Hubble Telescope Finds New Moon for Neptune

This illustration shows the orbits of Neptune's closest moons, all of which were discovered by Voyager 2 in 1989, except for the newly announced S/2004 N 1. Credit: NASA, ESA, and A. Feild (STScI)
This illustration shows the orbits of Neptune’s closest moons—all of which were discovered by Voyager 2 in 1989—except for the newly announced S/2004 N 1, which was discovered by Hubble. Credit: NASA, ESA, and A. Feild (STScI)

The Hubble Space Telescope‘s keen eye has revealed a previously undetected moon orbiting Neptune.  The July 1, 2013 discovery , 24 years after Voyager 2 swung by the icy-blue giant, expands the known retinue of circling moons to 14.

Known only by its temporary designation —S/20044 N1—the tiny celestial piece of real estate measures no more than 12 miles (19 kilometers) across and appears to have escaped detection until now because of its extreme faintness and far flung orbit beyond the planet’s ring fragment system known as arcs.

According to Mark Showalter, a planetary astronomer at the SETI Institute in California who discovered the moon, the newfound object is almost 100 million times fainter than the faintest star visible to the naked eye. But by tracking the movements of a mysterious white dot visible on 150 Neptune photographs taken by Hubble between 2004 and 2009, he managed to pin down this mini-moon.

“The moons and arcs orbit very quickly, so we had to devise a way to follow their motion in order to bring out the details of the system,” he said in a statement issued by NASA on Monday. “It’s the same reason a sports photographer tracks a running athlete—the athlete stays in focus, but the background blurs.”

This composite Hubble Space Telescope image shows the newly discovered moon, S/2004 N 1, in relation to other satellites orbiting the giant planet Neptune, nearly 3 billion miles from Earth.. Credit: NASA, ESA, and M. Showalter (SETI Institute)
This composite Hubble Space Telescope image shows the newly discovered moon, S/2004 N 1, in relation to other moons orbiting the giant planet Neptune, nearly 3 billion miles (4.8 billion kilometers) from Earth. Credit: NASA, ESA, and M. Showalter (SETI Institute)

S/20044 N1 orbits between the Neptunian moons Larissa and Proteus, and circles the planet once every 23 hours at an altitude of 65,400 miles (104,000 kilometers).

The origins of S/20044 N1 and some of its other tiny neighboring moons is still a mystery. But one theory is that Neptune’s largest moon Triton may have had something to do with it. Triton—nearly the size of Earth’s moon—is thought to be a gravitationally captured dwarf planet, which upon it’s arrival, may have broken apart the original Neptunian satellite system and created many of the small moons we see today. (Related: “Neptune Discovered a Year Ago Today*.”)

Follow Andrew Fazekas, the Night Sky Guy, on Twitter and Facebook.

Andrew Fazekas, aka The Night Sky Guy, is a science writer, broadcaster, and lecturer who loves to share his passion for the wonders of the universe through all media. He is a regular contributor to National Geographic News and is the national cosmic correspondent for Canada’s Weather Network TV channel, space columnist for CBC Radio network, and a consultant for the Canadian Space Agency. As a member of the Royal Astronomical Society of Canada, Andrew has been observing the heavens from Montreal for over a quarter century and has never met a clear night sky he didn’t like.

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