NASA's NEOWISE mission unannounced the discovery of two new Near-Earth Objects this week. One of the objects is a comet, while the other is an ambiguous comet-asteroid hybrid.

NEOWISE is the asteroid and comet hunting part of the Wide-Field Infrared Survey Explorer mission. The WISE space telescope was launched in 2009.

The comet-asteroid was first spotted by WISE in late November and named WF9. Over the course of its 4.9 Earth-year orbit, WF9 briefly follows Jupiter's orbital path before swinging in toward the sun, looping inside the orbits of Mars and Earth. The object will come within 32 million miles of Earth in late February.

Though scientists are confident in their understanding of WF9's trajectory, they're less sure about its origin and identity. It could be a migrated comet or runaway asteroid. WF9's body's shape, size and reflectivity are comet-like, but it lacks the gas and dust cloud and tail typical of a comet.

The certifiable comet is C/2016 U1. Its orbit lasts thousands of years. In January, it will make its closest approach to the twin, swinging inside Mercury's orbit before being catapulted back to the outer reaches of the solar system.

"[It] has a good chance of becoming visible through a good pair of binoculars, although we can't be sure because a comet's brightness is notoriously unpredictable," Paul Chodas, manager of the NASA Center for Near-Earth Object Studies at the Jet Propulsion Laboratory, said in a news release.

Both are large but relatively dark, making them hard to spot prior to their approach toward the inner solar system. But because NEOs absorb light and re-emit it as infrared radiation, WISE is able to pick them out of the night sky.

"These are quite dark objects," said NEOWISE team member Joseph Masiero. "Think of new asphalt on streets; these objects would look like charcoal, or in some cases are even darker than that."