Thanks to the supercritical properties of carbon dioxide, Venus may have once hosted vast oceans. While the planet is too hot to contain surface water, carbon dioxide in its supercritical state is a very likely contender for this beachfront scenario.
Supercritical describes a state where an element offers properties of both liquids and gases. Carbon dioxide, or CO2, can assume liquid, solid, and gas forms just like water. In its supercritical state, it can dissolve materials like a liquid but flow like a gas. Dima Bolmatov, a physicist at Cornell University, describes the appearance of this state as a soap bubble with a gas core and a liquid shell.
However, supercritical CO2 may also have the ability to exist solely as a liquid—under the right circumstances. The pressure of Venus’ atmosphere would crush these soap bubbles into liquid forcing them to resemble the oceans here on Earth.
Presently, Venus boasts an atmospheric pressure 90 times that of Earth. Early in its formation, that pressure was likely more immense allowing for the creation of these hypothetical oceans.
This is not the first time scientists believed Venus once contained surface liquid. Oceans of HO2 were considered impossible because the surface, which is hot enough to melt lead, would instantly evaporate the water. There would be no chance for the precipitation to build up an Earth-like sea of water.
CO2 was considered a distinct possibility for oceans due to these supercritical properties and the fact that it makes up 96.5 percent of Venus’ atmosphere. However, it was also believed that the transition to that state was too slow to be plausible.
Current computer models show differently. CO2 could adopt a supercritical status very quickly due to the unique combination of Venusian temperature and pressure conditions.
These oceans are likely responsible for the planet’s plains, rift valleys, and river beds, all formed over a period of 100 to 200 million years. They would have been up to 80 feet deep and covered the whole planet, with the liquid CO2 even evaporating and coming back as rain.
On Earth, CO2 is exhaled by animals and used by plants in photosynthesis. It traps heat and contributes to climate change. When preserved past a point of temperature and pressure, it enters a supercritical state and as a fluid, it can dissolve elements like a liquid but behave like a gas. Some theories even support a premise that supercritical CO2 can support unique life forms.
However, there is still more study necessary regarding the behavior of supercritical carbon dioxide. Evidence of oceans on Venus help clear-up the misconceptions and fill in information gaps regarding the potential of CO2.
Venus often inspires curiosity as it is similar to Earth in size, mass, distance from the sun, and its chemical make-up. But its character is completely different as hot temperatures, rocky terrain, a crushing atmosphere, and sulfuric acid clouds prevent it from being a cradle of life like Earth.
More information on the supercritical carbon dioxide oceans is forthcoming as NASA considers sending staffed missions to Venus. Many researchers advocate this mission taking priority over visiting Mars due to similarities with Earth and potential research opportunities.
By Jocelyn Mackie
Photo by NASA Goddard Space Flight Center – Flickr License