rationalskepticism.org

There's something weird going on with Ultima Thule, the distant object that NASA's New Horizons spacecraft will fly by just 10 days from now.

New Horizons team members don't think the 23-mile-wide (37 kilometers) Ultima is spherical; rather, the available data suggest that it's elongated or is perhaps even composed of two close-orbiting bodies. So, mission scientists were expecting to see a substantial "light curve" from Ultima: significant changes in brightness corresponding to different orientations of the object as it rotates.

But that's not what New Horizons observations in the lead-up to the epic New Year's Day encounter have shown. Instead, Ultima's brightness is relatively constant, like that of a spherical body...