Even before its launch in October 2021, NASA’s Lucy mission was already on track to break records by visiting more asteroids than any previous mission. Now, the mission can add another asteroid to the list, following a surprise result from a long-term observing campaign. The Lucy science team discovered on March 27 that the smallest of the mission’s Trojan asteroid targets, Polymele, has its own satellite. On that day Polymeli was expected to pass in front of a star. This would allow the team to observe the star twinkling as the asteroid briefly blocked or obscured it. The Lucy team planned to measure the position, size and shape of Polymele with unprecedented precision, while it was outlined by the star behind it. To do so, they spread 26 teams of professional and amateur astronomers along the entire path where the occultation would be visible. A graph showing the observed separation of the asteroid Polymele from the discovered satellite. Credit: NASA Goddard Space Flight Center These cloaking campaigns have been hugely successful in the past, providing the mission with valuable information about its asteroid targets, but this day would have a special bonus. We were delighted that 14 teams reported seeing the star twinkling as it passed behind the asteroid. However, as we analyzed the data, we saw that two of the observations were not like the others,” said Marc Buie, head of Lucy occultation science at the Southwest Research Institute, based in San Antonio. “These two observers spotted an object about 200 km (about 124 miles) away from Polymele. It had to be a satellite.” A graph showing the observed separation of the asteroid Polymele from the discovered satellite. Credit: NASA Goddard Space Flight Center Using the occultation data, scientists determined that this satellite is about 3 miles (5 km) in diameter, orbiting Polymele, which is about 17 miles (27 km) across its widest axis. The observed distance between the two bodies was about 125 miles (200 km). In accordance with planetary naming conventions, the satellite will not receive an official name until the team can determine its orbit. As the satellite is too close to Polymele to be seen clearly by telescopes on Earth or in orbit around Earth – without the help of a randomly placed star – that determination will have to wait until Lucy approaches the asteroid in 2027, unless if the team gets lucky with future concealment attempts before then. At the time of the observation, Polymeli was 480 million miles (770 million kilometers) from Earth. These distances are roughly equivalent to finding a quarter on a sidewalk in Los Angeles – while trying to spot it from a skyscraper thousands of miles away in Manhattan. Using the occultation data, the team estimated that this satellite is about 3 miles (5 km) in diameter, orbiting Polymele, which is about 17 miles (27 km) across its widest axis. The observed distance between the two bodies was about 125 miles (200 km). Credit: NASA Goddard Space Flight Center Asteroids hold vital clues to deciphering the history of the solar system—perhaps even the origins of life. Solving these mysteries is a high priority for NASA. Lucy’s team originally planned to visit one main-belt asteroid and six Trojan asteroids, a previously unexplored population of asteroids that lead and follow Jupiter in its orbit around the Sun. In January 2021, the team used the Hubble Space Telescope to discover that one of the Trojan asteroids, Eurybates, has a small satellite. Now with this new satellite, Lucy is on track to visit nine asteroids in this remarkable 12-year journey. “Lucy’s tagline started: 12 years, seven asteroids, one spacecraft,” said Lucy program scientist Tom Statler at NASA headquarters in Washington. “We keep having to change the motto for this mission, but that’s a good problem to have.” On January 9, 2020, the Lucy mission officially announced that it will visit not seven, but eight asteroids. As it turns out, Eurybates, one of the asteroids in Lucy’s path, has a small satellite. Shortly after Team Lucy discovered the satellite, both he and Eurybates moved behind the Sun, preventing the team from observing it further. However, the asteroids emerged behind the Sun in July 2020, and since then, the Lucy team has been able to observe the satellite with Hubble on several occasions, allowing the team to precisely determine the satellite’s orbit and allow the small satellite to finally reached an official name – Queta. Lucy’s principal investigator is based in Boulder, Colorado, an affiliate of the Southwest Research Institute, headquartered in San Antonio, Texas. NASA’s Goddard Space Flight Center in Greenbelt, Maryland, provides comprehensive mission management, systems engineering, and mission safety and assurance. Lockheed Martin Space in Littleton, Colorado, built the spacecraft. Lucy is the 13th mission in NASA’s Discovery program. NASA’s Marshall Space Flight Center in Huntsville, Alabama manages the Discovery Program for the agency’s Science Mission Directorate in Washington.
