[meteorite-list] Tracking A Mysterious Group of Asteroid Outcasts (Euphrosyne Asteroids)

[Ron Baalke]

http://www.jpl.nasa.gov/news/news.php?feature=4678

Tracking A Mysterious Group of Asteroid Outcasts
Jet Propulsion Laboratory
August 3, 2015


Fast Facts:

* A new NASA study has traced some members of the near-Earth asteroid 
population back to their likely source.

* The source may be the Euphrosyne family of dark, asteroids on highly 
inclined (or tilted) orbits in the outer asteroid belt.

* The study used data from NASA's NEOWISE space telescope, which has a 
second life following its reactivation in 2013.

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 at jpl.nasa.gov 

2015-256