I've read that claim attributed to John Mellish. It's a little hard to believe, unless you count the Hellas and Argyre basins as "craters", in which case they've been observed for a long time. Schiaparelli Crater's outline was observed, by Schiaparelli himself, but only because it cuts into the dark outline of Terra Meridiani (and of course he didn't identify it as a crater). It's hard to imagine anything smaller being resolved by early 20th-century telescopes, ideal viewing conditions or no. Even on Hubble images Martian craters are not very noticeable.

One reason Martian craters are hard to see from Earth-based telescopes is that, as with most cratered bodies, they aren't very obvious except near the terminator. And we very, very rarely see much in the way of a terminator on Mars. Most of the Mars views from Earth are nearly full-disk, the terminator fuzzed by being viewed through the maximum amount of Mars atmosphere it's possible to have between us and the Martian surface, and by foreshortening.

The human eye has far better naked-eye resolution of the Moon than we had of Mars through telescopes for hundreds of years, and even so, lunar craters weren't really identified as such until people started looking at the Moon through telescopes. And we get very good terminator views of the Moon from Earth. So, even if we were able to see Mars with a terminator crossing mid-disk through cratered terrain, it wouldn't be surprising if we missed craters...

-the other Doug

I think the whole issue of earth-based identification of craters on Mars is frequently misrepresented.

If I look up at the Moon without a telescope I can see Mare Crisium... it's a dark circular patch which lies in a crater, a big crater which we often call a basin, but a crater nonetheless. But I'm not seeing the crater, the depression, I'm only seeing the dark floor. I simply don't believe that Mellish or Barnard or anyone else ever saw a crater. They only saw - at most - circular albedo markings. The idea that they were craters was pure guesswork, based on the appearance of Plato, Crisium etc. on the Moon. The best proof of this is the case of Nix Olympica, a prominent circular bright spot, trumpeted as a crater when Mariners 6 and 7 appeared to resolve it as a crater with a central peak. But it wasn't.

Phil

To detect a dim object and to see fine details are two distinct skills, actually using two different portions of (and cell types on) the retina. I wouldn't know if the two abilities are positively correlated among people with non-troubled vision... they may even be negatively correlated.

The following are the best references I have found online:

The Venus-Halley Missions, Don P. Mitchell

The above covers the entire flights and the origins of the ballon plan. The following two pages from Astronautix.com provide additional information into the original VeGa plan, which would have seen four probes launched, two of which would have been dedicated ballon carriers.

Vega 5VS and Vega 5VK

Graham

Phil:

I got new glasses the other week, and can easily persuade myself that I see Aristarchus (well, the plateau) with the not-quite-naked eye. Contrast helps, true - but *knowing* it's there helps a lot more!

Bob Shaw

There was an article in Sky & Telescope magazine (exact issue I do not recall,
but likely within the last 10 years) that claims the craters he saw were actually
the Tharsis volcanoes.

But why were scientists so surprised when Mariner 4 found so many craters
on Mars? Did they really expect the planet to have more erosion mechanisms?

George Pal put craters on Mars in the 1950s! So they must have been not far below the surface of the semi-technical consciousness...

Bob Shaw





Graham:

Thanks - none of these offer very much in terms of detailed construction, though...

Bob Shaw

We're way off the topic of Venus, but an issue from this past year offers evidence that the relief of Argyre had been observed. The article asserts that some previous analysis (perhaps the one you mention above) goofed by forgetting that telescopes invert images, and reported the southern hemisphere phenomenon as a northern hemisphere phenomenon.

Beyond doubt, the best ground-based telescopic observations in 2003 showed a shadow at Olympus Mons. But that was with adaptive optics.



Sure. It was known that Mars was pretty cold, but warmer than Antarctica. Antarctica is pretty well eroded. Of course, the whole story behind craters, impactors, and the rate thereof over the age of the solar system had not yet been established either. And the seasonal shifts in color on Mars hinted (correctly, but vaguely) as to SOME kind of activity there. It turned out to be dust... but dust that happens not to provide much erosion. Who could have guessed that?

There was a full set of preliminary science papers from the Venus balloon experiments and I'm pretty sure a followup set of primary science results, published first <I think> in Science, then maybe in JGR <Journal of Geophysical Research, not sure which series>.

Regarding the whole craters on Mars surprise. Remember that essentially up to the Mariner 4 Mission, the best estimates for the martian surface pressure were around 1/10 th atmosphere, not 1/100 th. Improved precision spectroscopy had just shown a pretty solid measure of C02 surface pressure of 1/100 or 1/200 atmosphere, but nitrogen or argon were undetectable. The new figures had gotten attention, but not universal acceptance. So the whole vague arm-waving ideas of Martian geology were implicetly assuming a more active geology and surface environment.

We STILL were caught flat-footed. Sometimes EVERYBODY misses the obvious, including the people who didn't miss it but didn't keep screaming... "Hey.. this is important".

Replying to Bob about seeing Aristarchus with his new glasses:

Yes, but it's not Aristarchus the crater you're seeing, or the plateau, it's the Aristarchus ray system, which has much more contrast and is MUCH bigger. If you didn't know there was a crater in it, your observations would not tell you that.

Ditto Mars. Barnard, Mellish, Antoniadi - they were seeing spots and interpreting them as craters. Some were, merely because they had material of differing albedo on their floors. Some were not (e.g. Juventae Fons, Nix Olympica). They only saw spots.

Phil

The presentations from the second VEXAG meeting have just arrived ( http://www.lpi.usra.edu/vexag/May2006/presentations.html ). In the one on the latest update of the Solar System Roadmap ( http://www.lpi.usra.edu/vexag/May2006/VEXAG_52006_ELLEN.pdf ), Ellen Stofan's group recommends that for the projected Flagship-class Venus Surface Explorer, an "air mobility platform with long traversing" is now "preferred over a surface rover" for Venus, logically enough. (Not only does it allow much longer traversing, but in the case of Venus it would also allow the vehicle to land, hastily take a look around and grab some samples for later digestion, and then take off again for the cooler upper atmosphere, thereby reducing its heat burden.)

Actually, though, the single most useful presentation from this VEXAG meeting may be Larry Esposito's summation of our current scientific knowledge of Venus ( http://www.lpi.usra.edu/vexag/May2006/Chap...ummaryVEXAG.pdf ).

Also see Emily's series of very useful blog entries on the goings-on at VEXAG ( http://planetary.org/blog/ ).

I feel that the last proposal from VEXAG is more sensate and doable. So, I hope they will have a good common sense to agree and stick these objectives and start to work together without much missing time and money.

Rodolfo

Bob, what in particular did you want to know about the construction of the Vega aerostats?

Hi Don! That was quick!

Phil

Mr. Esposito's presentation was indeed informative, Bruce; thanks for posting the link!

2 By of oceans, huh...hmm. Although this is wild speculation, you have to wonder if maybe the advent of photosynthetic life on Earth was what saved us from becoming Venus' slightly bigger sibling in all respects.

Still, if oceans did persist that long, why wasn't more CO2 captured as limestone to prevent a runaway greenhouse? Did Venus all of a sudden become enormously more volcanically active than Earth ever was, causing that 'global resurfacing event' and a CO2 overload in the atmosphere that the oceans just couldn't process fast enough?

Lots of interesting and potentially quite significant contingency scenarios here...

Venus has almost no magnetic field, so like Mars, hydrogen has been preferentially blasted away by solar wind. It lost almost all its water that way. Venus also seems to have a lot more atmosphere than Earth, even taking into account carbonates in the Earth's crust. Perhaps the late collision that created the Moon, blasted away most of the original volatiles.

The current concept of Venus is that it was never quite warm enough to develop a genuine "runaway greenhouse", in which the greenhouse effect from all the water vapor initially in its atmosphere raised its temperature by a greater enough margin to evaporate a really huge additional amount of water into the air...and so on in a self-amplifying positive feedback that took the form of a diverging series that didn't stop until ALL the planet's water was in the form of atmospheric steam, after which enough of it soared into the upper atmosphere for solar UV to get at it and break it down.

Instead, it appears that early Venus was instead a "moist greenhouse". That is, its initial warmth was greater than Earth's by a relatively modest margin, so that the amount of additional water that was evaporated into the air by that warmth was also fairly modest and so produced only a small additional greenhouse effect...and so on, in a positive-feedback effect that took the form of a converging rather than diverging series and thus finally leveled off at a certain point (as indeed our own water-vapor-generated self-amplifying greenhouse effect does after warming Earth by a total of about 33 deg C).

This stabilized level of early Venusian warmth, however, was still high enough to loft the planet's water vapor to altitudes high enough that solar UV could break it down with tremendously greater efficiency than was happening on Earth even before our photosynthetically created ozone layer appeared. Thus Venus was still stripped of ALL its water supply after (according to the majority view) a few hundred million years, at which point its "carbonate thermostat" -- which depends on the existence of liquid water -- also shut down. That is: after Venus' liquid water vanished, all the atmospheric CO2 which had been turned into carbonate minerals by that liquid water got eventually dragged back down by the planet's still-functioning plate tectonics into its semi-molten asthenosphere, where the carbonates were broken back down into CO2, which was then belched back into the atmosphere again by its volcanoes -- and this time that CO2 did not get turned back into carbonates again, so that the volcanoes eventually belched the planet's entire large CO2 supply into the air as a permanent super-thick atmosphere whose greenhouse effect (even without the assistance of water vapor) was strong enough to raise its temperature to its current roasting level and keep it there.

The planet's plate tectonics, according to this model, did shut down a billion years or so after the planet lost all its surface liquid water. This is because mixing liquid water with rock greatly lowers its melting point -- and so, without water to do this, the planet's asthenosphere solidified and permanently jammed up its plate-tectonic conveyor belt. Thus there may still be some carbonates sitting around on Venus' surface that were not taken underground and broken back down into CO2, although most of them were thus destroyed before the plate tectonics shut down completely. But at any rate, there's no evidence that the advent of photosynthetic life did anything to prevent Earth from turning into a Venus-type oven -- we were safe from that fate whether life had ever evolved on Earth or not, simply because we were far enough from the Sun for virtually all of our atmospheric water vapor to stay trapped in our dense lower atmosphere by the "cold trap" of our stratosphere and thus be safe from breakdown by solar UV.

David Grinspoon has recently proposed an interesting variant of this idea, based on the assumption that the calculations of James Kasting -- which are what have led to the rejection of the "runaway greenhouse" model of Venus and the acceptance of the "moist greenhouse" model instead -- are (by Kasting's own statement, an upper limit) which ignores the possible cooling effect of the dense high-albedo water clouds which the initial warm Venus would have had. Grinspoon thus thinks that early Venus may have been cool enough that it didn't lose all its liquid water (and thus start building up a super-dense CO2 atmosphere) for fully 2 or 3 billion years -- and therefore that its plate tectonics may not have shut down until only about 500 million years ago, so that the fact that Venus' surface (in the opinion of most geologists) suddenly started retaining impact craters at that point was not due to a separate "catastrophic resurfacing" event at that time, but just to the fact that, before then, plate tectonics had been erasing most of the planet's craters just the way it still does for Earth.

As Grinspoon points out, one astonishing side aspect of his revisionist view of Venusian history is that Venus would have had time to evolve not just microbial life (which Kasting's classic moist-greenhouse view might also allow), but photosynthetic and maybe even primitive multicellular life -- unlike Mars, Europa, or any other place in the Solar System. Ah, but is there any chance that any fossils of such Venusian life could survive to the present day in such a savage environment? Now you can see one reason why geologists are so interested (as the 2002 Decadal Survey said) in looking for any evidence at all of surviving sedimentary rocks, carbonates, or other aqueous minerals on Venus' surface.

Thank you Bruce for reporting on Mr. Grinspoon's ideas. I think that he is one of
the more original and innovative members of the planetary science community.
I especially like David Grinspoon's proposal to include a manned mission to Venus,
as part of the VSE. As I recall, his plan calls for a crew to orbit Venus in a CEV and
use that vantage point to control a series of unmanned probes on the planet itself.


Another Phil

Don:

I've only seen (a very few) poor quality illustrations of their design - they've always struck me as being one of the more fascinating unsung planetary missions (probably well covered in French, though!). It's primarily the general layout, the deployment, and suchlike which I'd like to learn more about!

Bob Shaw

Blamont's book (in French) talks at length about this. The Vega balloon mission didn't have much to do with the French. In 1978, Blamont proposed an idea to send a much more complex mission to Venus that involved a big metal-foil balloon probe and an orbiter to relay its telemetry. As far as I know, nothing was ever built or designed in detail. The Mars sample-return mission was sucking the life out of their space budget though, so they sent the Venera-11/12 mission, and botched up some aspects of it. The head of NPO Lavochkin was fired after these probelms.

The Vega probes were designed at Lavochkin, based on a proposal by V. Linkin and others. It's made of teflon and nylon, and quite a bit smaller that what Blamont had proposed.

The idea of combining a Venus mission with a rendezvous with Halley's comet is from Vladimir Kurt. He and a mathematician worked out the celestial dynamics, and got it approved. Some kind of serious falling out occured between Kurt and Sagdeev though, so you don't see Kurt's name mentioned much, even though he was a primary mission planner for Vega.

Here is a diagram of the deployment:

Click to view attachment

Here are a couple pretty good diagrams of the aerostat:

Click to view attachment

Click to view attachment

Plate tectonics don't renew the whole surface, only the deep ocean part. The continents (including the continental shelf) are too light to be pulled down in the subduction zones. If Venus once had plate tectonics the "continents" (highlands) should be more heavily cratered than the "oceans" (basins). Whether this also implies that fossils and carbonates should be preferentially sought for in the highland areas is uncertain. The last life would have been found in the deepest parts of the basins, but these may have been "reprocessed" before plate tectonics stopped (here on Earth the ocean bottoms are completely "reprocessed" after ca 200 million years).

Incidentally there is evidence that Earth also had a "moist hothouse", not once but three times and that it saved rather than extinguishing life here. In the Late Proterozoic (600-800 million years ago) Earth suffered a series of extreme glaciations when all, or almost all, oceans froze over and continents were glaciated even in near-equatorial areas. Such a "snowball Earth" is climatically stable since the high albedo reflects most solar radiation back into space. However volcanism continued and since the oceans were ice-covered and the continents frozen no CO2 could be absorbed, but rather kept accumulating for maybe 20-30 million years. Temperatures slowly rose until the ice finally started melting, the albedo went down, the ice melted faster etc in a runaway process that converted Earth from Super-Antarctica to Super-Tropics in just a few thousand years. In this extreme hot-wet environment chemical weathering became intense and CO2 was rapidly drawn down and vast amounts of carbonates were deposited right on top of glacial deposits - a most unusual juxtaposition.

As for whether fossils could survive such extreme conditions, the answer is probably yes. Fossils can occasionally be recognizable in rocks that have been heated to similar temperatures on Earth. However here such heating is invariably linked to great depth and extreme pressures and also not continued for such a long period (500 mya), so it is difficult to make comparisons.


tty

Don:

Thanks!

I hadn't previously realised that the entry/deployment sequence was quite so complex - I'd presumed (for no good reason that I can think of) that the lander simply had a bolt-on atttachment which was the ballooon and whatever bits were required to set it going! It's really impressive that a clockwork spacecraft could do so much and so well.

Bob Shaw

Yeah, the balloon and helium bottles were stored on a ring-shaped unit that wraped around the lander antenna.

The Russians were very good at clockwork. You wouldn't believe what one of those PVUs looked like! Think, miniaturized Babbage difference engine.

The main spacecraft had a real computer on it, but not the lander or aerostat.

Couldn't get the parts, eh - no wonder Madame de Pompadour was so popular!

(don't ask)

Bob Shaw

Hmmm, over my head. :-) I meant to type PTU (program timing unit). Starting to think in Russian...

Over mine, too. IJFGI. Learn something new everyday.

This is why one of the biggest goals in Venusian exploration is whether there is anything on Venus that can be called "continents" -- that is, patches of lightweight granitic rocks floating on top of the basalt plates, and therefore resistant to being pulled down into the deep by crustal-plate subduction. Earth's continents are thought to be made of lightweight silica-rich melt rock that was produced and separated when Earth's original basalt was mixed with large amounts of liquid water while it was being pulled down into the asthenosphere and remelted -- so the existence and size of any continents on Venus is yet another factor that seems to depend on the size of any initial liquid-water oceans it had early on. (The 2002 Decadal Survey is very clear on this point -- find any large amounts of granite on Venus anywhere, and you have strong evidence that it had substantial water oceans early on.)

Thus the strong interest in using the future landers to inspect the two types of Venusian terrain suspected of being possible continents; the tesserae (which were the target of one of the twin landers in Donald Esposito's "SAGE" concept at the last New Frontiers submission), and the huge "Ishtar Terra" in Venus' north polar region.

(By the way, the JPL technical report on SAGE -- http://trs-new.jpl.nasa.gov/dspace/bitstre...4/1/03-2520.pdf -- implies (pg. 18 and 21) that the only reason it was rejected as a finalist is simply that its launch window to Venus didn't fit in with the assigned period during which NF 2 was supposed to be launched. If that's the only grudge they had with it, I think it will definitely be a front-runner for the NF 3 selection, whenever that is finally made -- espcially since the Inner Planets Subgroup of the 2002 Decadal Survey ranked a Venus lander as more important than a sample-return mission to the moon's Aitken Basin, and the only reason the Survey as a whole gave the latter such a high overall rating is that it said the automatic rendezvous and docking technology that they thought an Aitken Basin mission would need would be useful practice for a Mars sample return. As things turned out, the Aitken Basin proposal that was a finalist -- "Moonrise" -- didn't use unmanned R&D at all.)

I've read quite a bit about the two supposed "Snowball Earth" periods in the Precambrian, and the wild pogo-sticking in global temperature that's thought to have occurred during them. There are several explanations proposed for them -- ranging from continental drift breaking up an initial giant supercontinent to create a bunch of smaller continents with a larger total amount of shallow coastlines that thus pulled more CO2 out of the air by carbonate weathering, to the idea that the first photosynthetic cyanobacteria may have brought on one of the two crises themselves by producing enough oxyen to destroy the methane greenhouse that had been keeping early Earth warm. (And the latter, in turn, may perhaps have been originally created by the earlier generation of methanogenic bacteria!) There are still a few holdouts on whether the Snowball Earth episodes occurred at all, but the evidence seems to be growing steadily.

And as for the survival of fossils -- or at least microfossils -- under the savage surface conditions of Venus, there's a rather encouraging new LPSC abstract ( http://www.lpi.usra.edu/meetings/lpsc2006/pdf/1028.pdf ) on the apparent ease with which biochemical fossil evidence seems to survive even in giant-meteor impact melts on Earth. But if you think a fossil hunt on Mars will be difficult, consider one on Venus...

I'm not really a fan of either of his ideas. Carl Sagan suggested a long time ago that (Earth-born) microbes might be bred to survive in the Venusian clouds. Um, he probably says "Cytherean clouds". But that was in the early 1960s, before we knew better.

I'd be surprised if any molecule with more than a couple carbon atoms can survive in the Venusian atmosphere. Certainly there is no obvious sign of organics in the IR fourier-spectrometer measurments (Venera-15), while the Earth has clear CH-band structures. Keep in mind, the atmosphere of Venus is very dynamic-- convenction cells, high speed winds at the cloud level, etc. Those hapless microbes will alternate between being carried up into the zone of solar radiation, with no ozone or magnetosphere to protect them from every kind of ionizing radiation. Then down they go into the deep atmosphere to be pressure-cooked in suphuric acid. It's the kind of theory you propose to get your name spashed in the papers.

Then there is the manned orbiter around Venus. Kinda like ISS...except more expensive and dangerous. OK, now I said it, ..."ISS"

NASA is spending 4 times as much money as ESA, RKA and China combined. For $17 billion a year, just think about the kinds of science we could be doing all over the solar system. Rovers on IO, sample return missions to the planets and satellites, submarines under Europa. But here we with NASA wringing its hands, cancelling missions. Now why is that?

Google 'Madame de Pompadour and Dr Who' - I'd just watched it! And put not your faith in clockwork!

Bob Shaw

(behind the sofa)

Aha! I always wondered why Madame de Pompadour came up with that ridiculous hairdo. She was hiding her TARDIS in it!

Bruce:

Believe it or not, there are actually three or four left in Glasgow; or perhaps it's the same one...

Bob Shaw

So what exactly was the purpose of those Police boxes in the UK? Kind of an exclusive telephone booth for cops?

I watched Dr Who for years and never understood that.

I think UK mailboxes look far more like alien robots.

http://www.irelandinformationguide.com/Ima...htKaihsuTai.jpg

Yes - from the days before portable radios (they were designed in the 1920s). UK Police also carried whistles with a very distinctive sound, to call for aid (I always wondered what stopped the guys in the black hats getting hold of whistles in order to confuse matters, sorta like a 'whistle gap'!). Officer Dribble, er Dibble, in the classic Boss Cat cartoon show had exactly the same thing, but in his case it was just a phone in Top Cat's alley.

Bob Shaw

After clawing my way through my CD-ROM library of recorded Web documents on Venus, I find the following on Grinspoon's suggestion that Habitable Venus may have lasted a very long time. (There certainly must be more than these.)

http://www.aas.org/publications/baas/v35n4/dps2003/433.htm
http://sciencenow.sciencemag.org/cgi/content/full/2003/909/2
http://www.newscientist.com/article.ns?id=dn4136

And, on possible ways we might look for evidence of past liquid water on the surface:

http://solarsystem.wustl.edu/our%20reprint...97%20Icarus.pdf
http://www.lpi.usra.edu/meetings/lpsc2003/pdf/1152.pdf
http://www.lpi.usra.edu/meetings/lpsc2005/pdf/1992.pdf
http://www.aas.org/publications/baas/v37n3/dps2005/764.htm

Presentations from the last VEXAG meeting are now posted: http://www.lpi.usra.edu/vexag/may2008/presentations/

I found the presentation on the Japanese Venus Climate Orbiter and the Flagship mission analysis particularly interesting. The former is an imaging mission that will use a near equatorial orbit to achieve semi-synchronous coverage of the atmospheric rotation of the atmosphere.

The flagship report details the analysis for a possible 2020's (or so hoped) mission. As reported in the press, the proposal would include an orbiter (high resolution radar seems to be the key instrument), two landers with atmospheric composition capabilities and balloon ascent following sample acquisition, and two mid-altitude balloon platforms. Total cost is ~$3B (presumably in today's dollars).

Some thoughts on the flagship proposal:

The proposal seems to knock the legs out from under the New Frontiers VISE proposal, or any similar New Frontiers proposal. (This involved two short lived landers without balloon ascent.) This scale of mission receives the lowest science score. Yet for the price of two of VEXAG's short-lived landers (with balloon ascent), 4-6 VIS landers could be implemented.

The orbiter is actually fairly cheap, almost Discovery class, and would probably fit within that budget with some modest international participation. There's no claim in the presentation that there is much advantage to flying the orbiter with the other Flagship elements.

All medium altitude balloon options seem to cost ~$2B, as do the short-lived landers with balloon ascent.

VEXAG appears to be going to the full monty with a Flagship proposal. Yet, at best, Venus would be third in line after an outer planets flagship and a Mars sample return. Never hurts to make your request. But I would have two requests outstanding -- a high priority Discovery and a New Frontiers mission (fly something in the next decade) and a follow on flagship that might fly in the 2020s, and more likely (in my opinion) in the 2030s.

I think Venus rovers and balloons, someday, might be teleoperated by people somewhere closer to Venus.

Whilst it would be brilliant to have rovers on Venus, I doubt they'd work with todays materials technology, given the scorching temperatures and crushing pressure on the surface.

Maybe a balloon/blimp could be a viable concept?

Venus resembles a depiction of "Hell" so it will indeed be extremely difficult (read expensive) to get something working on the surface

The Venera landers did manage last about an hour on the surface.

I like to think that with all the improvements in instrumentation technology (and better luck), that a next generation lander could do great science even with only an hour of lifetime.

-Mike

The current lander plans seem to be counting on about an hour or two, so not much improvement there. However, there are a couple of ways of getting more science. First, you could grab samples, inflate a balloon, and do the analysis in the cool clouds. That is the official Venus lander goal for the New Frontiers Venus mission and I believe for the proposed Venus Flagship mission. However, it's recognized that that approach is expensive, so simply short lived landers are an acceptable alternative and were proposed for the first New Frontiers competition and are rumored to be proposed for the upcoming competition.

The other possibility is to use remote laser sensing (both a la MSL and Raman) to target multiple features at the landing site without the difficult problems of bringing samples inside the craft. My hope is that a periscope could sit atop the lander. An on board camera would analyze images of the site, identify a variety of targets, and target the laser accordingly.

I just posted a long discussion of possible New Frontiers Venus missions at http://futureplanets.blogspot.com/ that discusses these options and has links to proposed mission descriptions.

I'm definitely no expert on the surface composition of Venus, but I wonder if samples would undergo chemical changes when transported to a much cooler, lower pressure environment prior to analysis. Would any valuable science be lost this way?

I expect the collection system would seal samples off from the external environment. The samples would probably be very small.

An interesting Venus Flagship Mission Study

Hi Guys

Geoff Landis discusses aerobots and surface rovers in some detail. New Silicon carbide electronics can operate at 500 C for hundreds of hours, so they'd be ideal for the rover...

Landis Paper for NASA

VEXAG presentation from 2008

...such a mission would stretch the state-of-the-art, which is a worthwhile goal for NASA. Would also allow design of deep-probes for the gas-giants! Down to the 200 bar level on Jupiter, 300 on Saturn and 800 bar on Uranus/Neptune.

The Landis paper is really interesting, I did not realise electronics could operate reliably at 500 C.

I don't think they can, yet. I think automotive applications are pushing silicon CMOS electronics to over 200C, and coupled with the reliability requirements of cars, they might start using SiC when it gets to the VLSI stage. Reading the paper, they fully admit that SiC has been played with at 500C, but only on the order of a single logical gate. Their comment, not mine, is that this is comparable with the state of the art during the Mercury program. Between now and when it's used on a spacecraft, someone needs to progress the technology from 10 transistors to a few thousand for a microcontroller. And validate both volatile and nonvolatile memories of some sort. If they get a flip-flop working at 500C, they're golden. The nonvolatile memory can be magnetic coils, Apollo-style.

...as I keep reading... Yup, they say memory is still a big unknown in SiC. Oh, and they say it's not yet complementary, so it's higher power than CMOS (where the C stands for complementary).

They also waffle back an forth about what would be heavier:
Electronics running at 300C and a big cooling system.
Or Electronics running at 500C and a smaller cooling system.

Personally, I'd bet that any mission in the next few decades doesn't have any large ICs running at 500C. I'd love to be wrong, though. Maybe private industry will find some application that needs it. Geothermal power or efficient furnaces or something.

And recall, even with an electronic device operating at 500C, you still need insulators, conductors, capacitors, resistors, tuned circuits, etc. And to be able to resist a corrosive environment and high pressure.

This is quite a challenge from a materials engineering standpoint.

Yeah. One of the reports mentioned that resistors exist that work at 500C, but existing capacitors don't, really.