Sign up for CNN’s Wonder Theory science newsletter. Explore the universe with information on fascinating discoveries, scientific advances and much more..
CNN
—
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 — orbiting the asteroid like a moon.
This was the first time that a contact binary had been discovered orbiting an asteroid.
Researchers have now had the opportunity to study Lucy’s observations, and the results, published Wednesday in the journal Nature, reveal that “Dinky” and its contact binary, now named Selam, are even more complex than expected.
The complexity of the two space rocks could change the way astronomers understand how asteroids, and even planets like Earth, formed in the early days of our solar system.
“We want to understand the forces of small bodies in our solar system, because that’s key to understanding how planets like Earth got here,” said the study’s lead author, Hal Levison, Lucy’s principal investigator. at the Southwest Research Institute in Boulder, Colorado, in a statement. .
“Basically, planets formed when millions of smaller objects orbiting the Sun, like asteroids, collided. How objects behave when they collide, break, or stick together has a lot to do with their strength and internal structure.
Dinkinesh is located in the main asteroid belt, which exists between Mars and Jupiter.
In addition to Selam’s discovery, Lucy’s observations showed a crest and trough on Dinkinesh. At one point in Dinkinesh’s history, a quarter of the asteroid suddenly shifted and broke away.
NASA/Goddard/SwRI/Johns Hopkins APL
The Lucy mission captured additional images revealing that asteroid Dinkinesh’s moon is actually two space rocks touching.
“The trough suggests an abrupt rupture, more of an earthquake with a gradual buildup of stress then sudden release, instead of a slow process like the formation of a sand dune,” said Keith Noll, co-author of the study, Project Lucy scientist at NASA’s Goddard Space Flight Center. in Greenbelt, Maryland, in a statement.
Dinkinesh’s trough and seismic response help scientists better understand the asteroid’s internal structure.
Dinkinesh is not a perfect sphere, so the asteroid receives an unequal amount of sunlight from different sides.
“The solar radiation puts pressure on it, and over time the asteroid starts to spin, and when it gets fast enough, the material breaks away,” said study co-author Jessica Sunshine, professor in astronomy and geology at the University of Maryland, College Park. .
NASA/GSFC/SwRI/Johns Hopkins APL/NOIRLab
The yellow and pink dots identify the trough and crest features, respectively.
Dinkinesh’s heating and faster rotation likely occurred over millions of years, and centrifugal forces on the space rock caused part of the asteroid to take on an elongated shape and release debris. Then the debris entered a close orbit around Dinkinesh, with some of the material falling back onto the asteroid to form a ridge, while the remaining material likely formed Selam.
If Dinkinesh had been made of a weaker, sandier material, particles from the asteroid would have moved toward the space rock’s equator and released into space as it spun faster. But Lucy’s images show that Dinkinesh’s rocky body held together much longer and more strongly, eventually fragmenting into large pieces.
“These features tell us that Dinkinesh has some strength, and they allow us to do a little historical reconstruction to see how this asteroid evolved,” Levison said. “It broke, things separated and formed a disk of material in that failure, some of which came back to the surface to form the ridge.”
But Selam and the exact process behind its formation still baffle astronomers. No current theory explains how two pieces of nearly equal size flew out of Dinkinesh and eventually came together to form a binary contact, Sunshine said. But understanding how Selam formed is “part of the fun,” she said.
Sunshine was also part of NASA’s Double Asteroid Redirect Test research team. Also known as DART, the September 2022 mission intentionally sent a spacecraft hurtling to a moon, named Dimorphos, orbiting a larger near-Earth asteroid named Didymos to alter the motion of a celestial object in space.
“I am personally very excited to compare the Didymos binary system with (Dinkinesh), especially since they seem to share many similarities such as size, general shape and possibly composition, although they are in completely different parts of the solar system,” she said. “They have very different characteristics, but we think they may have undergone similar processes to become what we know today.”
NASA’s Galileo mission spotted the first asteroid known to have a lunar satellite, taking a photo of asteroid 243 Ida and its moon on August 28, 1993.
Since then, scientists have discovered more asteroids with moons, called binaries.
“About 15 percent of the near-Earth asteroid population now has binaries,” Sunshine said.
Lucy’s flyby of Dinkinesh was part of a test of the spacecraft’s equipment before tackling the mission’s primary objective: studying Trojan asteroid swarms around Jupiter. The Dinkinesh flyover, which means “wonderful” in the Ethiopian Amharic language, was only added to Lucy’s itinerary in January 2023.
Lucy’s next close encounter, scheduled for 2025, will be with another main-belt asteroid called Donaldjohanson. And then, the spaceship will set off to meet the Trojans.
The Trojan asteroids, which take their name from Greek mythology, orbit the sun in two swarms: one ahead of Jupiter, the largest planet in our solar system, and the other behind. Too distant to be seen in detail with telescopes, the asteroids will be in close-up when Lucy reaches the Trojans 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 Lucy team members from the NASA hopes their mission will achieve a similar feat when it comes to the history of our solar system.
Selam is named after the 3.3 million-year-old fossil of a little girl, considered the infant equivalent of the Lucy fossil. Selam means “peace” in the Ethiopian Amharic language.
Asteroids are like fossils themselves, representing the leftover material after the formation of our solar system’s giant planets, including Jupiter, Saturn, Uranus and Neptune.
“Our ultimate goal is to understand the formation of celestial bodies,” Sunshine said. “How are planets formed? How was the Earth formed? We know that large planets are made up of smaller bodies. Studying these small asteroids therefore allows us to see how materials behave and interact on a smaller scale. With Dinky and the other asteroids we fly by, we are laying the foundations for understanding how planets are made.