Moon's Big Bulls-Eye Studied

Researchershave used Earth-based radar to examine ejecta material from the massive impactthat formed the moon's Orientale impact basin. Orientale basin is located atthe very edge of the moon's visible face.

Previously,this crater was difficult to study because it is only partially visible totelescopes on Earth. Newly developed techniques now have been used to makehigh-resolution radar observations of this important region.

The Orientalebasin was formed early in the moon's history. The crater is surrounded by threeconcentric circles and has the appearance of agiant bulls-eye.

Studyingejecta from the impact that created this massive lunar bulls-eye can teach usabout the history of the moon and how it developed over time. Impact featureson the lunar surface can also help scientists understand the impact history ofEarth. Ancient impactson Earth have played a major role in the evolution of our planet. They'rethought to have caused a number of mass extinction events. Asteroids and cometsmay also have delivered important precursor molecules for the development oflife.


Studying ancientimpacts on Earth is difficult. Factors such as volcanism, plate tectonics andweather have erased the evidence of old craters on our planet.

Unlike theEarth, the surface of the moonisn't altered by wind, erosion or volcanoes. This is why the lunar surface isriddled with craters. Studying these impact features on the moon can helpscientists determine what types of impacts may have occurred on Earth and whenthey most likely happened.

Craters onthe moon are associated with ejecta materials — chunks of rockand dust that are tossed into the air by impacts. The dusty lunar regolith ismostly pulverized ejecta, and it can be several kilometers thick in places.Previously, scientists had difficulty figuring out which ejecta deposits wereassociated with specific impact basins.


The newEarth-based radar observations allow scientists to look deeper into theregolith, and to put a number to the rocks associated with Orientale basin. Theresearch team has determined what the different kinds of ejecta material looklike 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 southpolar highlands. In fact, material ejected by the impact contributes significantlyto the composition of the lunar regolith in this region.

The studywill help define the scientifically interesting places for future humanmissions 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 southpolar 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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