How Bennu Got its Name
Bennu was named by then third-grader Michael Puzio during an international student contest. He named it after the Egyptian mythological deity linked to rebirth, who is often depicted as a heron. The number 101955 in Bennu's official name refers to the order in which its orbit was confirmed among all the other asteroids, which happened in 1999.
101955 Bennu is a near-Earth asteroid that comes relatively close to Earth about every six years. Scientists have studied it extensively in visible and infrared red light and with radar and it is now the primary science target of the robotic OSIRIS-REx mission. The spacecraft is en route to map Bennu's surface and collect a sample of the asteroid to return to Earth. OSIRIS-REx is expected to arrive in 2018.
Bennu is a near-Earth asteroid with an orbit that brings it between 278,867 and 213,798,356 miles (0.003 AU and 2.3 AU) from Earth. Because it passed within half an Astronomical Unit (AU) from Earth, it is listed among the potentially hazardous asteroids (PHAs).
Bennu is roughly spherical, with an equatorial bulge. The equator's diameter is 1,805 feet (550 meters) but its mean diameter is about 1,614 feet (492 meters). It takes just over 4-1/4 hours to rotate once and about 1.2 Earth years to go around the Sun.
Bennu is a "B-type" asteroid, with a composition likely similar to meteorites known as "carbonaceous chondrites," which as their name suggests, are rich in carbon compounds. Bennu's high carbon content means it is very dark-colored, nearly black. B-type asteroids are thought to be primitive remnants of the original building blocks of our solar system and to contain clay minerals formed from rocks in the presence of liquid water.
Bennu was discovered by the Massachusetts Institute of Technology Lincoln Near Earth Asteroid Research (LINEAR) project on September 11, 1999. It was originally designated 1999 RQ36.