NASA's Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) may have only come back online last September after a 31-month hibernation, but it’s already producing results. According to the space agency, the unmanned spacecraft discovered a never-before-seen asteroid on December 29 – the first discovery of its new mission to seek out potentially hazardous near-Earth objects (NEOs).
Known by the prosaic catalog designation 2013 YP139, the asteroid is currently 27 million miles (43 million km) from Earth. By measuring its brightness in the infrared part of the spectrum, astronomers calculate that it is about 0.4 mi (650 m) in diameter and is extremely dark, “like a piece of coal.” NASA classifies it as potentially hazardous to Earth and says that it may one day come within 300,000 mi (480,000 km) of Earth, though this won’t happen within the next century.
NEOWISE discovered 2013 YP139 by scanning the sky several times over half a day. Special software then analyzed the scan, looking for movement against the stationary star background. At the time of discovery, 2013 YP139 was moving across the sky at about 3.2 degrees per day. For reference, the full moon is about 0.5 degree across.
According to NASA, the discovery was confirmed by the University of Arizona using Kitt Peak National Observatory with Peter Birtwhistle, an amateur astronomer at the Great Shefford Observatory in West Berkshire, England contributing follow-up observations. Launched on December 14, 2009, NEOWISE started life as the WISE space telescope, tasked with producing a full-sky survey in search of dim objects, such as brown dwarfs, in the infrared spectrum. Its ultra-sensitive telescope was supercooled down to as low as 7.6° K (-446° F/-266° C) by inserting it inside a cryostat containing solid hydrogen. WISE’s main mission ended when its hydrogen ran out and it was eventually decommissioned in February 2011 after receiving a four-month mission extension, but it was brought back online in September for its new mission after 31 months of hibernation.
It sits in a solar-synchronous orbit 326 mi (525 km) above the Earth, circling the globe once every 95 minutes. Now renamed and recommissioned, its new three-year mission focuses on the search for asteroids and comets that might pose a threat to Earth, or that may be suitable for an asteroid exploration mission as part of the US asteroid initiative.
During its original mission, WISE discovered over 34,000 asteroids and studied 158,000 more. NASA anticipates that the unmanned probe will find up to 150 new NEOs and will study the size, albedo and thermal properties of 2,000 others. According to the space agency, the data from NEOWISE will be sent automatically to the Minor Planet Center in Cambridge, Massachusetts, where it will be compared against the known catalog of Solar System objects. Professional and amateur astronomers will do follow-up observations to determine the orbits of discovered NEOs with greater accuracy.
"We are delighted to get back to finding and characterizing asteroids and comets, especially those that come into Earth’s neighborhood," says Amy Mainzer, the mission's principal investigator from NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California. "With our infrared sensors that detect heat, we can learn about their sizes and reflectiveness."