Identification of suspect features in Ptolemaeus crater (domes?)

Geologic Lunar Researches Group Written by R.Lena and PG. Salimbeni - Geologic Lunar Researches (Italy) Prepared 31 January 1999

Abstract:

Visual observations and CCD images of Ptolemaeus crater have been performed. In a previous work suspect features like domes have been recorded by visual observations (see homepage). The captured CCD images are examined and processed with computer software to achieve increased resolution for domes study and for comparison with Clementine and Apollo images of the moon. The results obtained by GLR group may indicate the presence of particular structures like domes in a lumpy terrains. NASA have analysed several of these images and they report the presence of the features as possible, probably hummocky material.

Introduction

In a previous work we have reported preliminary results about the presence of suspect features like domes in Ptolemaeus crater. These features were not detected in several images. These structures appear to be very subdued features and so might require very specific lighting to make they visible. No literature's data reported the presence of domes in Ptolemaeus crater. The features appeared located between 2,5-3,5 °E and 7,0-9,5°S.

Crater Imaging

Observations of the Ptolemaeus crater was conducted for the Geologic Lunar Researches (GLR) Project to capture images of the crater. The area of interest is shown in the lunar surface chart in Figure 1 below.

Fig.1 colongitude 5.5, features like domes are showed in dark spots (Salimbeni 28 september 1998 17.40 UT, SCT 200 mm f/10).

A possible presence of six suspect domes was observed visually by Salimbeni and Lena on september, 28, 1998 (17.40-20 UT). The visual observation was performed by Schmidt Cassegrain telescope of 250 and 200 mm of diameter f/10 (magn. 250, 278 x) respectively, seeing II (Antoniadi Scale).
The colongitude was beetwen 5.03° and 6.22°, longitude and latitude
selenograf. was -6.5 and -5.6 respectively. The solar altitude on Ptolemaeus at this time was beetwen 3.05 e 4.22°.

Fig. 2- At the 20.00 UT Lena recorded three features (28 september 1998, SCT 250 mm f/10, 250x)

The Sun's altitude above the lunar surface is one of the governing factors in the observation of these features. Infact the visibilty of these features decreased and in two hours it was hard to record the presence of the 3 features located on the south. Ptolemaeus shows a red color and it darken under blue light (W80A ). The central area of Ptolemaeus showed higher albedo values (4 Elger Scale) than soil surrounding the features at lower albedo (3 Elger Scale). Lena and Salimbeni estimated the probably domes at albedo values of 4,5 Elger Scale.

Grey Scale Surface of Ptolemaeus showed the brighter area corresponding to the presence of suspect domes. Their location appears to be also coincident with a localized belt of lower albedo value.

Only in 1 CCD image obtained by Therin G. (France) is visible a single feature that appears to be a dome. This is shown in one typical image in Figure 3.

Fig.3- Feature on the west of Ptolemaeus crater recorded by G. Therin (France).

Analysis of the CCD image gave an interesting result which showed a same feature. The surface plot of the marked area on the figure 1 can be compared with the CCD image above. The feature in question is about 8 km in diameter as compared to Ammonius crater (Robinson R.-IOTA).

The boxed area has been analysed to produce higher enlarged surface. This image is saturated and a flat plateau with small brighter crater was observed.

Fig 4- The feature on Ptolemaeus crater (Salimbeni's elaboration)

Several features have been seen in Ptolemaeus at last quarter as recorded by Thierry Legault (France).

Fig 5-Ptolemaeus crater last quarter (CCD image performed by T. Legault)

Other images performed by Higashida M. (Japan), Mengoli G. and Comolli L. (Italy) have been also examinated but no suspect features have been detected. This was due in part, to the high angle of incidence of the Sun leading to saturation of the image and poor contrast.

A second imaging session included a 3D surface modeling. Infact the application of this technique provides information on the distribution of surface units and the topographic altitude. Furthermore the surface modeling support the visual observations. The image shows the presence of a feature which seems to stand higher elevation. It could be correlated to a dome or a hill according to the observations performed by Salimbeni and Lena. Furthermore the image shows a chaotic surface morphology like hummocky terrain.

Fig 6- Surface modeling performed by Salimbeni (Italy).

It appears to be a very subdued feature and so might require very specific lighting to make it visible. It is interesting to note, that in the book "The Moon", by Wilkins and Moore, no mention was made of any domes located on the floor, on or near Ammonius (A).
Image Comparison

Images obtained by Clementine and Apollo (16 8 8 frames) were compared. Ptolemaeus is 164 km in diameter and is centered at 9.3 S, 1.9 W. The interior of the crater is covered by the Cayley formation, a light-colored unit characterized by the gentle ridges and depressions, and numerous small craters. The Cayley formation may be related to the nearby Fra Mauro formation. The picture was taken from 112 km . (Apollo 16, AS16-0989)

Fig 7- Ptolemaeus crater, Apollo 16 frame
Location & Time Information
Date/Time (UT): 1972-04
Distance/Range (km): 112.
Central Latitude/Longitude (deg): -09.5,359. E
Orbit(s): N/A
Imaging Information
Instrument: Metric Mapping Camera
Instrument Resolution (pixels): Film Type - 3400
Instrument Field of View (deg): 76.2 mm Focal Length
Filter: None
Illumination Incidence Angle (deg): 80.
Phase Angle (deg): 80.

Fig 8- Ptolemaeus crater. On the right our CCD image (circle deformation )

The our elaboration of the marked area can be compared with the image of Apollo 16 above. This comparison shows a different illumination of the crater. No data concerning same lighting conditions were available from ALPO, UAI and NASA. Even very small changes in
lighting conditions can make dramatic changes in the appearance of topography so this feature might not have been visible under other circumstances. It appears to be a very subdued feature and so might require very specific lighting to make it visible.
We have identified similar features only in the book Atlante fotografico della Luna (Hoepli editor) Tab-13. In fig. 9-10 are shown the images performed in date 21 march 1945. Here appeared the allineament of several features observed visually by Lena and Salimeni on 28 september 1998.

Fig 9- Image obtained on 21 march 1945 (Atlante fotografico della Luna).

Fig 10- Elaboration of the preceding image (Salimbeni PG.). The image shows same features recorded by Salimbeni and Lena (on 28 september 1998).

The soil is a lumpy and hummocks terrain and to the southern of the crater is visible a specific feature like dome. However the features does not casts a pointed shadow and the indipendent visual observations seem to confirm the presence of domes.

Hummocky Material
Debris avalanches produce thick, hummocky deposits that can extend as far as several tens of kilometers from a volcano and cover an area of a few tens of square kilometers, as occurred at Mount St. Helens in 1980, to a few hundred square kilometers, as occurred at Mount Shasta between 300,000 and 360,000 years ago. Debris avalanches are most likely at steep-sided volcanoes (From: Miller, 1989, Potential Hazards from Future Volcanic Eruptions in California: USGS Bulletin 1847, p.4-5. )
The debris-avalanche deposit at Mount St. Helens covers about 60 square kilometers. The most conspicuous feature of the deposit is its hummocky chaotic surface morphology.An avalanche is a large mass of moving fragments with blocks that range from 100's of meters (exceeding 1000 m) in longest dimensions, down to tiny particles less than 0.1 mm. They may form from the collapse of nearly any kind of rock, but the focus here is upon volcanic debris-flow avalanches that develop from the collapse of parts of volcanoes.

Fig 11- Debris-flow avalanche deposit from Mount St. Helens formed on 18 May 1980 (Courtesy by USGS). Hummocky surface is typical of avalanche deposits. The image may be compared with our 3d elaboration (Salimbeni PG.)

Gigantic avalanches can also originate by the structural collapse of a composite volcanoes and it is difficult to obtain specific relationships.

NASA Analysis

An independent analysis of our data was conducted by the NASA (NSSDC and USGS team). The fig. 3-4 was studied by Dr. L. Gaddish (USGS). The feature was a bright walls of a small crater which is superimposed on a portion of the ejecta blanket of Herschel crater, located to the north and east of Ptolomaeus. The floor of the degraded crater Ptolomaeus is indeed subdued, and in its northern portion it has a deposit of brighter, hummocky material with numerous small bright craters---this deposit and these craters are almost certainly from the younger Herschel crater. One can see these relationships more clearly in the Lunar Orbiter IV images IV-108-M and IV-108-H3 (although the latter has an artifact just below the area of interest). There are no named dome features in the area of Ptolemaeus crater. That doesn't mean there are no domes, just that there are no NAMED domes in that area. Future observations and CCD images are encouraged.

Conclusion

The agreement between visual observation performed the same day by Salimbeni and Lena and the corresponding CCD image is very good. The image provides further evidence of these features which are difficult to discern in different lighting conditions (see above). These features seems to be hummocky deposits like debris avalanches. The problem is: Are these debris avalanches originated by collapse of older vulcanoes ? Or are these debris originated by the formation of younger craters?
Our opinion is that these features seems to be domes.
Future observations and CCD images are encouraged. We hope in a future collaboration of several observers in the world !

Acknowledgments
The encouragement from Guido Santacana (PortoRico), Francis Ridge (Lunascan Project), Morio Higashida (Japan), Rob Robinson (IOTA), Gerard Therin (France) and Thierry Legault (France) is gratefully acknowledged.

Send your observations at :

Raffaello Lena - gibbidomine@iol.it
Piergiovanni Salimbeni- atlas@dido.net