Venusian meteorites? Options

[JRehling]

Today, reading of the discovery of an apparent Earth meteorite fragment contained within a sample from Apollo 14, a curious possibility crossed my mind, and it seems like someone else may have thought of this, but I haven't found any sign of it: Could we find Venusian meteorites on the Moon? Better yet, could we find samples that offer a snapshot of Venus' past conditions from previous eons as preserved on the Moon?

It seems like in principle the answer is yes, and the question is how much lunar regolith would be required. Additionally, would the process have destroyed information that we might hope to get from the sample? That seems like a more complex question.

There's a good bit of speculation that Venus may have had a radically different and more earth like climate in the past. It is noncontroversial that Venus has lost a lot of H2O over time, and if there was ever a large reservoir of H2O in the past, that seemingly would have meant an atmosphere with less CO2 partial pressure, which in turn would have made it easier for spallation of fragments from the surface to escape velocity. The fact that terrestrial material has made it to the Moon indicates that material can reach high orbit from Earth through spallation and that is quite close to the same velocity needed to go from the surface of Venus to escape.

Now, making the interplanetary journey is a somewhat bigger leap, but not much more so. A fraction of Venusian materials making it to solar orbit would accidentally get gravity assists from Venus to Earth/Moon.

Needless to say, a program of sampling lunar regolith for Venusian material would find a lot of other materials of interest in the process, including those sampling Mercury and the past environments of Earth.

Substantive appeal here would seem to include the following: There is no technical challenge beyond current technology, though the strategies needed to deal with the needed scale might not be straightforward. (A long-life rover could choose, via terrestrial control and/or onboard AI, which out of many potential samples to return.) There are some particularly high-interest questions here, and to put a rather dramatic point on this, with the Sun's output in the past being 70% of what it is now, the past of Venus is an outstanding candidate for an Earthlike planet, and it is unthinkable that we would ever get a sample return from any of the others in the next few centuries, while we could potentially have an Ancient-Venus sample before 2025. (It's possible that we already have some in the Apollo samples!) And the potential discoveries are… no need to get speculative here, but extremely striking, when we consider the idea of an earth-sized planet with earth like levels of heating and a known history of high water content.

I don't know if this idea has been mulled over before, but it seems like for the potential outcome, it should be of extremely high interest.

[tanjent]

JRehling, it sounds as if you have read something interesting pointing to an expected difference in rare earth abundance between Venus and the Moon. I did not know that any of the Soviet landers were able to make actual chemical analyses of the Venusian soil, so what is this prediction based on? Lack of groundwater and plate tectonics? It's the first time I have seen this topic mentioned, so if you can point me to a good article, please do.

[JRehling]

tangentm, good question, and I should have been more cautious on that detail. We should expect the differentiation of early Venus to be similar to that of Earth, but the rare earths are not as good of an indicator of that as I thought, now that I look into it.

The Venera landers did analyze the composition of the Venusian surface. This may, however, not represent the ancient Venusian surface. What would be useful information would be isotopic analyses of elements that are not represented in the Venusian atmosphere. So, most of the major crustal elements besides oxygen. (Though there is an outstanding possibility that iron of all things is present as a trace component of the Venusian atmosphere in the form of ferric chloride as a candidate for the UV absorber.)

[HSchirmer]

tangentm, good question, and I should have been more cautious on that detail. We should expect the differentiation of early Venus to be similar to that of Earth, but the rare earths are not as good of an indicator of that as I thought, now that I look into it.

The Venera landers did analyze the composition of the Venusian surface. This may, however, not represent the ancient Venusian surface. What would be useful information would be isotopic analyses of elements that are not represented in the Venusian atmosphere. So, most of the major crustal elements besides oxygen. (Though there is an outstanding possibility that iron of all things is present as a trace component of the Venusian atmosphere in the form of ferric chloride as a candidate for the UV absorber.)

Remember, an orbiter looking at Earth's (inorganic) surface areas would report back mostly- H2O (oceans and polar ice) silicate (sandy deserts) and phylosillicates (clays).

[JRehling]

The Venera landers got more detailed information about surface composition than an orbital observation might hope to make, as Table 2 here shows:

http://www.planetary.brown.edu/pdfs/3437.pdf

However, the mineralogy won't necessarily help us differentiate venusian rocks from lunar ones, particularly when we're interested in venusian eras very much before the present. Isotopic breakdowns would help, and we could get those with future landed missions. That might bear some signature that would differentiate them from native lunar rocks.