The Monadnocks of Sinus Honoris

A northwest-southwest oriented groove between two inselbergs in Sinus Honoris (12.276°S; 18.712°E), an embayment near the northwest extreme of Mare Tranquillitatis. LROC Narrow Angle Camere (NAC) frame M181944849L, LRO orbit 11796, January 12, 2012. Illumination angle of incidence 67.94°from the west, field of view roughly 5.8 km across, resolution in the original 1.21 meters per pixel from 122.13  km [NASA/GSFC/Arizona State University].

James Ashley
LROC News System

Most of the physical sciences are instructive in the art of piecing together observations made at vastly different scales. Note, for example, how climatologists look at pollen in soil samples to assess climate change through time on a global scale. Geologists use microscopes to examine mm-scale crystals in order to understand magma chambers many cubic miles in volume.

Astronomers attempt to make sense of subatomic particles in the context of the entire visible Universe. With this in mind, try to explain the sculpted mountains in today's Featured Image, located at the northwestern margin of Mare Tranquillitatis.

Field of view shown at high-resolution in the LROC Featured Image released April 25, 2013 is outlined in yellow in this Wide Angle Camera (WAC) monochrome (566 nm) observation M165726769C, swept up in orbit 9557, July 19, 2011. Field of view 45.8 km, resolution 58 meters per pixel from 40.97 km [NASA/GSFC/Arizona State University].

You may find that adjusting the scale is necessary. Indeed; we will have to zoom out until we can see a good deal of the lunar nearside before the features have the context they need to be understood. (Examine the image above and below to pull back for increasingly smaller-scale, wider-field of view LROC WAC context images.)

A mosaic of the LROC WAC image immediately above, stitched together to observations of the same latitude from one orbit prior and after, July 19, 2011. Field of view roughly 145 km [NASA/GSFC/Arizona State University].

The WAC mosaic context image released with the LROC NAC Featured Image covers a more familiar 1,500 km wide field of view (one that happens also to include four of six successful Apollo landing sites; Apollo 11, 15, 16 and 17) [NASA/GSFC/Arizona State University].

These mountains are members of a group of mare-surrounded highland structures nestled between Mare Tranquillitatis and Mare Serenitatis. Examination of the region will quickly reveal a strong northwest to southeast trending orientation to most of the upland features that points directly back to the Apennine Mountains, which form the southeastern rim of the Imbrium basin. Now we can see that this whole region was sculpted by ground-hugging forces unleashed in the terrible cataclysm that formed that basin. Imagine witnessing this awesome event from the Earth over 3 billion years ago; it would have been clearly visible to the unaided eye!

Isolated mountains like these, which rise from a surrounding plain, are often referred to by geologists as monadnocks or inselbergs ("island mountains," or "sky islands"). On Earth such features might be erosional remnants, but here in the Bay of Honor (Sinus Honoris) we know them to be isolated by surrounding mare deposits.

Click HERE to see the full NAC frame. Additional examples of large-scale features on the Moon can be explored with Four of a Kind in Catena Davy, Nearside Spectacular!, and A Scar in the Highlands.