Venus may have been habitable until 700 million years ago
Detailed maps of its surface from over 40 years of space probes indicate the existence of a shallow ocean of water
Despite Mercury being the closest to the Sun, Venus is the hottest planet in our Solar System due to the transformation that changed its atmosphere radically somewhere in the past. The average surface temperature of 462° C (864° F) of Venus can melt Lead. Add to this a dense atmosphere containing 96.5% carbon dioxide with sulphuric acid downpours, the hell exists literally next door in astronomical terms.
A recent study by the researchers, Michael Way and Anthony Del Genio of the Goddard Institute for Space Science (GISS) has concluded that things were not always as bad as they look today. On the contrary, Venus might have sustained liquid water for two or three billion years before runaway greenhouse effect changed things dramatically.
“Something happened on Venus where a huge amount of gas was released into the atmosphere and couldn’t be reabsorbed by the rocks. On Earth, we have some examples of large-scale outgassing, for instance, the creation of the Siberian Traps 500 million years ago which is linked to mass extinction, but nothing on this scale. It completely transformed Venus.” ~Michael Way
The team of two ran five different simulations based on different levels of water coverage on the surface of the planet. These included:
- An ocean with 310 m (1,000 ft) deep
- Another shallow one measuring 10 m (33 ft)
- One where the water was trapped within the soil like Earth
- And the last one where Venus was entirely underwater (158m or 580 ft)
The simulations were run through a 3D general circulation model, varying atmospheric conditions & the increases in solar radiation to depict the actual changes over time. The time period in consideration was 715 million years ago, 4.2 billion years ago and today.
Each simulation resulted in the planet remaining between a habitable range of temperatures [20° C (68 F) to 50° C (122° F)], where water can exist in liquid form. More encouraging was the fact that simulation showed that Venus could have sustained these temperatures for three billion years. Quite possible considering Venus falls in the habitable ‘Goldilocks zone’ of our solar system.
Venus had a pretty similar formation process as Earth — when it came into being 4.2 billion years ago, the planet cooled rapidly trapping most of the carbon dioxide in the crust with a nitrogen-rich atmosphere and small amounts of carbon dioxide & methane left in the atmosphere, similar to our own planet.
The team suggests that about 700–750 million years ago, an ‘outgassing’ of carbon dioxide due to massive volcanic activity spewed out molten magma before cooling off to form a thick protective coating, preventing the carbon dioxide in the atmosphere to be reabsorbed triggering a runaway greenhouse effect, which trapped all the carbon dioxide in the atmosphere making it thicker & hotter till it reached the present-day levels.
The team is still looking for conclusive evidence on whether water condensation took place on the planet in the distant past & whether the outgassing was a one-off event or the planet heating was a result of multiple events like this.
The findings of the research were presented at the EPSC-DPS Joint Meeting 2019.