NASA Finds a Surprise Second Asteroid During a Flyby Mission

While testing its tracking system, the agency’s Lucy spacecraft discovered that Dinkinesh is not one space rock, but two

A black and white photo of an asteroid with a second smaller asteroid below and behind it
The pair of asteroids, captured by NASA's Lucy spacecraft on November 1, 2023, from around 270 miles away. NASA / Goddard / SwRI / Johns Hopkins APL / NOIRLab

A NASA spacecraft en route to Jupiter’s orbit took a detour this year—and on November 1, it flew by and photographed an asteroid called Dinkinesh in the main asteroid belt. Now, the first of these images have reached Earth, and they revealed a surprise: that the asteroid is not a single space rock, but a pair of them.

“We knew this was going to be the smallest main belt asteroid ever seen up close,” Keith Noll, a project scientist for the mission at NASA’s Goddard Space Flight Center, says in a statement. “The fact that it is two makes it even more exciting.”

The spacecraft, called Lucy, is meant to study the Trojan asteroids, which share an orbit with Jupiter around the sun. These images of Dinkinesh served as a test of the spacecraft’s system that autonomously tracks asteroids.

“This is an awesome series of images,” Tom Kennedy, a guidance and navigation engineer at Lockheed Martin, says in the statement. “They indicate that the terminal tracking system worked as intended, even when the universe presented us with a more difficult target than we expected.”

Lucy launched on October 16, 2021, with the goal of uncovering details about the early days of the solar system. The Trojan asteroids are likely made from the same stuff that formed the outer planets, so they could contain clues about the birth and evolution of these gas and ice giants. No space mission has ever studied these distant asteroids before.

As a mission focused on our solar system’s early history, the spacecraft got its name from the fossil of an early human ancestor called Lucy, discovered in Ethiopia in 1974.

“Just as that fossil revolutionized our understanding of human evolution, we expect this mission to revolutionize our understanding of the origin and evolution of our solar system,” Noll said in a February statement from NASA.

The mission was not originally intended to fly by Dinkinesh (the Amharic name for the Lucy fossil), but a small course adjustment in May allowed the spacecraft to approach the asteroid and test its tracking system, writes the New York Times’ Katrina Miller.

As the spacecraft got closer to Dinkinesh, the team on Earth wondered if the object might be two asteroids, due to how its brightness was changing. The first images confirmed this theory—they revealed an asteroid about half a mile across at its widest, as well as a second one about 0.15 miles across.

“A binary was certainly a possibility,” Jessica Sunshine, a planetary scientist at the University of Maryland and mission co-investigator, tells Scientific American’s Meghan Bartels. “But it was not expected, and it’s really cool.”

NASA said Thursday that it would take up to a week to download the rest of the spacecraft’s data on the pair of asteroids. Lucy collects information with color and black-and-white cameras, a thermometer-like device and an infrared imaging spectrometer for measuring the composition of asteroids’ surfaces.

It also communicates with Earth using a radio signal, which will help scientists determine the asteroids’ masses by measuring the signal’s Doppler shift.

The early images have already provided insight into the surface features of both asteroids, per Scientific American. “It is covered in craters,” Sunshine tells the publication, describing the larger asteroid. “The silhouette, even, the outline of it is not smooth at all. It’s just hit after hit.” As for the second space rock, its shape is intriguingly odd.

Now, Lucy has a list of other small celestial bodies to visit. Next up is another main belt asteroid that the spacecraft will pass in 2025. Then, it will fly to eight Trojan asteroids, visiting the first in 2027 and the last in 2033, at which point the mission will end.

As it flies by these asteroids, Lucy will observe their surface geology, color and composition, as well as their masses, densities and sub-surface makeups. It will also look for satellites or rings around the rocks. Each of the objects, scientists say, will add a piece to the puzzle of how our bit of the universe came to be.

“Each [asteroid] is carrying with it a memory of a different part of the history of our solar system,” Thomas Statler, a NASA planetary scientist for the mission, tells the New York Times. “There is no such thing as just another asteroid.”

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