Nasa spots comet and mysterious celestial object flying towards Earth
Two massive space objects are heading towards Earth, but Nasa doesn't know what one of them is.
The American space agency has identified one of the objects as a comet, but is yet to classify the other, saying could be an asteroid or a comet.
Comet C/2016 was discovered by Nasa by in October 2016 and is expect to fly close to earth this week, according to the agency's website.
The mystery object, dubbed 2016 WF9, was detected by d by Nasa's asteroid- and comet-hunting Neowise project on November 27, 2016.
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Scientists say it is relatively large, roughly 500 metres to a kilometre across, and is rather dark.
However, they are not sure whether it is a comet or an asteroid.
James Bauer, deputy principal investigator at Nasa's Jet Propulsion Lab, said 2016 WF9 "could have cometary origins.
"This object illustrates that the boundary between asteroids and comets is a blurry one; perhaps over time this object has lost the majority of the volatiles that linger on or just under its surface."
It is expected to approach Earth's orbit in February 2017 at a distance of 51 million km from the planet.
Nasa said that the object was "not a threat to Earth for the foreseeable future".
Meanwhile, Comet C/2016 would visible this week to those in the Northern Hemisphere, shortly before sunrise.