In late 2018, as NASA’s OSIRIS-REx spacecraft neared its
target, Bennu, the asteroid grew in detail from a few tiny pixels
to an incredibly hi-resolution image. OSIRIS-REx confirmed the
asteroid’s basic shape, which was originally observed in 1999
by ground-based radar at Arecibo Observatory. What scientists
didn’t expect was just how rough and boulder-filled the asteroid
would turn out to be. While it can be difficult to fully grasp
Bennu’s unfamiliar surface, it’s helpful to understand the scale
of what you’re seeing here. In this image, the brightest
boulder is the length of a horse and the large boulder in this
image is the width of a soccer field. Another challenge for the
mission is the asteroid’s small size and weak gravity. This
means that OSIRIS-REx needs to fly daringly close to the
surface in order to enter into orbit. With its orbital A phase,
OSIRIS-REx successfully entered the closest-ever orbit for a
spacecraft, setting a Guinness World Record in the process.
Then, 6 months later, it beat its own record during its
orbital B phase and approached to within a few hundred meters
of the rocky surface. Because OSIRIS-REx flew so closely over
the surface during orbital B, the team was able to map the
topography and shape of Bennu better than we have our own
Moon. In addition to mapping Bennu, OSIRIS-REx plans to
collect and return a sample of the asteroid back to Earth. To
do that, the spacecraft will carefully tag the surface of
Bennu. The OSIRIS-REx team has selected four possible sample
sites for the mission: Osprey, Kingfisher, Nightingale, and
Sandpiper. The spacecraft has been closely imaging these sites
from different angles to select the best touch-down spot for
OSIRIS-REx. What was originally envisioned as a smooth and easy
touchdown on Bennu’s surface, has become a complex endeavor to
tag a small, crowded space on the asteroid – an area no larger
than a few parking spots, by mid 2020. The OSIRIS-REx team has
already pushed the boundaries of scientific exploration, going
from ground-based radar images all the way to being a few
hundred meters from the asteroid surface, and is now mere months
away from a sample collection attempt.