Nix is one of the smaller moons of Pluto, paired with Hydra after the massive Charon. Until this morning, the most detailed view we’d ever had was only a few pixels large. Now we’re seeing this elongated rock from just half a million kilometers away in the highest resolution photo we’re getting from New Horizons.

Nix was photographed during the flyby when the New Horizons spacecraft was just 590,000 kilometers (360,000 miles) away. This produced a view of the world in 4.0 kilometers per pixel resolution, the best view we’re getting of the little moon. It looks like the moon is about 40 kilometers across (25 miles) and slightly elongated, but we’ll need to look more closely to get the exact dimensions. We’ll see it again in colour in approximately the same resolution near the tail end of the initial failsafe downlinks.


Like Hydra, Nix has an intermediate albedo. That means its brightness is somewhere between that of Pluto and Charon. Earlier size estimates of the moon assumed it was the same brightness as Charon, so Nix is slightly brighter (thus smaller) than we thought. It’s going to be a tight call to decide which moon is bigger and claims the title of second-biggest moon in the system, but Nix probably wins. From the latest image, it looks like Nix is 40 kilometers across but elongated in the direction we aren’t seeing from this angle, so is likely larger than Hydra at a lopsided 48 kilometers by 33 kilometers.

Our previous views of Nix are downright tragic by comparison to the latest release:


Pluto, Charon, Nix, and Hydra seen by the Hubble Space Telescope in 2006. Image credit: NASA/ESA/H. Weaver/A. Stern

The orbit of Nix and the other smaller moons — Hydra, Styx, and Kerberos — don’t actually go around Pluto. Instead, they circle the barycenter of Pluto and Charon, the center of mass between the two behemoths of the mini-system.


An earlier view of Nix, Hydra, Styx, and Kerberos from when the New Horizons probe was first approaching the Pluto-Charon system. Image credit: NASA/JHUAPL/SwRI

Nix is named for the personification of night itself. That means we can expect any notable landmarks on this little world to take on other night deities as their namesakes.

Hi, Nix! It’s delightful to meet you.

Top image: Nix seen from 590,000 kilometers away by the New Horizons probe on July 13, 2015. Credit: NASA/JHUAPL/SwRI