A mystery from the seventies

The Venera and Pioneer Venus probes discovered a yellowish lower haze at the bottom of Venus' atmosphere in the nineteen seventies. The haze remained unexplained for decades until now.

Cosmic dust solves the puzzle

Planetary scientist Hiroki Karyu and his team at Tohoku University in Sendai City, Japan, discovered the haze is an accumulation of particles from meteorites. Shooting stars that burn up leave behind cosmic dust.

How the haze forms

After sulfuric acid interacts with cosmic dust particles, it leaves behind a haze. Karyu used a microphysical model involving micro-scale processes that create clouds and precipitation on planets.

Not volcanic ash

Previous speculation suggested the haze formed from volcanic ash. Venus is the most volcanically active planet in our Solar System, but Karyu found that volcanic ash is not the source of haze particles.

Cosmic dust acts as nuclei

Karyu said the continuous influx of cosmic dust sustains the lower haze layer. These haze particles act as efficient condensation nuclei, promoting cloud formation in the main cloud deck.

“The continuous influx of cosmic dust is sufficient to sustain this lower haze layer with the particle size distribution observed by the entry probes.”

Meteorites burn and scatter

When space rocks are pulled in by Venus' gravity, they shoot through the atmosphere and encounter gas particles causing friction. The meteorites burn up and leave a trail of particles hovering over Venus.

Particles cluster and sink

Meteorite particles increase cloud production on Venus, but more particles do not mean more cloud droplets. Several particles stick together and form larger clusters before sulfuric acid condenses around them.

Iron solves UV mystery

The discovery unexpectedly solved another mystery: something in Venus' atmosphere had been absorbing ultraviolet rays. Meteorites contain metals including magnesium, silicon, and iron. Iron sulfate matched the haze's properties.

Implications for gas giants

Upper hazes on gas giants have been studied extensively, but microphysical processes beneath the main cloud layer remain an enigma. Venus may have shed light on secrets of haze on Jupiter, Saturn, and Neptune.

Cosmic dust shapes planetary climates

Karyu said observing metal layers in the atmosphere of outer planets would help determine deposition rates of metals and resulting haze abundances. Cosmic dust is an essential component of planetary climates.

“These effects establish cosmic dust as an essential component of planetary climates, a role that is also likely to be important for exoplanets.”