Thanks to the Hubble Space Telescope, a 14th moon has been discovered orbiting the distant blue-green giant planet Neptune.
Dubbed S/2004 N 1, the moon is estimated to be no more than 19 kilometres across, making it the smallest known moon in the Neptunian system. It is so small and dim that it is roughly 100 million times fainter than the faintest star that can be seen with the naked eye.
Mark Showalter of the SETI Institute found the moon on 1 July, while studying the faint arcs, or segments of rings, around Neptune.
“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.”
The method involved tracking the movement of a white dot that appears over and over again in more than 150 archival Neptune photographs taken by Hubble from 2004 to 2009.
On a whim, Showalter looked far beyond the ring segments and noticed the white dot about 105 200 kilometres from Neptune, located between the orbits of the Neptunian moons Larissa and Proteus. The dot is S/2004 N 1. Showalter plotted a circular orbit for the moon, which completes one revolution around Neptune every 23 hours.