NASA’s Hubble Space Telescope has discovered a new moon orbiting the distant blue-green planet Neptune, the 14th known to be circling the giant planet.
The moon, designated S/2004 N 1, is estimated to be no more than 12 miles 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. It even escaped detection by NASA’s Voyager 2 spacecraft, which flew past Neptune in 1989 and surveyed the planet’s system of moons and rings.
While analyzing Neptune photos taken by the Hubble Space Telescope, astronomer Mark Showalter of the SETI Institute noticed an extra white dot about 65,400 miles from Neptune, located between the orbits of the moons Larissa and Proteus. Hubble’s extraordinary sensitivity and sharpness caught an object that is roughly one hundred million times fainter than the faintest star that can be seen with the naked eye. Thankfully, Showalter also had 150 archival Neptune photographs taken by Hubble from 2004 to 2009. The same white dot appeared over and over again. This allowed him to plot a circular orbit for the moon, designated S/2004 N 1, which completes one revolution around Neptune every 23 hours. His discovery raises the number of known moons orbiting Neptune to 14.
The moon was spotted on July 1. “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,” Mark Showalter 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 65,400 miles 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.
Top Image: This composite Hubble Space Telescope picture shows the location of a newly discovered moon, designated S/2004 N 1, orbiting Neptune. The black and white image was taken in 2009 with Hubble’s Wide Field Camera 3 in visible light. Hubble took the color inset of Neptune on August 2009. Image Credit: NASA, ESA, M. Showalter/SETI Institute
Filed under: Neptune
