200 mile long crater on the surface of Mars

Scientists have been left baffled by a long strange scar on the surface of Mars, close to the planet’s equator. The European Space Agency (ESA) has released new images of Orcus Patera -  an elongated crater which is located between the volcanoes of Elysium Mons and Olympus Mons in the planet's eastern hemisphere.
Scientists believe the most likely explanation for the crater is that it was made in an oblique impact, when a small asteroid struck the surface at a very shallow angle.
Its valley floor lies almost half a mile below the Martian plains that surround it. The term ‘patera’ is used for deep, complex or irregularly shaped volcanic craters but despite its name, scientists do not really know where Orcus Patera came from. It may be a large and originally round impact crater, which has changed shape through compression over time. Or it could have formed after a number of different impact craters were eroded.
The existence of tectonic forces at Orcus Patera is evident from the presence of the numerous ‘graben’, rift-valley-like structures that cut across its rim. Up to 2.5 km wide, these graben are oriented roughly east–west and are only visible on the rim and the nearby surroundings.
The dark shapes near the centre of the depression were probably formed by wind-driven processes, where dark material excavated by small impact events in the depression has been redistributed.
Source: (wateen.net)
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