Culture

Astronomy for Beginners: Venus

By Duncan Lunan

The grammatically correct adjective relating to Venus and derived from Latin would be  ‘Venereal’, like ‘Jovial’, like ‘Martial’, ‘Mercurial’, ‘Saturnine’, the words used by Jonathon Norton Leonard in “Flight into Space”  (Sidgwick & Jackson, 1953).   But all of them have hangover meanings from the remnants of astrology, so the rest of us use the ungrammatical modern versions when talking about the actual planets.  ‘Venusian’ is a particularly unattractive one and ‘Cytherean’ isn’t much better, but it’s sufficiently obscure that most modern writers say ‘Venusian’ anyway.

Views of Venus from Mariner 10 credit image NASA

Although it can be seen in daylight if you know exactly where to look, Venus is the morning and evening star, generally seen in twilight and hardly ever against a truly black sky.   Through a telescope no markings can be seen because the planet is covered by dense clouds, but it can be followed through its phases  (like the Moon’s)  which proved to Galileo that Venus was orbiting the Sun, not the Earth.

Venus’s orbit is virtually circular, and because it’s the closest planet to us at 63 million miles from the Sun, its orbit is in a recurring resonance with ours.  When its rotation was measured by radar, it proved to be longer than the planet’s year and retrograde, turning in the opposite direction to almost all the planets and moons in the Solar System.  That makes its surface almost tidally locked with Earth, keeping virtually the same face towards us, and it’s not known whether that is merely a coincidence.     

There are longer cycles in the motion of Venus and these were tracked by Maya astronomers, who worshipped Venus as the god Quetzalcoatl  (one of the few cultures not to regard Venus as feminine.)   One of the openings in the Caracol observatory at Chichén Itzá in Yucután is aligned with the northernmost setting of Venus, for their time, 1000 AD.  Venus’s extreme setting position is the most northerly of any planet in the Solar System, made possible because it’s the closest planet to us, and will be reached in 28,000 years.  An alignment to that is incorporated into the ‘Sunstones II’ sculpture by Prof. Richard O’Hanlon and Dr. David Cudaback, outside the Lawrence Hall of Science at the University of California at Berkeley.  It’s a little optimistic to suppose that it will still be accurate then:  at the foot of the hill is a football stadium whose two halves have not lined up since the earthquake of 1906.

In his books “Worlds in Collision” et seq, Immanuel Velikovsky maintained that somewhere c. 1500 BC, Jupiter exploded and released a comet which sterilised Mars, wrecked Earth and became the planet Venus.  Dynamically, it isn’t possible for something the size of Venus to escape intact from something the size of Jupiter;  even the old idea that the Moon split off from the proto-Earth is dynamically impossible  (it would be torn apart by tidal forces).   Although Velikovsky insisted there are no records of Venus prior to 1500 BC, there’s an unbroken sequence of Venus images in Mesopotamian art going back to 4000 BC.   Velikovsky enthusiasts make much of his prediction that the Venus surface would be hot, but he said it would be due to burning oil, not to a runaway greenhouse effect which is the reality  (see below).  And although the Magellan probe’s detailed radar mapping showed that the surface of Venus has been resurfaced by volcanic activity in the geologically recent past, in this case that means the last ten million years.  (David Harry Grinspoon, “Venus Revealed”, Helix, 1997.)   There is considerable evidence for catastrophe in the inner Solar System between 3000 and 2000 BC, including an impact in Iraq which gave rise to the Flood legend, but this is probably due to the break-up of a super-comet from the outer System.  (Victor Clube and Bill Napier, “The Cosmic Serpent”, Faber, 1982).

As noted earlier, neither Venus and Mercury can have permanent moons, because they’re too close to the Sun.  In our Solar System, the ecosphere  (where surface liquid water can exist and surface life would be possible)  extends roughly from the orbit of Venus to the orbit of Mars, though Mars is too small to be habitable and Venus rotates too slowly.  In fact Venus may have had oceans in its early history, but its day is longer  than its year, and the seas boiled on the side facing the Sun.  The greenhouse effect of water vapour is much stronger than carbon dioxide’s, and on Venus it melted the crust of the planet, triggering violent chemical reactions with the molten rock which created the hostile conditions on Venus today.   But now we know that Mars and probably Venus had oceans in their early history.  Had Venus rotated  more rapidly, had Mars been more massive, they might still be habitable today.  

The Surface of Venus

In the early 20th century it was thought that the clouds of Venus were water vapour and it might sustain life, possibly as an earlier form of Earth with dinosaurs;  or be covered in ocean and have a marine civilisation.  True Venus conditions, as we now know, are even more extraordinary and somewhat less inviting.  The atmosphere is almost all carbon dioxide.  At the surface of Venus pressure is 91 atmospheres, equivalent to three-quarters of a mile underwater on Earth, and in a story I wrote for Sydney Jordan’s Lance McLane strip in the Daily Record, I made use of that to have a Venus lander under test on the ocean floor off Easter Island.  On Venus, however, surface temperature is over 600o C, and no lander so far has lasted more than about 90 minutes.  Venus has been almost completely resurfaced by volcanic outflows within the last few million years, and that may partly explain why the clouds, which look so pure and white from here, are actually an orange smog of sulphuric acid droplets.  (Who, guessing, would have made such an obvious schoolboy choice?)     There’s disagreement over whether it actually rains sulphuric acid on the surface, but Soviet missions detected what seem to be huge lightning storms around the high volcanic plateaux.

The Venus crust is 60 miles thick, yet impact craters are shallow, as they are on the large moons of Jupiter;  this led to hypotheses about ‘crustal rebound’, which did occur on a large scale at Chicxulub off Yucutan in the impact which wiped out the dinosaurs.  Venus has a nickel-iron core like Earth’s but rotates very slowly indeed  (243 days), and has no magnetic field;  so the Solar Wind impinges directly on the upper  atmosphere, generating a bow shock, and perhaps some phenomena on the dark side.  Venus has one called the ‘Ashen Light’,  reported by amateur astronomers and argued about by professionals.  But not aurorae as we know them, the legendary spirits of dead warriors dancing in the northern sky. 

In the book “Flying Saucers Have Landed”  (Werner Laurie, 1953, principal author Desmond Leslie), George Adamski claimed to have met beautiful people in a flying saucer, Venusians who were blonde, beautiful telepaths, terribly concerned about the things we do to our planet.   If they were genuinely from Venus, we should be more worried about what they’ve done with theirs.

Mariner

Mariner 2, the first successful interplanetary probe, which reached Venus in 1962.  The Mariner probes were designed to be launched by the Atlas booster with the liquid hydrogen Centaur upper stage, later used successfully to launch Mariners 4 to 9.  But Centaur initially generated major technical problems and to meet the 1962 launch window the Jet Propulsion Laboratory created two smaller Mariner-R probes, based on the Ranger lunar series.  Mariner 1 went off-course during launch and had to be destroyed because of a ‘missing hyphen in the guidance programme’ – an expression which became proverbial and is often quoted by enemies of space research, invariable claiming that it has only just happened and has cost ‘billions of dollars’, a thousand times more than any space probe to date.  

The first close-up images of Venus were taken by Mariner 10 on its way to Mercury, and they revealed that the faint C- and V-shaped markings occasionally reported by observers were part of a much bigger atmosphere circulation system which was much more prominent in ultraviolet light.  It’s since been found to absorb 98% of the ultraviolet light which falls on Venus from the Sun, and it’s even been suggested that it might be some form of life, ‘not as we know it’, able to survive in the sulphuric acid smog of the clouds and perhaps driving their rotation.  In 2020 British scientists announced the detection of phosphine in the Venus clouds, in quantities suggesting the presence of life;  the finding has been challenged, but appears to be confirmed by a review of data from the Pioneer Venus Main Entry Probe in 1978.  The atmosphere rotates much faster than the planet, in just four Earth days instead of 243, and the dark bands come round from the night side in parallel streams, split to north and south of the high-pressure area at the sub-solar point, and spiral up to the poles  (M360).   Pioneer-Venus and Magellan imaged the north polar vortex, and in 2006 Venus Express confirmed that there’s a similar one at the south pole.  (David Powell, ‘Venus Does the Twist’, Astronomy Now, June 2006.)

Radar mapping by Pioneer Venus Orbiter made it appear that most of the surface was a single huge granitic plate, still preserving the crater record of the bombardment phase of the Solar System’s early history.  It now seems from Magellan that the surface has been flooded by much more recent lava flows.  It had seemed that the crustal material was much thicker than Earth’s and where volcanic action had forced basaltic rock through it, it came from greater depths than on Earth and the mountains and plateaux formed rose to greater heights.  There are several major volcanic plateaux, and the highest peak, twelve miles tall, is a curious anomaly.   It was named after James Clerk Maxwell, before the International Astronomical Union decreed that all other features on Venus should be named after famous women.   Unfortunately, apart from the three volcanic plateaux, surface relief on Venus is extremely low, so all the features named after women are lying prone around the towering elevation named after a man.  

During the Magellan probe’s radar mapping of Venus, however, I was contacted by the Glasgow Herald, asking why NASA wanted to name a crater on Venus after Mary Queen of Scots.  I gave the obvious answer, in Scots, that maybe the poor cratur deserved it… but I had to explain that under the rules of the International Astronomical Union, everything on Venus in supposed to be named after famous women.  I have often wondered, when we name features on the planets after people, whether their ghosts move there to haunt them.  Mary might well deserve our sympathy then, since the surface of Venus – aptly described by Carl Sagan as ‘Hell’ – must be a sight less congenial than Fotheringay.  

What prompted the Herald’s call was that the historian A.L. Rowse had objected to NASA’s nomination, arguing that if anything on Venus was to be named after a famous woman of that period, it had to be Elizabeth I.  To that I was able to reply that in order to have a Solar System feature named after you, you have to be dead, preferably for a century – and as all good Scots know, Elizabeth I is still on the throne to this day.

The Magellan mapping showed the highest peaks on Venus to be highly reflective, possibly due to caps of iron pyrites, ‘fool’s gold’ – perhaps looking like the original toppings of the Egyptian pyramids.  (“Venus Unveiled”, op cit.)  Whether they have gales is another matter.   Given the very high atmospheric pressure, winds of even ten miles per hour could be as erosive as coastal waves on Earth.  The main body of Venus’s atmosphere rotates much faster than the planet itself, but the shear zone is at the base of the clouds, 20 miles up, and the measured winds below that have been only 1-2 mph.  Nevertheless the Magellan radar maps show clearly what seem to be wind streaks in some regions, suggesting that powerful winds do blow on the surface at least from time to time.

Landing on Venus

Landing probes have survived only for an hour or two.  Balloon exploration of the atmosphere has already begun with French payloads, released by the Soviet Vega probes in their Venus slingshots en route to Halley’s Comet.  But their lifetimes were short, and they were at the 1-atmosphere pressure level, up in the acid clouds and out of sight of the surface.   At the surface, the high pressure and density of the atmosphere make flight absurdly easy:  using only wings, without any form of lifting cells, a given vehicle would require only 2% of the lifting surface needed for the terrestrial equivalent  (S.W. Greenwood, ‘Extraterrestrial Atmosphere Transport Considerations’, Journal of the British Interplanetary Society, Feb. 1974).  Using lift cells filled with helium, the gas lifting volume would be 1.6% that of a corresponding dirigible on Earth.  To cruise at a given speed, 3.4 times the propulsive thrust on Earth would be needed.  As there’s no chemical energy available for propulsion in a carbon dioxide atmosphere, electrical propulsion would have to be used – probably propellers.   In theory, for launch from the Venus surface to orbit a booster would be only slightly smaller than its terrestrial counterpart.  But since a dense surrounding medium slows down the exhaust gases of a jet or rocket exhaust and so reduces the reaction thrust, a Venus booster or shuttle would have to be scaled up by a factor of 2 to 4.  

At the base of the clouds the temperature is 500 degrees K, a full 200 degrees lower than on the surface, and pressure is 7.5 atm.   The cloudbase is ragged and turbulent, but the Pioneer-Venus entry probes reported that below the clouds, below 30 km altitude, the atmosphere was ‘immaculately clean’.  However, this may just have been a particularly clear day, because the Venera 11 and 12 entry probes reported acid strata lower down, dense enough to fall as rain  (J. Kelly Beatty, ‘Pioneers’ Venus:  More than Fire and Brimstone’, Sky & Telescope, July 1979).  Pioneer-Venus also detected flares in the lower atmosphere which seemed to be ‘chemical fires’ on or near the surface;  though what those could be, in such conditions, remains unknown  (‘New Light on Venus’, Spaceflight, Jan. 1980).

The Venera probes detected intense lightning activity and Pioneer Venus Orbiter located it at two mountainous, volcanic features, implying that they were active at the time.  According to Veneras 11 and 12 the lightning frequency reached 25 strikes per second, and in 91 atmospheres’ pressure the shockwaves from lightning bolts or volcanic outbursts would act like depth-charges.  For Sydney Jordan’s Lance McLane strip in the Daily Record I designed a Venus lander like an armoured bathyscaphe, and subsequently published its details in an article with Gordon Ross for Analog  (‘Flight in Non-terrestrial Atmospheres, or the Hang-glider’s Guide to the Galaxy’, January 1993), but it won’t be flying there any time soon.

Backup hardware for the European Space Agency’s Mars Express was used to create Venus Express, launched in 2005 and deorbited when its fuel ran out in 2014. Venus Express detected water vapour in the lower atmosphere of the planet, heightening the speculation that the mysterious dark streaks in the clouds may be some form of airborne life.  It has now been followed by the Japanese Akatsuki, which reached Venus in 2015 after an adventuruous journey, and is now finding more and more intriguing features in the Venus cloud layers.  The plot, and the mist, thickens!

To read more about Venus click on this link: NASA Science

When flying past Venus in July 2020, Parker Solar Probe’s WISPR instrument, short for Wide-field Imager for Parker Solar Probe, detected a bright rim around the edge of the planet that may be nightglow — light emitted by oxygen atoms high in the atmosphere that recombine into molecules in the nightside. The prominent dark feature in the center of the image is Aphrodite Terra, the largest highland region on the Venusian surface. Bright streaks in WISPR, such as the ones seen here, are typically caused by a combination of charged particles — called cosmic rays — sunlight reflected by grains of space dust, and particles of material expelled from the spacecraft’s structures after impact with those dust grains. The number of streaks varies along the orbit or when the spacecraft is traveling at different speeds, and scientists are still in discussion about the specific origins of the streaks here. The dark spot appearing on the lower portion of Venus is an artifact from the WISPR instrument. Credits: NASA/Johns Hopkins APL/Naval Research Laboratory/Guillermo Stenborg and Brendan Gallagher

See also: The Sky Above You – June 2021

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