On Nov 5, 2022, at 9:22 PM, jimcoble2000 via groups.io <jimcoble2000@...> wrote:



Jupiter was fairly boring so off to the moon tonight.

Seeing is quite good. The most interesting feature tonight are the Gruithuisen Domes located in the Imbrium basin a bit west of Sinus Iridium. These domes are a unique lunar feature and a bit enigmatic. They are volcanic domes but are quite unlike other domes on the moon. The pair are rounded mounds reminiscent of silicic domes on Earth. Fairly steep, they are quite unlike the basaltic domes found on the rest of the moon. Also, no such silica rock has been collected from any of the Apollo missions.

All materials from the moon have been either basalt, low in silica, or Anorthitic feldspars also low in silica. If the domes are a high silica feature, where did the silica come from? On Earth, the coastal volcanoes such as Mount Saint Helens and the Cascades are high silica volcanoes but that type of volcanoe requires continental granitic crust and plate tectonics to form.  Both these conditions are totally absent on the moon however. How were the lunar domes formed if they are silica? That question awaits a return to the moon but you can see these strange objects in your telescope from here. 

These domes show best when the terminator is sweeping through Aristarchus. They then stand in high relief and the dome like shape is obvious.

On Nov 5, 2022, at 9:22 PM, Mark Ost <jimcoble2000@...> wrote:



Jupiter was fairly boring so off to the moon tonight.

Seeing is quite good. The most interesting feature tonight are the Gruithuisen Domes located in the Imbrium basin a bit west of Sinus Iridium. These domes are a unique lunar feature and a bit enigmatic. They are volcanic domes but are quite unlike other domes on the moon. The pair are rounded mounds reminiscent of silicic domes on Earth. Fairly steep, they are quite unlike the basaltic domes found on the rest of the moon. Also, no such silica rock has been collected from any of the Apollo missions.

All materials from the moon have been either basalt, low in silica, or Anorthitic feldspars also low in silica. If the domes are a high silica feature, where did the silica come from? On Earth, the coastal volcanoes such as Mount Saint Helens and the Cascades are high silica volcanoes but that type of volcanoe requires continental granitic crust and plate tectonics to form.  Both these conditions are totally absent on the moon however. How were the lunar domes formed if they are silica? That question awaits a return to the moon but you can see these strange objects in your telescope from here. 

These domes show best when the terminator is sweeping through Aristarchus. They then stand in high relief and the dome like shape is obvious.