Alpha Centauri

The **Alpha Centauri** system is the closest stellar system to the Solar System, at a distance of 4.37 light-years away. The system actually consists of three stars, α Centauri A (officially Rigil Kentaurus), α Centauri B (officially Toliman), and α Centauri C (officially Proxima Centauri).

Alpha Centauri is the third brightest star in Earth's night sky, at a magnitude of -0.27. The system is also the closest known to host exoplanets, which made it a valuable target for the REVERIE-1 Mission.

Direct evidence from rock samples from Alpha Centauri Cc was used to date the system at around 4.83 billion years old, around 200 million years older than the Solar System.

## Stellar System

Alpha Centauri A and B are a binary pair, with C orbiting the common barycenter at around .2 light-years away.

### Orbital Properties

The AB binary pair orbit one another every 79.91 years, in somewhat eccentric orbits. Their periastron is 11.2 AU apart, and their apastron is 35.6 AU apart. The C component has been confirmed to be gravitationally bound to the AB pair in the year 2017, and further parallax measurements verified this further. The orbital period of Proxima Centauri takes about 536,200 years.

### Physical Properties

#### Alpha Centauri A

The most massive star in the system, Rigil Kentaurus is a Sun-like star, with a stellar classification of G2V and a total mass of 1.1 Solar Masses. The star itself has been monitored for centuries, and has shown to have its own solar cycle like that of the Sun's, varying in coronal activity. This cycle repeats every 34 years, opposed to the Sun's 11-year cycle. The star rotates once every 31.8 days.

#### Alpha Centauri B

The second most massive star in the system, Toliman is smaller and less massive than the sun at 0.907 Solar Masses, and a stellar classification of K1V, making it a more orange color. Toliman is very magnetically active, showing a cycle of 8.22 years, compared to the Sun's 11-year cycle. Its luminosity too varies between maximum and minimum, with its highest individual apparent magnitude being +1.35. The star rotates once every 22.5 days.

#### Alpha Centauri C

The smallest and least massive of the triple system, Proxima Centauri has a stellar classification of M5.5, putting it in the lower-mass category of M class stars. The star itself is incredibly active magnetically, producing many massive stellar flares and violent x-ray radiation. The one that was observed by the crew of Reverie was at least half the diameter of the star's disc. It has a rapid magnetic cycle, alternating maxima and minima every 442 days. The star rotates once every 82.6 days.

## Planetary System

### Alpha Centauri B

Toliman is the only star in the AB binary pair to host a planet, Alpha Centauri Bb. The planet was thought to be observed back in 2012, however scientists deduced in a follow-up paper that a planet did not exist. Twenty years later in 2032 did spectrographs pick up a variance in the star's light curve. Using more precise measuring techniques, there turned out to be a planet there after all, orbiting the star once every 11.3 days. The planet was found to have an incredibly small mass, at around 0.0098 Earth Masses. Its density is 3.4 g/cm^3.

#### Reverie's Observation

The planet's surface is not completely spherical, and is heavily cratered with a large impact crater near its south pole. It is dark gray in color and is not metal-rich. The planet is tidally locked to Toliman and has an orbital eccentricity of 0.095, and 0.1106 Earth Radii. The planet has a very weak magnetic field, with field measurements near low orbit reading 0.02 Gauss. Surface temperature is around 904 K. It's obliquity is less than 1°.

### Proxima Centauri

#### Proxima Centauri b

Proxima Centauri b was first observed by scientists in 2013 from archival observation data, and later confirmed the discovery in 2016. It was an amazing find, as measurements showed that the planet was within the habitable zone of Proxima, and radial velocity shows that it orbits every 11.184 days. It also has a very similar mass to that of Earth, at 1.172 Earth Masses, and a radius of 1.08 Earth Radii. Its density is 5.27 g/cm^3. Eccentricity is 0.298. Its obliquity is 22.7°.

##### Reverie's Observation

The planet does not have an atmosphere, which was to be expected due to Proxima's intense stellar wind. The planet does not have a magnetic field, and is very metal-poor, and has a tan-orange surface color. The planet is not tidally locked, and instead revolves around its parent in a .907:1 ratio.

#### Proxima Centauri c

Proxima Centauri c was announced to the public in 2020 as being a second confirmed exoplanet orbiting Proxima Centauri, discovered via Doppler Spectroscopy. The planet has a mass of 6.67 times that of Earth's, an obliquity of 32.42°, and an inclination of 133.3°. It completes one orbit every 1,923.410 days (5.4 years), and a semimajor axis of 1.489 AU. Its density is 7.73 g/cm^3, and a surface gravity of 2.36 Gs. The biggest fascination about this planet, however, is its apparent ring system that was hypothesized to encircle the planet. Other theories at the time were that it could be a dust cloud.

##### Reverie's Observation from Low Orbit

It was immediately apparent from a distance that Proxima Cc had a substantial ring system, stretching only 2.5 planet diameters in radius. Data taken from Reverie in Low Orbit found out many incredible things. The planet has a relatively strong magnetic field at 1.71 Gauss, compared to Earth's 0.65 Gauss. The planet also has a thin yet noticeable atmosphere. The atmosphere has a mass of 9,380,000,000,000,000 kg, around 0.375% of Mars' and 0.00182% of Earth's. The atmosphere itself goes up for only about 1 km, and is composed of 97.5% Ammonia, 1.9% Argon, and ~1% of Carbon Dioxide, with trace amounts of Oxygen, Neon and water vapor. The planet's ring system is primarily made up of ice and dust.

The planet is geologically active, denoted by cracks in the crust and large, wide volcanic calderas.

For more information on data collected and discoveries on the surface, see *Reverie's crash landing*.