Named after the satellite discovered by NASA’s Lucy mission

The satellite discovered during the first asteroid encounter by NASA’s Lucy mission has an official name. On November 27, 2023, the International Astronomical Union approved the name „Salem” or Salam, meaning „peace” in the Ethiopian language Amharic, for Dinginesh’s moon.

„Dinginesh is the Ethiopian name for the fossil nicknamed 'Lucy’,” says Raphael Marshall of the Observatoire de la Côte d’Azur in Nice, France, who first identified Dinginesh as a possible target for the Lucy mission. „It seemed appropriate. Name its satellite after another fossil, sometimes called Lucy’s Child.” Fossil Selam, discovered in 2000 by Jeresene Alemzeket in Tikika, Ethiopia, belonged to a 3-year-old girl of the same species as Lucy. Baby” actually lived 100,000 years before Lucy.

On November 1, 2023, the Lucy spacecraft flew by Dinginesh and Selam. While observations leading up to the encounter had indicated that something interesting was going on in the system, the team was surprised to discover that Dinginesh had a satellite, but the satellite was a interacting-binary, the first interacting-binary satellite ever observed.

The team has completed the downlinking of encounter data from Lucy’s first asteroid encounter and is continuing to process it. The Dinginesh rendezvous was added as an in-flight test of the spacecraft’s systems and instruments in January this year, and all systems performed well.

Instruments and techniques refined with data from this encounter will help the team prepare for the mission’s key targets, the previously unexplored Jupiter Trojan asteroids. In addition to images taken by Lucy’s high-resolution L’LORRI camera and its Terminal Tracking Cameras (T2Cam), Lucy’s other science instruments also collected data to help understand these enigmatic asteroids.

Goddard provided two components of the L’Ralph instrument, the Multi-Spectral Visible Imaging Camera (MVIC) and the Linear Etalon Imaging Spectral Array (LEISA), both of which successfully tracked the two asteroids from various points at close range. During the rendezvous, both components scanned the asteroid’s surfaces, enabling the team to collect color images and spatial spectra of the objects.

„To collect the final images, we need to carefully calculate the spacecraft’s motion, but Lucy’s precise pointing information makes this possible,” said Amy Simon of NASA’s Goddard Space Flight Center, Greenbelt, Maryland. „These images will help scientists understand the composition of the asteroids, allow the team to compare the makeup of Dinginesh and Selam, and understand how these bodies may be associated with other asteroids.”

The Lucy Thermal Emissions Spectrometer (L’TES) provided by Arizona State University also detected asteroids, although, unlike future Trojan asteroid targets, they filled only a small portion of the instrument’s wide field of view. Scientists expect the data will often provide insight into the surface properties of the large asteroid Dinginesh.

„L’TES was able to detect and measure the temperature of the system for about nine minutes as the spacecraft flew on its closest approach,” said Bill Christensen of Arizona State University, Tempe. „Particles of different sizes, such as sand, pebbles and boulders, heat up differently as the asteroid spins. L’TES temperature measurements will allow us to study the size and physical properties of materials on the asteroid’s surface.”

Lucy is expected to visit 9 more asteroids in 6 separate encounters over the next decade. After Earth’s gravitational pull in December 2024, the spacecraft will return to the main asteroid belt, where it will encounter asteroid Donald Johansson in April 2025. Lucy will cross the main belt and reach the mission’s primary targets, the Jupiter Trojan asteroids, in 2027. .