If there are planets around Alpha Centauri, the time to find them is now. Thanks to the current position of the star system, astronomers have the best conditions to spot new exoplanets in our cosmic neighbor, located just over 4 light-years away, making it the closest star system to us. While the hunt is on, researchers had fun describing the properties of a potential Earth-sized planet in the habitable zone of that system.
Alpha Centauri is made of three stars, Alpha Centauri A and B, which are a pair of Sun-like stars whose distance vary between the Sun and Pluto and the Sun and Saturn, and then Proxima Centauri, a red dwarf significantly further out with three planets.
Given their similarities to the Sun and the fact that Alpha Centauri A and B are 1.5–2 billion years older than our star, finding an Earth-like world would be an incredible site of exploration, though we haven't found one yet. In a new paper, published in The Astrophysical Journal, a team led by Haiyang Wang of ETH Zürich looked at the chemical makeup of the two stars to model what an Earth-like world would be like.
"The detailed analysis offers a new approach of investigation to what we may expect for Earth-sized planets in the habitable zones in the solar neighborhood," the authors write.
Geochemically, they expect "a-Cen-Earth" to be similar to our own planet. So, its mantle would be similar to the Earth’s mantle, dominated by silicate but with the enrichments of graphite and diamonds, the so-called carbon-bearing species. This could be important for the possibility of life there as it would have the capacity to store water just like Earth.
But while that is exciting, it would not be a perfect twin for our world. Researchers expect the presence of a larger iron core and a lower geological activity, with a possible lack of plate tectonics. Plate tectonics are believed to have played a crucial role in the evolution of life on our planet. The new planet might be more geologically similar to Venus in that respect.
The team reports that what they found most intriguing is the planet's potential atmospheric composition, based on the chemicals that we've already detected in the system, thanks to its proximity. Carbon dioxide, methane, and water vapor would be the main components of this modeled world. That’s the same atmosphere that Earth sported during the Archean eon, between 4 billion and 2.5 billion years ago.
The possibility of intriguing similarities is certainly exciting, but the team is now looking at expanding the model with variations of mass and radius of the world considered. This could create a menagerie of model planets that can be compared with the real ones. Of course, that is, if the real ones exist.
From 2022 to 2035, Alpha Centauri A and B are visually far enough apart that telescopes can hunt for exoplanets. Together with current and upcoming next-generation telescopes, both in space and on the ground, if there are worlds there, it is likely we will find them.