Future Venus Missions Options

[vjkane]

What's the story with disulfur oxide as a possible UV absorber as in this publication? Then we have this thread.

CUVE

[vjkane]

<personal opinion only>
The Venera/VEGA/Pioneer Venus generation are basically all retired, the Magellan generation (i.e. those
professionally active while the mission was in operation) still has a reasonable fraction of people in the field that can offer direct experience to missions developed and launched
in the 2020s, but if it takes until 2030 to go back, much of the intellectual heritage of the earlier missions and questions will be lost.
</opinion>

The ESA/NASA EnVision mission, if selected, would as I remember, begin to deliver data from it's low orbit in something like 2033 to 2035 (don't have time to look up actual date). So another half generation plus of scientists would retire before data begins to flow.

A NASA mapper mission, if selected for the ~2024 Discovery launch date, would presumably deliver data beginning a year or two later (flight time to Venus plus aerobraking).

[JRehling]

The OSSO abstract and CUVE proposal are both very interesting. I think what has allowed the identity of the UV absorber to remain indeterminate is the fact that the physical manifestation of the absorber is a wildcard: If it's not in a simple gaseous state, then the spectral properties of grains and droplets introduce complexity that is hard to account for. For example, if a solid particle has liquid droplets condense upon it, the resulting spectrum might be very hard to duplicate in the lab without knowing which permutation to look for. The lab work and something like CUVE are certainly positive steps forward, though. As the chromophores in the clouds of Jupiter and Saturn are also still unknown suggests how difficult something like this is to resolve.

It sticks in my mind that Venera 11 and Venera 12 found large amounts of chlorine in the clouds while Pioneer did not. That seems odd if chlorine were not part of what varies spatially and temporally in Venus' clouds. It seems to me like a clincher would be to have in situ cloud sampling measuring elemental composition occur at locations that are known to be, respectively, UV bright and UV dark would be the most definitive way to resolve the question. It would be nice to know, in retrospect, what the UV albedo was at the time and place of the Venera and Pioneer in situ measurements, but that information may be irretrievable.

[rlorenz]

I think what has allowed the identity of the UV absorber to remain indeterminate is the fact that the physical manifestation of the absorber is a wildcard: If it's not in a simple gaseous state, then the spectral properties of grains and droplets introduce complexity that is hard to account for. For example, if a solid particle has liquid droplets condense upon it, the resulting spectrum might be very hard to duplicate in the lap without knowing which permutation to look for. The lab work and something like CUVE are certainly positive steps forward, though. As the chromophores in the clouds of Jupiter and Saturn are also still unknown suggests how difficult something like this is to resolve.

<opinion>
I don't doubt that UV spectroscopy so far is inadequate to identify the UV absorber, nor that it is an important element of the Venus climate. But I havent seen a persuasive case that a better UV spectrum would be able to unambigously identify it (your chromophore analogy is a good one), nor that a UV spectrometer is the best payload for a smallsat Venus orbiter. I could be wrong about both these things, but havent seen it yet.

I do believe that a UV spectrometer able to yield a better spectrum *could* be implemented on a smallsat, so in the context of SIMPLEX (i.e. 'what could you do at a planet with a smallsat that might be scientifically interesting? : the overall data volume needed is modest) a proposal like CUVE makes sense.

On the other hand, LUVOIR claims to be able to do good UV spectro-imaging at Venus too (see https://asd.gsfc.nasa.gov/luvoir/reports/LU..._2019-08-26.pdf ). And/or maybe the Indian mission will have a decent UV spectrometer.

Even identifying the absorber from an in-situ mission will be challenging, but I'd venture that has a better chance (if it can sample the relevant altitudes) of providing a more definitive answer than any remote sensing would.
</opinion>

[JRehling]

Until the other day, I had assumed that the DAVINCI proposal (now called DAVINCI+) in the current set of Discovery proposals was basically DAVINCI from last time around with a modest change. The reality is dramatically different. What they have added since last time is arguably larger than what was proposed before.

In a nutshell, the new mission proposal is more like a Messenger for Venus with an entry probe rather than just an entry probe. It would flyby Venus twice while holding the probe, make significant scientific observations in IR and UV, of both the atmosphere and the surface, before releasing the probe, then the carrier would enter Venus orbit and continue making observations long after the probe's mission was complete.

Many details here. I'm not sure how the IR emissivity science would relate to that collected by VERITAS, should both of them be selected. It seems almost certain that VERITAS would collect more and better IR emissivity science, but each of them is doing a lot more than that.

https://www.hou.usra.edu/meetings/lpsc2020/pdf/2599.pdf

[vjkane]

Until the other day, I had assumed that the DAVINCI proposal (now called DAVINCI+) in the current set of Discovery proposals was basically DAVINCI from last time around with a modest change. The reality is dramatically different. What they have added since last time is arguably larger than what was proposed before.

In a nutshell, the new mission proposal is more like a Messenger for Venus with an entry probe rather than just an entry probe. It would flyby Venus twice while holding the probe, make significant scientific observations in IR and UV, of both the atmosphere and the surface, before releasing the probe, then the carrier would enter Venus orbit and continue making observations long after the probe's mission was complete.

Many details here. I'm not sure how the IR emissivity science would relate to that collected by VERITAS, should both of them be selected. It seems almost certain that VERITAS would collect more and better IR emissivity science, but each of them is doing a lot more than that.

https://www.hou.usra.edu/meetings/lpsc2020/pdf/2599.pdf

Here’s a summary of the VERITAS VEM instrument

VEM [7] covers >80% of the surface in six NIR bands located within five atmospheric windows sensi-tive to Fe mineralogy, plus eight atmospheric bands for calibration and water vapor measurements, all with significantly enhanced SNR relative to the VIRTIS instrument on the European Space Agency (ESA) Venus Express mission.

And the DAVINCI+

A multi-band imaging system that includes UV, Near IR (1 um), and an engi-neering wide-field mode, has been incorporated onto the Lockheed-Martin carrier/telecom/orbiter space-craft, with opportunities to acquire first-ever vantage points on Venus in the UV (where the mystery absorb-er is lurking) as well as in night-side 1 m emissivity.

So the VEMS is a more capable spectrometer but lacks UV VERITAS also will be in a circular orbit and I suspect DAVINCI+ will be in an elliptical orbit

[JRehling]

Good breakdown, Van.

The VEM approach is even more evolved and specific than a spectrometer in general. I won't pretend to have absorbed all of the details, but the design is based on analyses of Venus spectra and how the atmosphere absorbs different IR wavelengths so that new imagery in five specific IR windows can be processed to cancel out the noise from the atmosphere and provide a meaningful six-band spectrum of the entire surface at what would effectively be ~50km/pixel. That's much worse than our radar imagery, but if you picture a 12 inch/30 cm globe of Venus, those pixels are just 2 mm, which is quite nice. The six bands should be sufficient to distinguish different surface compositions (both the origin of the rock and its chemical weathering are relevant). The resulting map of Venus' surface, for the first time, in "color", will be practically a new planet compared to any data we have previously received. (VIRTIS data allowed a bit of this analysis, but with fewer spectral bands; it, however, provided the data that allowed for the design of the VEM approach.)

I think a decent analogy is that it will do for Venus was MGS' TES instrument did for Mars. It won't have the spatial resolution that VIMS had at Titan, but comparable spectral resolution. It would likely identify for us any recent lava flows on Venus and possibly their ages, as well as a compositional map of the whole surface. It is simply unlike any data we currently have and probably could not be improved upon without airships operating below the clouds.

[mcaplinger]

I think a decent analogy is that it will do for Venus was MGS' TES instrument did for Mars.

Could do, maybe, if it gets selected and if the massive complication of removing atmospheric signature actually works.

But perhaps I'm biased.

[vjkane]

In the previous discovery competition, proposers in phase a could suggest enhancements that NASA could decide to fund it not. For example, jpl was going to propose the Cupid atmospheric robe for the previous VERITAS proposal. (I have no idea if this is true for this round). I wonder if DAVINCI+ might propose VEMS (it would be DLR supplied), and VERITAS the CUVE UV spectrometer ( it’s only 1-2 U in size)

[JRehling]

Skepticism noted, Mike! Certainly the VEM instrument's success is subject to the yet-unknown realities of Venus itself, not only the atmosphere, but also the surface. It is exploration.

Is there any detail public yet about the nature of the DAVINCI imaging? I suppose one simple question I can't shake is whether it would all be down-looking or if there would be any side-looking panoramas made after or near touchdown.

Van, interesting thoughts about add-ons. It seems like DAVINCI has added a lot from the last time. I also would note that VERITAS, in utilizing a near-circular orbit, might therefore be pushing mass margins, but it would use aerobraking to achieve that orbit. Adding mass would make that more challenging, but the devil is in the details.

[mcaplinger]

Is there any detail public yet about the nature of the DAVINCI imaging?

There are a variety of public papers and LPSC abstracts about the 2016 incarnation of DAVINCI from which inferences can be made. I'm not free to say anything about what might have changed, sorry.

[JRehling]

I thought that was the likely response, but you can't blame a Venus fanatic for trying!

[vjkane]

I can't find the link, but the previous DAVINCI imager would have built up overlapping images that would have allowed photogrammetric point matching to create 3D surfaces from the images. The presentation I remember showed that at high resolution. I don't know if it could have been done from higher elevations over wider areas.

From the one DAVINCI+ abstract available, it looks like they are supplementing the visible imager with a near infrared imager to relate finer scale composition to what would be seen from orbit.

[dtolman]

If NASA (Congress) decides they are VERY interested in a out-of-cycle flagship or new frontiers class mission to Venus by middle of this decade to look at the... chemistry... of its atmosphere - do they collect new proposals, revisit the New Frontiers class missions that were turned down in 2019, or look at upscaling the current 2 Discovery class contenders?

I imagine that any proposed mission that wants to take a close look at the atmosphere's... composition... will want to include a sample return capsule or a balloon with an extensive chemistry lab on board. ISRO may be rethinking their decision not to include the atmospheric balloon on its payload as well.

[vjkane]

If NASA (Congress) decides they are VERY interested in a out-of-cycle flagship or new frontiers class mission to Venus by middle of this decade to look at the... chemistry... of its atmosphere - do they collect new proposals, revisit the New Frontiers class missions that were turned down in 2019, or look at upscaling the current 2 Discovery class contenders?

I imagine that any proposed mission that wants to take a close look at the atmosphere's... composition... will want to include a sample return capsule or a balloon with an extensive chemistry lab on board. ISRO may be rethinking their decision not to include the atmospheric balloon on its payload as well.

NASA and Congress follow the priorities set in the Decadal Surveys. Unless the new survey prioritizes a Flagship Venus mission, it almost certainly won't happen. The one exception to this rule I can think of was former Congressman Culberson's insertion of the Europa Clipper mission into law (and the budget) along with a follow on Europa lander. The Clipper mission was the Decadal Survey's #2 flagship priority, so he was supporting the Decadal Survey's priorities there. The lander was not a Decadal priority, and while excellent mission definition work continues, Congress isn't providing the funding to take it to development anytime soon.

However, Culberson was an exception, probably unique in both his strong interest and his powerful position that allowed him to push Clipper through. Usually when someone in Congress backs a NASA mission ardently, it is because it brings a lot of $s and jobs to their state or district (such as Senator Shelby's strong support for the SLS).

All that said, the next Decadal Survey may continue to prioritize a Venus mission in the New Frontiers line, and good missions can fit into the Discovery line (a number of Venus atmospheric missions have been proposed for the Discovery program). And don't count out the SIMPLEx program. There are some exciting cubesat-scale atmospheric instruments in development to study Venus' atmosphere.