Beyond our Sun, the closest star to Earth is Proxima Centauri. This small, faint star holds significant interest for astronomers due to its proximity.
Proxima Centauri: Our Nearest Stellar Neighbor
Proxima Centauri is a red dwarf star with a mass approximately 12.5% of the Sun’s and a diameter roughly 14% that of our Sun. With a surface temperature around 3,000 Kelvin, it is considerably cooler than the Sun. Its total luminosity is only about 0.16% that of the Sun, making it too faint to be seen with the naked eye from Earth. Proxima Centauri is located about 4.24 to 4.25 light-years away from Earth, or approximately 40 trillion kilometers. It is also known as a flare star, meaning it can experience sudden increases in brightness due to magnetic activity.
The Alpha Centauri System
Proxima Centauri is part of a triple star system known as Alpha Centauri, consisting of three gravitationally bound stars: Alpha Centauri A, Alpha Centauri B, and Proxima Centauri. Alpha Centauri A and B form a binary pair, orbiting each other with a period of about 80 years. These two stars are similar to our Sun, with Alpha Centauri A being a yellow G2-type star and Alpha Centauri B an orange K1-type star. The distance between Alpha Centauri A and B varies significantly due to their eccentric orbit, ranging from about 11.2 to 35.6 astronomical units (AU). Proxima Centauri, while gravitationally linked to this pair, orbits them at a much greater distance, roughly 13,000 AU (about 0.21 light-years away from the Alpha Centauri AB binary), with an orbital period around the central pair around 550,000 years.
Exoplanets in Proxima Centauri’s Orbit
Proxima Centauri hosts at least two confirmed exoplanets: Proxima Centauri b (Proxima b) and Proxima Centauri d (Proxima d). Discovered in 2016, Proxima b is a terrestrial planet with a minimum mass estimated to be at least 1.06 to 1.3 times that of Earth, orbiting its star at approximately 0.05 AU (7.5 million kilometers) and completing an orbit in roughly 11.2 Earth days. Proxima b is located within the habitable zone, where conditions might allow for liquid water to exist on a planet’s surface. However, due to Proxima Centauri’s nature as a flare star, Proxima b is subjected to intense bursts of radiation, which could pose challenges for the retention of an atmosphere and the potential for life. Proxima Centauri d was confirmed as a sub-Earth planet with a mass of at least 0.26 times that of Earth, orbiting Proxima Centauri every 5.1 days at roughly 0.029 AU (4.3 million km), making it too close to the star to be in the habitable zone.