Extract from ABC News
Venus is Earth's twisted sister; a planet of almost equal size and structure that has been cruelled by a runaway greenhouse effect.
Key points:
- Atomic oxygen (O1) has been directly detected in the clouds of Venus for the first time
- The detection provides a way to study the atmospheric circulation on Venus
- It may also hint at the idea that Venus once contained liquid water at its surface
Unlike the Roman god of beauty after which it is named, our sister world is constantly clothed, shrouded in an eternal haze; a dense, cloud-filled atmosphere composed mostly of carbon dioxide.
If you can see past the corrosive nature of its air, stained yellow by sulphuric acid, then conditions in the Venusian sky are far friendlier than on the ground, where its hot enough to melt lead.
In some layers of the planet's clouds, the average temperature reaches a balmy 30 degrees Celsius.
The Venusian atmosphere has long intrigued the world's planetary scientists because it holds the key to understanding Venus' past — and clues to why it became so hellish.
German researchers publishing in the journal Nature Communications, have now studied the atmosphere of the planet with unprecedented clarity, directly detecting atomic oxygen on the planet's dayside — the side facing the Sun — for the first time.
The detection, led by Heinz-Wilhelm Hübers of the Humboldt University in Berlin, opens a window to explore the atmosphere of our sick sister planet in greater detail.
"The oxygen distribution tells us about the temperature profile of the atmosphere, cooling processes [and] speed of winds," said Lucyna Chudczer, an astronomer and adjunct research fellow at the University of Southern Queensland, who was not involved in the study.
Along with future missions to Venus, the authors of the new paper say their measurements "may help improve our understanding of how and why Venus and Earth atmospheres are so different."
But
other planetary scientists are tantalised by the possibility the atomic
oxygen could be a sign that Venus was once wet and warm and far more
habitable than it is today.
An atomic answer
When you think about oxygen, it's likely you're thinking about breathable air and the molecular oxygen, or O2, in it.
But in the upper layers of Earth's atmosphere, atomic oxygen (O1) is abundant. It's a crucial component for energy balance and cooling the planet, typically formed when light breaks apart molecules such as ozone (O3) or nitrogen dioxide (NO2).
In 2021, Professor Hübers and colleagues realised they could use the now-retired Stratospheric Observatory for Infrared Astronomy, or SOFIA, to directly detect atomic oxygen in Earth's upper atmosphere.
SOFIA, a Boeing 747 kitted out with a reflective telescope in its fuselage, flew at around 12 to 14 kilometres above Earth's surface. At this height, it avoided practically all the pesky water vapour in the atmosphere that could obstruct measurements of molecules.
After finding atomic oxygen in Earth's atmosphere, Professor Hübers and his team turned their attention to Venus.
In the new study, they've used the same method to detect atomic oxygen in the hazy atmosphere of our sister planet.
Venus has an atmosphere that is predominantly carbon dioxide, so scientists had long-known oxygen was present on the planet.
There had previously been indirect evidence O1 existed in the higher layers of the Venusian atmosphere, but direct evidence of its distribution, particularly during the day time, was lacking.
A long day to night
A day on Venus is long. Like, really long. It takes 243 Earth days to go from day to night. During that time, the carbon dioxide and carbon monoxide in Venus's atmosphere is pounded by sunlight, breaking it down into atomic oxygen. It then gets whisked around the planet by atmospheric circulation.
Across three flights of SOFIA, the team studied 17 locations across the planet's atmosphere. Nine of these were on the night side, seven were on the day side and one was at the terminator — the location between day and night.
They found atomic oxygen was present at all 17 locations.
This finding enables researchers to study how the atmosphere changes and mixes, particularly in the region where atomic oxygen is most abundant, at 90 to 120km above the Venusian surface.
This region is notable because it's a transition region between two dominant circulation patterns in the Venusian atmosphere.
For Stephen Kane, professor of astronomy at the University of California Riverside who was not involved in the study, the detection points to a bigger question: Where might that atomic oxygen have come from?
"One of the fascinating parts of Venus, which we're still trying to resolve, is if it ever had past liquid water on the surface," he said.
If Venus had water, H2O, then as it started to heat up and transition to the runaway greenhouse state it's in today, the water would have evaporated.
Hydrogen atoms would have been ripped away from oxygen atoms and lost to space. But the oxygen might have stayed behind.
"This oxygen may be a significant component of past surface water, which now remains in the atmosphere," he said.
This starts to build a picture of a Venus completely unlike the one we see today. Perhaps, it even suggests that billions of years ago, Venus may have been habitable.
As further evidence for that hypothesis, Professor Kane also pointed to the discovery in March showing evidence of volcanic activity on the planet.
To further investigate that idea, space agencies are returning to Venus to probe its atmosphere in more detail and map its surface.
A future among the clouds of Venus
NASA and the European Space Agency are both preparing for interplanetary missions to Venus.
Professor Kane is a science team member 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 eye-opening, with plans to drop a probe through the clouds of Venus and onto its rocky surface.
NASA's VERITAS was a little different. It would conduct atmospheric studies and mapping of the surface from orbit, something planetary scientists have not been able to do since the Magellan mission of the 1990s. VERITAS has effectively been put on ice due to a budgetary freeze.
Fortunately, planetary scientists could get their orbiter data in the form of EnVision, an ESA spacecraft set to launch in 2031, that will conduct high-resolution radar scans of the planet's surface.
The missions will start to answer some of the key questions about Venusian history, building on the hypothesis of past water.
Professor Kane, for example, will be keenly interested in examining the ratio of two hydrogen isotopes — a more definitive way to tell if Venus once contained water. Current measurements vary greatly, so it's difficult to draw conclusions.
"DAVINCI is finally going to put that to rest," he said.
A richer understanding of Venus may also help guide exploration beyond our Solar System.
As we tend to discover very hot, irradiated planets close to their home stars, Venus — and the measurements we have of the molecules in its atmosphere — could act as a bit of a benchmark for what we expect to see in deep space, Dr Chudczer said.
"We can produce better models that include the photochemical reactions that lead to formation of atomic oxygen and compare our observation of other molecules with what we see on Venus," she said.
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