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Scientists have noticed something unexpected in the atmosphere of Venus – an increase in the level of deuterium relative to hydrogen. Okay, sure, that doesn’t sound like the most exciting statement. However, the consequences of this discovery may add to our current understanding of the amber world.
As it turned out, it would disrupt our perception of Venus as an unwelcoming planet forever. This is how.
“Venus is often called a twin Earth because of its similar size,” Hiroki Karyu, a researcher at Tohoku University and one of the study’s scientists, said in a statement. “Despite the similarities between the two planets, it has evolved differently. Unlike Earth, Venus has extreme surface conditions.”
Liquid water cannot exist in significant enough quantities due to the extreme temperatures and pressures beneath Venus’ thick cloud layer. “To put this in perspective, these altitudes have 150,000 times less water than comparable altitudes on Earth,” the scientists wrote in their study.
But that is not to say that this has always been the case.
Deuterium and hydrogen are isotopes of each other, meaning that they are different forms of the same element, with the same number of protons but different numbers of neutrons in their nuclei. As a result they have different atomic masses, but their chemical properties remain relatively the same.
Related: Venus may be able to support life, according to new atmospheric evidence
A lot can be gleaned from isotopic ratios. Take carbon dating, for example, which is a powerful tool scientists use to gather the age of organic matter using the relative proportions of the Carbon-12 and Carbon-14 isotopes. The ratio of these isotopes in matter changes over time as carbon-14 decays radioactively and is not replaced.
It is believed that Venus and Earth once had similar HDO/H2O ratios, as both planets formed in a hot region of the early solar system where water could not condense. Later, water is thought to have been delivered to the worlds by water-rich asteroids likely from the outer asteroid belt, which should have resulted in similar deuterium-to-hydrogen (D/H) ratios on both planets. Comparable levels of other volatile elements, such as carbon and nitrogen, between Venus and Earth support this hypothesis.
But after searching data from the Solar Emission Infrared Instrument (SOIR) on the Venus Express space probe (which operated from 2006 to 2014) there has been a blip in this story. Scientists found that the ratio of HDO is now 120 times higher compared to H2O in the atmosphere of Venus. “This enrichment is mainly due to solar radiation breaking down isotopologues of water in the upper atmosphere, producing hydrogen (H) and deuterium (D) atoms,” wrote the ESA scientists. “Since H atoms escape into space more easily due to their lower mass, the ratio HDO/H2O increases gradually.”
They also found that the concentration of water molecules, both H2O and HDO, increases with altitude, especially between 70 and 110 kilometers (43 and 68 miles) above the surface of Venus. In addition, they found that the ratio of HDO to H2O becomes very high at these altitudes, more than 1,500 times higher than that found in the Earth’s oceans. This shows that the atmosphere of Venus has much more deuterium-rich water compared to Earth, indicating significant differences in the atmospheric processes of the two planets.
The team speculates that climate mechanisms related to sulfuric acid aerosols (H2SO4) may be driving these processes, which make up the majority of Venus’ clouds.
“These aerosols form just above the clouds, where temperatures fall below the dew point of sulphurous water, which leads to the creation of deuterium-enriched aerosols,” the scientists explained. “These particles are carried to higher altitudes, where increased temperatures cause them to vaporize, releasing a more significant fraction of HDO compared to H2O. The vapor is then transported downward, restarting the cycle.”
Related Stories:
— shots of the Jupiter-bound SUZ probe from Earth en route to Venus (photos)
— How Venus ‘the Earth’s twin’ lost her water and became a hellish planet
— Zoozve — a strange ‘moon’ of Venus that earned its name by accident
How will the findings have wider implications for our understanding of the planet? First, the team hopes that future studies will look at how the ratio of deuterium to hydrogen (D/H) changes with altitude when calculating the total amounts of these gases in the atmosphere of Venus. Second, the rate at which hydrogen and deuterium escape into space is affected by the way D/H changes with height. For example, high in the atmosphere, much more deuterium is released than expected, which can affect the overall D/H ratio if some of this deuterium escapes.
This means that to get an accurate understanding of how Venus’ atmosphere evolved and how much water it may have lost over time, scientists need to use models that account for the changes in altitude this.
