Clearer and clearer, bit by bit. This latest photo of 2014 MU69 , better known by its informal name, Ultima Thule, is the clearest view yet of the icy asteroid. New Horizons took the photo from a distance of 4,200 miles (6,700 km) just 7 minutes before closest approach on Jan. 1. Earlier photos of the asteroid were taken with the sun at the spacecraft’s back, so the asteroid was lit like a full moon without shadow detail. The lighting here is more oblique so we can start to see details along the day-night boundary called the terminator, located near the top.
New details have emerged including lots of small pits up to 0.4 miles (0.7 km) in diameter. The large circular feature on the smaller lobe is about 4 miles (7 km) wide and also appears to be a deep depression. It’s tempting to call them craters since that’s what they look like, but they may also be collapse pits, similar to what Europe’s Rosetta spacecraft found at comet 67P/Churyumov-Gerasimenko. Pits form when ices below the surface vaporize and vent to the surface, creating sinkholes.
Both lobes also show fascinating light and dark patterns that hint at how it was assembled from smaller objects at the dawn of the solar system 4.5 billion years ago. Perhaps the most striking feature is the bright collar connecting both lobes, which might be icy materials that tumbled down the slopes of both objects when they met and “melded” together long ago. Better photos are still are on their way, and I’ll share them as they arrive.
New Horizons is approximately 4.13 billion miles (6.64 billion km) from Earth, operating normally and speeding away from the Sun (and Ultima Thule) at more than 31,500 mph (50,700 kph). At that distance, a radio signal reaches Earth six hours and nine minutes after leaving the spacecraft.