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- It appears some pieces of asteroid Vesta ended up
on asteroid Bennu, according to observations from
NASA's OSIRIS-REx spacecraft.
The new result sheds light on the intricate orbital dance
of asteroids and on the violent origin of Bennu, which
is a rubble pile asteroid that coalesced from the fragments
of a massive collision.
Six boulders, ranging in size from five to 14 feet,
were discovered scattered across Bennu's southern hemisphere
near the equator.
These boulders are much brighter than the rest of Bennu,
with some appearing as much as 10 times brighter
than their surroundings.
The unusual boulders on Bennu first
caught the team's eye in images from the OSIRIS-REx camera
suite instrument.
The team analyzed the boulders using
an onboard spectrometer, which separates light
into its component colors.
Since elements and compounds have distinct signature
patterns of bright and dark across a range of colors,
they can be identified using a spectrometer.
The signature from the boulders was
characteristic of the mineral pyroxene,
from Vesta and the Vestoids.
Smaller asteroids that are fragments
blasted from Vesta when a sustained significant asteroid
impacts.
The team tested a few different theories to determine
the origin of these boulders.
First, it's possible that the boulders were originally part
of Bennu or its parent body.
However, this is unlikely based on how pyroxene is created.
This mineral typically forms when rocky material
melts at high temperature.
Bennu is composed of water bearing minerals,
so it wouldn't have experienced very high
temperatures in its history.
Next, the team considered localized heating,
perhaps from an impact.
The scale of an impact needed to create large pyroxene boulders
is much more significant than what is expected to take place
in the main asteroid belt. So the team
ruled out these scenarios and instead considered
other pyroxene rich asteroids that
might have implanted this material
to Bennu or its parent.
This is possible because as asteroids move
through the solar system, their orbits
can be altered in many ways, including
by the pull of gravity from planets and other objects,
meteorite impacts, even the slight pressure from sunlight.
The new result helps pin down the complex journey
Bennu and other asteroids have traced
through the solar system.