Venus’s pale yellow clouds may hide something surprisingly dark

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.

Now, an international team of researchers has placed new numerical limits on what this mysterious material must be like. Using observations of Venus together with radiative-transfer modeling, the scientists estimated how strongly the liquid inside the planet's cloud droplets would need to absorb ultraviolet and blue light to match what spacecraft and telescopes observe.

The study, published in Astrobiology , examined the problem in an unusual way. Lead author Dr. Jan Spacek asked what Venus's cloud material might look like if the droplets could somehow be collected into a spectrometric cuvette and studied as a bulk liquid.