Tracking a mysterious group of asteroid outcasts

August 4, 2015, NASA
The asteroid Euphrosyne glides across a field of background stars in this time-lapse view from NASA's WISE spacecraft. WISE obtained the images used to create this view over a period of about a day around May 17, 2010, during which it observed the asteroid four times. Because WISE (renamed NEOWISE in 2013) is an infrared telescope, it senses heat from asteroids. Euphrosyne is quite dark in visible light, but glows brightly at infrared wavelengths. This view is a composite of images taken at four different infrared wavelengths: 3.4 microns (color-coded blue), 4.6 microns (cyan), 12 microns (green) and 22 microns (red). The moving asteroid appears as a string of red dots because it is much cooler than the distant background stars. Stars have temperatures in the thousands of degrees, but the asteroid is cooler than room temperature. Thus the stars are represented by shorter wavelength (hotter) blue colors in this view, while the asteroid is shown in longer wavelength (cooler) reddish colors. Credit: NASA/JPL-Caltech

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 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 , 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 . To date, U.S. assets have discovered more than 98 percent of the known NEOs.

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JustAnotherGuy
5 / 5 (1) Aug 04, 2015
"Captain! incoming Photon torpedoes!"


I would have preferred a title like that...
Now, a bit more seriously, the next statement should be checked:
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.

60% of Moon's diameter? (:/)
Although I would enjoy the discovery of a new dwarf planet in the main belt!
TechnoCreed
5 / 5 (2) Aug 05, 2015
...the next statement should be checked:
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.

60% of Moon's diameter? (:/)
Although I would enjoy the discovery of a new dwarf planet in the main belt!
Being in the Moon seems to be a natural place for DC Agle from JPL (the redactor of this article) http://www.jpl.na...ure=4678 . Last January he wrote that 67P/C-G was at "about 92 million miles (148 million kilometer) from the sun"??? I repeat last JANUARY although its closest approach from the sun will happen next week on the 13th of august and it will be at 185.98 million kilometer. The article in question has never been corrected, as you can see. http://www.jpl.na...ure=4456

tbc
TechnoCreed
5 / 5 (2) Aug 05, 2015
...

Still the very strange numbers in question in the present article intrigued me; WTF was he talking about exactly.

It turns out that the total number of minor planet known at this moment is very close to 700000: http://www.minorp...nter.net The minor planets are all the objects that orbits around the sun that are not a planet, not a satellite, not a comet and not Pluto. If you look at the list of minor planet you find Ceres at number 1 and you find Eris at number 136199. https://en.wikipe...93137000
Eris is as big as Pluto (60% the diameter of the Moon). All dwarf planets are on the minor planet list except Pluto; the odd one out again.

In conclusion the error is not in the numbers but in a set of words that are out of place: "in the main belt".
JustAnotherGuy
5 / 5 (2) Aug 05, 2015
In conclusion the error is not in the numbers but in a set of words that are out of place: "in the main belt".

And that seems to be the best way to address DC Agle failed paragraph. Well done!
On a first attempt, a tried 'radius' rather than 'diameter'... yet messy numbers...

About the minor planet topic, I found it curious about Pluto's number, so I checked. Its designation is 134340. https://en.wikipe...ki/Pluto
Which to me, using your words, seem to be a odd one! Closer to Eris than Ceres, so I checked again...
https://en.wikipe...ki/Pluto#IAU_classification
In the "IAU classification" section there is a story of how Pluto was designated 134340 on 2006 instead of 1164 if it would have been designated on 1930. An odd story huh? Well, hope DC Agle haven't edited that entry too... ;)
TechnoCreed
5 / 5 (2) Aug 05, 2015
In the "IAU classification" section there is a story of how Pluto was designated 134340 on 2006 instead of 1164 if it would have been designated on 1930. An odd story huh? Well, hope DC Agle haven't edited that entry too... ;)
Thank you JAG! This was team work and a demonstration of a good vetting process. Did you get that DC Agle?

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