It’s time to add one more tiny moon to Neptune’s icy family tree. Astronomers using the Hubble Space Telescope have spied a previously undetected satellite around the solar system’s eighth planet, bringing its total number to 14.

The discovery, formally reported Wednesday in Nature,is a reminder that there is much more to be found in our own backyard, with implications for our understanding of worlds around other stars in our galaxy.

“I think people have the impression that we know everything there is to know about the moons of Jupiter, the moons of Saturn, the moons of Uranus and the moons of Neptune — but we don’t really,” said Anne Verbiscer, a planetary scientist at the University of Virginia, who was not involved in the recent discovery. “We haven’t found everything.”

That’s especially true for Uranus and Neptune, which are known as the ice giants. While every other planet in our solar system has been poked and prodded by multiple spacecraft, these two remain largely unexplored. Voyager 2 did swing past Neptune 30 years ago, but the spacecraft was moving too fast and was limited by technology designed in the 1970s.

Mark Showalter, a researcher at the SETI Institute in Mountain View, California, was analyzing Neptune’s rings with a new technique to process old images. To his surprise, a tiny white dot appeared. Further analyses have confirmed that it is a moon, and a rather odd one.

Showalter’s team suspects that the new moon, which is roughly 20 miles in diameter, likely formed billions of years ago when an icy body from the outer solar system smashed into a larger moon, Proteus — tossing debris into orbit that later coalesced to form the small moon, which they named Hippocamp after a sea creature in Greek mythology.

“We’re basically seeing a chip off of Proteus itself,” Showalter said.

The findings highlight the challenges in making discoveries in the years since the Voyager flyby.

“Uranus and Neptune have been neglected in the history of space exploration,” Showalter said. “There’s a big hole in our understanding of the outer solar system.”

This article originally appeared in The New York Times.