Yep; Basilevsky has pointed out that the gamma-ray densitometers on Veneras 9 and 10 and the penetrometer on #13 -- instruments that I would have been willing to swear would be scientifically useless -- all indicate that the "rocks" are all rather low-density and slightly softer than standard volcanic rock. (#14's penetrometer, in that famous stroke of bad luck, landed squarely on one of the ejected camera covers.) Both these measurements and their visual appearance indicates that what we're actually looking at is flat sheets of ash or dust, fused together by a sintering process which also apparently explains the virtually total absence of aeolian soil movement on Venus -- one of Magellan's most astonishing discoveries, since even Venus' sluggish 1 meter/second surface breeze, in that super-thick air, should have pushed soil grains along pretty efficiently. (The only dune fields it saw on Venus were located near large craters -- apparently surface material blown along by the blast of air from the impact.)

One theory, backed up by lab tests, is that the reactive trace gases in Venus' lower atmosphere -- at the planet's high surface temperature -- have caused small amounts of calcite and other carbonates in the soil grains to fuse them together, so that Venus' surface soil is "crunchy".

This post left me thinking about the horizon details visible on the "new" reprocessed images. So I joined both V13 panoramas on the places were they overlap. This gives us some degrees of horizon on 2 opposite directions. The interesting thing is that there is continuity on the horizon features over the missing space.

Click to view attachment

I've traced the 2 horizons visible on the images with diferent colors and it's interesting to see that the "distant" horizon is only present on the "bottom" of the image. With so little actual data it impossible to tell for sure, but my interpretation is that the terrain is lower towards the bottom right of the image, and higher towards the top.

I'll do the same with V14 and post the results when I have the time!

This sort of landing site mapping is one of my goals in the next year or two. It's a bit tricky getting the geometry right. One other point of interest to cartographers: we don't know the orientation of the map.

Phil

Yes, and in fact you can see the shadow of dust deposits downwind from some of the meteorite impacts.

It isn't completely clear that the penetrometer on Venera-14 failed. Basilevsky tells the story of it hitting the lens cap, but the scientists who ran the experiment say it touched the surface and returned some data:

Click to view attachment







Very cool. Here is a perspective view from overhead, at the Venera-13 site. Notice the shadow all around the lander, as it blocks some of the uniform hemispherical light source.

Click to view attachment

Excellent! This view really helps me to see the geometry of the images. Do you have (or can easily make) the other landers' images in this view?

The next Venus's visit time by any other spacecraft would be Messenger's flyby on October 26, 2006. This spacecraft is carrying seven scientific playload, which are specially designated to study Mercury. However, some of its scientific instrument would be useful during its Venus' fly-by short time:

• Mercury Dual Imaging System (MDIS), a camera with wide and narrow fields-of-view, for monochrome, color and stereo imaging to take Mercury global pictures. It might be used during the Venus' fly-by.
  
• Gamma-Ray and Neutron Spectrometer (GRNS), which would be able to map the elemental makeup of Mercury's crust. Useless for Venus' fly-by.
  
• X-Ray Spectrometer (XRS), also used to map elemental abundances in crustal materials. It would not be used since the narrow mapping would not be justified.
  
• Magnetometer (MAG), which maps the detailed structure and dynamics of Mercury's magnetic field and searches for regions of magnetized crustal rocks. I think it would not be used since its usefulness is only valid if the mapping is of planet global range.
  
• Mercury Laser Altimeter (MLA), which measures the planet’s topography. Not used due to the same as MAG.
  
• Mercury Atmospheric and Surface Composition Spectrometer (MASCS), which measures the abundance of atmospheric gases and detects minerals in surface materials. It would be used during the fly-by.
  
• Energetic Particle and Plasma Spectrometer (EPPS), which measures the makeup and characteristics of charged particles within and around Mercury's magnetosphere. It would not be deployed on Venus' fly-by.

Any comments? Then after Messenger, the other spacecraft, BepiColombo, funded by ESA and ISAS of JAXA, would be flying-by on its way to Mercury by the year 2011-2012

Rodolfo

There will be no science observations from Messenger during its first Venus flyby because, by bad luck, this occurs near solar conjunction and its radio signals will be blocked -- but they have a massive science campaign planned during the second Venus flyby, including the use of several instruments which you predicted would not be used: http://www.lpi.usra.edu/vexag/Nov2005/MESSENGER_VEXAG.pdf

Maybe it will be possible to land a spacecraft at the (highest) point on Venus ,on a mountain i think because the temperature and the presure will be a bit lower at the highest point on Venus ,so a landing will be a bit easier then. But i dont know what the temperature and the pressure will be at the highest point at Venus. Anyone who knows about it?

Not that much of an advantage -- if I remember correctly, the temperature at the highest mountain top on Venus is less than 40 degrees C. lower than its average temperature. (I have a detailed sourcebook on the planet which may be able to give me this information precisely.)

The highest point is located on the northern highland is named Ishtar Terra and has Venus's highest mountains, named the Maxwell Montes (roughly 2 km taller than Mount Everest) after James Clerk Maxwell, which surround the plateau Lakshmi Planum. Ishtar Terra is about the size of Australia.

About the temperature's posted by Bruce, it is interesting, at 10-11 km above of the Venusian's datum has a survivable temperature. However, I still have no picture or map of the Maxwell Montes mountain to see if the top has large flat to permit an acceptable landing risk.

Rodolfo

Rodolfo:

The mean surface temperature of Venus is 464°C - 40°C less than that is hardly what one might call balmy...

Bob Shaw

Maxwell Montes is a large flat-topped plateau with plenty of room for a landing. It is geochemically distinct, so a prime target for landing. The slight temperature reduction would be useful, presumably, but it's an important goal anyway.

Go here:

http://pdsmaps.wr.usgs.gov/PDS/public/expl...ml/fmapintm.htm

for images.

Phil

Ooppsss... I haven't seen the word "less" Anyway, the cake would be tasty at that temperature!

Rodolfo

Yes, that's a little bit reminiscent of that scene in the second Addams Family movie in which Uncle Fester, who's about to get married, is holding his bachelor party accompanied by a swarm of strange-looking male Addams relatives. Lurch wheels in the giant cake, at which point one of the Addamses wrinkles his nose and asks, "What's that burned smell?" Fester snaps, "Lurch, you're supposed to put the girl in the cake after you bake it!"

I will shortly be going through my photocopied sections of Arizona State University's authoritative book on Venus, which should contain the information we need on surface temperatures on Venus' highest mountain top -- but it can already safely be assumed that they will be almost as savage as those on the ground. I'll also be looking up the stuff that I have on the apparent chemical/thermal fusion of Venus' soil particles into a hard crust.

"....It probably wasn't capable. Remember, it was the Bus that relayed the multiprobe data back, not PVO...."

Pioneer Venus Multiprobe and Orbiter were entirely separate missions, using a common bus spacecraft as orbiter and cruise-stage and flown at the same time. There was minimal operational interaction between the two missions, necessarily, as one might have had a launch or inflight failure.

The Multiprobe bus did not relay data from the probes, it just did a final maneuver to target it for a shallow entry near the limb as viewed from Earth, and used an ion mass spectrometer and neutral mass spectrometer (I'd have to double check) to measure extreme upper atmosphere composition and structure before burning up in an entry fireball.

The probes were direct to Earth transmitters, something like 64 bits/sec for the small probes, 256 or 512 for the large probe. Data tracking was by the Deep Space Net, additional Differential Very Long Base Line Interferometry was used to do 3 dimensional tracking (not telemetry) of the probes motions in the atmosphere. The probes were atmosphere probes only with little or no design for post impact science. The large probe shed it's heat shield and probably had it's bottom smashed-in on impact. The small probes retained their heat shield and their simple atmosphere structure instruments looked out or were suspended over the heat-shield edge. One probe (Night?) went silent on impact, one lasted about a second (I never heard any further information on that smidgen of data) and the Day probe lasted something like 67 minutes, seeing a puff of dust on impact with the nephelometer, transmitting till it FRIED. The US successfully landed a probe on Venus without trying!

With regard to temperatures and pressures, you want to get a copy of the Venus Standard Atmophere. Venus Atmosphere.

I use this to derive altitudes for events where pressure and temperature are given. It's more accurate than the contemporary figures, for things like PV or early Venera missions.

Page about Influenza from Venus??? but has a temperature profile from Magellan data.

http://www.datasync.com/~rsf1/vel/1918vpt.htm

Suggests that it would be tolerable only above 50Km where, strangely, the pressure is about 1000 millibars (roughly Earth sea level pressure) - Nice!

Nick

I will worry about that one right after we deal with those pesky body snatchers from Jupiter.

LOL. The website suggests that the 1918 flu virus came from Venus. Call me a skeptic, but I don't think so!

The other day a plumber was at my house to fix something, and while he was under the kitchen sink working he casually said, "Did you know that lasers and integrated circuits and photonic networks were all found in the alien spacecraft at Roswell?". A few months earlier, a man inspecting my furnace had told me that the Apollo Moon landings were faked by the government. Then you have this British hacker looney who was breaking into NASA computers to find out secret alien "zero energy" devices. The internet is just filled with this kind of garbage information.

How can people believe such things? What is wrong with our schools?

Is it true that you do not need a spacesuit when you are at an altitude at 20,30 or 50 kilometers (i dont know exactly how high) above the surface of Venus ,because the temperature and the pressure is almost the same like it is (at this moment) inside and outside my house. Can you explain that?

While temperature and pressure and the bulk composition of the atmosphere might do you little harm, I suspect that the clouds themselves would be chemically very nasty indeed for humans!

Bob Shaw

I lived in Pasadena in 1980, but I think the photochemical smog in the Venusian clouds is even worse! There is actually a little sulphuric acid in the upper atmosphere of Earth, probably from the same reaction as Venus:

(UV) + CO2 + SO2 -> CO + SO3
SO3 + H2O -> H2SO4

There are lots of other things in the clouds on Venus, especially the lower clouds. The Pioneer Venus large probe had a particle-size spectrometer that led some to think there might be large crystals in the lower clouds, although this is not so widely believed today (the so-called "mode 3 controversy").

The latest information comes from Vega-1 and 2, which had a battery of experiments for cloud study. There is a large amount of phosphorus in the lower layer, so some think it may contain phosphoric acid. Other possible components are Iron Chloride and Aluminum Chloride, which are both gases at surface temperatures. There is still really a lot that is not known. Probably only the upper clouds are simply sulphuric acid droplets.

I hope the ailing Fourier Spectrometer on VEX will recover and say more about this.

It might not be that much worse than L.A.'s smog. The clouds on Venus are surprisingly rarified. There are, after all, only very minute traces of both water vapor and sulfur compounds in Venus' air out of which droplets of sulfuric acid can be formed.

As with the haze on Titan, the fact that they block out our view of surface features from above is deceiving. I suspect, however, that in the case of Venus the explanation is somewhat different -- as Don pointed out above, even without any clouds the sheer density of Venus' CO2 atmosphere very seriously blurs features seen from any long distance through Rayleigh scattering, and I imagine the clouds just contribute to that effect in concealing Venus' surface features from our view.

Bruce:

Am I hearing volunteers for a 'briefly manned' spa holiday in the clouds of Venus?

Actually, that might not be so far off the reality - look at the stuff in (allegedly) health-enhancing spa baths, especially those associated with natural hot springs!

Bob Shaw

Click to view attachment

More fun with the Venera images!
This is an atempt at creating a 360º pan, with a vertical 50º field of view, from the V14 images.
With so many pans from the Moon and Mars, Venus must have them to!

Is there sometimes Sunshine on Venus or is the Sun (never) visible from the surface? Is there never a glimpse of sunshine at the surface of Venus?

On the contrary; there is a great deal of sunlight at the surface of Venus. It is, after all, close enough to the Sun that the intensity of sunlight hitting its cloud layer is about twice that at Earth -- and since about 20% of that punches through the clouds to the surface, surface illumination on Venus is about 40% that of daytime cloudless Earth. (What was less certain, until Venera 9 landed, was whether that sunlight was so diffused and dispersed in direction by the clouds and by Venus' thick atmosphere that shadows on its surface were largely washed out -- but the Veneras' surface photos reveal that even small bits of gravel have quite sharp and clear shadows, confirming that little of the incoming sunlight has its direction changed, either.)

But the disk of the Sun is never visible at the surface of Venus or am i wrong? And is Suncream needed when i am in a (hyphotetical) spaceship with allround glass just above the clouds of Venus at its equator? Is the Sun burning there? Can somebody explain that?

Believe me, if the windows in your spaceship aren't UV-proof, you will need MUCH more than Suncream. The Sun's UV, when not blocked by our ozone layer, is sufficient to give you a very bad sunburn in a matter of 20 seconds or so even at Earth's distance from the Sun.

As for the solar disk seen as a clear entity from Venus' surface: it's extremely unlikely -- although I've never read anything specific on the subject.

Beginning my project of telling you more about Venus than you wanted to know...

For starters, there are two superb overviews on the Web of our current knowledge about the place: Basilevsky's 2003 article ( http://www.planetary.brown.edu/pdfs/2875.pdf ) and Fegley's 2004 book chapter ( http://solarsystem.wustl.edu/Ch21Venus.pdf ). Indeed, on rereading all this stuff, I find I made some mistakes of memory.

(1) Venus air temperature drops 8 deg C for every rise of 1 km in altitude (or 23.2 deg F per mile). Thus, "The temperature is ~648 K [375 C, or 707 F] and pressure is ~43 bars at the top of Maxwell Montes, which is ~12 km above the modal radius of 6051.4 km and is the highest point on the planet." (Fegley, pg. 18)

(2) "All of the clouds are low density because the visibility inside the densest region of the clouds is a few km. The average and maximum optical depths (rho) in visible light of all cloud layers are 29 and 40, respectively, versus average and maximum rho values of 6 and ~350 for terrestrial clouds. Average mass densities for Venus’ clouds are 0.01-0.02 g/cubic meter, versus an average mass density of 0.1-0.5 g/cubic meter for fog clouds on Earth". (Fegley, pg. 18) And remember that Venus' cloud droplets are pretty close to being pure sulfuric acid, which has a molecular weight almost 5.5 times that of water. These droplets are really sparse.

(3) "Venus has the highest albedo of any planet (e.g., 0.75 vs. 0.29 for Earth). Even though the solar constant at Venus (2613.9 W/sq. meter) is ~1.9 times larger than that at Earth, Venus absorbs only ~66% as much solar energy -- i.e. ~160 W/sq. meter vs. 243 W/sq. meter -- as Earth. The energy deposition is dramatically different from that on Earth, where ~66% of the absorbed solar energy is deposited at the surface. In contrast, about 70% of the absorbed sunlight is deposited in Venus’ upper atmosphere and clouds, another 19% is deposited in the lower atmosphere, and only ~11% reaches the surface. The 'sunlight' at Venus’ surface is ~5 times dimmer than that on Earth." (Fegley, pg. 18)

(4) For Basilevsky and Head's speculations that the "rocks" seen in the Venera photos are really fused layers of fine ejecta dust from nearby giant impact craters, see:
http://www.planetary.brown.edu/planetary/i...8_Abs/ms007.pdf
http://www.planetary.brown.edu/planetary/i...8_Abs/ms025.pdf
http://www.lpi.usra.edu/meetings/lpsc2004/pdf/1133.pdf
http://www.planetary.brown.edu/pdfs/2875.pdf (pg. 9-11). In the latter, note something I'd forgotten: "During the Venera 13 touchdown event, clods of soil were thrown up onto the upper surface of the spacecraft supporting ring (see the dark spots on the ring close to the view-port cover on Venera 13 panorama A). Five sequential images of this place taken within a 68 min interval showed that the spots were shrinking with time, obviously due to deflation by near-surface wind." (pg. 10) And all four landers (like Pioneer 13's one surviving Small Probe) optically detected a dust cloud on landing. Also, "Direct (anemometry and spacecraft Doppler tracking) and indirect (wind noise) measurements showed that at the Venera/Vega landing sites (on plains, close to the mean altitude level) at a height of 1meter above the surface the wind velocity is about 0.3–1 meter/sec. Bearing in mind the very high density of the near-surface air, the mechanical load of the wind on Venusian surface features is rather large." Judging from what Venera 13 saw, the earlier calculations regarding the effects of Venus' surface winds on its soil were correct -- they really do blow Venusian soil around rapidly, if it's loose.

But at the same time we have Magellan's bewildering but solid observations of the rate at which Venus' surface features erode. Quoting Robert Strom's 1993 abstract (available indirectly at http://adsabs.harvard.edu/abs/1993LPI....24.1371S ): "Parabolic features are associated with 66 of [Venus'] 919 craters... [which] range in size from 6 to 105 km diameter. The parabolic features are thought to be the result of the deposition of fine-grained ejecta by winds...Since 66 of the 919 craters have parabolic features and the average age of the surface is 330 million years, then the average age of parabolic features is about 24 million years, but could be as short as 14 million years or as long as 50 million years. This suggests that eolian erosion, particularly for unconsolidated material, or burial rate on Venus is extremely low, compared to the Earth or Mars. Campbell et al estimate that the thickness of the parabolic deposits is several to tens of cm thick, possibly 0.16 to 3 meters. If the deposits average about 3 meters thick, then the maximum possible erosion rate is about 210 cm per million years, and the minimum rate is about 60 cm per million years. On the other hand, if the deposits are only 16 cm thick, then the maximum possible erosion rate is only about 1 cm per million years and the minimum rate is about 3 mm per million years. These low erosion or burial rates make it unlikely that eolian processes on Venus have been important in shaping its surface." The Magellan team had reached similar conclusions earlier; quoting Kevin Burke's 1994 abstract (available indirectly at http://adsabs.harvard.edu/abs/1994LPI....25..201B ): "The surface of Venus...seems to lack evidence of substantial landform degradation, particularly in comparison with the other two terrestrial planets with atmospheres, Earth and Mars. Those impact structures on Venus that have escaped direct involvement in tectonic or volcanic activity show very little evidence of topographic degradation. They retain bright block ejecta deposits and steep rim topography. Despite the evidence of approximately a billion years of endogenic and impact surface processing, there are relatively few sites on Venus where loose particulate surface material is available to be moved by the wind."

How in the world do we explain this grotesque contradiction? Burke devotes his abstract to showing how, in lab tests, grains of silicate minerals of the type likely to exist on Venus appear to slowly react with the CO2 in its air ( not with its sulfuric trace gases, as I had thought) to form a surface crust of calcium carbonate that cements the grains together. "Chemical cementation is a plausible means of keeping the global inventory of particulate material on Venus depleted in the absense of ongoing surface activity, and may stabilize surface debris and preserve steep slopes associated with impact craters and tectonic features. If so, there may be no correlation between age and surface slope measured over short length scales...Steep slopes as well as aeolian features, such as dunes and wind streaks, may be stabilized structures that record ancient rather than recent events. In the absense of significant atmospherically driven weathering, topographic degradation would be dominated by volcanic processes such as burial under lava, or tectonic processes such as folding and faulting."

Finally, regarding the Veneras' other measurements of the properties of the "rocks" they saw:

http://www.lpi.usra.edu/meetings/lpsc2004/pdf/1133.pdf : "...[S]oil mechanics measurements indicate
that these rocks are mechanically weak and porous (density ~ 1.5 g/cc)..."

http://www.planetary.brown.edu/pdfs/2875.pdf (pg. 11): "At the Venera 13 and 14 sites, the bearing capacity of the rocks was measured by two techniques... It was found to be only 3–10 kg/sq. cm; this implies that the rock material is porous. This, in turn, implies that it may be weakly lithified aeolian sediment (e.g. composed of debris initially produced by meteorite impact) or volcanic tuff."

Again, I have to say that's a pretty lame excuse for skipping science on the first flyby. The s/c is performing pre-recorded observations anyway and I don't get it why they simply don't choose to delay the science playback a week or two?


If, as Bruce suggests, even the small pebbles have sharply defined shadows, that implies a well defined, point-like light source. So yes, the sun should be clearly visible as a round disk from the surface, though it's likely the rest of the sky is pretty bright as well.

You don't want the spacecraft to be doing anything other than looking after itself, and maintaining appropriate pointing during Conjunction. Adding a science program into the mix would increase the risk of having a safing event, and frankly, on a Discovery budget - the money to get the people together to write, test, and then look at the resulting sequences and data isn't going to be easy.

Doug

True, but a safing event is equally as likely anytime, solar conjunction or not. Once the spacecraft safes itself, it should be... well, safe
Maintaining sun-point for solar panels and awaiting instructions from Earth. I don't see any non-catastrophic safing event doing anything bad to the spacecraft on a timescale of days (as opposed to hours when normal contact is maintained).
Though, you're right -- after all, this is a Mercury mission and anything beyond that is just bonus science. Reducing all unnecessary risks probably simply is good planning.
Still, one can't help but feel sorry about missed opportunities like this...

Well - remember, it's not as if Venus is the ignored neigbour at the moment...we have VEX giving it the once over. Without VEX, I'd be inclinded to agree with you in that any Venus science would be worth it (i.e. a drop of water when you're really really thirsty is great...but do you care about a drop of water when you've got a 25 litre water-bottle on your desk )

Doug

I don't think it is worth the risk. Should a course correction have to be made, and it ends up stuck in safe mode, it would be really bad news.

I'm a little suprised they aren't going to passively collect fields-and-particles data and store it for post-conjunction dump.

Course corrections would be made well in advance of the conjunction and the flyby, to precisely tune the flyby aimpoint. Why well in advance? Well, the same conjunction period would mess up the thing if the s/c ends up in a safe mode for days. So in any case, the TCM would be done BEFORE the flyby science and would not be jeopardized by the latter.
In case of a TCM performed AFTER the flyby, that also wouldn't present a problem as it would most likely be a cleanup maneuver and could be easily rescheduled with little delta-V expenses. Personally, I think the risk wouldn't be significant at all, but I'm not in charge of the mission and I can understand the mission folks-- a safe bet is a safe bet...

No, I do not believe so. Take a look at the overhead-view projection I posted. The illumination on the surface is form the uniformly bright hemisphere of the sky, no point source. Between clouds and rayleigh scattering, I do not believe the disk of the Sun is ever visible on the surface of Venus.

I'm planning to do a multiple-scattering montecarlo simulation of this soon, because I want to see if the color of the sky might be different. The spectrum of the Zenith was measured, and the panoramic cameras see some of the horizon, but it is not obvious that the two parts of the sky are the same color.

Click to view attachment

I generated this image a while ago, simulating scattering effects with data from Venus Standard Atmosphere. The image of Venus is rendered with 5 % of the actual density! That is because at full density, at this scale (200 km x 200 km squares), the true Venus atmosphere looks almost opaque near the surface.

I was merely following on Bruce's assumption. It did strike me a bit odd the sun would be visible through the thick cloud cover and enormous atmosphere.


This is awesome! This is the sort of rendering I see a lot of space simulation programs struggle to achieve (Celestia, Orbiter...). How did you produce this result and how computationally expensive was it?

Thanks. Actually, computer graphics research is my "day job". This was a special purpose renderer done in C++. It's a steadily growing program called "BookGraphics", which contains a large number of totally unrelated subroutines, each of which makes a figure for my book. :-)

Don:

You mentioned your book - can you tell us more about it, please? I'm sure it's one I *need* to buy!

Bob Shaw

I only now see this thread properly and - wow - I don't think I've ever seen the horizon on these Venera images (even though it's partly copied). Great job don!

I decided to write a book instead of just updating my website about the Soviet Exploration of Venus. I have a lot more material, photos and interviews with scientists, etc. I won't make back the money I've spent, which wasn't the point anyway. A problem with websites is they are not acknowledged officially, never reviewed, discussed or cited in the literature. You can't inject your work into the arena of public discourse unless you write a book, made out of paper and ink. Just a weird fact even in our modern times.

Verba volant, scripta manent.

TTT

Don:

Well, your website is a classic and one I've regularly visited, so I'm sure the book will be good!

Where are you in terms of publishers etc?

Bob Shaw

I'm writing and doing full layout now, and will look for a publisher when I've a book in hand.

Sometimes i read about lightning on Venus ,but what is the truth about that? Are there thunderstorms like we have here on Earth?

The question is still not completely resolved, but the evidence is mounting against Venusian lightning. The strongest item is that Cassini made a very sensitive check for radio bursts from lightning discharges during its second and last gravity-assist flyby of Venus and found nothing. And, from what we know of Venus' weather at this point, it seems unlikely that there are any strong storm-like phenomena in its cloud layers that could build up the sort of massive separation of electrical charge that is necessary to set up the conditions for a lightning bolt. (Its clouds seem to be quite rarified virtually everywhere.)

To repeat, though: the question isn't totally settled yet.

Great pictures Don P., and great posts. Here's to hoping we see more great pictures from future missions!

I confirm the images were reconstructed from RAW Russian Venera data given to me a long while ago...