NASA's NEOWISE mission has announced the discovery of two new space objects passing close to Earth's orbit. One of the celestial objects is a comet, but astronomers are uncertain whether the second object is a comet or an asteroid.
The first of the space objects currently passing through our inner solar system, according to NASA's Jet Propulsion Laboratory (JPL), is a rare comet known as C/2016 U1 NEOWISE. It was discovered by NEOWISE, NASA's asteroid-hunting mission, in October 2016.
C/2016 U1 NEOWISE reached its close point to Earth on December 13, 2016 at a distance of about 66 million miles (106 million kilometers). It is expected to be at its closest point to the Sun inside Mercury's orbit on January 14, 2017.
This is the first time in recorded history that the orbit of C/2016 U1 NEOWISE around the Sun has brought it close to Earth, according to astronomers. The comet is expected to be sufficiently bright until January 14 to be seen in the night sky using a good pair of binoculars or telescope.
According to Paul Chodas, manager at NASA's Center for Near-Earth Object (NEO) Studies at JPL in Pasadena, California, C/2016 U1 NEOWISE "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."
If visible it would be best observed from the Northern Hemisphere, shortly before dawn in the southern sky. It should remain visible, moving a little farther south each day until January 14 when it reaches its closest point to the Sun inside the orbit of Mercury.
Its proximity to the Sun on January 14 will make it difficult to observe. After January 14 it will begin moving away from our inner solar system into the outer Solar System.
"Comet C/2016 U1 NEOWISE is set to break binocular +10th magnitude brightness this week, and may just top +6th magnitude (naked eye brightness) in mid-January near perihelion," according to Universe Today.
"At its brightest, comet C/2016 U1 NEOWISE... is best visible in the dawn sky 12 degrees from the Sun at maximum brightness."
Magnitude measures the degree of brightness of an object in the night sky. The degree of brightness is higher for objects with a lower number for magnitude. Thus the Moon, with a magnitude of -12.7, is much brighter than Venus with a magnitude of -4.4.
Astronomers know very little about C/2016 U1 NEOWISE because this is the first time that it has been observed. It is believed that its orbital period could be millions of years. Thus this could be the first time it has come close to Earth in millions of years and the last time we would see it in millions of years.
Since it reached its closest approach to Earth on December 13, at a distance of 66 million miles (106 million kilometers), it has traveled closer to the Sun and reached a distance of 87 million miles (140 million kilometers) from Earth.
But NASA scientists are uncertain about the nature of the second object known as 2016 WF9. According to NASA, the object, about one kilometer across, appears to straddle the "blurry line between an asteroid and a comet."
Astronomers are uncertain as to whether it is a comet or an asteroid because it does not have a trail of icy debris like other comets. However, astronomers believe it could have "cometary origins" because it appears to have the reflective properties and body structure of a comet.
Comets are typically composed of ice, dust, and rocky material. They heat up as they approach the Sun and begin shedding material. The material forms a dust trail of debris. The loss of material could affect the degree of brightness and hence visibility of comets in the night sky.
"2016 WF9 could have cometary origins," said James Bauer at NASA's Jet Propulsion Laboratory.
"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."
Although it poses no threat to Earth in its current passage, scientists are studying 2016 WF9's orbital trajectory because they are concerned that its orbit could bring it closer to Earth during subsequent approaches to Earth.
2016 WF9 has an orbital period of only about five years. It passes Earth's orbit more frequently than C/2016 U1 NEOWISE because the furthest point of its orbit takes it only as far as Jupiter in our outer Solar System.
NASA's NEOWISE (Near Earth Object Wide-Field Infrared Survey Explorer) has been tracking potentially hazardous space objects since 2013.
[Featured Image by Solarseven/Shutterstock]