What will the descent probe's velocity be? Is it expected to be destroyed on contact with the terrain, or is there some outside chance of it surviving descent to give us some cock-eyed shots for a few minutes before the battery or other equipment succumbs to the environment?

From here.

That's excellent. Lets hope against hope for at least 30 minutes then.

Maybe a shot or two from the surface a la Huygens?

P

Reading up on the science of noble gas abundance in planetary reservoirs, I gained a newfound appreciation of why we need vastly better measurements than had previously been made at Venus.

While there is often an interesting story to be interpreted regarding the ratio of the top two or three isotopes, the full picture is much more complex, and to take the most challenging case, xenon has nine isotopes that are (basically) stable [seven truly stable, and two have extremely long half-lives]. In Earth's atmosphere, xenon abundance is 87 parts per billion, so the individual isotopes are, obviously, in some cases more than 9x less abundant than that. To measure their abundance with even one significant digit means measuring atmospheric components to better than 1 part per billion, and ideally even several times more accurate than that.

To date, 1970s-era instruments have returned the best data, and those placed only loose constraints on the abundance of xenon in Venus's atmosphere. Basically, good data for krypton and xenon don't exist at all.

Now, if this seems arcane, here's the stunner – we are still searching for an explanation for the unexpectedly low xenon abundance in Earth's atmosphere! (When we don't understand something about Earth, that's a strong sign that we don't understand it for planets in general.) In matters of noble gas abundance, Earth is just one case, with Mars, the solar wind, Jupiter, and meteorites being other cases. And so, Venus is potentially a very important case for understanding not merely the evolution of the atmosphere of Venus, but even of Earth… and, we can be sure, for understanding terrestrial exoplanets outside our solar system.

For what it's worth, Titan is apparently another beast altogether, due to the physical chemistry of ices and noble gases although ice has been at least discussed as a possible reservoir for Earth's "missing" xenon.

So, the atmospheric composition instruments on DAVINCI+ may lead to realizations of extremely broad reach, even so far as the history of Earth is concerned.

D+'s camera points down. So if the probe survives landing, there will be pictures of the camera pressed against the surface.

Of the 4 Pioneer Venus probes, which had a similar design posture to impact survival (as did Huygens), signals from 2 were lost immediately at impact, signals from one for a second or two (consistent, perhaps with toppling over and pointing the antenna away from Earth) without any real science content, and signals from one were received for an hour, showing some variation in light levels.

So the empirical odds are about 25% that we get something from the surface.

I suppose the ideal for DAVINCI would be to topple over in such a way that the camera points at the horizon, and the antenna happens to point at the right azimuth to maintain the data relay. Whether the camera lens is scratched up or dusty is another story. We'll at least be running the accelerometers to see if the microseisms indicated by Venera are seen, those measurements don't require any orientation except for radio link

But this would all be gravy, the descent imaging should be spectacular.

Ralph, are you on the DAVINCI+ team? If so, congratulations!

I'm hoping that the D+ team releases a video of equivalent descent imaging over a terrestrial location to give us a preview of the types of images expected. If I remember correctly, the images will have overlap, and the team will build photogrammetric 3D models of the surface.

If the probe does fall over, I wonder if the images would be useful. I expect that the camera will be designed to focus a few meters to infinity.

I for one was just looking at MARDI descent imagery to get an idea of the kind of imagery we might see on Venus. I'm expressing a hunch that some unsharp mask processing will be part of the fun.

Any luck with a putative sideways image and focus distance will pertain to additional luck of how the probe landed and the local slope. Tessera terrain is rough. It seems like with rough terrain you're somewhat likely to be looking at the sky or staring right into something point-blank. But this is all wrapped in many unknowns.

And indeed, congrats Ralph and Mike, who have a hand in these successes.

The last data may show the probe bouncing down a steep slope...

Perhaps the most valuable landed science simply would be additional atmospheric analyses.

I believe that the noble gas analyses will be the same near the surface as at the surface, but more time will mean lowered error bars, which is a good thing.

For other gases, there's the potential of surface/atmosphere chemistry or physical chemistry which is the sort of thing that might be more about specifically Venus than anything cosmic, but also exciting in its own right, for sure. Sometimes interesting things happen in that last meter.

As a reminder, Pioneer Venus suffered a failure in multiple systems on all probes at an altitude of 12.5 km, quite a long way from that last meter.

(See post 283)

IIRC Jim Garvin got some imaging from a helicopter as an analog to trial/showcase the photogrammetry and trajectory reconstruction. But MARDI / EDLCAMs are pretty good analogs, I suspect

Rumor has it ESA will announce its M5 mission selection today, choosing between Theseus and EnVision. Godspeed EnVision! Three Venus missions would be amazing...

EnVision selected!

Exciting times ahead for everyone interested in Venus. The launch of EnVision doesn't occur until ~2032 though.

Unbelievable! Venus sweeps three mission selections - four if you remember the CUVIS ride-along.

EnVision is a bit similar to Veritas, but many details set them apart. EnVision's VenSpec-M instrument and the VEM emissivity instrument on Veritas appear to be precisely the same instrument from the same provider under different names.

EnVision's suite of spectrometers is described here:
https://ui.adsabs.harvard.edu/abs/2019EGUGA....8665H/abstract

It will be interesting to compare data from EnVision's VenSpec-U ultraviolet spectrometer and CUVIS, which will fly on DAVINCI+. Together, the pair will provide far better data on the unknown ultraviolet absorber than presently exists. It remains to see if spectroscopy is capable of uniquely determining the nature of the ultraviolet absorber, but if so, these two separate investigations would be the best imaginable effort to do so.

While EnVision includes a subsurface radar instrument that Veritas does not, their main SAR instruments are also different in focus from one another. Veritas will launch first and map globally X-band (about 3 cm) while EnVision will map about 20% of the planet (most areas that are rough and high altitude) in S-band (about 10 cm) with higher spatial resolution. The map here suggests that Alpha Regio, the landing site of DAVINCI+'s probe might not be covered by EnVision's radar mapping, but perhaps that is subject to change:

https://sci.esa.int/documents/34923/36148/1...018_Summary.pdf