For the past several million years, Earth was a lush, clemental world teeming with life, opposed to Venus, which is hellish, with extremely high surface temperatures. However, using professional equipment, ESA’s scientists see that underneath the surface these two planets share many similarities.
For one, both planets are nearly identical in size, and their basic composition is very similar, says Hakan Svedhem, ESA Venus Express Project scientist. Obviously, one difference stands out: Venus has very little water, while Earth’s exterior is mainly water (approximately 71%).
Yet, when looking at the planets’ histories, it is evident that billions of years ago, Venus probably had much more water. Venus Express has certainly confirmed that the planet has lost a large quantity of water into space.
The cause for the water evaporation is ultraviolet radiation from the sun, which streams into Venus’ atmosphere and breaks up the water molecules into atoms. Each water molecule is divided into two hydrogen atoms and a single oxygen atom that escape to space.
Venus Express has measured the rate of this escape and confirmed that for each atom of oxygen, two atoms of hydrogen are escaping. Since this is about the same ratio found in water molecules, the team of scientists believes that water used to be abundant on Venus. Moreover, Venus Express has also shown that a heavy form of hydrogen, called deuterium, is progressively enriched in the upper echelons of Venus’s atmosphere, because the heavier hydrogen will find it less easy to escape the planet’s grip.
“Everything points to there being large amounts of water on Venus in the past,” says Colin Wilson, Oxford University, UK. However, ‘large amounts of water’ do not necessarily mean that Venus had oceans on its surface. In order to better understand the past of Venus, Eric Chassefière from Université Paris-Sud, France has developed a novel computer model. Using his software, he suggests that water was largely atmospheric and existed only during the very earliest times, when the surface of the planet was completely molten. When the water molecules were broken into atoms by sunlight and escaped into space, the subsequent drop in temperature apparently triggered the solidification of the surface, meaning there weren’t necessarily oceans – or seas – on Venus.
Sadly enough, this hypothesis is currently a mystery, as there isn’t enough data or adequate tools to pursue a conclusive result. “Much more extensive modeling of the magma ocean-atmosphere system and of its evolution is required to better understand the evolution of the young Venus,” says Chassefière. Still, it is considered a key question; If Venus ever did possess surface water, the planet may possibly have had an early habitable phase.
Even if further data retrieved by Venus Express will improve this computer model, there is no way to know if the existence of water on Venus is the result of internal process or a comet collision; therefore, there is still the chance that the additional water on Venus arrived after the surface crystallized. Such intriguing questions remain open – until future research will bring more data, leading to better results.
TFOT has also covered new evidence showing the existence of an ancient lake on Mars, and the theory regarding underground water on Saturn’s moon, proposed by NASA researchers. Another related TFOT story is the possibility of having an habitable planet in a distant galaxy, as researched at the Harvard-Smithsonian Center for Astrophysics.
For more information about ESA’s research of Venus, see the official press release.