"With our infrared sensors that detect heat, we can learn about their sizes and reflectiveness," said Mainzer.
2013 YP139 is about 43 million kilometres from Earth.
Based on its infrared brightness, scientists estimate it to be roughly 650 meters in diameter and extremely dark, like a piece of coal.
The asteroid circles the Sun in an elliptical orbit tilted to the plane of our solar system and is classified as potentially hazardous.
It is possible for its orbit to bring it as close as 482803 km from Earth, a little more than the distance to the Moon. However, it will not come that close within the next century.
NEOWISE was originally called the Wide-field Infrared Survey Explorer (WISE), which had made the most comprehensive survey to date of asteroids and comets.
WISE discovered more than 34,000 asteroids and characterised 158,000 throughout the solar system during its prime mission in 2010 and early 2011. Its reactivation in September followed 31 months in hibernation.
