Barnard's Star system

Barnard's Star system is a small, conjectured around. It is located just 5.95 s away in the constellation in the caelregio Tarandus. Barnard's Star is the second nearest star system after.

Star
Barnard's Star is a star of spectral type M4Ve. The star's magnitude seen from Earth is 9.54, which can only be visible by using at least a small telescope. The bolometric luminosity is that of the Sun and visual luminosity  of the Sun. Due to its very low luminosity, the center of habitable zone would have to be around 0.06 AU from the star and such a small separation can cause planets occupying this region to be tidally locked, meaning one hemisphere always face the star while the other never faces it.

The mass is of the Sun or 150 times more massive than Jupiter. It is 80% smaller than our Sun. The star is more than twice as old as our Sun at around 10 billion years old. Due to its old age, it takes 130 days to rotate once, over five times longer than 25 days for our Sun.

This red dwarf is also metal-deficient, 25% that of the Sun's. This means it is less likely to form planets, especially gas giants and rocky super-Earths.

Barnard's Star has the highest of any star, moving at 10.3"/yr. The star would take just 150 years to transverse the diameter of the full moon. The star is approaching the Sun at 90 km/s and will make its closest approach at 3.75 light-years around 9800 AD.

Planetary system
Barnard's Star contains three small planets orbiting within just 0.105 AU. The orbital periods range from just 16 hours to a month and all three have orbital eccentricities under 0.01. Planets have masses ranging from 0.078 to 0.138 M$⊕$ and have sizes from one-third to half the size of Earth. By the way, all three planets are denser than Earth's, the densest planet in our solar system.

Barnard's Star b
Barnard's Star b is the innermost planet of the Barnard's Star system. It orbits extremely close to the dim star at just 1.23 Gm, 120 times closer to the star than Earth is to the Sun. It takes just two-thirds of a day to orbit once around the star, which the year on this planet is very brief. Year on Earth in hours is 8766, but on this planet, just 16. Since orbital period lasts less than an Earth day, this planet rotates once quicker than Earth's despite it is tidally-locked. The orbit of this planet is almost a perfect circle with an eccentricity of just 0.00015, only 1% that of Earth's eccentricity. Planets in smaller orbits with same eccentricities would reduce distance differences. As in the case of this planet, 370 megameters. This miniscule eccentricity is caused by tidal circulation due to nearby star's gravity. Due to gravitational pull of two planets beyond this orbit, its eccentricity oscillates at a 6000-year cycle from as low as 0.000011 to as high 0.008. The planet's eccentricity is current increasing until it reaches its maximum around 5400 AD. It reached the minima around 800 BC. The current eccentricity is only higher than the minima, but during the 35$⊕$ century, eccentricity will start a much more rapid rise.

Barnard's Star b has a mass that of Earth's and slightly less massive than. It is the size of Earth, producing the density approaching 16 g/cm$3$. This super-high density would suggest that this planet was the core of a giant planet about the size of. Periods of intense stellar winds during flaring era must have blew away the gaseous envelope and evaporated all the remaining volatiles. The surface gravity is of that of Earth's, twice as strong as usual for this mass.

This planet is active despite it's age and small size, due to gravitational tug of the star as planet orbits, same way as Jupiter exerts on Io causing geological activity. The surface temperature is hot, at 1078°F, but much less hotter than this semimajor axis around solar-type stars. It is classified as a. It has a thin, metallic atmosphere made mainly of and  vapors as well as  and  vapors.

Barnard's Star c
Barnard's Star c is a planet orbiting in a 5:1 resonance with b with an orbital period of 3 days. The planet's eccentricity is similar to ' at 0.006. Like the inner planet, this one is tidally locked to the star, meaning that one side always faces the star. It is slightly more massive than Mars and is just under half the size of Earth. It's density is 7.24 g/cm$⊕$, less than half the density of the inner planet. It is a crater planet with the surface temperature of 368°F and has only a tenuous atmosphere.

Barnard's Star d
Barnard's Star d is the outermost of the three planets orbiting around Barnard's Star. It takes 30.8 days to orbit the star at an average distance of 0.1042 AU, which is one-tenth the Earth–Sun distance. Its eccentricity is 0.004, varying from 0.1037 to 0.1046 AU. It masses 0.078 Earth masses and sizing 0.376 Earth radii, producing a density of 8. g/cm$th$ and surface gravity of 0.55 g. The density suggests that this planet contains greater portion of iron and heavy metals like gold than Earth contains. Despite the planet orbits 10 times closer to its sun than Earth is, the planet's surface is cold with the surface temperature of −115°F. Despite this temperature, there is little ice on the surface as it is mainly deserted and cratered. It has a thin atmosphere made of 91% CO$3$.