LANDING SITE SELECTION FOR THE VENUS ENTRY PROBE MISSION. M. Aittola1, A.T. Basilevsky2, M.
Ivanov2 and J. Raitala1. 1Division of Astronomy, Department of Physical Sciences, P.O. Box 3000, 90014 University of Oulu, Finland (marko.aittola@oulu.fi), 2Vernadsky Institute, RAS, Kosygin Str., 19, 119991, Moscow,
Russia.
Introduction: The goal of this work is to identify and
evaluate the potential landing sites for the descent probe(s)
of the Venus Entry Probe Mission. The evaluation was
made by considering the primary scientific goals of the
VEP initiative regarding the surface and interior: Composition and mineralogy of the surface, surface morphology
(imaging) and the surface-atmosphere interactions. Based
on these goals and the information given by Venera landers
[1,2], we determined the terrain types, which would provide the most important and useful information from the
surface of Venus, and then selected few potential candidates for landing sites.
Approach for the selection and proposed terrain
types: The information provided by seven Venera landings
indicated mafic compositions of the surface materials [14]]. To evaluate if the volcanism of the planet was purely
basaltic, or if it was geochemically more evolved at least
locally, we should receive the data from other type of regions than the Venera landing sites. The most obvious
examples this type of terrain, which could be composed
non-basaltic material, are tessera regions. These regions –
which are proved to represent the oldest parts of the observed surface [5-7] - occupy about 8% of the Venusian
surface and are standing generally 1-3 km higher than the
typical basaltic plains surrounding them [8]. However,
there were no landing sites on tessera and thereby no information on the composition from this terrain type. Therefore, tessera terrains should, in our opinion, have the highest priority when selecting the landing site for the VEP
mission.
In the case of several descent probes, we suggest to
sample areas and single units, which would provide information from different types of regions and also from different eras of the planets’ geologic history. Venera/Vega
landers have already sampled rather well the most usual
type of volcanic plains (plains with wrinkle ridges), but the
plains with small shield (psh) and plains with lobate flows
(pl) would provide very important information from still
unknown type of terrains and, furthermore, could be compared with the results of Venera/Vega landers. One landing
on the lava plains could be associated with a volcanotectonic structure (volcano, corona…) as an example of
composition of lavas from the well identifiable source.
Thus, the proposed target types should include at least
tessera (highest priority, Fig. 1), shield plains material
(psh; Fig. 2) and lobate plains material (pl, Fig. 3). The
final instrumentation of the descent probe(s) will, however,
naturally affect the site selection. If the instrumentation
will eventually be more orientated to investigation of heat
balance (flux?) than planned so far, the selection should
definitely include at least one volcano-tectonic structure
(e.g. a corona).
Proposals for specific landing sites: When selecting
the specific landing sites we should take into account the
material ejected into the atmosphere by large meteorite
impacts [9]. This material is still seen around some impact
craters as dark parabolas, which are resulted from deposition of the crater ejecta material in the zonal (east to west)
winds [e.g. 10]. In many cases the material of parabola is
not more visible in radar data due increased roughness with
the time, but the material composing parabolas is mostly in
the place. Therefore, the impact craters have to be taken
into account when selecting the landing sites.
When choosing the site for tessera lander, we propose
to select the crater that hit the tessera and to land on its
smooth ejecta blanket (dark halo in radar image) to the
west of the crater. This way, the landing site should be
rather smooth and thereby safe. The tessera material composing crustal plateaus is thick enough so that the sampled
ejecta blanket will represent ejected tessera material. We
propose the surroundings of following craters as possible
candidates for the tessera landing: 1) Carter, Ovda Tessera,
5.3N, 67.3E, 17 km; (Fig. 1) 2) de Beausoleil, Ovda Tessera, 5S, 102.8E, 28.2 km; 3) Whiting, Thetis Tessera,
6.1S, 128.0E, 35.7 km; 4) Magnani, Clotho Tessera,
58.6N, 337.2E, 26.4 km.
Fig. 1. Carter Crater (5.3N, 67.3E) on Ovda Regio.
We have to consider the influence of impact craters
when selecting the landing site for sampling the vast lava
plains materials (psh and pl units). We can suppose that the
craters, which superpose these units, can penetrate though
them and, thus, their ejecta may contain unknown and
significant amount of material(s) what is beneath these
units. Therefore, we suggest to land on these units trying to
find places where there are no upwind craters in reasonably
close distance.
Possible landing sites on the plains with small shield:
1) Easternmost edge of Vellamo Planitia (centered at 43N,
131E), 2) Western side of Sedna Planitia at the NW edge
of Zorile Dorsa (centered at 43.5N, 333.5E). The proposed
landing sites for sampling the lobate plain materials: 1)
Northern flank of Sekmet Mons (47N, 242.5E). 2) Western
slope of Sapas Mons (8N, 187E). 3) Mylitta Fluctus (centered at 55S, 353.5E). All the proposed landing sites are
presented in Fig. 4.
Summary: In the case of four descent probe, we suggest to
sample tessera terrain, which should be ranked in first position. The other selected areas should provide information
from different types of terrain as well as different slices of
Landing site selection for the Venus Entry Probe Mission: M. Aittola et al.
the geologic history. In addition, when considering the
accurate landing site, the position of nearby impact craters
have to taken into account.
Fig. 3. Magellan SAR image and 3D view of the Western
slope of Sapas Mons (8N, 187E).
Fig. 2. Easternmost edge of Vellamo Planitia. Fields of
psh about 100 km across embaying the Tessera terrain.
Fig. 4. The proposed landing sites. Tessera landing sites are presented as white dots, Psh landing sites as green dots, and Pl
landing sites as blue dots.
Basilevsky, A. T. and J.W. Head. Planet. Space Sci., - v.
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