An artist's rendition of 2016 WF9 as it passes Jupiter's orbit inbound toward the sun.
Image credit: NASA/JPL-Caltech.
NASA's NEOWISE mission has recently discovered some celestial objects
traveling through our neighborhood, including one on the blurry line
between asteroid and comet. Another--definitely a comet--might be seen
with binoculars through next week.
An object called 2016 WF9 was detected by the NEOWISE project on Nov.
27, 2016. It's 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. Objects in these types of orbits have multiple possible
origins; it might once have been a comet, or it could have strayed from a
population of dark objects in the main asteroid belt.
2016 WF9 will approach Earth's orbit on Feb. 25, 2017. At a distance
of nearly 32 million miles (51 million kilometers) from Earth, this pass
will not bring it particularly close. The trajectory of 2016 WF9 is
well understood, and the object is not a threat to Earth for the
foreseeable future.
A different object, discovered by NEOWISE a month earlier, is more
clearly a comet, releasing dust as it nears the sun. This comet, 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," said Paul Chodas, manager of NASA's Center
for Near-Earth Object (NEO) Studies at the Jet Propulsion Laboratory in
Pasadena, California.
As seen from the northern hemisphere during the first week of 2017,
comet C/2016 U1 NEOWISE will be in the southeastern sky shortly before
dawn. It is moving farther south each day and it will reach its closest
point to the sun, inside the orbit of Mercury, on Jan. 14, before
heading back out to the outer reaches of the solar system for an orbit
lasting thousands of years. While it will be visible to skywatchers at
Earth, it is not considered a threat to our planet either.
NEOWISE is the asteroid-and-comet-hunting portion of the Wide-Field
Infrared Survey Explorer (WISE) mission. After discovering more than
34,000 asteroids during its original mission, NEOWISE was brought out of
hibernation in December of 2013 to find and learn more about asteroids
and comets that could pose an impact hazard to Earth. If 2016 WF9 turns
out to be a comet, it would be the 10th discovered since reactivation.
If it turns out to be an asteroid, it would be the 100th discovered
since reactivation.
What NEOWISE scientists do know is that 2016 WF9 is relatively large: roughly 0.3 to 0.6 mile (0.5 to 1 kilometer) across.
It is also rather dark, reflecting only a few percent of the light
that falls on its surface. This body resembles a comet in its
reflectivity and orbit, but appears to lack the characteristic dust and
gas cloud that defines a comet.
"2016 WF9 could have cometary origins," said Deputy Principal
Investigator James "Gerbs" Bauer at 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."
Near-Earth objects (NEOs) absorb most of the light that falls on them
and re-emit that energy at infrared wavelengths. This enables NEOWISE's
infrared detectors to study both dark and light-colored NEOs with
nearly equal clarity and sensitivity.
"These are quite dark objects," said NEOWISE team member Joseph
Masiero, "Think of new asphalt on streets; these objects would look like
charcoal, or in some cases are even darker than that."
NEOWISE data have been used to measure the size of each near-Earth
object it observes. Thirty-one asteroids that NEOWISE has discovered
pass within about 20 lunar distances from Earth's orbit, and 19 are more
than 460 feet (140 meters) in size but reflect less than 10 percent of
the sunlight that falls on them.
The Wide-field Infrared Survey Explorer (WISE) has completed its seventh year in space after being launched on Dec. 14, 2009.
Data from the NEOWISE mission are available on a website for the
public and scientific community to use. A guide to the NEOWISE data
release, data access instructions and supporting documentation are
available at: http://wise2.ipac.caltech.edu/docs/release/neowise/
Access to the NEOWISE data products is available via the on-line and API services of the NASA/IPAC Infrared Science Archive.
A list of peer-reviewed papers using the NEOWISE data is available at: http://neowise.ipac.caltech.edu/publications.html
News Media Contact
DC Agle
Jet Propulsion Laboratory, Pasadena, Calif.
818-354-5011
agle@jpl.nasa.gov
Laurie Cantillo / Dwayne Brown
NASA Headquarters, Washington
202-358-1077 / 202-358-1726
laura.l.cantillo@nasa.gov / dwayne.c.brown@nasa.gov
Source: JPL-Caltech
