The conditions for alien life might be closer than we thought.
The habitability of rocky, Earth-sized planets depends on several factors, including their chemical composition and interior structure. These, along with the planet's distance from and character of its host star, fundamentally shape long-term surface conditions. Not only in our neighborhood, but also for planets beyond our solar system.
And the nearest star system to Earth, which likely hosts at least one rocky planet in its habitable zone, might have "an equivalent water-storage capacity" to Earth, according to a recent study shared on a preprint server.
In other words, the closest alien world to our solar system might have oceans the size of Earth's.
The closest alien world could be like the early Earth
Lead author of the study Haiyang S. Wang, who is also a postdoctoral researcher in the Exoplanets Habitability Group at ETH Zurich, worked with several other scientists to use a model that studies the composition of rocky planets indirectly, but analyzing the conditions of their host star. This method was applied to the nearest sun-like stars — Alpha Centauri A and B, which make up a triad of stars together with Proxima Centauri — to estimate the bulk composition of any rocky, Earth-like planets positioned in the habitable zone of Alpha Centauri. Additional modeling from here reveals what the interiors and early atmospheres of these planets might look like. And the researchers found that compared to Earth, a planet located in the Alpha Centauri system's habitable zone probably has "a reduced (primitive) mantle that is similarly dominated by silicates albeit enriched in carbon bearing species", like the graphite and diamond on Earth.
Planets orbiting the Alpha Centauri system at a safe distance from their host stars are also likely to house an iron core slightly larger than Earth's, and roughly the same water capacity. But it might be too soon to live there, so don't pack your bags just yet. According to the study, planets there probably have an atmosphere much like Earth's early days, in an era called "Archean Earth," roughly 4,000 to 2,500 million years ago. In our planet's ancient history, this was a time when the surface had cooled, when continents were beginning to form, and the first signs of primitive life appeared. While there was liquid water at this stage on Earth, it may have been highly acidic, and the atmosphere was sorely lacking in free oxygen.
A nearby alien world might be friendlier to life than Mars
Additionally, while both Alpha Centauri A and B are sun-like in many respects, their metallicities are roughly 72% higher than our sun, which could modify the condensation and evaporation process on a rocky planet in their habitable zone. In February of this year, astronomers spotted signs of a potentially life-supporting planet orbiting the Alpha Centauri system — specifically, closer to Alpha Centauri A. Roughly 4.37 light-years away, the more recent study from Wang and colleagues helps us to better estimate the current conditions on rocky planets, like the one suspected to reside in the closest star system.
However, Wang believes more research is necessary to determine how the differences between Alpha Centauri A and B and our sun would affect a rocky planet's evolution before more may be said about the habitability of any Earth-like planets there. But, even with acidic oceans and no free air, a planet like the one described above could be far friendlier to human settlement than Mars. We just have to find a way to reach it within a single human lifetime.