Alpha Centauri is the closest stellar system to our sun. The inserted image shows the two main stars, A and B (a third star, Proxima, is at some distance). A new study shows that a planet could be within the habitable zone of Alpha Centauri A. Images via Zdenek Bardon and NASA / CXC / Univ. of Colorado / T. Ayres et al.
Astronomers have imagined something near the star Alpha Centauri A, in the stellar system next to our sun, just 4.4 light-years away. It’s an asteroid, or dust, or an image error, or … a planet? If it is a planet, it is the first known planet to be imagined directly in the habitable zone of a star, the region of a stellar system in which liquid water may exist and, therefore, in which it could produce -life is the way we know it.
The team of astronomers says the object they imagined was a “candidate planet.” This team is part of the Near Earth Experiment in the Alpha Centauri Region (NEAR), with the specific goal of imagining low-mass (Earth-like) planets in the habitable zones of stars. The group made the observations in May and June 2019 and reported them to the journal Communications on Nature on February 10, 2021.
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Because it is relatively close (only 26 trillion miles or 42 trillion km), Alpha Centauri A is a logical target for search. Alpha Centauri A is one of the two large stars in this system, and the two stars (A and B) orbit each other in an orbit about the size of Saturn. The stars are similar in size and temperature to our sun. The habitable zone, where liquid water is possible, will be at a distance similar to that in which the habitable zone of the Earth is located.
Astronomers used the Very Large Telescope in Chile to search for planets in the mid-infrared range of the electromagnetic spectrum. Earth-like temperate planets glow brighter at this wavelength. But the image was still a challenge, because 4.4 light-years away, any planet in the habitable zone of Alpha Centauri A would be just 1 arc of a second from its home star. Thus, the team collected 100 hours of observation time to get the most sensitive image ever taken of the habitable zone of the Alpha Centauri star system.
With this remarkable improvement in imaging capabilities, the team believes it can detect planets the size of Neptune within the habitable zone of the star. The astronomers’ goal was to see if the planets around the habitable zones of the stars I could that are shown directly, and now perhaps they have already found the first evidence of it.
In image b on the right (an enlarged image from one to the left), the white dashed circle represents the inner edge of the living area. The brightest area labeled C1 is the candidate planet. Image via Nature Communications / NEAR.
The little light they detected is between the size of Neptune and Saturn and is about 1 astronomical unit, or the distance between the Earth and the sun, far from its own star. Astronomers know that the candidate on the planet could prove to be as effective as a defect or artifact in the data, but they are excited about the possibility that they have found one on the test to see if it could even be done. They also hope to soon be able to imagine smaller planets, closer to the size of Earth.
Team member Kevin Wagner of the University of Arizona released the following video, which provides a summary of the ambitions of the NEAR experiment and the methods he used to find the candidate planet.
Their discoveries will have to be confirmed before a new planet can be definitively proclaimed.
At least 50 planets around other stars have been imaged directly, only none in this habitable zone “Goldilocks” near (but not too close) to its home star. The same telescope used in this study also made the first image of an exoplanet in 2004, when it was seen around a brown dwarf. Last year the telescope detected the first multi-planet system around a star.
Until now, the direct image worked best for planets that are far away from their parent stars. It has also been easier to see planets that do not pass in front of or behind the star from our point of view. The new medium infrared imaging method can change that and open up new avenues for finding planets that can support water and life.
Conclusion: It is possible that astronomers have directly imagined the first planet in the habitable zone of a star. The star is Alpha Centauri A, just 4.4 light-years away, in the star system closest to our sun.
Source: Image of low mass planets within the habitable zone of Alpha Centauri
