New Horizons discovers something mysterious about Ultima Thule ahead of next week's flyby

NASA launched the New Horizons spacecraft way back in 2006, and it has been making discoveries about our solar system since that launch. The next major target for New Horizons is a Kuiper Belt object called Ultima Thule. On New Year's Day, New Horizons will zip past Ultima Thule at a distance of only 2,200 miles away. New Horizons first spotted Ultima Thule back in August.

With only days to go before that flyby, the spacecraft has made a mysterious discovery about its intended target. New Horizons hasn't been able to detect the predictable and consistent variation in reflectivity of Ultima Thule; this is called "light curve" in astronomy terminology. All celestial objects in orbit near a bright star show this phenomenon.

Scientists are currently unsure as to what would cause Ultima Thule to have such a small light curve. NASA's Alan Stern, the principal investigator of New Horizons, says that Ultima Thule has such a tiny light curve that they "can't even detect it." Stern says that he and his team are confident that when the close flyby is completed that observations will explain this mystery.

However, the scientist does expect that the flyby will also raise other mysteries about Ultima Thule for the team to ponder. There are a few theories about why there is no light curve. One is that the object is facing directly toward New Horizons as it approaches preventing the spacecraft from seeing the shifts in brightness.

Another theory is that Ultima Thule is surrounded by a cloud of dust that obscures its light curve. New Horizons has been a successful mission since its 2006 launch. The 67-pound spacecraft is about 43 AU (each AU is approximately 93 million miles) from Earth over a decade after its launch and is traveling at 31,500 mph.