Spotting A Satellite

Apr 25, 2023

On the evening of February 3, 2023, over 100 telescopes deployed across two continents hoping to catch an otherwise unremarkable star as it blinked out for a fraction of a second.

Scientists working for the NASA Lucy Mission had predicted that Polymele—a small Trojan asteroid on the mission’s tour to a record-breaking number of asteroids—would pass in front of that star, briefly obscuring it. The team had seen this cosmic coincidence occur a handful of times before, but none had garnered such a large gathering of people and equipment. This time was different as the team’s primary objective on this deployment was not just observe the shadow of Polymele, but to catch a glimpse of its satellite. The team was very lucky to spot this tiny satellite during the March 27, 2022, campaign. With another occultation predicted to cross the heartland of America, the Lucy team decided to make their own luck, putting together the largest centrally-organized occultation campaign in history.

“This satellite only is a few miles wide, so it’s shadow would only be visible across a few-mile wide path on the Earth’s surface.” says Brian Keeney of Southwest Research Institute, occultation specialist for the Lucy Mission. “But we didn’t know where the satellite would be relative to Polymele. It’s shadow might easily have fallen 50 miles or more away from Polymele’s shadow. So if we wanted a high probability to catch this satellite, we needed to organize a deployment on a scale that we had never done before.” In the end the campaign involved over 165 observers in the United States alone, several dozens of them college students without prior experience. These citizen scientists from all over the country gathered in a warehouse in Mead, Colorado, to prepare for this expedition specifically designed to get a second look at this tiny satellite.

Polymele’s shadow first crossed Spain and Portugal before crossing the United States, following the center of the pink curve, at times marked by the blue stars. The width of the pink curve shows the planned region where telescopes were deployed in the search for the satellite. The purple circles mark the locations of the 107 observers across two continents, with the two insets showing the 96 telescopes deployed in Kansas and the 10 telescopes deployed in Spain and Portugal. Credit: NASA/SwRI with Map Data from Google, INEGI.

Fifty cars carried the observing teams and their 95 telescopes to Salina, Kansas. From there, the teams fanned out over 120 miles (200km), covering half the state of Kansas from North to South. Another 11 telescopes in Spain and Portugal joined in the endeavor. Each telescope would observe the target star from a different location on the Earth, watching to see if it was occulted by the either Polymele or its satellite, allowing the team to map out the shadow that the two bodies cast on the Earth’s surface.

The Lucy occultation volunteers learning how to use their equipment in a warehouse parking lot in Mead, Colorado while the temperature dipped below 5°F (-15°C). Credit: Simon Porter

“We had some technical issues on with the telescope the first couple nights, and my partner and I were worried that we might not be able to get on field the night of the occultation,” said University of Alabama, Huntsville student Haylee Winter. “We were making changes to our telescope the day of the event, hoping we could fix it in time. That night, we were able to set up smoothly sure enough, we saw the star blink out! It was incredible that our hard work paid off and we managed to catch the moment that the distant asteroid passed in front of the star.”

While some teams were able to confirm that they had observed the Polymele occultation that evening, it took a few more days to know that the team had successfully captured its satellite. Out of the 107 telescopes deployed that night, a single scope managed to catch the tiny satellite—but that was enough.

“While we would have loved to have had another telescope confirm the detection and get more shape information, this signal is robust,” says occultation campaign lead Marc Buie, of Southwest Research Institute. “We got it.” The team will use this new data, along with the information about the shape of Polymele inferred by this and other occultations, to place constraints on the orbit of this satellite. However, it will likely take another observation, and perhaps another large campaign, to pin down this tiny satellite’s orbit.

“The occultation was a very rewarding experience, aside from the awesome task of recording a special event, we got to volunteer alongside people from all walks of life and academic backgrounds,” says Embry-Riddle Aeronautical student Roberto Del Bosque. “I would definitely clear my schedule to assist again whenever they need volunteers.”

Banner Image: The path of Polymele’s shadow on the surface of the Earth (blue) overlayed on the full path to search for Polymele’s satellite (pink). Image Credit: SwRI with map data from Google, SIO, NOAA U.S. Navy, GHA, GEBCO Landsat/Copernicus IBCAO U.S. Geological Survey PGC/NASA