Researchers
have used Earth-based radar to examine ejecta material from the massive impact
that formed the moon's Orientale impact basin. Orientale basin is located at
the very edge of the moon's visible face.
Previously,
this crater was difficult to study because it is only partially visible to
telescopes on Earth. Newly developed techniques now have been used to make
high-resolution radar observations of this important region.
The Orientale
basin was formed early in the moon's history. The crater is surrounded by three
concentric circles and has the appearance of a
giant bulls-eye.
Studying
ejecta from the impact that created this massive lunar bulls-eye can teach us
about the history of the moon and how it developed over time. Impact features
on the lunar surface can also help scientists understand the impact history of
Earth. Ancient impacts
on Earth have played a major role in the evolution of our planet. They're
thought to have caused a number of mass extinction events. Asteroids and comets
may also have delivered important precursor molecules for the development of
life.
Impact
evidence
Studying ancient
impacts on Earth is difficult. Factors such as volcanism, plate tectonics and
weather have erased the evidence of old craters on our planet.
Unlike the
Earth, the surface of the moon
isn't altered by wind, erosion or volcanoes. This is why the lunar surface is
riddled with craters. Studying these impact features on the moon can help
scientists determine what types of impacts may have occurred on Earth and when
they most likely happened.
Craters on
the moon are associated with ejecta materials — chunks of rock
and dust that are tossed into the air by impacts. The dusty lunar regolith is
mostly pulverized ejecta, and it can be several kilometers thick in places.
Previously, scientists had difficulty figuring out which ejecta deposits were
associated with specific impact basins.
Digging
deeper
The new
Earth-based radar observations allow scientists to look deeper into the
regolith, and to put a number to the rocks associated with Orientale basin. The
research team has determined what the different kinds of ejecta material look
like and just how far they spread over the lunar surface.
Surprisingly,
ejecta from the Orientale basin can be found over much of the moon's south
polar highlands. In fact, material ejected by the impact contributes significantly
to the composition of the lunar regolith in this region.
The study
will help define the scientifically interesting places for future human
missions to explore, and what scientists should be looking for when they land.
The research team, led by Rebecca Ghent of the University of Toronto, feels that the findings have "implications for future exploration of the south
polar region and the South Pole–Aitken basin," both of which are
"likely targets for future landed and sample return missions."
The study was published in the May edition of the journal Geology.
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