Day-night cloud asymmetry prevents early oceans on Venus but not on Earth

TL;DR

This study uses 3D climate models to show that cloud asymmetry on early Venus prevented water condensation, explaining why Venus remained dry, while Earth’s conditions allowed oceans to form under lower insolation levels.

Contribution

It demonstrates the critical role of night-side cloud formation in inhibiting water condensation on Venus, a factor not captured by previous 1D models.

Findings

Water clouds on early Venus prevented surface water condensation.

Earth's oceans could form at lower insolation levels due to faint young Sun.

Venus likely remained dry because of cloud-induced warming effects.

Abstract

Earth has had oceans for nearly four billion years and Mars had lakes and rivers 3.5-3.8 billion years ago. However, it is still unknown whether water has ever condensed on the surface of Venus because the planet - now completely dry - has undergone global resurfacing events that obscure most of its history. The conditions required for water to have initially condensed on the surface of Solar System terrestrial planets are highly uncertain, as they have so far only been studied with one-dimensional numerical climate models that cannot account for the effects of atmospheric circulation and clouds, which are key climate stabilizers. Here we show using three-dimensional global climate model simulations of early Venus and Earth that water clouds - which preferentially form on the nightside, owing to the strong subsolar water vapour absorption - have a strong net warming effect that inhibits surface water condensation even at modest insolations (down to 325 W/m2, that is, 0.95 times the Earth solar constant). This shows that water never condensed and that, consequently, oceans never formed on the surface of Venus. Furthermore, this shows that the formation of Earth's oceans required much lower insolation than today, which was made possible by the faint young Sun. This also implies the existence of another stability state for present-day Earth: the 'Steam Earth', with all the water from the oceans evaporated into the atmosphere.