Blue asteroids are rare, and blue comets are almost unknown. An international team led by Teddy Kareta, a graduate student at the University of Arizona's Lunar and Planetary Laboratory, (3200) studied Phaethon, a bizarre asteroid that sometimes behaves like a comet and finds it even more enigmatic than previously thought.
The research team's findings will be presented at a press conference on October 23 at the 50th Annual Meeting of the Planetary Science Division of the American Astronomical Society at Knoxville, Tennessee.
Using telescopes in Hawaii and Arizona, the team studied the reflected sunlight Phaethon, which is known to be blue in color. Blue asteroids, which reflect more light in the blue part of the spectrum, make up only a fraction of all known asteroids. Much of the asteroid is dull gray to red, depending on the nature of the material on its surface.
Phaethon differs for two reasons: it seems to be one of the "blueest" similarly colored asteroids or comets in the solar system; and its orbit brings it so close to the sun that its surface heats up to about 800 degrees Celsius, hot enough to melt aluminum.
Astronomers are also fascinated by Phaethon for other reasons. It has the properties of both an asteroid and a comet because of its appearance and behavior.
Phaethon always appears like a dot in the sky, like thousands of other asteroids, rather than a blurry spot with a tail, like a comet. But Phaethon is the source of the annual Geminid meteor shower, easy to see, beginning to mid-December.
Meteor showers occur when the earth passes through the trail of dust happening in the orbit of a comet. When they occur and where they seem to come from depends on how the orbit of the comet is aligned with respect to the earth. Phaethon is believed to be the "parent" of the Geminid meteor stream, since its orbit is very similar to that of the Geminids.
Until Phaeton was discovered in 1
"At the time, the assumption was that Phaethon was probably a dead, burned-out comet," said Kareta, "but are comets typically red and not blue, so even though Phaeton's highly eccentric orbit should scream "dead comet," it's hard to say if Phaethon is more like an asteroid or more like a dead comet. "
Phaethon also releases a tiny dust tail when it comes closest to the sun in a supposed process similar to cracking a dry riverbed in the afternoon heat. This type of activity has been observed only on two objects throughout the solar system – Phaeton and another similar object that seems to blur the line that traditionally separates comets and asteroids.
The team received several new insights into Phaethon after analyzing data from NASA's infrared telescope facility on Mauna Kea, Hawaii, and the Tillinghast telescope operated by the Smithsonian Astrophysical Observatory on Mount Hopkins, Arizona. They think Phaethon may be related or demolished by (2) Pallas, a large blue asteroid farther out in the solar system.
"Interestingly, we found that Phaethon was even darker than previously observed, half as reflective as Pallas," Kareta said, "which makes it harder to say how Phaethon and Pallas are related."
The Team observed also that the blue color of Phaethon is the same on all parts of its surface, suggesting that it has been cooked evenly by the Sun lately
The team is now conducting observations of 2005 UD, another small blue asteroid , which astronomers think is related to Phaethon, to see if they share the same rare properties, and this and other work will help unravel the mystery surrounding Phaethon.
Moon and Planet Lab
Asteroid and Comet Mission News, Science and Technology
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NASA's OSIRIS-REx Performs the Second Asteroid Approach Maneuver [19659028GreenbeltMD(SPX)22October2018
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