, and even planets like Earth, formed during the early days of our solar system.
“We want to understand the strengths of small bodies in our solar system because that’s key to understanding how planets like Earth got here,” said lead study author Hal Levison, principal investigator of the Lucy Institute Southwest Research in Boulder, Colorado, in a statement.
“Essentially, the planets formed when millions of smaller objects orbiting the Sun, such as asteroids, crashed into each other. How things behave when they collide, whether they break apart or stick together, has a lot to do with their strength and internal structure.”
Dinkinesh is in the main asteroid belt, which is between Mars and Jupiter.
In addition to reaching Selam, Lucy’s observations revealed a ridge and trough on Dinkinesh. At some point in Dinkinesh’s history, a quarter of the asteroid suddenly shifted and broke.
“The trough suggests a sudden failure, more like an earthquake with a gradual increase in stress and then a sudden release, instead of a slow process like dune formation,” the study author said Keith Noll, Lucy project scientist at NASA’s Goddard Space Flight Center. in Greenbelt, Maryland, in a statement.
The trough, and a reaction similar to the Dinkinesh earthquake, are helping scientists better understand the internal structure of the asteroid.
Dinkinesh’s rocky history
Dinkinesh is not a perfect sphere, so the asteroid receives an unequal amount of sunlight on different sides.
“The solar radiation puts pressure on it, and over time, the asteroid starts to spin up, and when it gets fast enough, material breaks off,” said study co-author Jessica Sunshine, a professor of astronomy and geology at the University of Maryland. College Park. .
Faster heating and spinning of Dinkinesh likely occurred over millions of years, and the centrifugal forces on the space rock caused part of the asteroid to shift into an elongated shape and shed debris. Then, the debris entered a close orbit around Dinkinesh, and some of the material fell back onto the asteroid to form a ridge, and the remaining material likely formed Selam.
If Dinkinesh had been made of weaker, denser material, the asteroid’s particles would have shifted toward the equator of the space rock and it would have been released into space as it rotated faster. But Lucy’s images show that Dinkinesh’s rocky body stayed together for much longer and stronger, eventually splitting into large pieces.
“These features tell us that Dinkinesh has a certain strength, and they allow us to do a bit of historical reconstruction to see how this asteroid developed,” Levison said. “It broke up, moved things apart and created a disc of material during that failure, some of it raining back on the surface to form the ridge.”
But Selam and the exact process behind how it was formed still compel astronomers. No current theories explain how two pieces of nearly equal size flew away from Dinkinesh and then came together as a contact binary, Sunshine said. But finding out how Selam was formed is part of the fun,” she said.
Sunshine was also part of the research team of NASA’s Double Asteroid Test. Also known as DART, the September 2022 mission sent a purpose-built moon-penetrating spacecraft, named Dimorphos, orbiting a larger near-Earth asteroid named Didymos to alter the motion of a celestial object in space.
“I am personally very happy to compare the binary system of Didymos with (Dinkinesh), especially because they seem to have a lot of similarities in size, general shape and maybe composition although in places completely different from the solar system,” she said. “They have very different features, but we think they may have gone through similar processes to become what we know today.”
NASA’s Galileo mission spotted the first asteroid known to have a lunar satellite, photographing asteroid 243 Ida and its moon on August 28, 1993.
Since then, scientists have discovered more asteroids with moons, called binaries.
“Something like 15% of the near-Earth asteroid population has binaries,” Sunshine said.
Unlock the secrets of asteroids
Lucy’s flight from Dinkinesh was part of a test of the spacecraft’s equipment before tackling the mission’s main goal: surveying the Trojan asteroid swarm around Jupiter. Even the Dinkinesh trip, which means “wonderful” in the Ethiopian Amharic language, wasn’t added to Lucy’s itinerary until January 2023.
Lucy’s next encounter, in 2025, will be with another main-belt asteroid called Donaldjohanson. And then, the spaceship will depart to see the Trojans.
The Trojan asteroids, which borrow their name from Greek mythology, orbit the sun in two passes – one ahead of Jupiter, the largest planet in our solar system, and the other behind it. Too distant to be seen in detail with telescopes, the asteroids will be close by when Lucy reaches Troy in 2027.
The mission takes its name from the Lucy fossil, the remains of an ancient human ancestor discovered in Ethiopia in 1974. The skeleton has helped researchers piece together aspects of human evolution, and NASA’s Lucy team hopes that their mission the same achievement out regarding the. history of our solar system.
Selam was named after a tiny 3.3-million-year-old female toddler fossil, thought to be the baby counterpart of the Lucy fossil. Selam means “peace” in the Amharic language of Ethiopia.
Asteroids are like fossils themselves, representing the material left hanging around after the formation of giant planets in our solar system, including Jupiter, Saturn, Uranus and Neptune.
“Our ultimate goal is to understand the formation of celestial bodies,” Sunshine said. “How do planets form? How was the Earth formed? We know that smaller bodies make large planets, so studying these small asteroids allows us to see how materials behave and interact on a smaller scale. With Dinky and the other asteroids we’re flying by, we’re laying the groundwork for understanding how planets are formed.”
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