Scientists may have identified a molecule that played a key role in draining the planet Venus of water and turning it into the barren, hellish world we see today.
Venus is often called “Earth’s twin” because both planets are roughly the same size and density; also, both are rocky planets located in the inner region of the solar system. However, in many essential respects, Venus could not be less similar to Earth, reports Space.com
While our planet is full of life, Venus, the second planet from the Sun, is a virtual hell. It is the hottest planet in the solar system (even hotter than Mercury, which is closest to the Sun) and has temperatures of about 880 degrees Fahrenheit (471 degrees Celsius). This is hot enough to melt lead. Plus, Venus has pretty scary surface pressures.
Also important is that Venus lacks a key element for life that is abundant here on Earth: water. This is despite the fact that the planet is in the sun’s so-called “Goldilocks zone”, referring to the region around our star that is neither too hot nor too cold to allow liquid water to exist – and also, despite the fact that scientists know that Venus probably had water.
In fact, billions of years ago, Venus is thought to have had as much water as Earth – but at some point in its evolution, the carbon dioxide clouds in the planet’s atmosphere triggered the most intense effect of greenhouse in the solar system. This caused temperatures to rise to where they are today. This triggered the evaporation of water from the planet, after which it was lost to space.
However, even considering this process, scientists don’t know how Venus became so desert-like or how it continues to lose what little water it has left to space. Now, a team of scientists from the University of Colorado Boulder may have discovered the secrets of this process, telling what they call the “story of water on Venus.”
“Water is really important for life,” Eryn Cangi, team co-leader and researcher at the Laboratory for Atmospheric and Space Physics (LASP), said in a statement. “We need to understand the conditions that support liquid water in the universe and that could have produced the very dry state of Venus today.
“We’re trying to figure out what small changes happened on each planet to bring them to these wildly different states.
To put into context the difference in water content between planetary neighbors Earth and Venus, Cangi explained that if all the water on our planet were spread evenly over its surface, it would create a global layer of nearly 3.2 kilometers depth. Doing the same for Venus, removing the rest of the water from the atmosphere, would create a global layer only 3 centimeters (1.2 inches) deep.
“Venus has 100,000 times less water than Earth, even though it’s basically the same size and mass,” Michael Chaffin, team co-leader and fellow researcher at LASP, explained in the statement.
To determine how it got to its current state, Cangi, Chaffin and their colleagues used computer models of the planet, treating it almost like a giant chemistry laboratory. This allowed them to get an improved look at the various reactions taking place in Venus’s swirling atmosphere and identify a suspect for the water loss.
What the team found was that a molecule called HCO+ – made up of one hydrogen atom, one carbon atom and one oxygen atom – high in Venus’ atmosphere could have been responsible for delivering the last amounts of water on the planet.
“As an analogy, let’s say I threw the water out of my water bottle,” Cangi said. “There would be a few drops left.”
HCO+ could remove these droplets from Venus’ atmosphere. In fact, the same team previously suggested that HCO+ was also the culprit in causing Earth’s other neighbor, Mars, to lose its water.
The researchers say that HCO+ is constantly produced in the Venusian atmosphere, but that these ions do not survive long. An ion is a positively or negatively charged molecule that has gained its charge either because it lacks the electrons needed to balance the positive charge on its protons, or because it has extra electrons to create a net negative charge in the molecule.
HCO+ lacks the electrons needed to balance the positive charge of the molecule’s protons and is therefore positively charged (hence the + symbol).
Electrons in Venus’ atmosphere quickly recombine with HCO+, causing the molecule to split in two. From here, the team argues, the hydrogen atoms drift away and possibly even escape into space. Hydrogen atoms form two of the components of the water molecule (H2O), which is composed of two hydrogen atoms and one oxygen atom, so Venus lacks the primary ingredients of water.
The team believes that for Venus to have reached its extreme dry state, the planet must have had an excess of HCO+ molecules in its atmosphere.
“One of the surprising conclusions of this work is that HCO+ should, in fact, be among the most abundant ions in Venus’ atmosphere,” Chaffin said.
However, there is a major obstacle to this conclusion. To date, we have never seen HCO+ in the atmosphere of Venus.
However, Chaffin and Cangi don’t think this is because the molecule doesn’t exist, but rather because humanity hasn’t had the tools to see it. Although Earth’s neighbor Mars has been visited by many Earth-based spacecraft, few missions have passed by our other neighbor, Venus—and none of them had the right equipment to see HCO+.
But a number of future space missions have Venus in their sights. NASA’s DAVINCI (Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging) mission is a particularly important one. Set to launch in 2029, DAVINCI will blast a probe through Venus’ hot atmosphere to determine the chemical composition of this world.
However, even DAVINCI will not have the right equipment to detect HCO+.
However, the team hopes that a general interest in Venus will emerge thanks to DAVINCI (and the European Space Agency’s upcoming EnVision mission), which will eventually lead to a space mission that is indeed capable of detecting HCO+, adding thus veracity of the team’s story regarding the loss of water.
“There haven’t been many missions to Venus,” Cangi concluded. “But the newly planned missions will leverage decades of collective experience and a burgeoning interest in Venus to explore the extremes of planetary atmospheres, evolution and habitability.”
The team’s research was published Monday (May 6) in the journal Nature.
