Una mappa geologica della regione di Posidonius è stata ottenuta mediante l'applicazione di alcune tecniche quali le stime di albedo, l'indice di colore e le immagini CCD. Alcuni particolari rilievi sembrano essere attribuibili alla presenza di domi. Le conclusioni tratte sono in accordo con i dati ottenuti dal Lunar Orbiter IV.
INTRODUCTION
This work is based on visual and CCD
observations of the region including
Posidonius. Estimated albedo and color data were obtained by Elger
Scale. Mare Serenitatis (18°N, 21° E) was used as control standard area. Blink
were performed by W80 , W44 (blue) and W 25 (red)
filters and approximate Index Color was obtained . Albedo variations have been
very useful for mineralogic interpretations.
PG. Salimbeni (SC 200mm f/10 200x). Posidonius crater on 14 march 1997 at 18,40 UT, colongitude 338,5. R corresponds to the darker and red soil. A-C area correspond to higher albedo.
PG. Salimbeni (5 december 1997 SC 200 mm f/10 200x at 18,22 UT colongitude 334,4). Presence of the rilles.
VISUAL OBSERVATION
The floor of Posidonius is red.
In blue light the crater Posidonius appeares more dark than in red light.
The albedo of central craters ( Posidonius A and Posidonius C) increased during
the lunar phase. The soil on the south and north, north-west shows a lower
albedo (3° Elger Scale) than the central area (4° Elger Scale). Lena
and Salimbeni recorded the presence of a red and dark area to the north and
west of the crater. Bright spots are due to relatively
recent impact craters which have exposed immature soils. These craters
and the internal walls show higher albedo (average value 6,5 Elger, range
6-7 ). Furthermore with red filters Posidonius appears more bright than Mare
Serenitatis. Small hills on the east of Posidonius A and the presence
of some narrow rilles have been recorded by visual observations . Only
the west and east rilles were observed in good condition of seeing. The internal
walls appear very degraded. These walls probably are part of the ancient
and destroyed crater in this area.
Several spots of higher albedo have been observed in the central area at W and
NW of the small crater called Posidonius A.
R. Lena, (SC 250 mm f/10 250 x). Sketch
on 22 genuary 1999
at 17,30 UT colongitude 336,5. The presence of
features like domes was recorded.
CCD IMAGES
The CCD images confirmed the presence
of 2 different types of soil. The exposed material in Posidonius
is brighter than the surrounding material and ejecta are formed. We interpret
these data to mean that cratering event at Posidonius penetrated through the
mare fill and exposed underlying upland material. Furthermore different soils
in Posidonius crater have been recorded by CCD images. These images show also
the arcuate rilles on the floor. The presence of several features
as domes was recorded, according to the visual observations.
CCD image performed by M. Higashida (Japan). Probably domes at east of Posidonius
A
are also visibly.
CCD image performed by T. Legault (France). In this image are visible several
probably domes or hills near Posidonius A. Furthermore
a fine network of rilles between Posidonius A and the east wall was recorded.
The rille meanders along the edge
of the crater floor. It reaches a hole in the crater rim and vanishes
into Mare Serenitatis. The rille, probably, is also only the last stage
of mare volcanism within this crater. It lies on
top of an older, smooth mare unit which buries part of the crater floor and
much of the western crater wall, as recorded by
Lunar Orbiter IV.
Images acquired by the Lunar Orbiter IV (image IV-86-H3).
The frame is corresponding to some visual observations performed
by GLR group.
FALSE COLOR ELABORATIONS
False color elaboration has been very useful for our interpretations. Infact
we have obtained a false color map by amatorial CCD images.
In orange is represented the mare unit, in
yellow is represented the fresh material and in black is represented the ancient
mare soil. The state of degradation of the rim is very representative
of the story of Posidonius. Several lava flows covered much of the outer and
inner elements of the crater. This results are in accordance to the data
obtained by Lunar Orbiter IV.
Posidonius, like Gassendi, is a floor fractured craters. The lava
that filled Posidonius covered over the central uplift and much of the terracing
of the side walls, so that these age no longer seen.
False color image of Posidonius crater.