How would an Earth-like planet look in Alpha Centauri?

We now know that our nearest neighbor, Proxima Centauri, is host to at least two planets. But we’re not sure if there are any planets near Alpha Centauri, a binary system just beyond that. If there are, however, we now know what they might look like. New research has used modeling and spectroscopic data of the system’s two stars to estimate what a rocky planet in the system’s habitable zone might be made of.

To estimate the composition of this hypothetical planet—dubbed α-Cen-Earth—the team developed what they call a devolatilization model. To start, they looked at the amounts of volatile (hydrogen, carbon, oxygen, etc.) and non-volatile elements (like iron and silicon) in the Sun and the Earth and looked at how they differed.

Armed with this data, the team then looked at high-resolution spectroscopy data about the elements in the α Centauri A and α Centauri B stars—which provided them information about 22 elements. From their model and this data, they could estimate possible compositions of a hypothetical rocky planet in the system’s habitable zone. “You get a model of the chemical composition of rocky planets that would be in the habitable zone,” Charley Lineweaver, one of the paper’s authors, told Ars.

Show me what you’re made of

It is likely that α-Cen-Earth—if it exists—would be geochemically similar to Earth, with a mantle likely dominated by silicates. But it may have more graphite and diamond, thanks to a higher ratio of carbon to oxygen, according to Lineweaver.

The planet’s water-storage capacity would also be similar to Earth’s core, but it would also have lower geological activity—possibly lacking plate tectonics altogether—and a smaller iron core. “The planet that results from it will be interestingly different in terms of the mineralogy and the abundance of rock versus, say, methane and carbides, graphite, and maybe even diamonds in the core,” Lineweaver said.

According to Lineweaver, the model could also be applied to other hypothetical planets. He added that, personally, he suspects that rocky planets are much more common in other solar systems than we have discovered so far—it’s not so much that they aren’t there, it’s just that our ability to detect them is somewhat limited.

It is possible, however, that α-Cen-Earth—or any other planet—may differ from the model as meteors bearing other elements often impact planets, potentially affecting their overall chemical composition. However, the team’s model could help researchers in the future identify habitable planets, Lineweaver said.

The Astrophysical Journal, 2022. DOI: 10.3847/1538-4357/ac4e8c (About DOIs)