麻豆影院

Venus is losing water faster than previously thought鈥攈ere鈥檚 what that could mean for the early 麻豆影院 habitability.

Today, the atmosphere of our neighbor planet Venus is as hot as a听听and drier than the听听鈥� but it wasn鈥檛 always that way.

Billions of years ago,听. If that water was ever liquid, Venus听.

Over time, that water has nearly all been lost. Figuring out how, when and why Venus lost its water helps听听understand what makes a planet habitable 鈥� or what can make a habitable planet transform into an uninhabitable world.

Scientists have theories explaining why most of that water disappeared, but more water has disappeared than they predicted.

, my colleagues and I revealed a new water removal process that has gone unnoticed for decades, but could explain this water loss mystery.

Energy balance and early loss of water

The solar system has a听听鈥� a narrow ring around the Sun in which planets can have liquid water on their surface. Earth is in the middle, Mars is outside on the too-cold side, and Venus is outside on the too-hot side. Where a planet sits on this habitability spectrum depends on how much energy the planet gets from the Sun, as well as how much energy the planet radiates away.

The theory of how most of Venus鈥� water loss occurred is tied to this energy balance. On early Venus, sunlight broke up water in its atmosphere into hydrogen and oxygen. Atmospheric hydrogen heats up a planet 鈥� like having too many blankets on the bed in summer.

When the planet gets too hot, it throws off the blanket: the hydrogen escapes in a flow out to space, a process called听. This process removed one of the key ingredients for water from Venus. It鈥檚 not known听听听this process occurred, but it was likely within the first billion years or so.

Hydrodynamic escape stopped after most hydrogen was removed, but a little bit of hydrogen was left behind. It鈥檚 like dumping out a water bottle 鈥� there will still be a few drops left at the bottom. These leftover drops can鈥檛 escape in the same way. There must be some other process still at work on Venus that continues to remove hydrogen.

Little reactions can make a big difference

Our听听that an overlooked chemical reaction in Venus鈥� atmosphere can produce enough escaping hydrogen to close the gap between the expected and observed water loss.

Here鈥檚 how it works. In the atmosphere, gaseous HCO鈦� molecules, which are made up of one atom each of hydrogen, carbon and oxygen and have a positive charge, combine with negatively charged electrons, since opposites attract.

But when the HCO鈦� and the electrons react, the HCO鈦� breaks up into a neutral carbon monoxide molecule, CO, and a hydrogen atom, H. This process energizes the hydrogen atom, which can then exceed the 麻豆影院 escape velocity and escape to space. The whole reaction is called HCO鈦� dissociative recombination, but we like to call it DR for short.

Water is the original source of hydrogen on Venus, so DR effectively dries out the planet. DR has likely happened throughout the history of Venus, and our work shows it probably still continues into the present day. It doubles the amount of hydrogen escape听听by planetary scientists, upending our understanding of present-day hydrogen escape on Venus.

Understanding Venus with data, models and Mars

To study DR on Venus we used both computer modeling and data analysis.

The modeling actually began as a Mars project. My Ph.D. research involved exploring what sort of conditions made planets habitable for life.听, though less than Venus, and also lost most of it to space.

To understand martian hydrogen escape, I developed a听听that simulates Mars鈥� atmospheric chemistry. Despite being very different planets, Mars and Venus actually have similar upper atmospheres, so my colleagues and I were able to extend the model to Venus.

We found that HCO鈦� dissociative recombination produces lots of escaping hydrogen in both planets鈥� atmospheres, which agreed with measurements taken by the听, a satellite orbiting Mars.

Having data collected in Venus鈥� atmosphere to back up the model would be valuable, but previous missions to Venus haven鈥檛 measured HCO鈦� 鈥� not because it鈥檚 not there, but because they weren鈥檛 designed to detect it. They did, however, measure the reactants that produce HCO鈦� in Venus鈥� atmosphere.

听made by听, a combination orbiter and probe mission that studied Venus from 1978-1992, and using our knowledge of chemistry, we demonstrated that HCO鈦� should be present in the atmosphere in similar amounts to our model.

Follow the water

听has filled in a piece of the puzzle of how water is lost from planets, which affects how habitable a planet is for life. We鈥檝e learned that water loss happens not just in one fell swoop, but over time through a combination of methods.

Faster hydrogen loss today via DR means that less time is required overall to remove the remaining water from Venus. This means that if oceans were ever present on early Venus, they could have been present for longer than scientists thought before water loss through hydrodynamic escape and DR started. This would provide more time for possible life to arise. Our results don鈥檛 mean oceans or life were definitely present, though 鈥� answering that question will require lots more science over many years.

There is also a need for new Venus missions and observations.听听听听will provide some atmospheric measurements, but they won鈥檛 focus on the upper atmosphere where most HCO鈦� dissociative recombination takes place. A future Venus upper atmosphere mission, similar to the MAVEN mission at Mars, could vastly expand everyone鈥檚 knowledge of how terrestrial planets鈥� atmospheres form and evolve over time.

With the technological advancements of recent decades and a flourishing new interest in Venus, now is an excellent time to turn our eyes toward Earth鈥檚 sister planet.

Eryn Cangi is a听NASA FINESST Fellow听in the Department of Astrophysical and Planetary Sciences听at the听.

This article is republished from听听under a Creative Commons license. Read the听.

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