Image credit: NASA/JPL-Caltech. › Full image and caption
High above the plane of our solar system, near the asteroid-rich
abyss between Mars and Jupiter, scientists have found a unique family of
space rocks. These interplanetary oddballs are the Euphrosyne
(pronounced you-FROH-seh-nee) asteroids, and by any measure they have
been distant, dark and mysterious -- until now.
Distributed at the outer edge of the asteroid belt, the Euphrosynes
have an unusual orbital path that juts well above the ecliptic, the
equator of the solar system. The asteroid after which they are named,
Euphrosyne -- for an ancient Greek goddess of mirth -- is about 156
miles (260 kilometers) across and is one of the 10 largest asteroids in
the main belt. Current-day Euphrosyne is thought to be a remnant of a
massive collision about 700 million years ago that formed the family of
smaller asteroids bearing its name. Scientists think this event was one
of the last great collisions in the solar system.
A new study conducted by scientists at NASA's Jet Propulsion
Laboratory in Pasadena, California, used the agency's orbiting
Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE)
telescope to look at these unusual asteroids to learn more about Near
Earth Objects, or NEOs, and their potential threat to Earth.
NEOs are bodies whose orbits around the sun approach the orbit of
Earth; this population is short-lived on astronomical timescales and is
fed by other reservoirs of bodies in our solar system. As they orbit the
sun, NEOs can occasionally have close approaches to Earth. For this
reason alone -- the safety of our home planet -- the study of such
objects is important.
As a result of their study, the JPL researchers believe the
Euphrosynes may be the source of some of the dark NEOs found to be on
long, highly inclined orbits. They found that, through gravitational
interactions with Saturn, Euphrosyne asteroids can evolve into NEOs over
timescales of millions of years.
NEOs can originate in either the asteroid belt or the more distant
outer reaches of the solar system. Those from the asteroid belt are
thought to evolve toward Earth's orbit through collisions and the
gravitational influence of the planets. Originating well above the
ecliptic and near the far edge of the asteroid belt, the forces that
shape their trajectories toward Earth are far more moderate.
"The Euphrosynes have a gentle resonance with the orbit of Saturn
that slowly moves these objects, eventually turning some of them into
NEOs," said Joseph Masiero, JPL's lead scientist on the Euphrosynes
study. "This particular gravitational resonance tends to push some of
the larger fragments of the Euphrosyne family into near-Earth space."
By studying the Euphrosyne family asteroids with NEOWISE, JPL
scientists have been able to measure their sizes and the amount of solar
energy they reflect. Since NEOWISE operates in the infrared portion of
the spectrum, it detects heat. Therefore, it can see dark objects far
better than telescopes operating at visible wavelengths, which sense
reflected sunlight. Its heat-sensing capability also allows it to
measure sizes more accurately.
The 1,400 Euphrosyne asteroids studied by Masiero and his colleagues
turned out to be large and dark, with highly inclined and elliptical
orbits. These traits make them good candidates for the source of some of
the dark NEOs the NEOWISE telescope detects and discovers, particularly
those that also have highly inclined orbits.
NEOWISE was originally launched as an astrophysics mission in 2009 as
the Wide-field Infrared Survey Explorer, or WISE. It operated until
2011 and was then shut down. But the spacecraft, now dubbed NEOWISE,
would get a second life. "NEOWISE is a great tool for searching for
near-Earth asteroids, particularly high-inclination, dark objects,"
Masiero said.
There are over 700,000 asteroidal bodies currently known in the main
belt that range in size from large boulders to about 60 percent of the
diameter of Earth's moon, with many yet to be discovered. This makes
finding the specific point of origin of most NEOs extremely difficult.
With the Euphrosynes it's different. "Most near-Earth objects come
from a number of sources in the inner region of the main belt, and they
are quickly mixed around," Masiero said. "But with objects coming from
this family, in such a unique region, we are able to draw a likely path
for some of the unusual, dark NEOs we find back to the collision in
which they were born."
A better understanding of the origins and behaviors of these
mysterious objects will give researchers a clearer picture of asteroids
in general, and in particular the NEOs that skirt our home planet's
neighborhood. Such studies are important, and potentially critical, to
the future of humanity, which is a primary reason JPL and its partners
continue to relentlessly track these wanderers within our solar system.
To date, U.S. assets have discovered more than 98 percent of the known
NEOs.
NASA's Jet Propulsion Laboratory in Pasadena, California, manages the
NEOWISE mission for NASA's Science Mission Directorate in Washington.
The Space Dynamics Laboratory in Logan, Utah, built the science
instrument. Ball Aerospace & Technologies Corp. of Boulder,
Colorado, built the spacecraft. Science operations and data processing
take place at the Infrared Processing and Analysis Center at the
California Institute of Technology in Pasadena. Caltech manages JPL for
NASA.
NASA's Near-Earth Object Program at NASA Headquarters, Washington,
manages and funds the search, study and monitoring of asteroids and
comets whose orbits periodically bring them close to Earth. JPL manages
the Near-Earth Object Office for NASA's Science Mission Directorate in
Washington.
For more information about NEOWISE, visit: http://www.nasa.gov/neowise
More information about asteroids and near-Earth objects is available at: http://neo.jpl.nasa.gov - http://www.jpl.nasa.gov/asteroidwatch
Media Contact
DC Agle
Jet Propulsion Laboratory, Pasadena, Calif.
818-393-9011
agle@jpl.nasa.gov
Source: JPL-Caltech
