NASA Lucy mission discovers a small moon orbiting a Trojan asteroid

Trojan asteroids are space rocks that are locked into orbit near larger space objects – typically planets. Two trojan asteroids are known to be orbiting near Earth, with one, called 2020 XL5, having been confirmed by observations in February this year.

NASA’s Lucy mission: Observing Polymede from Earth

The Lucy spacecraft won’t reach its first target until 2025, but the Lucy team has already made the impressive discovery of the moon orbiting an asteroid called Polymele. They were able to make observations of the asteroid as it aligned between Earth and a distant star, casting a strong silhouette.

The new discovery of the moon orbiting Polymede means the Lucy spacecraft will observe more space rocks than originally anticipated. “Lucy’s tagline started out: 12 years, seven asteroids, one spacecraft,” said Lucy program scientist Tom Statler from NASA headquarters in Washington. “We keep having to change the tagline for this mission, but that’s a good problem to have.”

The measurements were taken earlier this year, after which scientists and astronomers analyzed the findings. Twenty-six teams made observations on March 26th from different parts of the Earth. Taking observations from different vantage points, the international teams were able to collaborate to precisely measure the shape, size, and location of Polymele.

“We were thrilled that 14 teams reported observing the star blink out as it passed behind the asteroid, but as we analyzed the data, we saw that two of the observations were not like the others,” Marc Buie, from the Lucy team at the Southwest Research Institute, said in NASA’s press statement. “Those two observers detected an object around 200 km (about 124 miles) away from Polymele. It had to be a satellite.”

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