During the week of December 10th ATLAS made a trio of new discoveries: two Near Earth Objects (NEOs) and one comet. Their orbits were determined automatically by the ATLAS software, and reported to the IAU Minor Planet Center at the Smithsonian Astrophysical Observatory.
The largest object, numbered 2015XU378, has an estimated diameter of 250 meters, and is classed as a Potentially Hazardous Asteroid (PHA). It passed within 0.066 AU (10 million km) of the Earth on December 8th.
The other NEO, 2015X168, has an estimated size of 50 meters: its perihelion distance is 0.82 AU, which means that during some parts of its orbit it is closer to the Sun than is the Earth.
The comet that ATLAS found, C-2015X7, has a perihelion distance of 3.8 A.U, so no threat to Earth. UH astronomer Richard Wainscoat confirmed the discovery by taking a pair of images (below) using the CFHT telescope. They confirm both the extended shape of the image and its changing position relative to the background stars.