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In December 2018, after traveling for two years, one hundred and one days,
and over one-point-two billion miles…
NASA’s OSIRIS-REx spacecraft arrived at its target: near-Earth asteroid Bennu.
OSIRIS-REx is the first mission to explore this primitive remnant
from the origins of the solar system, designed to study the asteroid and return a sample to Earth.
Bennu is a dark, diminutive world, roughly the height of a skyscraper,
and now, the smallest body to be orbited by a spacecraft.
Prior to arrival, it was known to have low thermal inertia,
a characteristic of fine-grained materials like sand.
An infrared spectrometer on OSIRIS-REx confirmed this property,
leading scientists to expect a predominantly smooth surface.
But the first close-up views of Bennu delivered a major surprise.
In exquisite detail, the mission’s cameras revealed an unrelenting rock-scape,
dominated by boulders.
By combining these images from OSIRIS-REx with its laser altimetry data,
we can take a tour of Bennu’s remarkable terrain.
The first stop is Simurgh Saxum.
This prominent boulder defines the asteroid’s prime meridian,
and serves as the basis of its coordinate system.
In Persian mythology, the Simurgh is a large and benevolent bird,
and the possessor of all knowledge
Saxum is Latin for "stone."
To the northeast lies the largest boulder on Bennu.
Measuring over three-hundred feet in length, Roc Saxum is a colossus,
longer than a football field.
It is also rich in a type of iron oxide called magnetite,
which was used by mariners as an early form of magnetic compass.
In Arab folklore, the Roc is an enormous bird of prey that can clasp elephants in its talons,
as well as stranded sailors, like the hero Sinbad.
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Continuing northeast, over the equatorial ridge, we arrive at Gargoyle Saxum.
This striking boulder is among the darkest on Bennu,
though it clutches a much brighter rock that is about the size of a person.
In Medieval legend, Gargoyles are dragon-like, winged monsters that can breathe fire,
and that guard cathedrals from evil spirits.
Our next destination takes us far to the east.
At the northern end of a small crater lies Ocypete Saxum,
a comparatively bright boulder measuring about thirty-three feet in diameter.
Ocypete Saxum is located near one of three sites where Bennu ejected small particles into space
in early 2019, displaying its dynamic and evolving nature.
In Greek mythology, Ocypete is one of the three harpies – the half-maiden, half-bird
personifications of storm winds, who would carry evildoers away from the Earth.
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In the creation stories of ancient Egypt,
the universe began as a formless, endless expanse of water.
From this primordial sea arose the primordial mound: Benben.
It was upon this rock that the god Atum settled, in the form of the Bennu bird,
and sent forth the call that shaped creation.
The story of Benben hearkens to the mounds of fertile silt that once emerged
from the receding floodwaters of the Nile
and it provides a fitting namesake for the tallest boulder on Bennu.
Protruding by over seventy feet,
Benben Saxum is so tall that it was first detected from Earth.
Now, we can appreciate this monumental feature in detail using data from OSIRIS-REx.
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The final stop on our tour is a cluster of exceptionally bright boulders,
scattered across the southern hemisphere.
They bear the spectral fingerprint of pyroxene
a mineral found in igneous rock, that is unlikely to have formed on Bennu.
These boulders most likely originated on the large asteroid Vesta,
and were delivered to Bennu’s parent body through meteoroid impacts.
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Although it is small in small in size, asteroid Bennu has proved to be a fascinating world…
abundant in geographic features that have defied our expectations.
Thanks to OSIRIS-REx, we can now explore Bennu
to uncover its composition…
its evolution…
and its ancient memories from the origins of the solar system.
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