Astroblog: The Mysterious Streaks in the Clouds of Venus. Clues to Life or Strange Cosmic Chemistry?

Friday, October 02, 2026

The Mysterious Streaks in the Clouds of Venus. Clues to Life or Strange Cosmic Chemistry?

To be read in conjunction with the tangent section of the astrophiz podcast #243

https://soundcloud.com/astrophiz/astrophiz-243-october-sky-guide-saturn-opposition-orionids-venus

This month as Venus swells in size and becomes a wire thin crescent, visible even in binoculars (although best seen at twilight as its brightness may cause reflection artifacts), let us reflect on its reflective atmosphere.

Seen through ordinary binoculars and telescopes, Venus is plain (almost blindingly) white and featureless, its surface eternally cloaked in clouds.

But if you put a (swingingly expensive) UV filter on your telescope, you can see structures in the clouds, dramatic dark and bright patterns moving with the planet's sulfuric acid clouds.

Venus in false colour from the Akatsuki UVI instrument
https://www.researchgate.net/figure/Global-view-of-Venus-in-ultraviolet-from-Akatsuki-May-2016-A-false-color-image-using_fig3_356985876

Astronomers have known about these bands for around a century, yet the chemical identity of the material responsible, the "unknown absorber", remains a mystery. In a recent study, an international team modeled the nature of the cloud droplets and the absorption characteristics. Venus's cloud droplets are approximately the size of cigarette smoke, and very effective at scattering light. The researchers concluded that to cause these dark patterns the droplets must be very dark, and from the characteristics of the UV absorption band, a likely candidate was an organic compound.

But, in the words of one of the researchers "If the observed light absorption is due to conjugated organic matter, the relatively sharp absorption profile is consistent with a chemically defined absorber that resists conversion into the tar-like mixture we typically observe with organics dissolved in concentrated sulfuric acid" https://scientificinquirer.com/2026/09/02/venuss-mysterious-clouds-may-hide-an-exceptionally-strong-light-absorber/

So what could this mysterious organic compound(s) be? Something with a defined structure that is stable in sulfuric acid?

Hot on the heels of the unknown absorber announcement comes the finding that peptides may persist in Venusian clouds. Peptides are short chains of amino acids that are not quite proteins. It was suspected that peptides would rapidly breakdown in sulfuric acid into the tar-like mixture mentioned above, but it turns out they don't. Peptides adopt stable omega-loop structures in concentrated sulfuric acid and hydrolysis is limited in nearly water-free acidic solutions like those in the clouds on Venus.

But this lead to another question, where do the peptides come from? With the surface the temperature of molten lead and a crushing atmosphere of sulfuric acid droplets, could there be any living things that could make these peptides?

Not on the surface, but perhaps high in the cloud deck, at around 50-60 Km above the surface the pressure is around 1 atmosphere and the temperature around 60°C. Life could possible find a home in the region. But it would be at the mercy of down drafts into the hotter regions below. However, the presence of updrafts could keep a microbial community circulating in the upper atmosphere.

After all, even on Earth there are microbial communities that thrive in hot high pressure systems around black smoker hydrothermal vents under crushing pressures, high temperatures and acidic conditions and can grow at temperatures of 90°C. In the more "temperate" regions of the upper cloud with temperatures around 60°C and pressures of around 1 earth atmosphere, microbial communities could find a home.

But is there any evidence for life as a potential source of peptides (or maybe the signature is from desiccated microbial spores)?

Remember phosphine (PH₃)? Back in 2020 it was allegedly detected in the atmosphere of Venus, and phosphine is a potential bio-signature, suggested for detecting life on exoplanets. It is hard to explain the existence of phosphine in Venus's atmosphere on geochemical processes. So there was much excitement.

However this was an extremely controversial claim, it was suggested that the detection was an artifact and the SOFIA infrared telescope mounted in a747 could not replicate the finding. Subsequently reanalysis of the Pioneer Venus Probe mass spectrometer in situ data from 1978 suggest the presence of phosphine at part-per-million (ppm) levels within the clouds, while the ALMA and JCMT data indicate 10-20 part-per-billion (ppb) levels above the clouds.

So at the moment there is plausible data the suggesting that organic material may be the "unknown absorber" possibly adding another line of support for life in Venus's atmosphere hinted at by phosphine. However, much more needs to be done with more sophisticated analysis and missions to Venus itself, rather than relying on inferences and modeling.

Ironically, as I was writing this another paper was published suggesting that the "unknown absorber" was due to metals from cosmic dust sinking into the cloud deck. The identity of the "unknown absorber" and the possibility of life on Venus remains unresolved and will have to await future missions to Venus. whatever the outcome, this will refine our ability to look for bio-signatures on exoplanets.

Labels: Astrophiz, bio-signatures, life, Venus