Could Dark Streaks in Venus' Clouds Be Signs of Alien Life?

The question of life on Venus, of all places, is intriguing enough that a team of U.S. and Russian scientists working on a proposal for a new mission to the second planet — named Venera-D — are considering including the search for life in its mission goals.

If all goes as planned, an unmanned aerial vehicle (UAV) could one day be cruising the thick, sulfuric-acid clouds of Venus to help determine whether dark streaks that appear to absorb ultraviolet radiation could be evidence of microbial life.

Venus has long been a focus of Russian planetary science, which has the proud legacy of the record-breaking Venera space probes that landed on the Venusian surface in the late 1970s and early 1980s.
With many questions remaining unanswered, the joint mission of Roscosmos and NASA, if approved, would see an orbiter launch toward Venus in 2025 with the aim to make remote-sensing observations of the planet and its atmosphere; deploy a lander on the surface; and search for future landing sites.


Among several possible additions to the mission are a small sub-orbiter to study Venus' magnetosphere, and either a balloon or an UAV taking measurements of the atmosphere over a long duration.

Should the UAV be approved, its main goal would be to take meteorological measurements to determine why the atmosphere rotates so fast relative to the surface, a phenomenon known as super-rotation. This fast rotation was discovered in the 1960s by astronomers tracking the motion of the dark streaks in the atmosphere. Puzzlingly, astronomers do not know the origin and composition of these dark streaks, nor do they understand why the streaks haven't mixed with the rest of the atmosphere and why they are absorbing ultraviolet light.

"These are questions that haven't been fully explored yet, and I'm shouting as loud as I can, saying that we need to explore them," said Sanjay Limaye, an atmospheric scientist from the University of Wisconsin, Madison and a former chair of NASA's Venus Exploration Analysis Group (VEXAG).

According to Limaye, the nature of the UV absorber is completely unknown. It could be particulate matter mixed into the clouds, or a substance that has been dissolved by the droplets of sulfuric acid, or it may be crystalline in nature, like ice. Iron chloride has been proposed, but there is no confirmed mechanism that could loft particles of iron chloride 31 to 37 miles (50 to 60 kilometers) above the surface, particularly as winds near the surface only blow weakly through the dense lower atmosphere.


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