Thanks to evidence provided by missions like NASA’s Magellan spacecraft, scientists have theorized that Venus likely experienced a catastrophic resurfacing event about 500 million years ago (give or take 200 Mya). This is believed to be the reason why Venus is such a hellish place today, with an atmosphere that is 92 times as dense as Earth’s, predominantly composed of carbon dioxide (CO2), and temperatures hot enough to melt lead.
The question of what Venus was like before this event took place – particularly, whether or not it had oceans – has been the subject of debate ever since. While many believe that Venus’s surface was covered in large bodies of water, a recent study has contradicted this claim. Using a state-of-the-art climate model, a team of French researchers has developed an alternative scenario of how Venus evolved to become what it is today.
The research was conducted by a team scientists from the Observatoire Astronomique de l’Université de Genève, the Laboratoire d’astrophysique de Bordeaux, the Centre National de la Recherche Scientifique (CNRS) , and University of Versailles-Saint Quentin-en-Yvelines (UVSQ). The paper that describes their findings, titled “Day–night cloud asymmetry prevents early oceans on Venus but not on Earth,” was published in the Oct. 13th issue of Nature.
Artist’s impression illustrating the lack of water on Venus. Credit and ©: Manchu
For over a century, scientists have speculated whether or not its surface was covered in oceans. At first, the dense clouds that obscure the surface were thought to be rainclouds, which fueled speculation that Venus’ surface was covered in oceans. By the 1960s, this notion was dispelled as multiple Soviet, and NASA missions conducted flybys of the planet (and even attempted to land on the surface) that demonstrated just how hot and hellish the planet is.
According to current planet formation models, Venus formed from the protoplanetary disk that orbited the Sun 4.5 billion years ago. Like the other rocky planets (Mercury, Earth, and Mars), the accretion process left Venus covered in magma for much of its early history. Over time, the surface slowly cooled and solidified to the point that water would condense in the atmospheres and rainfall could occur.
This process gave rise to the oceans on both Earth and Mars and is believed to have played an indispensable role in the emergence of life on Earth ca. 3.7 billion years ago. Whereas Mars failed to hold onto the water that once flowed across its surface, evidence of its watery past is retained in the form of flow channels, sedimentary deposits, and clays – all features that form in the presence of water.
While Venus was also very different, the existence of surface water has remained an unresolved question. For this reason, five missions surveyed Venus’ atmosphere between 1994 and 2010 – NASA’s MagellanCassini–Huygens, and MESSENGER missions, the ESA’s Venus Express, and JAXA’s Akatsuki. Other missions contributed by gathering data from Venus during flybys and gravity assists, such as the NASA’s Parker Solar Probe, the ESA/JAXA BepiColombo, and the NASA/ESA Solar Orbiter.
Artist’s impression of Venus Express performing aerobraking maneuvers in the planet’s atmosphere in June and July 2014. Credit: ESA/C. Carreau
As Martin Turbet, a postdoctoral researcher at the Observatoire Astronomique de l’Université de Genève and the lead author on the study, explained to Universe Today via email:
“There are basically two main scenarios that have been considered so far. In the first one, Venus had liquid water oceans on the surface, and this global resurfacing (which could have started well before 500 Mya) coincided with the complete evaporation of the oceans. In the second, which is