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Proxima Centauri is a member of the Alpha Centauri star system, being identified as component Alpha Centauri C, and is 2.18° to the southwest of the Alpha Centauri AB pair. It is currently 12,950 AU (0.2 ly ) from AB, which it orbits with a period of about 550,000 years.
Given the different Sun incidence in different positions in the orbit, it is necessary to define a standard point of the orbit of the planet, to define the planet position in the orbit at each moment of the year w.r.t such point; this point is called with several names: vernal equinox, spring equinox, March equinox, all equivalent, and named considering northern hemisphere seasons.
Proxima Centauri b is the closest exoplanet to Earth, [20] at a distance of about 4.2 ly (1.3 parsecs). [5] It orbits Proxima Centauri every 11.186 Earth days at a distance of about 0.049 AU, [1] over 20 times closer to Proxima Centauri than Earth is to the Sun. [21] As of 2021, it is unclear whether it has an eccentricity [e] [24] but Proxima Centauri b is unlikely to have any obliquity. [25]
The scope of the list is still restricted to the main sequence spectral types: M, K, F, G, A, B and O. It may be later expanded to other types, such as S , D or C . The Alpha Centauri star system is the closest star system to the Sun .
The stars with the most confirmed planets are the Sun (the Solar System's star) and Kepler-90, with 8 confirmed planets each, followed by TRAPPIST-1 with 7 planets. The 1007 multiplanetary systems are listed below according to the star's distance from Earth. Proxima Centauri, the closest star to the Solar System, has three planets (b, c and d).
However, Proxima Centauri's classification as a red dwarf casts doubts on the habitability of any exoplanets in its orbit due to low stellar flux, high probability of tidal locking, small circumstellar habitable zones and high stellar variation. Another likely candidate is Alpha Centauri, Earth's nearest Sun-like star system 4.37 light-years away.
Counting them among the planets became increasingly cumbersome. Eventually, they were dropped from the planet list (as first suggested by Alexander von Humboldt in the early 1850s) and Herschel's coinage, "asteroids", gradually came into common use. [140] Since then, the region they occupy between Mars and Jupiter is known as the asteroid belt.
The closest system is Alpha Centauri, with Proxima Centauri as the closest star in that system, at 4.2465 light-years from Earth. The brightest, most massive and most luminous object among those 131 is Sirius A , which is also the brightest star in Earth's night sky ; its white dwarf companion Sirius B is the hottest object among them.