Bennu and Jupiter as Seen by PolyCam
As OSIRIS-REx draws closer to Bennu, images from the spacecraft are beginning to give hints of the asteroid’s true shape and reflectivity. This pair of images showing Bennu (left) and Jupiter (right) were both taken with the spacecraft’s PolyCam imager using an exposure time of 4.2 milliseconds.
The image of Jupiter was captured a year-and-a-half ago, on Feb. 12, 2017, during OSIRIS-REx’s Earth Trojan Asteroid Search. At the time, Jupiter was about 418 million miles (673 million km) from the spacecraft. The image of Bennu was captured Oct. 22, 2018 when OSIRIS-REx was approximately 2,270 miles (3,650 km) away, or roughly the distance from Los Angles to Washington, DC. Even though both objects are distant and the images are pixelated, there are discernible differences in shape between Jupiter’s spherical form and Bennu, which appears diamond-shaped as predicted by ground-based radar observations.
Also noticeable is a difference in the amount of light reflected by the two objects. When these images were taken, Bennu was about five time closer to the Sun than Jupiter was, so the asteroid was receiving significantly more sunlight. If Bennu and Jupiter were equally reflective, the asteroid would appear about 25 times brighter in this image due to its proximity to the Sun. But Bennu’s surface is so dark (only reflecting about 3 to 4 percent of the incoming sunlight) that it appears darker than Jupiter despite being much closer to the Sun.
Date Taken: Oct. 22, 2018 and Feb. 12, 2017
Instrument Used: OCAMS (PolyCam)
Credit: NASA/Goddard/University of Arizona
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