Hubble And SETI Find A New Moon Around Neptune

Image Credit: NASA, ESA, M. Showalter/SETI Institute


In 1989, Voyager 2 did a detailed survey of Neptune, its rings, and its moons. But it missed something, all those years ago - Neptune's 14th moon, which NASA announced has been discovered in photos taken by the Hubble Space Telescope.

Don't be too hard on the little space probe, though. The moon, which is currently designated S/2004 N 1 until it is officially named, is tiny - only about 12 miles across, making it Neptune's smallest moon.

The moon's discovery was almost an accident, too. It was discovered by the SETI Institute's Mark Showalter, who found it while studying photos of Neptune's rings that had been taken by the Hubble Space Telescope between 2004 and 2009. The moon went undiscovered for so long simply because it was so hard to see.

"Like fidgety children, moons are unwilling to sit still for the camera," Showalter wrote in a blog post.

That's a problem that astronomers tackle by analyzing the images with computer programs that can track objects across multiple exposures. As the program examines images taken at different times, it can slowly notice objects appear for astronomers to analyze.

"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," Showalter wrote. "I developed this procedure (and I am certainly not the first) to study some peculiar arcs in the rings of Neptune. However, I soon realized it could be useful for moons as well. 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 addition to being tiny, S/2004 N 1 is also incredibly fast. Located about 65,400 miles above the surface of Neptune, the small moon orbits the planet in only about 23 hours. It also provides astronomers some insight into how Neptune evolved over time.

"The discovery of one little moon might not be Earth-shaking, but somehow it is has to fit into the big picture of how the Neptune system formed," wrote Showalter.

That picture has to do with the fact that unlike most moons, which form at about the same time as their planets and evolve in their orbit, Neptune's biggest moon, Triton, was "captured" by the planet's gravitational pull at some point in the past. That in turn disrupted the orbits of Neptune's other moons. The discovery of this new moon will help astronomers learn more about what happened during that time.

"With the discovery of S/2004 N 1, the key points of this story have not changed," concluded Showalter in his post. "But we now have one more piece of the puzzle to fit into place."


I'm an Associate Editor covering science and cutting edge tech.