American space agency NASA's Hubble Space Telescope has hit a new milestone by discovering a new moon orbiting Neptune.

Estimated to be around 20 kilometres in diameter, the newly discovered moon is the 14th known moon orbiting Neptune. It is located nearly 105,251 kilometres from the planet.

The new moon has been designated S/2004 N 1; and as per NASA scientists' estimates, it is the smallest moon orbiting the planet. It takes just 23 hours to complete one revolution around Neptune.

It was spotted by US astronomer Mark Showalter when he pay heed to a tiny dot while studying segments of Neptune's rings.

Sharing the newest discovery, Showalter said, "We had been processing the data for quite some time and it was on a whim that I said, `OK, let's just look out further'."

A deep analysis of other archived Hubble pictures of Neptune helped astronomers verify that the object was a moon. As per the astronomer, the S/2004 N 1 was nearly one hundred million times fainter than the dimmest star visible to naked eyes.

Triton, Neptune's largest moon, was discovered in 1846. The planet's second and third largest moons are Proteus and Nereid, respectively. The list of its other moons includes Larissa, Naiad, Thalassa and Despina.