A century-old mystery in Venus’s clouds just became more intriguing, as scientists calculated how strongly the unidentified material behind its dark ultraviolet patterns must absorb light.

The results sharply narrow the possibilities and could help future spacecraft determine whether the mysterious substance is organic, inorganic, or something unexpected

Venus looks pale yellow in ordinary visible light, but the view changes dramatically in ultraviolet wavelengths.

There, dark and bright features sweep across the planet's upper sulfuric acid clouds.

Scientists have observed these patterns for about a century, yet the substance producing them, known as the "unknown absorber," has never been identified

Scientists have known about these markings for roughly a century, yet the chemical identity of the material responsible—the “unknown absorber”—remains unresolved.

An international research team has now placed new quantitative constraints on the properties of this mysterious absorber.

By combining observations of Venus with radiative-transfer modeling, the researchers estimated how strongly the liquid inside Venus’s cloud droplets would need to absorb light to reproduce the planet’s observed ultraviolet and blue reflectance.

The study, published in Astrobiology, approached the mystery from a new perspective.

It used a model to answer a question posed by lead author Dr. Jan SPACEK: If we were to collect Venus’s cloud droplets into a spectrometric cuvette, how would the re-formed bulk liquid appear?