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Dark Object Investigated While Making One of the Closest Ever Comet Flybys of Earth

Alan Fischer
Public Information Officer
Planetary Science Institute
fischer [at]
Dark Object Investigated While Making One of the Closest Ever Comet Flybys of Earth
March 24, 2016, Tucson, Ariz. -- Astronomers at the Planetary Science Institute made observations of Comet Pan-STARRS (P/2016 BA14) using the NASA Infrared Telescope Facility (IRTF) on Mauna Kea, Hawai’i that show that it reflects less than 3 percent of the sunlight that falls on its surface. For comparison, fresh asphalt reflects about 4 percent of the light that falls on it. 
Comet Pan-STARRS made a close flyby of the Earth at a distance of 3.6 million kilometers (2.2 million miles) on March 22.  This is one of the closest flybys of a comet in recorded history and the last one to come closer was Lexell’s comet that flew by the Earth at a distance of 2.2 million kilometers (1.4 million miles) on July 1, 1770.  
“We measured the spectral and thermal properties of the comet using the NASA IRTF and found that the comet reflects between 2-3 percent of the sunlight that falls on it,” said Vishnu Reddy, research scientist at the Planetary Science Institute in Tucson, Arizona. “This is typical for comets,” Reddy added. Based on its reflective properties, Reddy estimates the size of the comet to be between 600 meters and 1.2 kilometers  (0.4 miles and 0.75 miles) in diameter. 
Comet Pan-STARRS was originally discovered as an asteroid and later found to have cometary properties when astronomers realized its orbit is similar to another short period comet 252P/LINEAR, which also made a close flyby of the Earth at 5.3 million kilometers (3.3 million miles) on March 21. 
"It is an extremely rare opportunity to be able to study a pair of comets with historically close flybys.  Measuring the physical properties of both comets will help us understand the evolution of comets in general," said Jian-Yang Li, Senior Scientist at PSI. Li was observing 252P/LINEAR with the Hubble Space Telescope during its close encounter.
This research was funded by NASA Near-Earth Object Observations program. The Infrared Telescope Facility is operated by the University of Hawaii under contract NNH14CK55B with the National Aeronautics and Space Administration.
Vishnu Reddy
Research Scientist
reddy [at]
Jian-Yang Li 
Senior Scientist
jyli [at]
Mark V. Sykes
sykes [at]
The Planetary Science Institute is a private, nonprofit 501(c)(3) corporation dedicated to solar system exploration. It is headquartered in Tucson, Arizona, where it was founded in 1972.
PSI scientists are involved in numerous NASA and international missions, the study of Mars and other planets, the Moon, asteroids, comets, interplanetary dust, impact physics, the origin of the solar system, extra-solar planet formation, dynamics, the rise of life, and other areas of research. They conduct fieldwork on all continents around the world. They also are actively involved in science education and public outreach through school programs, children’s books, popular science books and art.
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