Whitepeak Observatory, Tacoma, WA

Cassini and the Valley


While observing this very beautiful & popular area on the Moon, I couldn't help but notice that it's also a very interesting area geologically as well, with many rather unique & plain features present, all in one telescopic view! I had quite a bit of fun observing and imaging the new dawn creeping down Plato's slopes last evening with my trusty little 5" and today i took a closer look at the nature of what's in view here...

All in one view...brooding Plato, the mysterious & anomolous crater Cassini, the famous Alpine valley and glorious Mons Piton dominating the surrounding maria.

The graphic above indicates the locations of some of the more prominent features of interest in this area.

First, indicated in the upper left of the graphic, lies an excellent and plain example of a otherwise typically very discreet lunar featuire, the lava flow front, otherwise known as a "lobate flow" or lava scarp. The leading edge of an ancient massive lunar magma flow, which worked it's way across the maria over 3 billion years ago, is here frozen in time.

The utter ferocity of the gigantic Imbrium impact which formed the Imbrium basin wherein Mare Imbrium lies, is witnesed here as well, it's ejecta plowing through the lunar Alps like a giant comb.

Untouched by this catastropic impact is Lower-Imbrium Cassini, a very odd crater indeed. No one really knows for certain in what manner Cassini came to appear the way it does today, unusually shallow, filled with lava and surrounded by an uncharacteristicly lobate and almost pristine looking ejecta "skirt". One of the posited explanations for this wierd surround is that Cassini impacted into either still warm or even a still molten, layer of fresh maria inside the relatively newly formed Imbrium basin, landing with more of a splash-- than a thud!

Near Cassini is a little 'galaxy' looking feature which peeked my curiosity enough to use the Lunar Orbiter to take a closer look. Turns out this is an area which, along with other nearby protuberences like Mons Piton, are exposed peaks from another age, remnant from the Imbrium impact, or perhaps from impacts which occured shortly after the basin was formed, and still visible standing above the younger lavas which subcequently flooded the giant impact basin during the upper Imbrium period, making these peaks as islands in a rocky sea. Our lunar 'galaxy' owes it's brightness to the fresh Copernican craterlet that smacked in to the middle of this hilly area sometime within a billion or so years ago, frosting the hills with it's bright, fresh ejecta. A time lapse camera would have been safe, refuged on this highground, to record the entire history of the flooding of the Imbrium basin and the creation of Mare Imbrium!

I can't seem to write an article about the Moon without mentioning at least one ghost crater it seeems ...one is outlined on the graphic, as big as Plato itself, this one. Where Plato impacted in the uplands edging the Imbrium basin and, escaping being inundated by mare lavas is thus preserved for us to view today, the old ghost adjacent to it appears to have formed at a lower elevation, placing it inside the basin, which would account for it's almost complete burial under the mare lavas which later flowed freely here.

Hope you enjoyed our little jaunt through Plato country!


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