Venus Express Options

[tedstryk]

If all goes well, Venus Express will be a major topic for discussion in this forum a year from now. Does anyone know how good the surface coverage will be from VIRTIS and VMC? My understanding is that VIRTIS will obtain low resolution multispectral maps, and that VMC will, in addition to cloud monitoring, have one channel that can see the surface, but I don't know at what resolution or at what quality. It will be nice to have some non-radar images of Venus' surface besides the Venera snapshots and the shadowy images from Earth and Galileo's NIMS.

Ted

[Guest_BruceMoomaw_*]

Here's my long-promised entry on whatever I've got regarding VIRTIS' possible ability to map Venusian surface composition.

Unfortunately, the two most important documents on this aren't available for free on the Web: the Nov. 2000 Icarus article by Langevin et al ("Detection of Sub-Micron Radiation from the Surface of Venus by Cassini/VIMS"), and the March 2002 article by V.I. Moroz in "Planetary and Space Science" ("Estimates of Visibility of the Surface of Venus from Descent Probes and Balloons"). I have a photocopy of the former, but can't find the copy I thought I had of the latter. Anyway, the former is optimistic about the possibility: "The 5 spectral windows between 0.85 and 1.18 microns now proven to be sensitive to surface spectral sensitivity provide a potentially effective means for remotely mapping the mineralogical composition of the surface of Venus" [something co-author Kevin Baines was saying for previously]... [They] can be effectively used to distinguish ferric (hematite) and ferrous minerals (e.g., the pyroxenes augite and hypersthene, and olivine). The hydrous mineral tremolite -- thought to be stable on geologic timescales on Venus -- also displays a detectable absorption feature...Both wollastonite -- a CO2 buffer mineral thought to be relating the CO2 surface pressure -- and pyrite are spectrally flat, but have distinctly different ablbedos." There's an accompanying graph of these various minerals' near-IR reflectivities, with the Venusian surface spectral windows overlaying it.

The Moroz article is much more pessimistic: "Constraints on the mineral surface composition would be difficult to derive from orbital observations due to multiple reflections between the surface and the atmosphere." The VIRTIS group itself, the Japanese VCO group and the Vernadsky-Brown Venus group are all intermediate in optimism: they think that it will almost certainly be possible to map FeO, thus distinguishing between felsic and mafic minerals and thus between granites and basalts, and also looking for magnetite on the highly radar-reflective mountaintops -- but aren't sure they can go any farther. (The two longest-wavelength windows seem to be the most useful.) Moreover, it seems much more possible to do this in the north polar regions than elsewhere (which, by an agreeable coincidence, is where Ishtar Terra -- Venus' most likely continent -- is located).

As for spatial resolution (including for temperature and near-surface volcanic gases), estimates are all over the place. Moroz sets it at 50-100 km, the VCO group at 100 km, and David Crisp at no better than 250 km (based on Galileo's flyby results). The VIRTIS group itself initially set it as high as 30 km, but now seems to have it pegged at 90-150 km ( http://irsps.sci.unich.it/~luciam/VEX/DOC/...ence_VIRTIS.pdf and the May 2005 report at the VIRTIS site: http://irsps.sci.unich.it/~luciam/VEX/ ).

As for quake detection through sensing pressure waves in Venus' dense CO2 air, they are still very interested in that -- although it will require special observational techniques (see the Dec. 2003 and May 2005 reports at the VIRTIS site).