Guest post by John Tillman

Disulfur Dioxide, the Solar Cycle and Cosmic Rays in the Venusian Atmosphere

In 1928, Yerkes Observatory astronomer and physicist Frank Ross published a journal paper, “Photographs of Venus”.  It reported finding in the Venusian atmosphere a strong absorption between 320 and 400 nm, ie in the near-UV, just overlapping light visible to humans.  The observation of dark patches has since been repeatedly confirmed both from Earth and space.

The identity of the UV-absorber remained incognito for 90 years, and the now leading candidate is still not universally accepted.

Among the hypotheses seeking to explain the absorber is ET atmospheric microbes, probably first suggested by the astonomical Dr. Carl Sagan and biophysicist Harold Morowitz in their 1967 Nature article “Life in the Clouds of Venus?”.  (The previous year, then Lynne Sagan had proposed that mitochondria are endosymbiotic bacteria.  This was a young couple welcoming academic notoriety.)

After 50 more years of observations by short-lived landers and long-orbiting probes, three researchers from the University of Copenhagen (home town of GCR-proponent Henrik Svensmark) and Cal Tech proposed a more conventional, chemical solution to the enigma.  Their 2016 study positing isomers of disulfur dioxide as the mystery absorber is not pay-walled:

https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2016GL070916

Identification of OSSO as a near‐UV absorber in the Venusian atmosphere

“The planet Venus exhibits atmospheric absorption in the 320–400 nm wavelength range produced by unknown chemistry. We investigate electronic transitions in molecules that may exist in the atmosphere of Venus. We identify two different S2O2 isomers, cis‐OSSO and trans‐OSSO, which are formed in significant amounts and are removed predominantly by near‐UV photolysis. We estimate the rate of photolysis of cis‐ and trans‐OSSO in the Venusian atmosphere and find that they are good candidates to explain the enigmatic 320–400 nm near‐UV absorption. Between 58 and 70 km, the calculated OSSO concentrations are similar to those of sulfur monoxide (SO), generally thought to be the second most abundant sulfur oxide on Venus.”

This hypothesis soon enjoyed confirmation:

https://www.ncbi.nlm.nih.gov/pubmed/29532825 

The near-UV absorber OSSO and its isomers.

“Disulfur dioxide, OSSO, has been proposed as the enigmatic “near-UV absorber” in the yellowish atmosphere of Venus. However, the fundamentally important spectroscopic properties and photochemistry of OSSO are scarcely documented. By either condensing gaseous SO or 266 laser photolysis of an S2O2 complex in Ar or N2 at 15 K, syn-OSSO, anti-OSSO, and cyclic OS([double bond, length as m-dash]O)S were identified by IR and UV/Vis spectroscopy for the first time. The observed absorptions (λmax) for OSSO at 517 and 390 nm coincide with the near-UV absorption (320-400 nm) found in the Venus clouds by photometric measurements with the Pioneer Venus orbiter. Subsequent UV light irradiation (365 nm) depletes syn-OSSO and anti-OSSO and yields a fourth isomer, syn-OSOS, with concomitant dissociation into SO2 and elemental sulfur.”

Not everyone is convinced, however.  There are still holdouts for cloud-dwelling organisms, as argued for in other recent studies.  At the very least, the ET life hypothesis might help sell space missions to explore the dense, sulfuric acidic Venusian atmosphere.

However, an August 2019 Astronomical Journal paper by Lee, et al., notes that the (possibly still) unknown absorber shows a marked correlation with the solar cycle and cosmic ray flux modulated thereby.  The University of Wisconsin=Madison (Yerkes’ state) press report on the paper below is surprisingly good:

https://news.wisc.edu/mysterious-cloud-absorbers-seen-to-drive-venusian-albedo-climate/

Here is the paper itself, again blessedly open-access:

https://iopscience.iop.org/article/10.3847/1538-3881/ab3120

Long-term Variations of Venus’s 365 nm Albedo Observed by Venus

Express, Akatsuki, MESSENGER, and the Hubble Space Telescope

“An unknown absorber near the cloud-top level of Venus generates a broad absorption feature from the ultraviolet (UV) to visible, peaking around 360 nm, and therefore plays a critical role in the solar energy absorption. We present a quantitative study of the variability of the cloud albedo at 365 nm and its impact on Venus’s solar heating rates based on an analysis of Venus Express and Akatsuki UV images and Hubble Space Telescope and MESSENGER UV spectral data; in this analysis, the calibration correction factor of the UV images of Venus Express (Venus Monitoring Camera) is updated relative to the Hubble and MESSENGER albedo measurements. Our results indicate that the 365 nm albedo varied by a factor of 2 from 2006 to 2017 over the entire planet, producing a 25%–40% change in the low-latitude solar heating rate according to our radiative transfer calculations. Thus, the cloud-top level atmosphere should have experienced considerable solar heating variations over this period. Our global circulation model calculations show that this variable solar heating rate may explain the observed variations of zonal wind from 2006 to 2017. Overlaps in the timescale of the long-term UV albedo and the solar activity variations make it plausible that solar extreme UV intensity and cosmic-ray variations influenced the observed albedo trends. The albedo variations might also be linked with temporal variations of the upper cloud SO2 gas abundance, which affects the H2SO4–H2O aerosol formation.”

While the hypothesis that GCRs affect cloud formation, weather and climate, modulated by the solar cycle, is heretical to consensus “climate science” for planet Earth, apparently it’s respectable for Venus.

Study co-author, UWM planetary scientist Sanjay Limaye, notes, “The difference between Earth and Venus is that on Earth most of the energy from the sun is absorbed at ground level while on Venus most of the heat is deposited in the clouds”. 

So, while Venus’ hellish heat has generally been attributed to an ancient runaway greenhouse effect, the GHE no longer works on Venus as it allegedly does on Earth.  Due to high albedo and absorption in the dense, cloudy atmosphere, very little light makes it to the surface.  In in any case, the ground is so hot that it doesn’t even radiate in the peak wavelength bands of CO2.If I can find the time and am permitted to do so, I’d like to discuss an alternative scenario for the history of our planet’s fraternal twin when Venus was young.  The consensus is that for up to two billion years, Venus had liquid water on its surface, as some evidence suggests.  But it’s possible that the planet was always too hot for seas to form, even presuming initially high atmospheric pressure.  The RGHE hypothesis is based upon evaporating or even boiling water (as per Jim Hansen), not CO2.  The alternate hypothesis supposes loss of hot atmospheric water vapor rather than liquid from the surface.

Both hypotheses remain speculative until more probes and especially landers can explore our evil twin’s world.  Characterized as straight out of a “steam-punk” fantasy, NASA is designing a tough, back-to-the-future analog, tracked rover with a mechanical computer capable of surviving the hostile Venusian land conditions.

https://www.jpl.nasa.gov/news/news.php?feature=6933

A Clockwork Rover for Venus

An airship craft to search for ET extremophiles in the clouds might be less challenging for space engineers.