(Photo: NASA)
While the American space agency has
pinpointed one as a comet, the other has left it slightly more baffled.
The comet is set to fly close to Earth this week, but the mystery object isn't expected to make an
appearance until February.
The
object, dubbed "2016 WF9", was detected by NASA's asteroid- and
comet-hunting NEOWISE project on 27 November 2016.
It
is roughly 0.3 to 0.6 miles (0.5 to 1 kilometres) across and is in an orbit
that takes it on a scenic tour of our solar system.
At its farthest
distance from the sun, it approaches Jupiter's orbit.
Over the course of 4.9 Earth-years, it travels inward,
passing under the main asteroid belt and the orbit of Mars until it swings just
inside Earth's own orbit.
After that, it heads
back toward the outer solar system.
However, NASA scientists are not sure whether it is a comet or
an asteroid .
"2016 WF9 could
have cometary origins," said Deputy Principal Investigator James
"Gerbs" Bauer at NASA's JPL.
"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."
While 2016 WF9 is dark like a comet, it appears to lack
the characteristic dust and gas cloud that defines a comet.
On 25 February, 2017
WF9 will approach Earth's orbit at a distance of nearly 32 million miles (51
million kilometres) from our home planet.
NASA said that the
object is "not a threat to Earth for the foreseeable future".
Below is an artist's rendition of WF9
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