As Earth’s sister planet, Venus has endured a love-hate relationship when it comes to exploration. Now, new results suggest the presence of a potential habitability on Venusand the long-forgotten brother may find himself in the spotlight again.
With its orbit close to the rising or setting sun, Venus shone clearly to early ancient astronomers. As humanity began exploring the solar system, a world with nearly the same mass and radius as Earth seemed the most promising target. Venus it lies at the edge of the habitable zone of our sun, the region around a star where a planet should be able to host liquid water on its surface and ideas of a true twin planet swam before the eyes of scientists and the public.
“The idea of a temperate or jungle-like environment on the surface of Venus remained until the mid-1
When NASA’s Mariner 5 flew to Venus in 1967, it revealed a surface temperature of 860 degrees Fahrenheit (460 degrees Celsius). “The swamps have digitally evaporated before their eyes,” Suzanne Smrekar of NASA’s Jet Propulsion Laboratory in California told Space.com via e-mail. Smrekar is the principal investigator of NASA proposed the VERITAS mission to Venus. (The name is short for Venus Emissivity, Radio Science, InSAR, Topography and Spectroscopy.)
No longer a swampy sister, our vision of Venus became a hellish world with thick clouds, losing much of the attention it had garnered earlier in the science fiction tradition. With a surface hot enough to melt lead, the planet was too hot to house water on its surface. Its life potential seemed to evaporate with the swamps.
But as the fickle public turned their eyes to the redest world of Mars, scientists continued to study Earth’s twin. “We started the task of trying to figure out how the surface of Venus could be so far removed from previous ideas,” Kane said.
For the past 50 years, humans have been trying to solve this puzzle. The Soviet Union continued to send Venera missions to Venus until the early 1980s, some orbited the world and others land on its surface. NASA’s Viking and Pioneer missions have exploded, taking photos and collecting data as they travel to the outskirts of the solar system.
In 1990, NASA’s Magellan mission mapped the planet’s surface and that of the European Space Agency Venus Express has been orbiting the world for eight long years, studying its atmosphere. In 2015, The Akatsuki mission of Japan started a probe of the Venusian atmosphere that continues today. Meanwhile, missions across the solar system regularly use Venus as a gravitational pull towards distant worlds, making a few brief observations in their path.
The myriad of observations, coupled with advances in understanding the evolution of planets, have presented a slowly changing image of Venus. The results can help resolve questions about the evolution of life.
“Although the realization during the 1960s of Venus’ infernal conditions led many to believe that Venus had nothing to do with habitability, we have since changed our perspective to understand that Venus has everything it has to do with habitability, ”Kane said.
The future of the Earth, the past of the Earth
During the initial stages of the exploration, scientists quickly realized that Venus was suffering from a severe case of greenhouse effect. The planet’s thick atmosphere acted as a blanket to trap heat, raising temperatures to unbearable extremes.
“Many people assumed that Venus was a ‘solved problem’, where a scenario fleeing a greenhouse went haywire and that was the end of the story,” Kane said. “However, now we are realizing that this is only the beginning.”
The conditions that once led scientists to suspect that Venus might be an Earth-like world had not changed. Both planets appear to have the same origins: rocky worlds large enough to hold their atmosphere with mature initial conditions to collect water on the surface. So where did Venus go wrong?
This is a question that still plagues Venus researchers as they try to determine the conditions that lead to habitability and those that lead to an overheated catastrophe. Immediately behind it is the question of whether the Venusian atmosphere changed radically in a single catastrophe or whether it was a slow change over time.
Ongoing observations have also revealed that Venus is far from inactive. Low-resolution radar images of the surface showed evidence recent explosive volcanism, over the past 100 million years. If our sister planet continues to erupt gas into the air through its peaks, this would indicate a slow change in the atmosphere rather than a single cataclysm.
These questions are particularly important for the Earth, where man-made greenhouse gases continue to accumulate in the atmosphere. Some point to Venus as a sign of our planet’s future if human behavior doesn’t change.
But the planet next door it may not only reveal our future, it can also show our past. According to Smrekar, Venus is the only place in the solar system that can have continents and subduction, the first step in kicking off plate tectonics. Despite a seemingly long list of missions that have toured the planet, however, our view of the surface remains incredibly poor. If Venus has continents, planetary scientists want to know when and how they formed, which could help researchers better understand the early Earth.
“The Earth’s continents and the plate tectonic system have shaped the evolution of Earth’s climate and habitability,” Smrekar said. “But they were born billions of years ago; little data remains from that time.”
It is also possible that it was Venus, not Earth, where life first appeared in the solar system. According to Smrekar, our sister planet has many of the characteristics required for a habitable world: an internal geological engine to drive volcanism, tectonics, surface weathering, and even a potential ocean in the past. “While its surface looks extremely inhospitable today, it may have been the first habitable planet in the past,” he said.
The exoplanet next door
As the number of known exoplanets rises into the thousands, Venus could hold the key to unlocking and understanding which of those worlds are habitable. Planets around other stars are seen from an incredible distance and humans are unlikely to step on any of them in the foreseeable future. But from a distance, a potentially habitable exo-Earth looks just like an exo-Venus.
“When viewed as exoplanets, Venus and the Earth are identical,” Smrekar said. “Yet today they are completely different.”
In 2015, Kane established a “Venus area, “the region around a star where a planet’s atmosphere could turn into a greenhouse world. At the time, he said he wanted to emphasize only that dimension, one of the main methods of characterizing a world as” similar to Land “is not enough to indicate habitability.
To fix the Venus-like hell worlds you need to know what made Venus the planet it is today. “The key to understanding planetary habitability and how it evolves over time lies in understanding the evolution of our sister planet,” Kane said.
This is one of the reasons scientists like Smrekar and Kane support another mission to Venus. Further exploration could look for signs that water has existed on the surface relatively recently, which could indicate that the planet has slowly lost its habitable state rather than suffering a rapid catastrophe.
“We absolutely need to return to Venus to answer the many outstanding questions, especially related to when Venus lost its liquid water,” Kane said.
Kane adds that Venus can help provide a better view of the evolution of life on other worlds than other non-terrestrial planets in the solar system.
“The topic of habitability in the context of exoplanets will always focus on the Earth and Venus-sized planets, not the size of Mars,” Kane said. “The quest to detect life in the universe necessarily requires understanding the incredible Venus-Earth dichotomy.”
After decades of ignorance, Venus may soon take center stage.
New results, released on Monday (September 14), reveal the presence of a potential biological signal that could come from life hidden in the clouds of the planet. Earth’s twin clouds have long been considered a potential home for lifebut the discovery of phosphine, a flammable gas that, on Earth, can come from the breakdown of organic material, gives the topic new urgency.
“Biology in the atmosphere may be the last surviving members of a previous Venusian biosphere,” Kane said. “If confirmed as the result of life in the clouds, this result would be an extraordinary lesson in how life can truly adapt to all the riches available within an environment.”
But Kane has issued some caveats for this conclusion. If life is currently living in the clouds of Venus, it must have found a way to continue staying in the atmosphere rather than falling back to the planet’s surface, which he calls “a difficult problem to solve”. As life was discovered in the clouds of Earth, that material was lifted off the surface through convection, as the warmer, less dense material moved upward. That mechanism doesn’t exist on Venus, Kane said.
Additionally, Venus’s atmosphere is hot, dry, and surrounded by large reservoirs of sulfuric acid, which can make it difficult for life to survive for the past billions of years by the time the surface may have harbored life, Kane said. And the new research is based on phosphine production on Earth, while Venus’s surface and atmosphere are significantly different.
He thinks the new findings highlight the need to look for active and recent volcanism. While the authors have dismissed active volcanism as an explanation for their detection, he points out that the process is difficult to observe on Venus, where the lava signal can disappear within days or weeks. Understanding the surface chemistry and processes that produce volcanism is key to interpreting the new research, which he said is “intriguing and underscores the need to better understand our sister planet.”
For Kane, the new findings underscore the need to return to Earth’s twin in the near future.
“Since the request has been made and we currently don’t have a good explanation for the observations, we have a responsibility to investigate further and determine what the true source of the phosphine is,” he said. He pointed to upcoming missions, including VERITAS, which will help scientists understand the planet’s atmosphere and geology.
“It is through these kinds of missions that we will be able to fully answer this question about possible life in the Venusian clouds,” said Kane.
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