[meteorite-list] NASA's NEOWISE Mission Spies One Comet, Maybe Two

[Ron Baalke]

http://www.jpl.nasa.gov/news/news.php?feature=6712

NASA's NEOWISE Mission Spies One Comet, Maybe Two
Jet Propulsion Laboratory
December 29, 2016

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 at jpl.nasa.gov

Laurie Cantillo / Dwayne Brown
NASA Headquarters, Washington
202-358-1077 / 202-358-1726
laura.l.cantillo at nasa.gov / dwayne.c.brown at nasa.gov

2016-328