When Asteroid Bennu was discovered on Sept. 11, 1999 by the Lincoln Near-Earth Asteroid Research project (LINEAR), it was called 1999 RQ36 — a provisional designation assigned by the Minor Planet Center. After follow-up observations determined the asteroid’s precise orbit, it was issued the official number 101955, indicating that it was the 101,955th asteroid to be officially recognized.
Bennu’s orbit brings it relatively close to Earth every six years (in 2018, for example, the asteroid comes within 0.352 AU or about 33 million miles), giving astronomers better opportunities to image the asteroid with telescopes. Additional ground-based observations of Bennu have been made a number times since the asteroid’s discovery, including these images captured by telescopes based in Arizona:
Sept. 17, 2005 — Six years after its discovery, Bennu was was observed by researchers using the 1.5-meter Kuiper Telescope at the University of Arizona. Credit: Carl Hergenrother/University of Arizona
Sept. 26, 2011 — A few months after NASA selected the OSIRIS-REx mission for funding to visit and sample Bennu, researchers using the 1.5-meter Kuiper Telescope at the University of Arizona observed the asteroid. Credit: Carl Hergenrother/University of Arizona
April 20, 2012 — Researchers using the 1.5-meter Kuiper Telescope at the University of Arizona observed Bennu again in the spring of 2012. Credit: Carl Hergenrother/University of Arizona
May 15, 2012 — Bennu was observed using the 1.8-meter Vatican Advanced Technology Telescope (VATT) on Mount Graham in Arizona in May 2012. Credit: Carl Hergenrother/University of Arizona/Vatican Observatory
Scientists have also used radar data from the Arecibo Observatory in Puerto Rico and NASA’s Deep Space Network antenna in California to estimate Bennu’s shape and size. However, to this day, no one has ever seen or imaged the asteroid up close.
That’s where OSIRIS-REx comes in.
Starting in the summer of 2018, the spacecraft will begin imaging asteroid Bennu with its PolyCam imager. The first images will be similar to ground-based observations: the asteroid will appear as a point of light in the distance. As the spacecraft approaches Bennu, the images will become clearer and more detailed, eventually zooming in on the asteroid’s precise shape, size and surface features.
The mission team will use these detailed images, along with data collected by the spacecraft’s other instruments, to create maps of Bennu and, ultimately to select the location where OSIRIS-REx will collect a sample of its surface material for return to Earth in 2023.