It was a New Year’s Eve like no other. First of all, the big celebration started a half hour after midnight. Children were waving mini-flags, surrounded by throngs of giddy planetary scientists. And four billion miles away, one billion miles past Pluto, the New Horizons spacecraft was flying past an enigmatic object called 2014 MU69–better known by its nickname, Ultima Thule.

When radio signals from New Horizons finally reached Earth the next morning, they revealed that the mission was a