The veil floating beneath Venus’s clouds could have an unexpected origin.
Probes sent to Venus detected a layer of very small particles beneath the main clouds as early as the 1970s. This haze is found mainly below an altitude of about 47 km. Its origin remained unknown.
Two treatments of an image of Venus taken by Mariner 10: on the right, enhanced contrast reveals more structures in the cloud cover.
Credit: NASA/JPL-Caltech.
The researchers incorporated its formation directly into a model describing the atmosphere’s small particles. Their scenario begins with cosmic dust that constantly falls onto Venus. The tiny grains arriving from space heat up dramatically as they enter the atmosphere, vaporize, and then reform into extremely small mineral particles.
These particles then become embedded in sulfuric acid clouds. As they descend toward warmer layers, the sulfuric acid evaporates. The small mineral cores are left alone, encounter one another, and stick together. Their accumulation gradually forms the haze observed beneath the clouds.
The result is particularly convincing because the model reproduces the size of the particles measured by the old probes. The calculations show that a continuous supply of space dust is enough to maintain the observed layer.
Artist’s view of the DAVINCI probe descending through Venus’s atmosphere above Alpha Regio.
Credit: NASA Goddard Space Flight Center.
These grains also play a role higher in the atmosphere. They provide surfaces on which sulfuric acid can condense, facilitating cloud formation. In the simulations, their presence increases the amount of clouds produced by about 20 to 30% compared with a model without this supply.
A second mystery may also be starting to find an explanation. Venus’s atmosphere strongly absorbs part of the ultraviolet radiation, although the responsible substance has not yet been clearly identified. Cosmic dust contains iron and magnesium, among other elements. The researchers believe that certain iron compounds could contribute to this absorption.
The mechanism could extend beyond Venus. Dust from space also falls onto giant planets and other worlds surrounded by a thick atmosphere. It may therefore contribute to the formation of hazes and clouds there as well.
New measurements will be needed to directly verify this origin. The researchers are particularly counting on future probes capable of analyzing the atmosphere during their descent. NASA’s DAVINCI mission is specifically intended to study the composition of Venus’s atmosphere in detail during a future dive toward the surface.