Astronomers discovered a new moon orbiting Uranus, and two new moons orbiting Neptune. After hours of ground-based observations, the tiny satellites appear as faint specks in the outer reaches of the solar system.
Using observatories in Chile and Hawaii, Scott Sheppard, an astronomer at the Carnegie Institution for Science, first discovered Uranus’ moons on November 4, 2023, and two more in September 2021. A previously unknown satellite of Neptune.These were discovered using ground-based telescopes around the two ice giant planets,” Shepard said in a report statement. “Special image processing is required to reveal such a faint object.”
Uranus’ new moon is the first discovered around the ice giant in more than 20 years, and is likely the smallest of its 28 moons. The moon is only 5 miles (8 kilometers) wide and takes 680 days to orbit Uranus. Most of Uranus’ moons are named after Shakespearean characters (e.g., Ophelia, Sycorax, Juliet, Desdemona, etc.). Although it is currently labeled S/2023 U1, the moon will eventually be renamed to keep up with tradition.
The brighter of Neptune’s two moons, S/2002 N5, is 14 miles (23 kilometers) wide and takes nearly nine years to orbit the farthest known planet from the sun. Shepard used the Magellan Telescope in Chile to confirm the orbit of S/2002 N5 in October 2021 and again in 2022 and November 2023, tracing it back to its first discovery near Neptune in 2003 of an object that was lost before its orbit could be confirmed.
Neptune’s fainter crescent moon, S/2021 N1, is 8.6 miles (14 kilometers) across and takes 27 years to complete one cycle. As the faintest satellite ever discovered through ground-based observations, S/2021 N1 requires ultra-pristine conditions from the European Southern Observatory’s Very Large Telescope and the Gemini Observatory’s 8-meter telescope to ensure the safety of its orbit, according to Carnegie Science.
Shepard, with help from scientists at NASA’s Jet Propulsion Laboratory, the University of Hawaii, Northern Arizona University and Kindergarten University, took three to four hour-long, five-minute exposures over several nights to confirm the discovery.
“Because the movement of the satellite relative to background stars and galaxies only takes a few minutes, a single long exposure is not ideal for capturing depth images of moving objects,” Shepard said. “By stacking these multiple exposures together, stars and galaxies will appear in their tracks behind them, and moving objects similar to the host planet will be seen as point sources, bringing the satellite out from behind the background noise in the image.”
All three new moons have eccentric, distant and tilted orbits, suggesting they were captured by the gravitational tug of Uranus and Neptune after the ice giants formed.
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