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NASA's WISE Finds That Most Centaurs Are Comets

Celestial centaurs — the small sub-planetary bodies that are found orbiting the sun somewhere between Jupiter and Neptune — have remained something of a mystery since their discovery. What exactly are they? Asteroids? Comets? Well new research done using NASA’s Wide-field Infrared Survey Explorer (WISE) may finally be providing an answer to those questions — most centaurs are comets.

"New observations from NASA's NEOWISE project reveal the hidden nature of centaurs, objects in our solar system that have confounded astronomers for resembling both asteroids and comets. The centaurs, which orbit between Jupiter and Neptune, were named after the mythical half-horse, half-human creatures called centaurs due to their dual nature. This artist's concept shows a centaur creature together with asteroids on the left and comets at right." Image Credit: NASA/JPL-Caltech
“New observations from NASA’s NEOWISE project reveal the hidden nature of centaurs, objects in our solar system that have confounded astronomers for resembling both asteroids and comets. The centaurs, which orbit between Jupiter and Neptune, were named after the mythical half-horse, half-human creatures called centaurs due to their dual nature. This artist’s concept shows a centaur creature together with asteroids on the left and comets at right.”
Image Credit: NASA/JPL-Caltech

Previously, astronomers weren’t entirely clear whether centaurs were simply asteroids that were flung out into the outer solar system, or perhaps comets which entered a stable orbit after traveling in toward the Sun from afar. As a result of their “dual nature”, the sub-planetary bodies were given the name of the creature in Greek mythology that possessed the head and torso of a human and the body of a horse.

“Just like the mythical creatures, the centaur objects seem to have a double life,” stated James Bauer of NASA’s Jet Propulsion Laboratory. “Our data point to a cometary origin for most of the objects, suggesting they are coming from deeper out in the solar system.”

What Bauer means when he says ‘cometary origin’ is “an object likely is made from the same material as a comet, may have been an active comet in the past, and may be active again in the future.”


NASA has more:

The findings come from the largest infrared survey to date of centaurs and their more distant cousins, called scattered disk objects. NEOWISE, the asteroid-hunting portion of the WISE mission, gathered infrared images of 52 centaurs and scattered disk objects. Fifteen of the 52 are new discoveries. Centaurs and scattered disk objects orbit in an unstable belt. Ultimately, gravity from the giant planets will fling them either closer to the sun or farther away from their current locations.

Although astronomers previously observed some centaurs with dusty halos, a common feature of outgassing comets, and NASA’s Spitzer Space Telescope also found some evidence for comets in the group, they had not been able to estimate the numbers of comets and asteroids.

Infrared data from NEOWISE provided information on the objects’ albedos, or reflectivity, to help astronomers sort the population. NEOWISE can tell whether a centaur has a matte and dark surface or a shiny one that reflects more light. The puzzle pieces fell into place when astronomers combined the albedo information with what was already known about the colors of the objects. Visible-light observations have shown centaurs generally to be either blue-gray or reddish in hue. A blue-gray object could be an asteroid or comet. NEOWISE showed that most of the blue-gray objects are dark, a telltale sign of comets. A reddish object is more likely to be an asteroid.

“Comets have a dark, soot-like coating on their icy surfaces, making them darker than most asteroids,” stated study co-author, Tommy Grav of the Planetary Science Institute. “Comet surfaces tend to be more like charcoal, while asteroids are usually shinier like the moon.”

The new research indicates that somewhere around 2/3 of centaurs are comets — having originated somewhere in the cold outer reaches of the solar system. It’s not clear whether or not the rest are asteroids, comets, or perhaps something else.

The new research was just published online in The Astrophysical Journal.




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