NASA’s Lucy mission: Space rock recovered by moon after solar-induced earthquake

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Astronomy was in for a surprise when NASA’s Lucy mission flew past an asteroid named Dinkinesh in November and spotted a contact binary — two smaller space rocks touching each other — orbiting the asteroid like a moon.

It was the first time a contact binary orbiting an asteroid had been discovered.

Now scientists have had the chance to study Lucy’s observations, and the findings, published Wednesday in the journal Nature, reveal that “Dinky” and its contact binary star, now named Selam, are even more complex than expected.

The complexity of both 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 merits of small bodies in our solar system because that’s critical to understanding how planets like Earth got here,” said lead study author Hal Levison, Lucy’s principal investigator at the Southwest Research Institute in Boulder, Colorado. .

“Essentially, the planets formed when millions of smaller objects orbiting the Sun, such as asteroids, crashed into each other. How objects 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 that exists between Mars and Jupiter.

In addition to Selam’s discovery, Lucy’s observations pointed to a ridge and trough on Dinkinesh. At some point in Dinkinesh’s history, one quarter of the asteroid suddenly shifted and broke off.

“The elongation suggests a sudden failure, rather an earthquake with a gradual build-up of stress and then a sudden release, rather than a slow process like the formation of a sand dune,” said study co-author Keith Noll, Project Lucy scientist at NASA’s Goddard Space Flight Center. in Greenbelt, Md., in a statement.

Trough and Dinkinesh’s earthquake-like response helps scientists better understand the asteroid’s internal structure.

Dinkinesh is not a perfect sphere, so the asteroid receives an unequal amount of sunlight on different sides.

“The sun’s radiation puts pressure on it, and over time the asteroid starts spinning, and when it gets fast enough, the material loosens,” said study co-author Jessica Sunshine, a professor of astronomy and geology at the University of Maryland, College Park. .

The heating and faster rotation of Dinkinesh had probably been going on for millions of years, and the centrifugal forces on the space rock caused part of the asteroid to shift into an elongated shape, throwing off the debris. The debris then entered a close orbit around Dinkinesh, with some of the material falling back onto the asteroid to form the ridge, while the remaining material was likely formed by Selam.

If Dinkinesh had been made of a weaker, sandier material, the asteroid’s particles would have shifted toward the equator of the space rock and been released into space as it rotated faster. But Lucy’s images show that Dinkinesh’s rocky body held together much longer and stronger until it finally shattered into large pieces.

“These features tell us that Dinkinesh has some power and allow us to do a little historical reconstruction to see how this asteroid evolved,” Levison said. “It broke up, things separated and formed a disk of material during that failure, some of which rained back to the surface to form the ridge.”

But Selam, and the exact process behind how it came to be, still baffles astronomers. No current theory explains how two pieces of virtually the same size flew away from Dinkinesh and then eventually merged as a contact binary, Sunshine said. But figuring out how Selam came to be is “part of the fun,” she said.

Sunshine was also part of NASA’s Double Asteroid Redirection Test research team. The September 2022 mission, also known as DART, intentionally sent a spacecraft hurtling toward a lunar moon named Dimorphos orbiting a larger near-Earth asteroid named Didymos to alter the celestial object’s motion in space.

“Personally, I’m very excited to compare the Didymos binary system to (Dinkinesh), especially since they seem to share many similarities, such as size, general shape and possibly composition, despite being in completely different parts of 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 about them today.”

NASA’s Galileo mission spotted the first asteroid known to have a lunar satellite, snapping a photo of asteroid 243 Ida and its moon on August 28, 1993.

Since then, scientists have discovered other asteroids with moons, referred to as binaries.

“Something like 15% 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 the mission’s primary objective: surveying the Trojan asteroid swarms around Jupiter. A fly-by of Dinkinesh, which means “wonderful” in Ethiopia’s Amharic, has even been added to Lucy’s itinerary until January 2023.

Lucy’s next close encounter in 2025 will be with another main belt asteroid named Donaldjohanson. And then the spaceship goes after the Trojans.

The Trojan asteroids, which borrow their name from Greek mythology, orbit the Sun in two clusters – one in front of Jupiter, the largest planet in our solar system, and one that lags behind it. Asteroids that are too distant to see in detail with telescopes will get their 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 members of NASA’s Lucy team hope their mission will achieve similar success when it comes to the history of our solar system.

Selam was named after a 3.3-million-year-old fossil of a small toddler, believed to be the child counterpart of the Lucy fossil. Selam means “peace” in Ethiopian Amharic.

Asteroids are like fossils themselves, representing the remnants of material hanging around after the formation of the 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 large planets are made up of smaller bodies, 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 fly by, we are laying the groundwork for understanding how planets form.”