Physical characteristics




Mass, radius, and temperatureedit

The apparent inclination of Proxima Centauri b's orbit has not yet been measured. The minimum mass of Proxima b is 1.17 M⊕, which would be the actual mass if its orbit were seen edge on from the Earth. Once its orbital inclination is known, the mass will be calculable. More tilted orientations imply a higher mass, with 90% of possible orientations implying a mass below 2.77 M⊕. The planet's exact radius is unknown. If it has a rocky composition and a density equal to that of the Earth, then its radius is at least 1.1 R⊕. It could be larger if it has a lower density than the Earth, or a mass higher than the minimum mass. Like many super-Earth sized planets, Proxima Centauri b might have an icy composition like Neptune, with a thick enveloping, hydrogen and helium atmosphere; the likelihood that this is the case has been calculated to be greater than 10%. The planet has an equilibrium temperature of 234 K (−39 °C; −38 °F), somewhat colder than Earth’s 255 K (−18 °C; −1 °F).

If the orbit of Proxima Centauri b is coplanar with that of the candidate exoplanet Proxima Centauri c, for which estimates of the true mass were recently calculated using various combinations of its spectroscopic orbital parameters, Gaia DR2 proper motion anomaly, and astrometric measurements, then a true mass of Proxima b can be estimated. For example, in 2020, a paper published by Kervella et al. estimated 2.1+1.9
−0.6 Earth masses, and another by Benedict et al. estimated 3.0±0.3 Earth masses, as true mass values for Proxima b.

Host staredit

The planet orbits an M-type red dwarf named Proxima Centauri. The star has a mass of 0.12 M☉ and a radius of 0.14 R☉. It has a surface temperature of 3042 K  and is 4.85 billion years old. In comparison, the Sun is 4.6 billion years old  and has a surface temperature of 5778 K. Proxima Centauri rotates once roughly every 83 days, and has a luminosity about 0.0015 L☉. Like the two larger stars in the triple star system, Proxima Centauri is rich in metals compared with the Sun, something not normally found in low-mass stars like Proxima.citation needed Its metallicity (Fe/H) is 0.21, or 1.62 times the amount found in the Sun's atmosphere.note

Even though Proxima Centauri is the closest star to the Sun, it is not visible to the unaided eye from Earth because of its low luminosity (average apparent magnitude of 11.13).

Proxima Centauri is a flare star. This means that it undergoes occasional dramatic increases in brightness and high-energy emissions because of magnetic activity that would create large solar storms. On 18 March 2016, a superflare was observed with an energy of 1026.5 joules. The March 2016 flare reached about 68 times usual level, thus a little brighter than the Sun. The surface irradiation was estimated to be 100 times what is required to kill even UV-hardy microorganisms. Based on the rate of observed flares, total ozone depletion of an Earth-like atmosphere would occur within several hundred thousand years.

Orbitedit

Proxima Centauri b orbits its host star every 11.186 days at a semi-major axis distance of approximately 0.05 astronomical units (7,000,000 km; 5,000,000 mi), which means the distance from the exoplanet to its host star is one-twentieth of the distance from the Earth to the Sun. Comparatively, Mercury, the closest planet to the Sun, has a semi-major axis distance of 0.39 AU. Proxima Centauri b receives about 65% of the amount of radiative flux from its host star that the Earth receives from the Sun – for comparison, Mars receives about 43%. Most of the radiative flux from Proxima Centauri is in the infrared spectrum. In the visible spectrum the exoplanet receives only ~3% of the PAR (400–700 nm) of Earth irradiance – for comparison, Jupiter receives 3.7% and Saturn 1.1%. – so it would usually not get much brighter than twilight anywhere on Proxima Centauri b's surface. The maximum illumination of horizontal ground by twilight at sunrise is about 400 lux, while the illumination of Proxima b is about 2700 lux with a quiet Proxima. Proxima also has flares. The brightest flare observed until 2016 had increased the visual brightness of Proxima about 8 times, which would be a large change from the previous level but, at about 17% the illumination of Earth, not very strong sunlight.note However, because of its tight orbit, Proxima Centauri b receives about 400 times more X-ray radiation than the Earth does.

Comments

Post a Comment

Popular posts from this blog

Proxima Centauri b

Image
Proxima Centauri b (also called Proxima b or Alpha Centauri Cb ) is an exoplanet orbiting in the habitable zone of the red dwarf star Proxima Centauri, which is the closest star to the Sun and part of a triple star system. It is located approximately 4.2 light-years (4.0 × 1013 km) from Earth in the constellation of Centaurus, making it and Proxima c the closest known exoplanets to the Solar System. Proxima Centauri b orbits the star at a distance of roughly 0.05 AU (7,500,000 km; 4,600,000 mi) with an orbital period of approximately 11.2 Earth days, and has an estimated mass of at least 1.2 times that of the Earth. The planet is subject to stellar wind pressures of more than 2,000 times those experienced by Earth from the solar wind and the habitability of Proxima Centauri b has not yet been definitively established. The discovery of the planet was announced in August 2016. The planet was found using the radial velocity method, where periodic Doppler shifts of spectral lines of th...
Read more

Habitability

Image
The habitability of Proxima Centauri b has not been established, but the planet is subject to stellar wind pressures of more than 2,000 times those experienced by Earth from the solar wind. This radiation and the stellar winds would likely blow any atmosphere away, leaving the subsurface as the only potentially habitable location on that planet. The exoplanet is orbiting within the habitable zone of Proxima Centauri, the region where, with the correct planetary conditions and atmospheric properties, liquid water may exist on the surface of the planet. The host star, with about an eighth of the mass of the Sun, has a habitable zone between ∼0.0423–0.0816 AU. In October 2016, researchers at France's CNRS research institute stated that there is a considerable chance of the planet harboring surface oceans and having a thin atmosphere. However, unless the planet transits in front of its star from the perspective of Earth, it is difficult to test these hypotheses. Even though Proxima Cen...
Read more

View from Proxima Centauri b

Image
Viewed from near the Alpha Centauri system, the sky would appear much as it does for an observer on Earth, except that Centaurus would be missing its brightest star. The Sun would be a yellow star of an apparent magnitude of +0.5 in eastern Cassiopeia, at the antipodal point of Alpha Centauri's current right ascension and declination, at 02h 39m 35s +60° 50′ (2000). This place is close to the 3.4-magnitude star ε Cassiopeiae. Because of the placement of the Sun, an interstellar or alien observer would find the \/\/ of Cassiopeia had become a /\/\/ shapenote nearly in front of the Heart Nebula in Cassiopeia. Sirius lies less than a degree from Betelgeuse in the otherwise unmodified Orion and with a magnitude of −1.2 is a little fainter than from Earth but still the brightest star in the Alpha Centauri sky. Procyon is also displaced into the middle of Gemini, outshining Pollux, whereas both Vega and Altair are shifted northwestward relative to Deneb (which barely moves, due to its ...
Read more