During the course of a single night our telescopes can find more than 10,000 moving objects. Fortunately our software geniuses are able to sort through this pile to allow us to focus on unknown objects which require additional observations. Most of the time asteroid hunters are able to decide if an unknown moving object is an Earth approaching asteroid by observing it for a few nights to determine it's path around the Sun. However, recently my Catalina Sky Survey teammates Alex Gibbs, Greg Leonard, Carson Fuls, and Richard Kowalski as well as observers in Hawaii, New Mexico, Australia, and Kitt Peak in Arizona had to follow an unknown object for nearly a month to determine its nature.
The new object they discovered is now called 2016 EJ203. It is about 3000 feet in diameter and takes 504 years to orbit the Sun on a path which goes from between Mars and Jupiter out to 3 times Pluto's distance from the Sun. In 2016 humans were able to spot 2016 EJ203 during the two weeks every 500 years that it is bright enough for us to detect. The Minor planet Center has classified 2016 EJ203 as a Trans-Neptunian object. Our catalog of these distant places now has several hundred entries ranging in size from Pluto and 4 other large dwarf planets to small objects like 2016 EJ203.
This object may be the nucleus of a burned out comet or a fragment left over from the formation of the solar system.