Researchers have confirmed that mysterious haze particles in Venus’ atmosphere are composed of cosmic dust, specifically iron sulfate.
Solving the Mystery of the Ultraviolet Absorber
For decades, scientists have grappled with the identity of a mysterious substance in Venus’ clouds that absorbs ultraviolet light. While researchers previously speculated that iron compounds might be responsible, these theories remained unconfirmed for years. New evidence shows that iron sulfate matches the properties of the haze, finally identifying the source of the absorption. Venus is very dry by Earth standards, but its atmosphere does contain some water in the form of vapour beneath its cloud layer. Venera and the Vega probes had previously detected atmospheric iron, while the mass spectrometer aboard the Pioneer Venus Large Probe found the compound iron sulfate, though these discoveries eluded explanation for decades.
The discovery relies on the behavior of particles between 40 and 50 kilometers (about 25 to 31 miles) above the surface. At this altitude, condensation is not possible because the high energy of the particles creates a nucleation barrier that does not allow droplets of sulfuric acid to stick to their surface. While previous observations had suggested this, the team now has stronger evidence. This process explains how ultraviolet-dark material, produced beneath the cloud tops, is forced upward through the atmosphere, according to data from the Venus Express satellite.
The Role of Aphrodite Terra and Atmospheric Circulation
The movement of materials within Venus’ atmosphere is deeply tied to the planet’s rugged surface. One primary instance involves an area situated over the Aphrodite Terra mountain range, which reaches an elevation of 4,500 meters. We used observations from Venus Express spanning a period of six years, from 2006 to 2012, which allowed us to study the planet's longer-term weather patterns,
noted Jean-Loup Bertaux of LATMOS (Laboratoire Atmosphères, Milieux, Observations Spatiales) near Versailles, France, and lead author of the new Venus Express study.
This mountain range forces water-rich air from the lower atmosphere upward, creating a distinct weather pattern. Håkan Svedhem, Venus Express Project Scientist at the Directorate of Science, European Space Agency, noted that knowing more about Venus’ circulation patterns may help to constrain the identity of the planet’s mysterious ultraviolet absorber.
Implications for Planetary Science
The identification of cosmic dust as a key component of Venus’ haze offers a new framework for understanding other planets. Upper hazes on gas giants have been studied repeatedly, but microphysical processes beneath the main cloud layer remain an enigma, and Venus may have shed light on at least some of the secrets of haze.
According to the team’s findings published in Nature Astronomy, further studies could give more insight into how cosmic dust promotes cloud and haze formation on planets across the solar system. Similar to the situation on Venus, monitoring metal layers within the atmospheres of outer planets would assist in calculating metal deposition rates and, consequently, the density of the resulting haze. Cosmic dust is therefore established as a vital factor in planetary climates, a function that likely extends to exoplanets as well.