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Eratosthenes Domes: an overview and classification

By Raffaello Lena, KC Pau and Brendan Shaw - Geologic Lunar Research group.

Introduction

In this paper we discuss the domes near Eratosthenes, a well-known crater located near the southern extremity of Montes Apenninus. We report further measurements and include CCD imaging obtained during our survey. This has made it possible to extract additional information for theirclassification and interpretation.

Lunar domes are gentle swellings between 3 and 60 km across, at most a few hundred meters in height. Domes may be formed in a variety of different ways, e.g. as an effusively created dome or as a subsurface intrusion of magma [4]. Classic domes like Kies P are the same type of feature as the Earth’s shield volcanoes. Domes like the Valentine dome and its northern dome [1-2] are probably formed by subsurface intrusions, similar to laccoliths on the Earth. The GLR has an ongoing project to discover such domes. Our activity has shown both the elusive nature of these volcanic structures and the utility of CCD imaging and digital image analysis in the elucidation of their character [1-2].

Observations

A CCD image by KC Pau taken on September 22, 2004 at 11:25 UT (figure-1) shows the presence of two domes near the craters Wallace K and Eratosthenes A (marked as 1 and 2) . This high resolution image was taken using a 250 mm f/6 Newtonian. Another image by Pau was taken on June 26, 2004 at 12:27 UT (figure-2). This image reveals much finer detail in the Eratosthenes region, including two domes marked as 3 and 4 (solar altitude = 4.92°, Co-longitude = 16.43°). Another CCD image (figure-3) was made by Pau on February 13, 2004 at 21:13 UT (solar altitude = 4.36°, Co-longitude = 186.04°). Table-1 give the positions of these four domes, described in [5].

Lena reported the presence of the domes in another observation, carriFIG.6ed out on September 22, 2003 at 19:10 UT using an f/15 100mm refractor (solar altitude = 3.54° above -0.183 +0.344, co-longitude = 14.70°, seeing II/III on the Antoniadi scale). Figure-4 shows the drawing by Lena.

A CCD image by Shaw (figure-5), using a 5" f/9 refractor, was taken on July 7, 2003 at 21:02 UT (solar altitude = 2.42° above -0.183 +0.344, Co-longitude = 13.41°). This image also shows the domes. Another interesting image (figure-6) by Shaw was taken on July, 8, 2003 at 21:22 UT. The dome marked 3 is easily visible under a high solar altitude (solar altitude = 13.80 above -0.191 +0.320, Co-longitude = 25.79°).

FIG.1

We received another, confirming, image from E. Crandall, taken on September 23, 2004 at 00:06 UT with a 254 mm f/7 Newtonian.

FIG 2

FIG 3

TABLE 1

Position of the domes marked as 1,2, 3 and 4.

Discussion

It is interesting that the ALPO list describes -0.191+0.320 as a dome. This object is also visible, in our images, under a solar altitude of 14°. It may thus be described as some sort of volcanic swelling, perhaps a lava flow bulge, rather than a dome.

FIG.4

It should be noted that the ALPO dome list, available on the Web [6-7], doesn’t contain the dome –0.183+0.344.However, we found in [5] that this dome has also been reported by Reverend Kennet J. Delano. Although not specifically described in the other domes list, it is certain that Delano observed these domes during his study of this region.

FIG.5

Interestingly, –0.183+0.344, with a dimension of 10 x 6 km , was identified without specific details as to the slope, summit features and classification[5]. In our observations it appears to have a flat top, which is unlike the Earth's shield volcanoes. The shading on its antisolar slopes are not black, indicating that the slopes are of low inclination. The images show several protrusions on the dome, which appears similar to the well-known Valentine dome [2].

None of these domes in the Eratosthenes region seem to have a summit pit, so it is likely that subsurface magmas have swelled, but not punctured, the lunar surface [4]. It seems plausible that the domes marked 1, 2 and 4 were formed in a similar fashion. Using the Westfall Classification Scheme [3], we categorise these domes as shown in table 1.

FIG.6

Conclusion

These domes, just north of Eratosthenes, are another example of the elusive nature of lunar volcanic structures. This report illustrates the need for more work in this challenging area to help obtain specific classifications for the Moon's many domes.

Finally, the international participation in the GLR dome-project demonstrates a favourable response to our efforts to foster increased co-operation among lunar observers worldwide.

Acknowledgements

We wish to thank Jim Phillips and Charles Kapral (author of a revised dome list) for their stimulating discussions.

Many thanks also to Ed Crandall for the submitted images.
 
   

References

[1] Lena R, Pau KC, Fattinnanzi C (2003). "The Valentine Dome: Observations and Classification." Selenology,Vol. 22, No. 4: pp. 8-10.

[2] Lena R, Pau KC (2004). "The dome to the north of Valentine +0.151+0.528" The Lunar Observer , Sept. 2004, p. 5.

[3] Westfall, J (1964). "A Generic Classification of Lunar Domes." Journal of the Assn. of Lunar & Planetary Observers, Vol. 18, Nos. 1-2: pp.15-20.

[4] Wilhelms, D (1987). The Geologic History of the Moon. USGS Prof. Paper 1348. Washington:

[5] Jamieson, H.D.; Phillips, J.H.; "Lunar Dome Catalog (April 30, 1992
Edition)",J.A.L.P.O.36, No.3, pp.123-129.

[6] http://www.lpl.arizona.edu/~rhill/alpo/lunarstuff/domes.html

[7] http://www.geocities.com/kc5lei/lunar_dome_catalog.html

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