Though they’re very totally different immediately, Venus, Earth, and Mars had been very comparable of their youth. All three had been heat, with thick, water-rich atmospheres. However over time, Mars turned a chilly, dry planet with a skinny environment, and Venus turned superheated, with a crushing, poisonous sky. Solely Earth turned a heat ocean world teeming with life. However why?

We all know that Mars as soon as had huge seas. It had the best situations for all times at first, however with much less gravity than Earth and a weak magnetic area, Mars misplaced a lot of its environment over time, and most of its water both froze beneath the floor or turned chemically locked in Martian clay. If Mars had been bigger and extra geologically energetic, maybe it could have change into one other residing world.

Which raises the query of Venus. When it comes to mass and composition, Venus appears to be almost a twin of Earth. Its floor gravity is 90% of Earth’s. Whereas it doesn’t have a powerful magnetic area like our world, it’s geologically energetic. We will even see proof of volcanic exercise on its floor. Venus additionally retained a thick environment, so why is it a hell-world in comparison with Earth?

The commonest mannequin of early Venus is that the planet was Earth-like as soon as. Its water-rich environment would have rained upon the floor to create heat seas and rivers, identical to Earth and Mars. Some fashions counsel that Venus might have been Earth-like till 700 million years in the past. However finally, both due to its proximity to the Solar, a scarcity of magnetic area, or some geological course of, Venus underwent a greenhouse transformation. Its oceans dried, and its environment thickened to change into the lethal world we see immediately. Maybe we on Earth ought to take a look at Venus as a cautionary story of what occurs when greenhouse gases dramatically improve.

However new analysis argues that Venus was by no means a moist world. Whereas it did have a water-rich early environment early on, it by no means retained the water, and seas by no means shaped on our planetary sibling.

The research begins by calculating the speed at which water, carbon dioxide, and different molecules are decomposed inside the environment. Ultraviolet radiation hanging the higher environment in addition to chemical interactions can break aside these molecules. To keep up secure ranges of water, for instance, it have to be replenished by way of volcanic exercise.

On Earth, the volcanic gases launched are principally water vapor as a result of Earth’s inside is wealthy in water. This permits our planet to switch water that decomposes in our higher environment. However the inside of Venus is way more dry, with solely 6% of the gases being water vapor. The remainder is generally carbon dioxide and sulfur compounds. On this mannequin, the composition of volcanic gases is the primary driver of how a planet’s environment evolves, not the preliminary composition of the environment. So, with little volcanic exercise, the environment of Mars thinned. With dry, sulfur-rich volcanic gases, Venus turned a greenhouse world. With water-rich volcanic gases, Earth remained an ocean planet.

Presently, there may be proof for each evolutionary fashions on Venus, and neither could be dominated out. Future initiatives akin to NASA’s DAVINCI mission might give us a richer view of the Venusian environment, however till then, it stays to be seen whether or not the destiny of a planet is written in its rock or its sky.

Reference: Constantinou, Tereza, Oliver Shorttle, and Paul B. Rimmer. “A dry Venusian inside constrained by atmospheric chemistry.” Nature Astronomy (2024): 1-10.