Proxima b

==Overview==
Proxima b, also known as Proxima Centauri b or α Centauri C b, is an exoplanet orbiting Proxima Centauri. The exoplanet is well known for being its host star, Proxima Centauri being the closest star to the Solar system, as well as its possible habitable conditions as it is situated in the habitable zone, but its own star being a flare star and a likelihood for the exoplanet being tidally locked say otherwise.
==Discovery==
Before Proxima b was discovered, Proxima Centauri was a target for an exoplanet search. Before the year 2016, the star experienced anomalies that couldn't be explained through chromospheric activity or stellar flares based on observations at the European Southern Observatory in Chile.https://ui.adsabs.harvard.edu/abs/2016Natur.536..437A/abstract This led to the Pale Red Dot project in January 2016 to prove the existence of a hypothetical exoplanet. On August 24, 2016, a group led by Anglada-Escudé announced the discovery of Proxima Centauri b, suggesting a terrestrial exoplanet in the habitable zone could explain these anomalies.
==Habitability==
Despite Proxima b orbiting within the habitable zone, any life on the exoplanet will be difficult for them if they don't adapt. Its own parent star, being a flare star, could emit extreme doses of radiation, which could hinder the possibility of life on Proxima b as the stellar flares and coronal mass ejections wear off any kind of basic necessities for life to at least exist, such as an atmosphere, liquid water, and an ozone layer. Any magnetic field couldn't exist if Proxima b is tidally locked due to its rotational period being identical to the orbital period, also known as tidal locking.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5820795/ Despite this, red dwarfs have a lifespan longer than orange dwarfs or yellow dwarfs, as their nuclear reactions are much slower. Given enough time, life could develop even in these harsh conditions.https://www.cambridge.org/core/journals/international-journal-of-astrobiology/article/could-photosynthesis-function-on-proxima-centauri-b/4418B56656F8EE751FAF7D3304851836
===Transporting liquid water===
Proxima b orbits within the habitable zone, a zone where water stays liquid instead of turning into ice or vapor. It is unclear as to how much water Proxima Centauri b gained, but plenty of mechanisms can bring water to a developing planet.https://www.aanda.org/component/article?access=doi&doi=10.1051%2F0004-6361%2F201629576 Some studies suggest that the water loss on Proxima b could be considerably larger,https://www.aanda.org/articles/aa/abs/2017/07/aa30582-17/aa30582-17.html while others are far smaller.https://link.springer.com/book/10.1007/978-3-319-97658-7 Exocomet collisions might also replenish water to Proxima b if they're available.https://academic.oup.com/mnras/article/480/3/3595/5064248?login=false
===Atmosphere===
The existence of an atmosphere on Proxima b similar to ours is uncertain due to many factors that could destroy or preserve it. An atmosphere like ours is essential for supporting life, which can be challenging due to negative factors emitting from the star itself, such as UV and X-ray radiation exposure at excessive doses.https://link.springer.com/book/10.1007/978-3-319-97658-7 When hydrogen is heated by UV and X-ray radiation, it absorbs the energy and keeps it, causing the atmosphere to dissipate. They move at an increasingly immense speed due to this process until they escape the gravitational pull.https://iopscience.iop.org/article/10.3847/1538-4357/aa7846 The atmosphere is at greater risk from stellar winds and coronal mass ejections emitting from the star,https://iopscience.iop.org/article/10.3847/2041-8205/833/1/L4 which might have an impact 4–8 times greater than that of Earth. Further loss could result from lifting the planet's atmosphere beyond the magnetic field by the strong UV and X-ray radiation. Proxima b is in extreme proximity to the star, so the stellar wind produced may be potentially denser. It is unknown whether or not Proxima b possesses a magnetic field, and it's possible that its upper atmosphere does. Based on the intensity of its own magnetic field, the star's activity may reach the planet's atmosphere and remove portions of it.
Volcanic activity has the ability to regenerate Proxima b's atmosphere gradually if it has diminished completely. A second atmosphere would almost certainly consist of carbon dioxide,https://iopscience.iop.org/article/10.3847/1538-3881/aa7fbc producing a much more stable atmosphere than an Earth-like atmosphere.https://www.aanda.org/articles/aa/abs/2021/07/aa40176-20/aa40176-20.html
==Tidal locking==
Tidal locking is a threat to any chances of habitable conditions on Proxima b due to the extreme climate it generates.https://iopscience.iop.org/article/10.3847/2041-8205/832/1/L12 Tidal locking means the process of a change in the rotational characteristics, turning the rotational period of the planet the same as the orbital period. This mechanism causes one hemisphere of a planet to face permanently on its host while the other hemisphere does the opposite. If Proxima Centauri b's eccentricity is greater than 0.1https://iopscience.iop.org/article/10.3847/1538-4357/aba8a5 to 0.06, it might not be tidally locked since it could undergo a higher-order resonance or a 3:2 resonance similar to Mercury.https://www.aanda.org/articles/aa/abs/2016/12/aa29577-16/aa29577-16.html The existence of a moon orbiting Proxima b may delay the process of tidal locking; even so, any moon orbiting Proxima b may not last long in the timescales of billions of years. Higher eccentricities might be provoked by interactions between its neighboring star, Alpha Centauri, and other planets orbiting Proxima Centauri.
==Physical properties==
The exoplanet orbits its star at about 11.1 days, with a distance to its host star at about 0.049 AU.https://www.aanda.org/articles/aa/abs/2022/02/aa42337-21/aa42337-21.html Proxima b may not have an axial tilt. How old the exoplanet is, its orbital eccentricity, and its inclination are unknown. The estimated mass of Proxima b is 1.07 Earth masses with a small margin of error. Its estimated radius is difficult to ascertain; with a range of 0.94 to 1.4 Earth radii, depending on the composition of the exoplanet, it could be a planet with a large core, similar to Mercury, or a water-abundant world.https://doi.org/10.3847%2F2041-8205%2F831%2F2%2Fl16 It is expected that its equilibrium temperature is -39 °C (234 K; -38 °F).https://www.nature.com/articles/nature19106
==Gallery==
File:Proxima-002.png|View of the Proxima centauri system
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