Report on 27 October 2003

by KC Pau, Raffaello Lena

 Geologic Lunar Research Group
 
 
Abstract
This study describes a dome  located at +0.151+ 0.528 (longitude 10.26° E latitude 31.89° N).  This structure does not appear in the A.L.P.O. Lunar Dome Survey database and seems to require specific lighting conditions to be visible.
 

Introduction
 
 Lunar domes are gentle swells between 3 and 60 km across, and at most a few hundred meters in height. Most have very low angle of inclinations, only a few degrees at most [1-4]. Domes probably formed with two basic modes of formation:

a) as constructional forms. These formed at the end of a volcanic era, where the rate of extrusion is lower, and the temperature of eruption is lower;

b) as subsurface intrusions. This would be similar to a laccolith on the Earth.

In a previous paper [5] in print in Selenology, the Journal of the American Lunar Society, some of us  have described a very well known dome designated  as "Valentine dome" by Alika Herring [6] . In  [5] we reported further   measurements and include our CCD imaging where the rille crossing  the "Valentine dome"  was detected.
As described by Harold Hill in [6],  the presence of a rille was also reported and drawn by  Alika Herring on June 25 1966, using a 61'' reflector. This dome appears flat with a series of protrusions on its summit.

Recently, we detected near "Valentine" the presence of another smaller dome; the latter dome is the subject of this paper. Our study of this elusive dome is the first to be added to the A.L.P.O. Lunar Dome Survey and to include CCD imaging. This has made it possible to extract additional information on  this dome.

Observations
 
The Valentine dome has been well monitored from 1998 to 2003  during an observational program carried out by the GLR group. During this period the large "Valentine dome"  located at +0.152  +0.510 (longitude +10.18° , latitude +30.66 ° ) was recorded.

On July 16 October  2003 at 19:02 UT Pau imaged a flat dome located to the north  of the "Valentine dome" (Co-longitude 165.134°, Solar Altitude 4.26°). This observation was carried out under good seeing conditions using a 250mm f/6 Newtonian telescope ( Figure 1).
 

FIGURE 1

 Figure 1 reveals much finer detail in the dome than can be detected by traditional earth-based imaging, including two  small prominences. This dome requires a specific solar altitude in order to be observed clearly.
 
Another  CCD image by Pau was taken on September  16 2003 at 21:11  UT (see Fig. 2) . The dome located at 0.151+0.528 is not clearly evident in this image because the sun angle was already too high (Co-longitude 160.431°, Solar Altitude over the structure 8.690°).
 

FIGURE 2

This dome can be well observed under a setting sun, near the moon's last quarter. Since this is period during lunation when comparatively fewer observers are active, this dome has generally eluded detection until now.

The dome appears flat and elliptical in shape, it appears a miniature of the famous Valentine dome.  This could favor the second theory mentioned in the introduction under point b: a  subsurface intrusions of magma. Its slope appears moderate from the fact that its shadow is not black at the time image was taken.
In addition, there are 2 protrusions on the dome. These are difficult to clearly define.
Two possible mechanisms for the origin of these protrusions are (1) that they are peaks  which were embayed by the dome, and (2) that they are endogenic, created as small cinder cones on top of the dome. Given the geologic setting of this structure the present authors feel that it does represent a real unlisted dome.
 

 Conclusion
The lunar dome we have described here (0.151+0.528) is located just north of the very well known "Valentine dome".  This dome is another clear example of the elusive nature of these volcanic structures on the moon and the need for more work in this challenging area.
Using the Westfall Classification Scheme [7], we categorize the unlisted
dome as DW/2b/6g/8p.
Finally, international participation in our project continues in a favorable response to our efforts to foster increased cooperation among lunar observers worldwide.

[1] Salimbeni Pg. , Lena R., Mengoli G., Douglass E., Santacana G., J.A.L.P.O.,  2000, Vol 42,2.
[2] Lena R., Salimbeni Pg. , Douglass E., Santacana G., Higashida M., J.A.L.P.O, 2003, Vol 45, 1.
[3] Lena R.,  Mengoli G., Badalotti F.,  Salimbeni Pg., Douglass E., Santacana G.,  J.A.L.P.O, 2003, Vol 43, 4.
[4] Viegas R., Lena R., Douglass E., Selenology, 2002, Vol 21, 2.
[5] Lena R., Pau. KC, Fattinnanzi C., Selenology, 2003, Vol 22,4.
[6] Harold Hill, "A Portfolio of Lunar Drawings" , Cambridge University Press (1991).
[7] Westfall, John; J.A.L.P.O. 1964, Vol 18, no 1-2.