A new study suggests that Venus was once a habitable planet thanks to a protective atmosphere like that of the Earth today.

Modern day Venus is uninhabitable thanks to extremely high temperatures, but the study suggests that this may not have always been the case. The full results of the study were published in the journal Geophysical Research Letters.

Ancient Venus
Image source: Wikimedia Commons

Ancient Venus was very different than today

Scientists have previously suggested that Venus started out from the same materials as the Earth, before taking a different evolutionary path. The new study resumes some of the main comparisons between the planets.

Today Venus sees surface temperatures of up to 462 degrees Celsius, and carbon dioxide accumulates in a thick atmosphere because there is almost zero water vapor on the planet. However during the 1980s NASA’s Pioneer mission beamed back data which raised the possibility that an ocean had previously existed on the surface of Venus, sparking theories that the planet was once habitable.

One theory is that early oceans on Venus evaporated due to the intense amount of sunlight received by the second closest planet to our star. The water vapor molecules may have been broken down by ultraviolet radiation, before the hydrogen dissipated into space.

How has Venus’ atmosphere changed?

This could in turn have allowed carbon dioxide to gather in the atmosphere, leading to a greenhouse effect which led to the development of the conditions found on Venus today.

Another factor believed to affect the habitability of a planet is its rotation. Scientists believe that a thick atmosphere, as currently found on Venus, are necessary for a planet to rotate slowly on its axis.

However new research shows that even planets with a thin atmosphere, like the Earth, could have led to a slow rotation. As a result an ancient Venus with a thin, Earth-like atmosphere could have rotated at the same rate as Venus does today.

Researchers simulate ancient Venus

Researchers at the NASA Goddard Institute for Space Studies (GISS) simulated an ancient Venus, with Earth-like atmosphere. One Venus day is the same as 117 Earth days in the simulation, and there is also a shallow ocean, as reported by Pioneer.

Astronomers discovered that a slow spin would leave the dayside of Venus exposed to the sun for two months at a time. Study co-author Anthony Del Genio says that the slow rotation leads to a warming of the surface, producing rain that leads to thick clouds.

“[This] acts like an umbrella to shield the surface from much of the solar heating,” said Del Genio, who is also a GISS scientist.

As a result of the rotation and the thick clouds, ancient Venus would have had temperatures a few degrees lower than modern day Earth.