Pluto’s intriguing moons Available to Purchase

Roaming around the complicated gravitational field of Pluto and its large moon, Charon, are four smaller satellites—Styx, Nix, Kerberos, and Hydra—all of which were discovered only within the past decade. Now, based on an analysis of Hubble Space Telescope images, Mark Showalter (SETI Institute) and Douglas Hamilton (University of Maryland) have deduced several novel properties of the Plutonian system. The two researchers found, for example, that the orbital periods of Styx, Nix, and Hydra—but not Kerberos—are in simple, whole-number ratios. An analysis of the four moons’ light curves (reflected light versus time) yielded other surprises. The data for Nix and Hydra are incompatible with rotation about a fixed axis. Instead, Showalter and Hamilton posit, the oddly shaped moons—and possibly Kerberos and Styx too—tumble chaotically, as illustrated in the accompanying simulated images of Nix, courtesy of Showalter and Greg Bacon (Space Telescope Science Institute). The light curves also indicate that Kerberos...