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New scientific research suggests that planets similar to Venus are about twice as common as Earth-like planets with stable oceans. These findings were shared at the European Geosciences Union General Assembly in Vienna. The data provides a fresh view on how rocky planets are spread throughout the galaxy. The study shows that forming a thick atmosphere of carbon dioxide is a likely and simple process for rocky planets. This usually happens after a planet’s surface becomes completely molten. Scientists call this hot, liquid stage a "magma ocean."
Sean Jordan, an expert in exoplanet studies at ETH Zurich in Switzerland, presented these insights. He explained how planetary atmospheres change over time. Jordan argued that it is very likely for a planet to develop a carbon dioxide-heavy atmosphere after its magma ocean phase. This early stage is a crucial part of a planet’s long history. Because the shift from a molten state to a toxic atmosphere is a natural physical process, such conditions should be extremely common in the universe. He noted that building a model to show how a Venus-like atmosphere forms is relatively easy. This simplicity suggests that Venus-like conditions are not rare anomalies. Instead, they appear to be a standard outcome for planetary formation.
Jordan, the lead author of the study, emphasized that the galaxy is very good at making rocky planets. As a result, there are vast numbers of these celestial bodies scattered across space. At the time of the presentation, scientists had identified several dozen exoplanets that might be Venus-like. However, none have been confirmed as such. Researchers know there will be significant differences between these worlds. Even if their chemical makeup is similar, they will exist in many different environments. Their conditions depend on their host stars and their orbits.
These planets orbit a wide variety of stars. Our own solar system offers a critical example. Venus orbits inside the habitable zone. This zone is the area around a star where temperatures allow liquid water to exist on a surface. Venus circles the Sun, a G-2 yellow dwarf star. This typical star makes Venus a key reference point for astronomers. By studying Venus, scientists can guess the conditions of exoplanets that orbit near the inner edges of their habitable zones.
A major question for researchers involves rocky planets in close orbits around red M-dwarf stars. These stars are the most common type in the galaxy, but they pose unique challenges for habitability. The main uncertainty is whether these planets have atmospheres. If they do, there is no guarantee they can keep them. Jordan suggested that within a few years, it might become clear that rocky exoplanets around M-dwarf stars lack significant atmospheres.
The core issue is a planet’s ability to hold onto its atmosphere against the forces of its star. Planets in close orbits must withstand high-energy radiation and intense particle flows. These forces strip away atmospheric gases, a process called atmospheric erosion. This difficulty explains why scientists cannot yet confirm a Venus-like atmosphere on any exoplanet. Whether a planet has a stable atmosphere determines if it can support life or remains a barren rock.
Jordan highlighted that the study of Venus has been limited by a lack of direct data. He noted that Venus has been underexplored compared to other bodies. Despite this, scientists have gathered significant details about its deep atmosphere. This data includes information on trace gases and chemical markers. This dataset provides a foundation for studying exoplanets.
Some skeptics question the value of studying a planet seen as inhospitable. However, there is a strong link between understanding Venus and understanding extrasolar Venus-like planets. These alien worlds have not yet been confirmed orbiting other sun-like stars. Jordan explained that our knowledge of solar system planets will help us predict exoplanet behavior. As we learn more about exoplanet atmospheres, this knowledge will help us scrutinize Earth and Venus with new clarity.
When asked why Venus became hostile, Jordan offered a different perspective. He challenged the idea that Venus "went wrong" or changed from an Earth-like state. It might simply have been born that way. It is easier for scientists to model how a planet ends up as Venus today, starting from its magma ocean phase. In contrast, it is hard to model how a planet forms stable liquid water oceans from the start.
It is even harder to model how a planet passes through a runaway greenhouse phase after establishing liquid water. This difficulty suggests that forming a stable, temperate climate is delicate and rare. Forming a habitable system might be much more difficult than forming a Venus-like atmosphere. The scientific goal is to understand how a planet develops an Earth-like atmosphere with stable oceans over long periods.
Researchers want to know when we will understand the true number of exo-Venuses. Jordan stated that it will take a couple of decades to answer this. This timeline assumes that proposed missions to Venus happen. It also assumes future space telescopes are deployed and operational. These tools are essential for distinguishing between different planetary atmospheres.
The broader question remains: Does the galaxy produce more inhospitable rocky planets? These might hover near the inner boundary of the habitable zone. Or does it favor creating an Earth 2.0 that is habitable long-term? Jordan explained that there is no strong preference for planets to orbit just inside the runaway greenhouse boundary compared to just outside. The difference is not just about location. It is about the complex chemistry and physics of atmospheric retention.
Ultimately, the prevalence of hellish worlds suggests that habitable Earth-like planets might be the exception rather than the rule. This does not mean they do not exist. It means the conditions for liquid water and stable atmospheres are fragile. The ease of forming a thick carbon dioxide atmosphere makes Venus-like worlds common. Understanding these differences is key to finding true Earth analogs. The journey to confirm these exo-Venuses requires new missions to our neighbor and advanced telescopes to peer across the stars.