Evaluation of the potential landing sites for Venus Entry Probe Mission.

1. Evaluation of the potential landing sites for Venus Entry Probe Mission. J.Leitner1, M.Aittola2, V-P.Kostama2, T.Törmänen2 and M.G. Firneis1. 1Dept. of Astronomy, University of Vienna, Austria, 2Division of Astronomy, Department of Physical Sciences, P.O. Box 3000, 90014 University of Oulu, Finland (marko.aittola@oulu.fi),

2. Criteria for selecting the landing sites: • When selecting the landing sites we have to consider several important aspects: • The primary scientific goals of the VEP initiative regarding the surface and interior. • The data provided by Venera mission • We have to reckon with the fact that we do not yet know the final instrumentation of the descent probe. Therefore, we should select the target sites, which would serve the versatile scientific goals. • To take into an account the impact craters and possible airfall material produced by the cratering events.

3. Proposed target types: Uplands • The main reasons to select the higher plateaus as the areas to be studied by descent probes, are the age and the nature of tessera terrains. • It is accepted that the tessera areas are among the oldest units in the Venusian surface – although not necessarily formed simultaneously. • Furthermore, the composition of tessera material is still unknown – not studied by the Venera landers - and rather pristine compared to the other surface, which is covered by younger mafic lava flows. • It should be extremely important to sample this still unknown material of the Venusian surface. • Tessera terrains should be ranked first when selecting the landing sites.

4. Proposed target types: Alternative landing sites: • In the case of several (4) landers, we should be able to determine landing site, which provide divergent surface characteristics. • We have to consider the altitude differences (highland-lowland; weathering conditions), divergences in target ages, good coverage (north-south) etc. • In contrast to supposedly old tessera terrain, we should also find the landing site on the fresh-looking lava-flow. • If we can define the source for the lava flow, we can analyze the properties of certain type of volcanic feature. • This landing site could be for example in connection to high-standing corona(volcano)-feature with fresh lava flows. • Depending the instrumentation, also good site to study the heat balance of the planet

5. Proposed target types: Alternative landing sites: • To sample the lavas of older volcanic activity and to have a sample from lower altitudes, the destination of one descent probe could be in the lowlands, where there is no evidence of recent lava flows. • The last landing site could represent an example of probable more “exotic” Venusian surface composition to have an idea how heterogeneous the surface is. • Steep sided domes, “pancake volcanoes”, • high reflectance area, e.g. in Ishtar Terra. • Also, regarding the quality of the camera onboard, the micro-dune fields could provide important information from the interaction of the loose material and the low-altitude wind as well as the composition.

6. Detailed landing sites: Ovda Regio. • Defines the western part of Aphrodite Terra • The largest crustal plateau on Venus. • Located mostly on the equator from 50E to 110E and from 5N to 15S, covering 1.5 x 107 km2. • Why this region would be good landing site? • It is a good example of tessera terrain, • It is not studied by Venera landers, • Tesserae could represent the areas of non-basaltic crust? (at least can be something different than analyzed by Venera landers), • We have relative good topographic data from the region • It is located on high altitude (weathering conditions), • It is large enough to find a appropriate landing site, • We have geologic map from the Eastern side of the Ovda (e.g. Carter Crater).

7. Detailed landing sites:

8. Detailed landing sites: Pavlova Corona (14N/40E; Eastern Eistla Regio). • The landing site from where we can sample the young lava flows inside a corona structure. • Relatively high elevation (corona itself 6052.88 km and the nova 6053.06 km) and represent rather young volcanic activity. • The size and the topography will make it “easy” target, because it is relatively large (360 x 400 km) and flat, excluding the radial structure on the western part of the corona. • There is only one small crater to the NWW from the target site, and no evidence that its airfall deposit would overlay the young lava flows.

9. Detailed landing sites: • Pavlova Corona (14N/40E) • corona floor altitude 6052.88 km • 6053.26 km

10. Detailed landing sites: Mbokomu Mons (15S/215). • Same kind of target than Pavlova corona • Alternative landing site of this type. • Also located on highland and represents young volcanism. • “hybrid” structure (characteristic of both volcano and corona), • The lack of the impact craters on the eastern side of it • no “disturbing” airfall material, and also the lava flows which provide relative smooth landing site. • These both corona structures (Pavlova and Mbokomu Mons) are rather well studied  general interest

11. Detailed landing sites: • Mbokomu Mons (15S/215) • Highest point: 6053,16 km • Floor: 6052,65 km

12. Detailed landing sites: Neyterkob-Cerridwen (49,5N/203) • As a site to sample the lowland material and older lava fields as well as to get good global coverage • Is located on Ganiki Planitia. • Consists of two circular components (double corona) • Both of which are  200 km wide with the floor altitude of 6051.1 km. • Located in lowlands as a rather isolated feature. • Relative easy to land due to the large size and rather smooth interiors. (small shields) • The structure is located close to the impact crater the southwest of it. • The airfall deposit can cover the western part of the structure, but there are no impact craters to the east of the area. • In the case that instrumentation enable the studies of heat balance, the double corona target would be useful

13. Detailed landing sites: • Neyterkob-Cerridwen (49,5/203) • Floor altitude 6051.1 km

14. Detailed landing sites: Steep-sided domes “pancake volcanoes” • On Venus the shape of the shield volcanoes, length of the lava flows and the data received by the Venera landers all suggest that the volcanism is basaltic. • The “pancakes” are circular flat-topped volcanic domes on the Venusian surface • Their unusual morphology suggests that they may have a composition different from that of shield volcanoes on Venus. • Possible area of this kind is located on Eistla Regio (Carmenta Farra; 13N/8E), which includes group of pancake domes. • The largest of these domes is 65 kilometers across. • Small impact crater to the east of them  Possible airfall deposits? • Other possibe site is the pancakes related to Aine Corona (59S/169E)

15. Detailed landing sites: 100 km • Pancake volcano • Located on Eistla Regio (Carmenta Farra) (13N/8E)

16. Detailed landing sites: • Pancake volcano • Located at 13N/8E, on the annulus of Aine Corona

17. Detailed landing sites: Ishtar Terra Neyterkob-Cerridwen; old lowland Pavlova Corona; young lava flow Carmenta Farra; pancakes Ovda Regio; tessera Mbokomu Mons; young lava flow Aine Corona; pancakes

18. Summary: • The most important target type for landing site is tessera terrain (1). • Possible other landing sites should selected so that they would represent as versatile properties of the Venusian surface as possible. • The landing sites of this kind could be for example: • Young lava flows in association with e.g. corona structure (2), • Older lava fields in lowlands(3) • Some target that would represent unusual properties of the surface, e.g. so called “pancakes” (4).