Venus may have been a temperate planet with liquid water for 2-3 billion years, until a dramatic transformation that began over 700 million years ago, reverted to 80% of the planet showed up. A study presented today by Michael Way of the Goddard Institute for Space Science at the 201
NASA's Pioneer Venus mission found tantalizing evidence that the planet's & # 39; twisted sister & # 39; Earth once had the water of a shallow ocean. To find out if Venus has ever had a stable climate that could support liquid water, Dr. Way and his colleague Anthony Del Genio created a series of five simulations that assumed different water coverages.
In all five scenarios, Venus was able to maintain stable temperatures of no more than about 50 degrees Celsius and a minimum of about 20 degrees Celsius for about three billion years. A temperate climate might even have been sustained today on Venus if there had not been a series of events that would have led to a release or "outgassing" of carbon dioxide in the rocks of the planet some 700 to 750 million years ago.
"Our hypothesis is that Venus has a stable climate for billions of years. It's possible that the near-global event of surface renewal is responsible for transforming an Earth-like climate into a hellish bulb that we see today, "Way said.
Three of the Five Scenarios Investigated by Way and Del Genio Assumed The topography of Venus as we see it today looked at a deep ocean averaging 310 meters, a shallow water layer averaging 10 meters, and a small amount of water trapped in the ground. For comparison, they also included a scenario with the topography of the Earth and a 310 meter ocean, and finally a world completely covered by a 158 meter ocean.
To simulate the environmental conditions 4.2 billion years ago, it was 715 million years ago and today researchers have adapted a general 3D circulation model to increase the solar radiation during the warming of our sun and the change in atmospheric composition The new study suggests that this may not be the case.
"Venus currently has nearly twice the solar radiation that we have on Earth. However, in all the scenarios we modeled, we found that Venus can still tolerate surface temperatures suitable for liquid water, "said Way.
4.2 billion years ago, shortly after its creation, Venus would have completed a period of rapid cooling and its atmosphere would have been dominated by carbon dioxide. If the planet had developed earth-like over the next 3 billion years, the carbon dioxide would have been extracted from silicate rocks and trapped on the surface. In the second epoch, modeled 715 million years ago, the atmosphere would probably have been dominated by nitrogen with traces of carbon dioxide and methane, as it is today on Earth, and these conditions could have remained stable to this day.
The cause of the outgassing that led to the dramatic transformation of Venus is a mystery, although it is probably related to the volcanic activity of the planet. One possibility is that large amounts of magma bubble into the air and release carbon dioxide from molten rock into the atmosphere. The magma froze before it reached the surface and a barrier formed which meant that the gas could no longer be absorbed. The presence of large amounts of carbon dioxide triggered a runaway greenhouse effect that resulted in the searing average temperatures of 462 degrees as found on Venus today.
could not be absorbed by the rocks. On Earth, there are some examples of large-scale outgassing, for example, the creation of the Siberian traps 500 million years ago, which are associated with a mass extinction, but nothing to that extent. It totally changed Venus, "Way said.
There are two more important unknowns that need to be addressed before the question of whether Venus could have been habitable can be fully answered. The first one relates to how fast Venus initially cooled and whether it could ever condense liquid water on its surface. The second unknown is whether the global emergence event is a single event or simply the latest event in a series of billions of years of events in the history of Venus.
"We need more missions to study Venus and to better understand its history and evolution," said Way. "Our models, however, show that there is a real possibility that Venus was habitable and fundamentally different from the Venus that we see today. This opens up all possible implications for exoplanets found in the so-called "Venus Zone", which may harbor liquid water and temperate climates. "