The Lucy mission discovers a moon on the Trojan asteroid Polymele

Aug. 16 () –

A prolonged observing campaign with NASA’s Lucy spacecraft has revealed that the smallest Trojan asteroid in its mission to a group of these objects, Polymele, has its own satellite.

On March 24, Polymele was expected to pass in front of a star, allowing the team to watch the star flicker as the asteroid briefly blocked or obscured it.

Distributing 26 teams of professional and amateur astronomers across the path where the occultation would be visible, Lucy’s team planned to measure Polymele’s location, size, and shape. with unprecedented precision as the star behind him outlined it.

These cloaking campaigns have been hugely successful in the past, giving the mission valuable information about its asteroid targets, but this day would have a special edge.

“We were delighted that 14 teams reported seeing the star flicker as it passed behind the asteroid, but when we analyzed the data we saw that two of the observations were not like the others,” he said. it’s a statement Marc Buie, Lucy Occultation Science Lead at the Southwest Research Institute. “Those two observers detected an object about 200 kilometers away from Polymele. It had to be a satellite.”

Using the occultation data, the team assessed that this satellite is about 5 kilometers across, orbiting Polymele, which is about 27 kilometers along its widest axis. The observed distance between the two bodies was about 200 kilometers.

Following 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 ground-based or Earth-orbiting telescopes, without the aid of a fortuitously positioned star, that determination will have to wait. until the team gets lucky with future cloaking attempts or until Lucy gets closest to the asteroid in 2027.

At the time of the observation, Polymele was 770 million kilometers from Earth. These distances are approximately equivalent to finding a quarter on a sidewalk in Los Angeles, while trying to spot it from a skyscraper in Manhattan.

Asteroids hold vital clues to unraveling the history of the solar system, perhaps even the origins of life, and 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 her way to visit nine asteroids in this incredible 12-year journey.

“The Lucy catchphrase started: 12 years, seven asteroids, one spacecraft,” Lucy program scientist Tom Statler said at NASA Headquarters in Washington. “We still need to change the tagline for this mission, but it’s a good deal.”