In fact, a recent study says, the closest solar system to our own could contain two potentially life-supporting planets.
In 2016, scientists discovered that Proxima Centauri, part of the three-star Alpha Centauri constellation, which lies about 4.37 light-years from Earth, is approximately Earth-sized. In the "habitable zone," the earth, known as Proxima b, orbits the range of distances from the star at which liquid water could occur on the surface of a moon. (A second planet, Proxima c, was later also found orbiting the star, but it orbits further out, outside the outer limits of the habitable zone.)
However, considering that its parent star is a red dwarf, there is some controversy regarding the true habitability of Proxima b. These stars are tiny and faint, the most prominent in the Milky Way, because their habitable zones are very similar to them, so close, in reality, that planets living there appear to be tidally bound, always giving their host stars the same profile, just as the moon always reveals its near side to Earth. Moreover, red dwarfs, especially when they're young, are prolific flares, so it's unknown whether their worlds in the habitable zone will hold onto their atmospheres for long.
In the Alpha Centauri trio, however, the other two stars are sun-like, a pair called Alpha Centauri A and B, which together make up a binary orbiting the same mass center. And according to the recent study, which was published online today (Feb. 10) in the journal Nature Communications, Alpha Centauri A may have its own habitable-zone earth.
The research presents findings from the Alpha Cen Region's (Close) Near Earths, a $3 million initiative led by the European Southern Observatory (ESO) and Breakthrough Watch, a program that searches around nearby stars for potentially Earth-like planets.
Using ESO's Very Large Telescope (VLT) in Chile, Close has been looking for planets in the habitable zones of Alpha Cen A and B. With several innovations, including a thermal coronagraph, the Close team upgraded the VLT, an instrument designed to block the light of a star and allow the heat signatures of orbiting planets to be spotted.
The scientists observed a thermal imprint in the habitable zone of Alpha Centauri A after analyzing 100 hours of data obtained by Close in May and June of 2019. The signal theoretically correlates to a planet of approximately Neptune scale orbiting from the star between 1 and 2 astronomical units (AU), research team members said. (One AU, approximately 93 million miles, or 150 million kilometers, is the average Earth-Sun distance.)
But the planet has not been confirmed yet, so for now, it remains a contender.
"We were amazed to find a signal in our data. While the detection meets every criterion for what a planet would look like, alternative explanations — such as dust orbiting within in the habitable zone or simply an instrumental artifact of unknown origin — have to be ruled out," test lead author Kevin Wagner, a Sagan Fellow at the University of Arizona Hubble Fellowship Program of NASA, said in a study lead author Kevin Wagner, a Sagan Fellow at the University of Arizona.