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A DOME NEAR CRATER VENDELINUS

located at longitude +57.83 ° and latitude -15.74°

By Raffaello Lena, Christian Wöhler, Jim Phillips, Maria Teresa Bregante, andKC PAU - GLR Group

Vendelinus is an ancient lunar impact crater located on the eastern edge of Mare Fecunditatis. To the north of Vendelinus lies the prominent Langrenus crater, while to the southeast lies Petavius crater. Due to its location, the crater appears oblong due to foreshortening. The floor of Vendelinus is flat and covered by a dark lava flow. It lacks of a central peak, but includes multiple impact craters of various dimensions [1].

The smaller Lohse crater overlaps the rim to the northwest, and at the south end there is the Holden crater.

A number of domes are reported in this region but they are not easy to image as the crater is close to the lunar limb [2]. Observation of these domes requires low solar altitude for maximum detail. Recently this region was monitored by the GLR group. In addition, a low feature has been observed in this area, near the crater Vendelinus, and it is reported here. It lies at longitude +57.83 ° and latitude -15.74° (Xi = 0.815, Eta = -0.271). The dome was detected by J. Phillips (Fig. 1, with an image scale of 323 m per pixel). The image was taken on February, 26, 2005, at 09:30 UT, using a TMB 8” f/9. Another image, here proposed as Fig. 2, was taken by Pau on October 12, 2003, at 16:11 UT using a 25 cm Newtonian telescope.

For each of the observations, the local lunar altitude of the Sun (Alt) and the Sun's selenographic colongitude (Col) were calculated using the Lunar Observer's Tool kit by H. D. Jamieson (Table 1).

Preliminary estimations indicate a diameter (E-W direction) of 16.8 km and a rather low slope; moreover no black shadow is cast by the dome (see Fig. 1) which confirms its low relief character. It is, to our knowledge, previously unreported; neither is it on the ALPO list nor classified.

Table 1:Local lunar altitude of the Sun (Alt) and the solar selenographic colongitude (Col) calculated for the dome located at +57.83° longitude and -15.74° latitude. Figures 1 and 2 are oriented North to the right and West (IAU) to the top.

FIG.1

FIG 2.

Due to the higher solar altitude, this feature appears only faintly on Lunar Orbiter frame IV-052-H2 (North to the top and West to the left), displaying a craterlet on its summit. We believe that this is an impact crater, due to its large depth implied by the shadow cast by its rim (Fig. 3). As a note of interest, the images from the Consolidated Lunar Atlas (i. e. plate F2), taken under higher solar altitude, do not show the dome that we are dealing with.

The height values reported in Table 2 were obtained by determining elevation differences between the summit of the dome and its surrounding on the corresponding 3D profiles derived by photoclinometry and shape from shading analysis [5-7]. The height of dome 1 in the image shown in Fig. 1 was measured as (80±10) m. Fig. 4 shows the 3D reconstruction results.

Table 2:Morphometric properties of features marked in Fig. 1.

From Table 2 it follows that the average slope angle is smaller than 2°, corresponding to a dome having a very gentle slope.This dome is presumably of class 2, according to the classification scheme for lunar mare domes introduced by Head and Gifford [4]. In Table 2 we categorize the present dome and other structures using the Westfall scheme [3].

Moreover, several other dome-like features are located to the SW of crater Vendelinus (see Fig. 1, structures labelled as 1-3). They could be very gentle intrusive swells, but a different origin cannot be excluded at this stage of our study. However, these structures are situated close to positions in the ALPO dome catalogue and likely represent the same domes or swells.

A possible further dome is indicated in Fig. 1 (dome 2 in Fig. 1 and Table 2). It lies at longitude +59.00° and latitude -17.75° (Xi = 0.817, Eta = -0.305). Our preliminary estimation indicates a height of (30±10) m and a thus a very gentle slope. A summit crater is visible, for which we estimated a diameter of (3.0±0.6) km. For a similar, even more subtle feature (structure 2 in Fig. 1 and Table 2) we obtained a height of (40±10) m.

FIG.3

Clearly these preliminary data can be improved bynew specific observations. Any observations that readers can make about these unlisted domes will be gratefully received for our GLR survey (lena@glrgroup.org).

FIG 4

In the next issue of TLO we will describe another unlisted dome, recently detected during an our survey. It islocated near crater Hortensius E at longitude -25.17 ° and latitude 6.07 º.The activities of the GLR group are described at www.glrgroup.org

References

[1] D. Wilhelms, The geologic history of the Moon, USGS Prof. Paper 1348, 1987

[2] H. D. Jamieson, The Lunar Dome Survey – Fall, Strolling Astronomer, 1992 Progress Report, 37 (1), pp. 14-17, 1993.

[3] J. Westfall, A Generic Classification of Lunar Domes, J.A.L.P.O., vol. 18, no. 1-2, pp. 15-20, 1964.

[4] J. W. Head, Ann Gifford, Lunar Domes: Classification and Modes of Origin, Moon and Planets, vol. 22, pp. 235-258, 1980.

[5] B. K. P. Horn, Height and Gradient from Shading, MIT technical report, AI memo no. 1105A, 1989.

http://www.people.csail.mit.edu/people/bkph/AIM/AIM-1105A-TEX.pdf

[6] R. Lena, K.C. Pau, J. Phillips, C. Fattinnanzi, C. Wöhler, Lunar domes: a generic classification of the dome near Valentine, located at 10.26° E and 31.89° N, JBAA, 2005, article in press.

[7] A. S. McEwen, Photometric Functions for Photoclinometry and Other Applications, Icarus, vol. 92, pp. 298-311, 1991.

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