That Venus is dry should come as no surprise. It is known for its hellish conditions, with thick sulfur clouds, acid rains, air pressure as high as Earth's deepest oceans, and a surface temperature high enough to melt lead. But its water shortage isn't just a lack of rain and oceans: There's no ice or water vapor either. Like Earth, Venus is in the Goldilocks zone of our solar system, so it must have had plenty of water when it formed. So where did all of Venus' water go?
Venus is an extremely dry planet, although it wasn't always this way. At some point in its history, a runaway greenhouse effect began, leading to its current extreme state. Most models agree that this process would have displaced most of the original water, but that some should still remain. And yet observations show that there is virtually no water at all. Planetary scientists at the University of Colorado Boulder believe they have found an explanation: a molecule called HCO+ high up in Venus' atmosphere may be responsible. Unfortunately, they may have to wait for future missions to Venus before they can confirm this.
Until the mid-20th century, Venus was thought to be Earth's twin. The two planets are roughly the same size and mass, and both lie in the Sun's habitable zone—the region where temperatures can be warm enough to melt ice, but not so hot that water turns to steam. For a long time, it was assumed that, beneath its brilliant white cloud cover, Venus must have a climate similar to Earth's. Science fiction writers even wrote stories about visitors to Venus exploring verdant jungles and meeting exotic civilizations. But the truth is much harsher: Venus is an extreme place, with sulfuric acid rains, suffocating air pressure, and a surface temperature hot enough to melt lead. But it wasn't always this way.
Astronomers and planetary scientists generally assume that both Earth and Venus had similar amounts of water at the beginning of life. But something happened and released enormous amounts of carbon dioxide into the atmosphere, causing an extreme greenhouse effect. The high temperatures melted all ice and evaporated all liquid water, filling the atmosphere with water vapor. Much of this hot vapor would eventually escape into space and dry out the planet, but some was bound to remain. The puzzle is that the usual models predict much more remaining water vapor than actually exists. So what happened?
According to a study led by Dr. Eryn Cangi and Dr. Mike Chafin, both of the Laboratory for Atmospheric and Space Physics (LASP), the answer may be a molecule called HCO+. In their previous work studying the atmosphere of Mars, they discovered a process by which this molecule can remove water from planetary atmospheres. In their new work, they suggest that the same process may be at work on Venus. The only catch is that this molecule has never been detected in Venus' atmosphere.
Unfortunately, there is little evidence to support this theory. HCO+ has never been detected in Venus' atmosphere. However, Cangi and Chafin point out that this is because no one has ever looked for it and none of the missions sent to Venus so far have been equipped with instruments that could detect it. However, they are optimistic about future missions.
Illustration of NASA's DAVINCI probe falling to the surface of Venus. (Source: NASA GSFC visualization by CI Labs Michael Lentz and others)
“One of the surprising conclusions of this work is that HCO+ should actually be among the most abundant ions in the Venusian atmosphere,” says Chaffin.
“There haven't been many missions to Venus yet,” Cangi adds. “But newly planned missions will leverage decades of collective experience and a growing interest in Venus to explore the extremes of planetary atmospheres, evolution and habitability.”
Planetary scientists are increasingly interested in Venus, and several future missions are planned to study it in more detail. One example is NASA's planned Deep Atmosphere Venus Investigation of Noble gases, Chemistry, and Imaging (DAVINCI) mission. DAVINCI will drop a probe onto the surface that will study the atmosphere at different altitudes as it falls. Unfortunately for Cangi and Chafin, the probe is not specifically designed to search for HCO+, but it could provide other clues that either confirm or disprove their theory. However, they remain optimistic that more missions will be conducted in the future with the necessary instruments to test their work.
For more information, see CU Boulder's announcement at https://www.colorado.edu/today/2024/05/06/venus-has-almost-no-water-new-study-may-reveal-why.
Like this:
Is loading…
