Aita

Aita (Tau Ceti e, P849) is the fourth in orbit around, a star just 12 s away. It is one of the five detected planets discovered on December 19, 2012 and is one of roughly thirteen in this planetary system. Aita orbits over half the distance between Earth and the Sun and is over half bigger than Earth. It is a 4.5-Earth mass sulfur planet with its year lasting 24 weeks.

was named after the of the, equivalent to the Greek god.

Discovery and chronology
Aita was discovered on December 19, 2012, together with four other planets in this system. This discovery was made by carefully watching the wobble of Tau Ceti caused by gravitational tug of planets. It was successfully done using high resolution spectrograph mounted on the 3.6-meter telescope in  located in the Atacama Desert in Chile. Aita became the 841st exoplanet discovered since 1992 and is the 160th planet discovered in 2012. It is also the 33rd planet discovered in and 101st in Hippocampus.

Orbit
Aita lies halfway between the orbits of and  at 0.55 AU (82.2 gigameters). As it is typical for other planets orbiting Tau Ceti, its eccentricity is low. For Aita, the eccentricity value is 0.05455, which means that periastron distance from the star is 5.455% closer than average distance while apastron is 5.455% farther away. Aita's orbital circumference is 3.45 AU (516 Gm), calculated by multiplying average distance by 2π. is defined as the area of space within the planet's orbit with star at the center. The value is 0.95 AU² (21200 Gm²), which is 30% the area within Earth's orbit.

Aita's year is defined as the period it takes to revolve around the star. It takes 168 days, 24 weeks, or 0.46 Earth year to make one orbit. Using orbital circumference and its year can be used to calculate as 35.66 km/s, or more appropriate in astronomical terms 7.5 AU/yr. Planets typically have orbital planes tilt just within few degrees of the plane of star's equator due to mechanism where planets form from  flattened and rotated with the rotation of the star.

Rotation
Like every other planet, Aita rotates on its axis, whether slow or fast. One 360° spin of this planet lasts 15 days or about 366.8 hours, which the rotation is slow. When taken from its rotation period and planet's circumference, the rotation velocity is just 167 kph or 104 mph. The rotation tilts 2.9° to the orbital plane, meaning that the parent star seen from the planet would reach its northernmost point at +2.9° and southernmost point at −2.9°.

Aita's angle of rotation, orbit, and inclination to line of sight would combine to have planet's poles pointing to different directions relative to Earth's, resulting in having different pole stars. On this planet, north pole points to the constellation, which is an equatorial constellation from Earth. The south pole points to the opposite side of the celestial sphere to north pole. The south pole points to, which for Earth is a northern constellation.

Parent star observation and irradiance
According to the inverse square relation between light and distance, Aita receives 3⅓ times more sunlight than Earth receives since it orbits 55% of the distance between Earth and the Sun. But actually, since the different stars give off different amount of light, this is the case of Tau Ceti as being different from the Sun. Tau Ceti gives out less than half of the light Sun emits at any given time, meaning that Aita receives just 1½ times more sunlight than Earth receives instead. The apparent size of the star is inversely proportional to the distance, so Tau Ceti would appear 55% bigger than the Sun seen from Earth. But since Tau Ceti is just 80% of the Sun's size, then Tau Ceti as seen from Aita is just 15% bigger than the Sun seen from Earth. The amount of time taken for light to reach this planet depends on the same factor as apparent size but it does not depends on its physical size or even brightness. In this case, light takes 4.57 minutes for starlight to reach Aita, 45% shorter than sunlight to reach Earth.

Since the parent star is 1½ times brighter as seen from Aita than the brightness of Sun seen from Earth, then the insolation is 1½ times greater than Earth's. The is 1368 W/m², while Aita's insolation is 2082 W/m².

Mass and size
Aita has a mass 4½ times that of Earth's and the size is ⅓ the value of mass relative to Earth. The planet's surface area is 2⅓ times that of Earth's and volume 3 times that of Earth's. Volume is smaller in value relative to Earth than mass, resulting in matter being more compressed, thus making the planet denser. By dividing mass by volume relative to Earth, we can find planet's density relative to Earth. So we divide 4½ by 3 and we get approximately 1¼, which means that Aita is 1¼ times denser than Earth. The planet's density is 6.95 g/cm³, compared to 5.52 g/cm³ for the solar system's densest planet Earth.

Gravitational influence
Aita's surface gravity is 1.92, meaning it is almost twice the gravity of Earth. Falling objects would accelerate at 18.86 m/s², compared to 9.81 m/s² for Earth. Due to planet having mass, it is at the center of the gravitational sphere, called. It extends to 3.76 s with boundary where gravitational influence from the planet is equal to influence from the parent star. For a satellite to have an orbital period identical to the planet's rotation period, which is about 37. days, it would orbit at a shade over two lunar distances and would have a velocity of just over 2.0 km/s. In addition to the outer limit allowing for the moon's existence at hill sphere boundary, there is also an inner boundary. If it orbits within that boundary, which is 0.042 LD or 16.2 megameters, a moon would tear apart by the tidal forces assuming a density of 3 g/cm³.

Interior
Like other terrestrial planets, Aita underwent, an event in which denser materials sink to form the core. The planet's core is made of 82%, 13% , and 5% , plus trace amounts of. Surrounding the core and underneath the crust is mantle, where molten rocks are that causes volcanism. There is strong convection currents in the mantle in which hotter, molten rocks rise while cooler, solid or semisolid rocks sink. The convection current is what causes crust to break apart, however strong gravity acting on convection current would make crust stronger, and thus more resistent to breaking. So Aita would be a "one-plated planet" like Mercury, Venus, and Mars.

Aita's abundance of sulfur don't confine to its core, but also layer-by-layer. Molten rocks in the mantle are sulfur-rich, which is responsible for large amounts of sulfur gases in the atmosphere through volcanism. In the crust, sulfur is the second most abundant element after, then then.

Surface
Aita's surface is littered with varied terrains. There are mountain ranges connected to another, as well as other terrain like plateaus, canyons, valleys, and ridges. Due to its high surface gravity, mountains don't rise that particularly high. The highest peaks have heights just over a mile. Aita's highest point is located at 43°N latitude whose height is 2.2 miles (3.6 km). The deepest canyon is 3.8 miles (6.1 km). In addition to all the forementioned terrains, there are volcanoes and craters. But there are very few impact craters due to atmosphere being so thick that it shields meteors so effeciently. There are numerous volcanoes on Aita due to its active interior but no plates to subduct away volcanoes.

On the surface, there are sulfur-rich rocks and pure sulfur deposits can be found near volcanoes. Due to sulfur richness both on its surface and in the interior, Aita is classified as a sulfur planet. When viewed from space, much of the planet's surface would appear yellow or yellowish and would have high reflectivity because yellow is a light color.

Atmosphere
Since Aita is a sulfur planet, then it atmosphere surrounding the planet should be sulfur-rich of course in the form of gases. Nature does follow the rules as chief sulfur gas,, makes up 23% of the planet's atmosphere, with the other sulfur gas, , makes up 3%. SO$⊕$ is in the shadow of, making up 61% of the atmosphere by volume. The remaining gases that make up between 1–10% are (9%) and  (4%). Aita's atmosphere also contains trace amount of other gases with volumetric proportion well under 1%, including, , , , , and. Of all the mentioned gases, only sulfuric acid and water are capable of forming clouds. Since the concentrations are low, clouds would be rare and thin on Aita.

Aita's atmosphere is dense, having the pressure 25 times greater than Earth's and 27% the pressure on Venus, measuring at 364 compared to just 14 for Earth. The mean atmospheric molecular weight is 38 g/mol and has atmospheric volume of 12 Mm³.

Magnetic field
Aita has a weak due to its slow rotation. The strength is measured at 0.7 nanotesla, compared to over 300,000 for Earth. When the parent star emits ionizing radiation and charged particles, they hit Aita's atmosphere quite easily and would readily form bright planet-wide auroras. Stellar winds is responsible for washing away the two lightest gases, and, and much of water vapor.

Moons and rings
Aita has no moons nor rings. The planet never had a moon but it formed faint temporary rings a couple times after s.

Future studies
Aita poses a challenge since it does not transit its star. An alternative is to observe reflected light, which is difficult as it only been done for Jupiter-size planets. Future generations of telescopes can pick up reflected light from Aita and study its atmosphere as well as physical characteristics such as its actual mass and size. In addition to reflected light, this planet can be studied using direct imaging, which is difficult given that planet orbits close to the glare of its star and is small, though future generations of technologies can make it lot easier. Direct imaging can be used to what planet appears like as well as if moons actually exist. Spectroscopy can be carried out to see if Aita is actually a sulfur-rich planet.