A small, dim, moon has been discovered orbiting Neptune; it's the 14th of the blue-green planet's known satellites

The moon, called S/2004 N 1, is believed to be only 12 miles across, making it the smallest-known Neptunian moon, NASA reported.

The lunar object is 100 times dimmer than the faintest star visible to the human eye.

NASA sent the Voyager 2 to fly past Neptune in 1989, but the moon was so tiny and dark it went undetected.

Mark Showalter, of the SETI Institute, noticed the moon in early July while studying Neptune's rings.

"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. "It's the same reason a sports photographer tracks a running athlete -- the athlete stays in focus, but the background blurs."

Showalter found the mini-moon by following a white dot that showed up in over 150 photographs taken of Neptune by the Hubble Space Telescope between the years of 2004 and 2009.

The researcher found the moon to be about 65,400 miles away from Neptune, sandwiched between the satellites Larissa and Proteus.

Showalter determined S/2004 N 1 makes one complete revolution around its parent planet every 23 hours, it is believed to have a circular orbit.

Neptune's first moon was first noticed by 19th century English astronomer William Lassell. The amateur astronomer used a telescope funded by money from his brewery to make the discovery.  He found Triton in 1846, only 17 days after Neptune itself was discovered.

Proteus and five of Neptune's other moons are considered to be some of the darker objects in the solar system, so they were not discovered until the 1980s Voyager 2 flyby.

The rest of Neptune's moons (until this new discovery) were found in the early 2000s using "improved ground-based telescopes."