If such an alien world does exist, it could help us better understand the future of our own planet.
We can find our Solar System’s nearest neighboring stars at a distance of just over four light-years away; Proxima Centauri.
The star Proxima Centauri is already known to host three planets: Proxima b, which orbits the star every 11 days and has a mass comparable to Earth, candidate Proxima c, which is on a longer orbit of five years around the star, and Proxima d, discovered in February 2022.
In addition, this system has a binary system of Sun-like stars called Alpha Centauri AB, at a distance of 4.37 light-years, and a red dwarf called Proxima Centauri, at 4.2 light-years.
As of yet, we are unsure if the binary, Alpha Centauri AB, hosts any planets similar to Earth. Current technology can only detect a very small fraction of such exoplanets.
However, a study headed by planetary scientist Haiyang Wang of ETH Zürich in Switzerland has given us a better idea of what it might be like if there is one.
Inferring the chemical composition of the hypothetical rocky world in the habitable zone of the binary system was done by studying the chemistry of the two stars, Rigil Kentaurus and Toliman.
“We present an analysis of planetary bulk composition, interiors, and (early) atmospheres for a model Earth-sized planet in the habitable zone of Alpha Centauri AB,” the researchers write in their paper.
“The detailed analysis offers an alternative approach of investigation to what we may expect for Earth-sized planets in the habitable zones in the solar neighborhood.”
Understanding the long-term evolution of rocky exoplanets and their habitability depend on these characteristics. The mineral composition of rocky worlds is reflected in the composition of host stars, as observed in the solar system and other planetary systems.
Our knowledge of Alpha Centauri AB’s chemical composition is extensive thanks to measurements of its spectrum. By absorbing and re-emitting light, different elements in the star can produce dark (absorption) and bright (emission) profiles on the spectrum of light that is seen by our telescope. The chemical composition of a substance can be determined by these features.
The spectral analyses of Rigil Kentaurus and Toliman reveal the presence of rock-forming elements (magnesium, silicon, iron), as well as volatiles (carbon and oxygen) that evaporate rapidly.
α-Cen-Earth–a hypothetical alien world
By analyzing the spectra, we can even make rough calculations of the amounts of each element present, helpful for extrapolating hypothetical rocky worlds in the habitable zone – that ‘sweet spot’ in a solar system where the planets and the Sun are located just at a proper distance for liquid water to exist on a planet’s surface.
They named their theoretical world “α-Cen-Earth”, and they determined that it would likely resemble Earth in terms of its mineral composition. Among them is a rocky mantle, which is similar to our own in that it stores water similarly, but also contains carbon-bearing minerals such as diamond and graphite.
Moreover, this planet might have a somewhat larger iron core than Earth, and it may have fewer geological features, as well as a lack of plate tectonics, which would make it more like Venus.
This might have an impact on whether it might be habitable.
Since the relationship between stellar composition and atmosphere is much weaker for airy volatiles, it becomes more difficult to predict an exoplanet’s atmosphere using stellar composition.
For the last few years, Wang has worked on developing and refining a quantitative model that is able to link Sun-like stars with star-like exoplanets, both in terms of their refractory and volatile elements.
Using this information, the researchers were able to construct a model of the atmosphere of α-Cen-Earth; interestingly, a model of the exoplanet’s early atmosphere would have resembled that of early Earth during the Archaean eon, the time when life emerged. The team says that methane, carbon dioxide, and water would have been dominant in the historic atmosphere.
It would be very interesting if such a world exists, and if it does, it will offer key clues to the future of Earth. Since Alpha Centauri AB is 1.5-2 billion years older than the Sun, this means that any exoplanets discovered by Rigil Kentaurus and Toliman would also be older than our Sun. Luckily, we’re in an excellent position of discovering such hypothetical worlds in the near future, and future space telescopes will help in our exploration of the cosmos.
In the near future, astronomers will also be able to detect many more exoplanets that were so far elusive, some of which may be similar to Earth due to their distances from their stars.
Our techniques for finding exoplanets are becoming more sensitive, and in the near future, we will be able to detect many smaller exoplanets that have remained hidden so far.
Starting in 2022, Kentaurus and Toliman will see their orbits drift further apart. During this divergence, which will continue until about 2035, it will be less likely that light from the stars interferes with observations of exoplanets.
A relatively small exoplanet orbiting the star Rigil Kentaurus has already been detected by scientists. The exoplanet is believed to be between 3.3 and 7 times the size of Earth.