07/15/2013 06:57 pm ET Updated Dec 06, 2017

New Neptune Moon Discovered As Astronomers Stumble Upon Planet's Smallest (IMAGES)

Astronomers may have thought they had already detected all the satellites orbiting Neptune. They were wrong.

As one keen-eyed astronomer recently pointed out, images taken by the Hubble Space Telescope show that Neptune has another moon. Senior research scientist Mark Showalter of the SETI Institute, the private California-based organization, first discovered the new Neptune moon on July 1.


Designated S/2004 N 1, the moon was previously overlooked by astronomers due to its small size and the speed at which the tiny body orbits the planet -- one time every 23 hours.

Using a method similar to one often employed by action photographers, Showalter stumbled across the moon in Hubble images of Neptune taken between 2004 and 2009.

"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 released 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."

The astronomer further detailed the process he used to spot Neptune's moon in a blog on Cosmic Diary:

The procedure I devised predicts where any given moon ought to move from one image to the next, and then combines the images with a "twist" that compensates for the expected motion. ... It was only when I expanded my analysis out to regions well beyond Neptune’s ring system that an extra little dot turned up, over and over again. In less than a week, we went from our first detection to ten.

The finding makes S/2004 N 1 the 14th known moon of Neptune and the planet's smallest. Astronomers previously derived a majority of their discoveries about Neptune from data obtained during NASA's Voyager 2 trip to observe the planet in 1989.

As Showalter notes in his blog post, the discovery is also significant since astronomers studying Neptune's moons previously thought that the smallest moons orbit closer to the planet. However, S/2004 N 1 is located between Proteus and Larissa, Neptune's second- and third-largest moons.

new neptune moon

This diagram shows the orbits of several moons located close to the planet Neptune. (Image credit: NASA, ESA, and A. Feild, STScI)

new neptune moon

This composite Hubble Space Telescope picture shows the location of a newly discovered moon, designated S/2004 N 1, orbiting the giant planet Neptune, nearly 3 billion miles from Earth. (Image credit: NASA, ESA and M. Showalter, SETI Institute)



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