Venus is Earth’s twisted sister; a planet of almost equal size and structure that has been cruelled by an uncontrollable greenhouse effect.
Key points:
- Atomic oxygen (O1) was detected for the first time directly in the clouds of Venus
- Detection makes it possible to study atmospheric circulation on Venus
- This may also allude to the idea that Venus once contained liquid water on its surface.
Unlike the Roman god of beauty for whom it is named, our sister world is constantly clothed, shrouded in eternal mist; a dense, cloud-filled atmosphere composed primarily of carbon dioxide.
If you can see past the corrosive nature of its air, stained yellow by sulfuric acid, then conditions in the Venusian sky are far friendlier than on earth, where it’s hot enough to melt lead.
In some cloud layers on the planet, the average temperature reaches 30 degrees Celsius.
The Venusian atmosphere has long intrigued planetary scientists around the world because it holds the key to understanding Venus.‘ past – and clues as to why it became so hellish.
German researchers publication in the journal Nature Communicationshave now studied the planet’s atmosphere with unprecedented clarity, for the first time directly detecting atomic oxygen on the dayside of the planet – the side facing the Sun.
The detection, led by Heinz-Wilhelm Hübers of Humboldt University Berlin, opens a window to explore the atmosphere of our ailing sister planet in more detail.
“The distribution of oxygen tells us about the temperature profile of the atmosphere, cooling processes (and) wind speeds,” said Lucyna Chudczer, an astronomer and assistant research scientist at the University of Southern Queensland. who did not participate in the study.
Alongside future missions to Venus, the authors of the new article say their measurements “could help improve our understanding of how and why the atmospheres of Venus and Earth are so different.”
But other planetary scientists are attracted by the possibility that atomic oxygen could be a sign that Venus was once moist and warm and much more habitable than it is today.
An atomic response
When you think of oxygen, you probably think of breathable air and the molecular oxygen, or O2, it contains.
But in the upper layers of the Earth’s atmosphere, atomic oxygen (O1) is abundant. It is a crucial element for energy balance and planetary cooling, usually formed when light breaks down molecules such as ozone (O3) or nitrogen dioxide (NO2).
In 2021, Professor Hübers and his colleagues realized that they could use the now-retired Stratospheric Observatory for Infrared Astronomy, or SOFIA, to directly detect atomic oxygen in the Earth’s upper atmosphere.
SOFIA, a Boeing 747 equipped with a reflecting telescope in its fuselage, flew approximately 12 to 14 kilometers above the Earth’s surface. At this height, it avoided virtually all of the pesky water vapor in the atmosphere that could obstruct measurements of molecules.
After discovering atomic oxygen in the Earth’s atmosphere, Professor Hübers and his team turned their attention to Venus.
In the new study, they used the same method to detect atomic oxygen in the hazy atmosphere of our sister planet.
Venus has an atmosphere composed mostly of carbon dioxide, so scientists have long known that oxygen was present on the planet.
There was previously indirect evidence for the existence of O1 in the upper layers of the Venusian atmosphere, but direct evidence for its distribution, particularly during the day, was lacking.
A long day until night
A day on Venus is long. Like, really long. It takes 243 Earth days to go from day to night. Meanwhile, carbon dioxide and carbon monoxide in Venus’ atmosphere are pounded by sunlight, breaking them down into atomic oxygen. It is then transported around the planet by atmospheric circulation.
Over the course of three SOFIA flights, the team studied 17 locations in the planet’s atmosphere. Nine of them were on the night side, seven on the day side, and one at the terminator – the location between day and night.
They found that atomic oxygen was present at all 17 sites.
This discovery allows researchers to study how the atmosphere changes and mixes, particularly in the region where atomic oxygen is most abundant, between 90 and 120 km above the Venusian surface.
This region is remarkable because it is a transition region between two dominant circulation patterns in the Venusian atmosphere.
For Stephen Kane, a professor of astronomy at the University of California, Riverside, who was not involved in the study, the detection raises a larger question: Where could this atomic oxygen come from?
“One of the fascinating parts of Venus, which we are still trying to resolve, is whether it ever had liquid water on the surface,” he said.
If Venus had water, H2O, then as it began to warm up and transition into the uncontrollable greenhouse state it is in today, the water would have evaporated.
The hydrogen atoms would have been torn from the oxygen atoms and lost in space. But the oxygen may have remained.
“This oxygen could be an important component of ancient surface waters, which remain in the atmosphere today,” he said.
This begins to paint a picture of a completely different Venus than the one we see today. Perhaps it even suggests that billions of years ago Venus might have been habitable.
As further evidence for this hypothesis, Professor Kane also highlighted the discovery made in March showing evidence of volcanic activity on the planet.
To explore this idea further, space agencies are returning to Venus to probe its atmosphere in more detail and map its surface.
A future among the clouds of Venus
Both NASA and the European Space Agency are preparing for interplanetary missions to Venus.
Professor Kane is a member of the science team on one of these missions, known as DAVINCI.
NASA had planned to send DAVINCI and an orbiting spacecraft, known as VERITAS, to Venus by 2031. The DAVINCI mission would be particularly revealing, with plans to drop a probe through the clouds of Venus and on its rocky surface.
NASA’s VERITAS was a little different. It would conduct atmospheric studies and surface mapping from orbit, something planetary scientists have not been able to do since the Magellan mission of the 1990s. VERITAS was effectively put on ice due to a budget freeze.
Fortunately, planetary scientists could get the data from their orbiter in the form of EnVision, an ESA spacecraft scheduled for launch in 2031, which will perform high-resolution radar scans of the planet’s surface.
The missions will begin to answer some of the key questions about Venusian history, building on the past water hypothesis.
Professor Kane, for example, will be keenly interested in examining the ratio between two isotopes of hydrogen – a more definitive way of knowing whether Venus once contained water. Current measurements vary widely, so it is difficult to draw conclusions.
“DAVINCI will finally put an end to this,” he said.
A richer understanding of Venus could also help guide exploration beyond our solar system.
While we tend to discover very hot, irradiated planets near their home stars, Venus – and the measurements we have of the molecules in its atmosphere – could serve as a benchmark for what we expect to see in the deep space, Dr. Chudczer said.
“We can produce better models that include the photochemical reactions that lead to the formation of atomic oxygen and compare our observation of other molecules with what we see on Venus,” she said.
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