Venus could have endured life for billions of years

In 1978, NASA's Pioneer Venus (or Pioneer 12) mission reached Venus ("The Sister of the Earth") and uncovered clues that Venus may already have had oceans on its surface. Since then, several missions have been sent to Venus and have collected data on its surface and atmosphere. From there, an image of how Venus made the transition from a "Earth-like" planet to the hot and infernal region it is today emerged.

It all started about 700 million years ago when a massive resurfacing triggered a greenhouse effect that caused an extremely dense and burning atmosphere in the atmosphere of Venus. This means that for 2 to 3 billion years after the formation of Venus, the planet could have maintained a livable environment. According to a recent study, it would have been long enough for life to appear on Earth's Sister.

The study was presented yesterday (20 September) at the joint meeting of the European Congress of Planetary Science (EPSC-DPS) of 2019, which took place from 15 to 20 September in Geneva, Switzerland. It is here that Michael Way and Anthony Del Genio of the NASA Goddard Institute for Space Science (GISS) presented a new vision of Venus' climatic history, which could have implications for the search for habitable exoplanets.

As part of their study, MM. Way and Del Genio created a series of five environmental simulations of Venus based on different levels of water coverage. This involved adapting a 3D general circulation model that took into account changes in atmospheric composition and the gradual increase in solar radiation as the Sun warmed during its lifetime.

In three of the five scenarios, Way and Del Genio assumed that the topography of Venus was about the same as today, the ocean ranged from a minimum depth of 10 m (~ 30 ft) to approximately 310 m ( ~ 1000 ft) and a small amount of water was trapped in the soil. They also considered a scenario with the topography of the Earth and an ocean of 310 meters and another where Venus was completely covered by an ocean of 158 m (~ 500 feet).

In the end, the five simulations indicated the same thing: Venus could have maintained stable temperatures – from a low of 20 ° C (68 ° F) to a high of 50 ° C (122 ° F) – for about three billion d & # 39; years. If it was not a series of events that caused the resurfacing of 80% of the surface of the planet (which resulted in the degassing of CO² contained in the crust), it could even be habitable today. As Way explained:

"Our hypothesis is that Venus could have a stable climate for billions of years. It is possible that the near-global resurfacing event is responsible for its transformation from a hell-like hot earth-like climate we see today.

It all started about 4.2 billion years ago, a few hundred million years after the formation of Venus and had just completed a period of rapid cooling. At this point, assuming that Venus has undergone a process similar to that of the Earth, its atmosphere would be dominated by carbon dioxide. This would have been slowly absorbed by the silicate rocks to form carbonates which would then be enclosed in the earth's crust.

About 715 million years ago, according to the Way and Del Genio study, the atmosphere would have been similar to that of the Earth: composed mainly of nitrogen containing minute quantities of CO² and methane. These conditions could have remained stable until now if it was a massive degassing.

The cause of this remains a mystery; However, scientists believe that this is due to a geological event that has caused the re-emergence of 80% of the planet. This could have resulted in the formation of large quantities of magma and the release of massive amounts of CO² into the atmosphere. The magma would have solidified before reaching the surface, thus creating a barrier preventing reabsorption of CO². As Way explained:

"Something happened to Venus where a huge amount of gas was released into the atmosphere and could not be reabsorbed by the rocks. On Earth, we have some examples of large scale degassing, for example the creation of Siberian traps 500 million years ago that is related to mass extinction, but nothing on this scale. It completely transformed Venus.

This would explain how the atmosphere of Venus thickened to 90 times more dense than that of the Earth (92 bars against 1 bar). Combined with high concentrations of CO², this would have led to a greenhouse effect that would explain how the planet has become the hellish place we know today, with surface temperatures averaging 462 ° C (864 ° F). ).

This goes against conventional notions of habitability, according to which Venus' orbit places it beyond the inner edge of the habitable zone of our Sun (HZ). In this "zone of Venus", according to conventional wisdom, a planet absorbs too much solar radiation to be able to maintain a liquid water on the surface. But as Way has indicated, their simulations all indicate the opposite:

"Venus currently has almost twice the solar radiation we have on Earth. However, in all the scenarios we modeled, we found that Venus could still withstand acceptable surface temperatures for liquid water. "

These findings are consistent with a similar study conducted in 2016 by Way and Del Genio with colleagues at NASA's Goddard Space Flight Center, the Planetary Science Institute (PSI), the University of Uppsala, and Columbia University. For this study, their team created a suite of 3D climate simulations using data from Magellan mission that examined the impact of the presence of an ocean on the ancient Venus on its livability.

They deduced that if Venus had a rotation period of less than 16 terrestrial days, its climate would have remained habitable up to 715 million years. However, there are still two major unknowns to consider before scientists can say with certainty that Venus was habitable until recently.

Scientists will first need to determine the cooling rate of Venus and its ability to condense liquid water to the surface. Second, it is not possible to determine whether the global resurfacing event that led to the Venus transition was an isolated event or was simply part of a series that had been going on for billions of years.

"We need more missions to study Venus and get a more detailed understanding of its history and evolution," said Way. "However, our models show that it is quite possible that Venus was habitable and radically different from the Venus we see today. This opens up all sorts of consequences for the exoplanets present in what is called the "zone of Venus", which can in fact host liquid water and temperate climates.

Think about it … if Venus had not undergone a massive resurfacing event (or a series of them), humanity would only have needed to look for evidence from her home. alien life. Moreover, if Mars had not lost its magnetosphere 4.2 billion years ago, it could have produced its own life that would still be topical. Our only solar system could have had not one, but three living planets (neighbors)!

These findings are probably encouraging for those who think that Venus should be terraformed someday. Knowing that the planet once had a stable climate and could maintain it in spite of its orbit, this would mean that any ecological engineering that we would do there would remain.

This means that Venus could someday become a soft world, mostly ocean-covered with few large continents and large archipelagos. It sounds like any place you know?

Further reading: Europlanet Society, EPSC