Contribution GLR
By   R. Lena, C. Fattinnanzi, S. Nardella, PG. Salimbeni, R, Porta, A. Bares, F. Padulosi

During a project we studied the Pons region . It was observed a structure positioned at longitude 20, 00º E and  latitude 25,95 ºS ( Xi 0.3075 and Eta  -0.4376).
On June 16, 2002 at  20:45  UT ( Colongitude 346.97°, Solar Altitude over 0.3075 -0.4376 corresponding to 6.19°) Raffaello Lena   observed a  dome-like feature located near  the crater Pons (fig.1).
This observation was carried out under good seeing conditions (II on the Antoniadi scale) using a 100mm refractor at f/15  and 300 magnifications.
As depicted in the drawing, the dome reveals a small depression on the top.

Fig 1- Lena

This dome was observed    and imaged on the  same night as Lena's  observation (on June 16, 2002 )  by R. Porta (SCT 250 mm f/6 at 19:55 UT), S. Nardella (SCT 200 mm f/10 at 19:52 UT) and F. Padulosi  (at 20.10 UT with a Meade ETX90). These observations were  carried out independently by both observers.  The image reported in fig. 2 was made by F. Padulosi using a webcam and a Meade ETX90 at  20.10 UT, seeing II-III on Antoniadi scale and elaboration with IRIS 6.0.
 

Fig 2- Padulosi
 

Fig 3- Fattinnanzi
 
 

An  image by Cristian Fattinnanzi  obtained on June 16, 2002 at  19:51  UT  reveals much finer detail in the dome than is available from preceding  imaging (see Fig. 3 above) .
The image was obtained using a 200 mm Newtonian  f/6  and a webcam Vesta Pro (21 frames with Astrostack) with a seeing II  on Antoniadi Scale.

This image shows a clear central depression on the summit and the dome borders seem well-defined.
 

Pons as  imaged by S. Nardella SCT 200 mm f/10 at 19:52 UT
 

Pons as observed by Porta

A. Bares: another image . The structure is visible marked by the arrows.
 

The Consolidated Lunar Atlas has an image of the dome at 0.3075 and  -0.4376. The dome is detectable on the CCLA F8  (fig. 4).
 

Fig IV CLA image
A more detailed image was found in the Lunar Orbiter frame IV-89- H1 (fig.5). It is interesting the comparison from the LO IV-089-H1 and our image reported in fig 3 (By Fattinnanzi).

Fig 6- LO frame
From our available images, and using the lunar aeronautical chart from The Times Atlas  of the Moon,  the position of the dome was measured. It is corresponding to   longitude 20, 00º E and  latitude 25,95 ºS ( Xi 0.3075 and Eta  -0.4376).
The diameter values are:
 E-W diameter (km)  8.5
N-S diameter (km)    11.6
Major-Minor Axes ratio  1.365
 
We estimate its height at  370  meters by using   Jamieson's Lunar Toolkit program (ALPO).

Lunar Orbiter IV frame

The  lunar orbiter IV image of this section. shows a  'pit' at the center is not single, but there
are four apparent craterlets. In a feature this size, it is unlikely that such a set of pits is volcanic. Volcanic pits do occur in small features, but they tend to be aligned.

Furthermore when we  examined the image from the Lunar Orbiter Photographic Atlas of the Moon, there were a numerous other features that looked similar to this structure. They all have the same 'hummocky' appearance. This suggests that this feature is (perhaps)  hummocky
terrain from a basin ejecta.

Geology

 Petrologic mapping of the moon does not suggest that this is a volcanic province, but that it is comprised primarily of highland materials. It is predominately anorthositic in mineralogy. The flat areas are more likely impact ejecta materials (similar to Cayley units), and not volcanic in origin.

So the  feature under earth-based imagery does have the appearance of a lunar dome. Under spacecraft imagery, this is more questionable. It is possible that it is a dome, but one that is highly eroded from impacts. However, we must then wonder why the units around
it are not as highly eroded. Certainly, the surrounding plains-unit could have covered such erosion (resurfacing), but the plains unit is at least 3.3 billion years of age, and domes were generally not being formed in this period. Coupled with the presence of many hummocky units
around this feature (in the LO imagery), this suggests that the feature is part of a larger hummocky unit from a basin's ejecta (and thus comparable to the Janssen formation or the Fra Mauro formation). This is similar to the Apollo 16 geology. Thus, it is possible
that this is a dome, but the evidence leans away from it; and if it is a dome, then you must first construct a geologic history that explains the various findings.
It shows how a earth-based imagery may look like a dome, but that spacecraft
imagery is necessary to confirm it.
 
 

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