Future Venus Missions Options

[Phil Stooke]

Oh well, might as well start that new topic since it's already well advanced in the Juno area...

My perspective on landers is as follows. All the landers we've had so far were dropped blind onto an essentially unknown surface. Any future landers can be targeted for specific terrains. It really is not true that we have had representative landings. Even a descent image or two, a panoramic photo plus a bit of surface composition, from a simple Venera-class lander just updated a bit, would be useful if we could put several down at well chosen targets. My choices would be:

Examples of the main plains units (smooth, fractured, ridged)

tesserae

high elevation radar-bright tesserae

large fresh lava flow unit ('fluctus')

crater dark parabola

crater ejecta outflow unit

dunes area.

And I have always assumed, rightly or wrongly, that it would be relatively easy to put these down, so they ought to be fairly inexpensive as planetary landers go.

Phil

[dtolman]

Wondering about whether VEX could have picked up signatures, I noticed this in an article in Forbes - could VEX's VIRTIS have collected evidence of Phosphine's presence already?

Phosphine has an absorption band in the infrared spectrum at roughly 3.05 microns, Julie Castillo, a planetary scientist at NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, told me. So, one should check the observations of the VIRTIS instrument on Venus Express for the possible presence of that phosphine in its VIRTIS observations, she says.

[JRehling]

It has been well noted that the SO2 composition of Venus' atmosphere has varied dramatically over the duration of observations. It remains possible that the phosphine detected on Venus in 2017 wasn't present when Venus Express ended in 2014. (I'm not sure when VIRTIS last took measurements, so the EOM in 2014 may not be the relevant start of the window between last Venus Express measurement and the phosphine detection.

The Sousa-Silver paper notes that "phosphite can disproportionate to phosphine at T > 323K and acidic pH." If a volcanic event on Venus liberated phosphorus-bearing minerals in the last few years, the detection of phosphine could record a very temporary event.

In fact, I wonder if Venus provides a loophole here that hasn't been discussed (Sousa-Silver, et al were talking about exoplanets in general, not Venus), that a non-volcanic mass movement event on Venus (earthquakes, landslides) could introduce subsurface minerals to surface conditions and begin chemical reactions at the time of the event. The "acidic pH" condition might be met at the surface, but not in the subsurface. No volcano required. No inherent paradox that a gas that should be destroyed quickly in Venus' atmosphere is present now.

From my armchair (I am literally sitting in an armchair right now), VERITAS would likely provide better insight as to the rate and recency of mass movement events on Venus, while DAVINCI+ obviously provides different opportunities to investigate the phosphine result.

[Gerald]

The Sousa-Silver paper notes that "phosphite can disproportionate to phosphine at T > 323K and acidic pH."...

H₃PO₃ is thermally decomposed ("disproportionated") into PH₃ and H₃PO₄ near 200°C.
If there would exist some catalytic process in the presence of H₂SO₄ and CO₂ to recover the H₃PO₃ from H₃PO₄, we would get a closed cycle, depending a bit on the oxidation products of PH₃, and less supply from exogenic sources would be required.
Just to get rid of that one easy-looking O is probably the point where some "new chemistry" is needed. At least I wasn't able to find a paper describing or providing at least a hint how to track this way back.