Future Venus Missions Options

[JRehling]

If either or both current proposals for Discovery missions to Venus succeed, then that would certainly change the balance sheet of outstanding scientific questions regarding Venus. They would also almost certainly raise new questions regarding Venus' surface and reorder the list of Venus priorities in ways that are difficult to foresee. Record of ancient sea floors? Active volcanoes? Something pertaining to the commonality of the origins of Earth's and Venus' respective atmospheres? I think it's likely that any Discovery mission would give us new information that would take time to gestate and would push any possible Venus flagship mission further into the future.

[Explorer1]

Given that Venus is already trending on Twitter (and it is not entirely about tennis), I expect public interest would definitely play a role in whether a major mission will be funded, "changing the balance sheet" as you put it.
I do wonder how a sample return from the atmosphere could be affected. Possibly even trickier then Mars sample return. An airship or balloon with a solid stage to carry a capsule to orbit for rendezvous and Earth return?

[JRehling]

Multiple options for Venus atmospheric sample return are discussed here.

The DAVINCI+ Discovery proposal would measure Venus' atmospheric composition in situ with unprecedented accuracy. Until we know what that might find, we can't say if it would address many of the questions regarding Venus' atmospheric composition or if it would raise new ones.

Also note that an in situ measurement from the lower atmosphere could answer some questions better than a sample return from the upper atmosphere at certainly less cost.

https://www.hou.usra.edu/meetings/V2050/pdf/8164.pdf

[dtolman]

Well - its officially released now. Phosphine gas has been found at the mid-latitudes (but not the poles) of the Venusian atmosphere by two different telescopes (very definitively by the ALMA array). There are no *known* abiotic processes to produce the concentrations found (up to 20 parts per billion).

So I imagine that the immediate focus from a space robotics perspective will be on the private Rocketlab and Indian missions which are both slated for launch in 2023, to see if they could get a more specific data on phosphine concentration at different altitudes and latitudes, and its chemical precursors.

[mcaplinger]

Phosphine has been detected in the atmospheres of Jupiter and Saturn without exciting much comment I'm aware of. https://ui.adsabs.harvard.edu/abs/2009Icar......543F/abstract

[dtolman]

The paper is paywalled, but section 4.3 of this 2019 paper on phosphine discusses that the pressures found at Jupiter and Saturn can produce this abiotically - but these conditions are not found on terrestrial sized planets (not even Venus) according to the discussion within the paper:

Theformation of PH3 on temperate, rocky planets is thermodynamically disfavored, even in high-reducing environments, unlike the fermentative
production of methane or hydrogen sulfide. In thermodynamic equilibrium,phosphorus can be conservatively expected to be found in the form of PH3
only at T > 800K, and at P > 0.1 bar (Visscher et al. 2006), which is why PH3 has been detected in Jupiter and Saturn, where these extreme temperatures
occur (in the deep layers of the atmosphere). We also note that the critical temperature of water is 647 K so there are no surface conditions that favor
both PH3 production and allow for the presence of liquid water

This chemistry was discussed in their press briefing just now as well.

[Explorer1]

RAS briefing here is still going:
https://www.youtube.com/watch?v=y1u-jlf_Olo

[centsworth_II]

Phosphine gas in the cloud decks of Venus

Even if confirmed, we emphasize that the detection of PH3 is not robust evidence for life, only for anomalous and unexplained chemistry. There are substantial conceptual problems for the idea of life in Venus’s clouds—the environment is extremely dehydrating as well as hyperacidic. However, we have ruled out many chemical routes to PH3...

[dtolman]

So putting aside the out-of-forum scope questions... are their instruments planned on the upcoming Indian mission to Venus - or the two Discovery candidates (DAVINCI+, VERITAS) that are capable of detecting phosphine gas in the atmosphere? If not, are any suitable with modification? Or will this require instruments designed from the ground-up - or even a dedicated in-atmosphere mission - to better answer this question?

The team mentioned during the press conference they were working with RocketLab's 2023 Venus team - so presumably it will carry *something* that can help confirm the result, and further refine where phosphine is in the atmosphere.

[mcaplinger]

It will be an interesting moderator challenge to figure out how, or even if, this discussion can occur in light of rule 1.3.

[JRehling]

The phosphine news release led me to write some, I assure you, very funny and snarky comments that I won't post because of board rules, but in the realm of the safe-to-say: Venus has conditions well different from Earth's and undoubtedly, some interesting chemistry different than the chemistry here.

We still await a mission that performs Venus in situ surface science as thorough as Viking provided at Mars and the old conundrum one can't ignore is that temperatures require a viable strategy for survivability; there is a set of distinct strategies for making that work; as far as I know, there's no doubt that more than one of the strategies is viable, but nothing is going to come to fruition until a mission picks one of them and gets funded.

IMO, making a virtue of necessity, a mission architecture that seems promising for surface analysis is an aerobot that makes very short stays on the surface to grab samples, then inflates a helium balloon, ascends to cooler and survivable temperatures, performs analysis, and transmits results back to Earth while floating near cloud level. Winds at the cloud level could transport the craft almost unlimited distances downwind for touching down on and analyzing a second, etc. location. This would be in many ways analogous to Dragonfly at Titan, but with much greater capability for horizontal transport. One mission could conceivably visit all of the major terrain types on Venus – plains, tesserae, recently active volcanic surface, radar-reflective high altitude regions. With any other architecture, we would hope to drop two or more stationary landers and begin to understand the surface chemistry.

For a "Venus Insight" mission that includes a seismometer, I think it's a lot more hopeful that robust electronics could operate a surface station for long durations.

We are about a year away from learning if Venus scores one or two Discovery missions that would be preliminary to whatever next-generation surface mission.

[JRehling]

It seems to me that phosphine at Venus is analogous to methane and other phenomena at Mars: We can make spectacular leaps in hypothesizing, but we're at an early point in the understanding and there's no doubt that we'd all like to understand the origin of methane at Mars and phosphine at Venus. How spectacular or mundane reality turns out to be is a matter that we don't control.

[mcaplinger]

a mission architecture that seems promising for surface analysis is an aerobot that makes very short stays on the surface to grab samples, then inflates a helium balloon, ascends to cooler and survivable temperatures...

I'm not believing that this technology will be practical any time soon. See https://www.hou.usra.edu/meetings/exoplanet...ons/Gilmore.pdf for the current thinking of what could be done with a flagship budget, which has a goal of a lander that lasts 4-8 hours and a 30-day minimum lifetime balloon.

[Bjorn Jonsson]

Phosphine has been detected in the atmospheres of Jupiter and Saturn without exciting much comment I'm aware of. https://ui.adsabs.harvard.edu/abs/2009Icar......543F/abstract

I noticed that someone asked about this at the RAS briefing. The reason if I understood correctly is different conditions at Jupiter and Saturn: Lots of hydrogen and much higher pressure where the phosphine forms.

[stevesliva]

It will be an interesting moderator challenge to figure out how, or even if, this discussion can occur in light of rule 1.3.

As JRehling said, history shows we can civilly talk about the elephant in the room (methane spikes), you just can't argue about whether the elephant is biogenic. That's fine by me.