Prima

Prima (47 Lupi d, P590) is an which orbits the yellow-white   , similar to our. It is approximately 48 s or 15 s from towards the   in the caelregio Simianus.

Prima is the outermost of the three known planets in 47 Lupi system. Prima is an nearly 3⅔ times the size of the Earth. It is a midplanet massing 14.9 es. The planet takes over 15 weeks to orbit the star in a 2:1 tidal lock ratio.

is named after the goddess.

Discovery and chronology
Prima was discovered on September 12, 2011 by a team of astronomers led by. The team used the  mounted on the  in, located in the  in. The team discovered that 47 Lupi is wobbling in three different cycles simultaneously caused by the presence of three orbiting planets, including Prima. This wobble is relatively weak, which implies that all three orbiting planets are low-mass, either super-Earths or midplanets. Prima is one of 41 planets announced on September 12, 2011 and one of 84 found in that month, the monthly record.

Prima is the 582$⊕$ exoplanet discovered overall, 556$⊕$ since 2000, 202$⊕$ since 2010, and 94$⊕$ in 2011. It is the 6$⊕$ exoplanet discovered in the constellation Lupus (4$⊕$ in 2011) and 52$⊕$ exoplanet discovered in the caelregio Simianus (6$⊕$ in 2011). Since Prima is the third planet discovered in the 47 Lupi system, the planet receives the designations 47 Lupi d (a is not used because the parent star uses this letter to reduce confusion) and 47 Lupi P3. Note that the chronology does not include planets that are speculatively s.

Orbit
Prima orbits the star at an of 2.13 s or 0.44, slightly beyond the orbit of. Prima orbits eccentrically with twice the eccentricity of Mercury's. Prima's distance from the star ranges from 1.21 μpc (0.25 AU) to 3.05 μpc (0.63 AU). The planet takes 9.221 s or 106.72 days to orbit the star at an of 9.12 AU/yr (43.4 km/s, 26.9 mi/s). Prima is in a 4:1 with the middle known planet Crom and 9:1 resonance with the innermost planet Irpa.

Parent star observation and irradiance
Viewed from Prima, 47 Lupi would have a −28.55, over 1.8 times brighter than the Sun seen from Earth. However, observers on Prima would not see light from 47 Lupi the same time as it emits, but it takes about 3. minutes for light emitted from 47 Lupi to reach the planet. The parent star would have an of 1.26° on average, which is 2½ times the angular diameter of the  we sometimes see at night.

Prima receives on average five times more energy from its star than Earth receives from the Sun, and it varies from over 3300 W/m² to over 21000 W/m².

Rotation
Prima is in a 8:3 ratio, meaning every time the planet orbits the star thrice, it completed its rotation eight times. Since the planet takes 106.72 days to orbit the star, then it would take 40.02 days to rotate once on its axis. So the year on Prima lasts exactly 2. days compared to 366 Earth days in an Earth year. The planet tilts 13.1° to the plane of its orbit, compared to the Earth's 23.4° tilt. The north pole points to the constellation (subdivision of the caelregio Avis) while the south pole points to  (in Selachimorphus).

Mass and size
Prima is a midplanet, massing 14.9 es, more massive than but less massive than. Prima is over 3.64 times the size of the Earth with the radius of over 23 s, slightly smaller than Uranus and Neptune, corresponding that this planet is slightly denser than either s.

Gravitational influence
The acceleration due to gravity is 11.1 m/s², which is 13% stronger than 9.8 m/s² acceleration due to Earth's gravity. So if you weigh 150 on Earth, you would weigh just 19 more pounds on Prima than your weight on Earth at 169 pounds.

Based on its periastron distance and the mass ratio between planet and star, Prima's radius is calculated to be about 2.5. Within the hill sphere is where the orbit of satellites would be stable, outside of it would be unstable. The region of orbit closest to the planet is the, where satellites break up via tidal forces. Moons with a density 3 g/cm³ would tear apart if it orbit within 0.063 LD. Denser moons would be required to orbit closer to the planet in order to break up. A 5 g/cm³ moon would have to orbit within 0.053 LD in order to tear apart by tidal forces. Because Prima rotates so slowly caused by tidal forces of the parent star, taking 53.36 days to complete a rotation, the satellite would have to orbit far from the planet beyond the stable zone of its hill sphere for orbital period to be synchronized with the planet's rotation, called stationary orbit. The stationary orbit, analogous to the Earth's, where its orbital period is 53.36 days, is calculated to be 3 LD, compared to nearly one-tenth of a lunar distance for Earth's. If a satellite orbits at that distance, it would eventually escape the planet's orbit into the orbit around the star.

Interior
With the density of 1.71 g/cm³, Prima has no crust but deep oceans of water, mantle of exotic forms of water ice, lower mantle of diamond, and rocky core. Its structure is similar to Tuonetar orbiting around because these planets have similar densities. Despite the surface temperature of 381 K (108°C, 226°F, 686°R), slightly above the boiling point of ordinary water at 373 K (100°C, 212°F, 672°R), all of the planet's surface is covered by liquid water with an estimated depth of 1303 kilometers or 810 miles, approximately two hundred times deeper than average ocean depth of Earth. The upper mantle composes of the exotic form of water ice called or "hot ice" with the radius of 8377 km or 5205 mi under the pressure of 43.8. The lower mantle composes of with the radius of 4708 km or 2925 mi under the pressure of 74.0 MPa. At the center of this planet is a hot rocky core with a temperature of 6900 K and a pressure 1.23 GPa. The core has a radius of 8793 km or 5464 mi.

Diamond abundance
In its lower mantle, Prima has an estimated 133 million times more diamond than Earth has! There would be enough diamond to build cities covering about 80% the surface area of this planet with every building and appliances made of diamond!

Atmosphere
Prima has one-quarter the thickness of the atmosphere as and about 41 times thicker than. More than half of all gases in the atmosphere is with considerable amounts of. The second most abundant gas is, making up 29% of the , compared to 21% of the Earth's atmosphere. makes up 3.1% of the atmosphere, compared to 1% for Earth's depending on. makes up 37, less than the proportion in the Earth's atmosphere. The atmosphere contains merely 0.276%. This gas must be produced when a lot of oxygen reacts with methane incompletely caused by the presence of water vapor.

The planet is virtually cloudless most of the times except near apastron when there are few clouds.

Magnetic field
Prima has an extremely weak, about 42 millionths of a or 4.2 s, which is about 350 times weaker than. The reason for its weakness is because the planet rotates so slowly because it orbits the star in a 2:1 tidal lock ratio. Because the magnetic field is so weak, stellar radiation and cosmic rays bombard the surface almost constantly.

Moons and rings
Prima has no moons nor rings.

Transits
It is speculated that Prima will not transit since the inclination of Prima is about 40°. If Prima does transit, its signal can be found with considerable effort because Prima only transits once every 107 days, which is the planet's orbital period. Transit is useful for determining its size and inclination of this planet. The derivative parameters, including density and surface gravity, can then be calculated using the radius constrained from transit and true mass calculated by inclination. Using the calculated density, astronomers can model the interior of this planet.

Astrometry
If Prima does not transit, as speculated, then this planet can still be studied using different methods, such as. This method can be used to study this planet using (launched in December 2013) and  (JWST, to be launched around 2018), or even the current  (HST) guidance sensor. However, this planet would be too small and orbits too close to the star for even Gaia and JWST to be studied astrometrically.

Direct imaging
The direct imaging can see what the planet may really look like. But directly imaging this planet would be super difficult because it orbits only 0.44 AU, well within the glare of its star. The between the planet and the star is 29.7 s.  (to be launched between 2025–35) may be able to image Prima and other planets in the 47 Lupi system.

Astroseismology and spectroscopy
Astronomers may eventually use to study the interior, including the extent, features and compositions by layers. Using the mounted on the JWST, the atmosphere can be studied, including temperatures, chemical makeup, and features. Using the same method, the rotation rate can be constrained using s, which in turn can then be calculated.

Detecting moons and rings
Moons transiting Prima can reliably be detected while the planet transit its star if it does so.

Related links

 * Irpa (47 Lupi b, P588)
 * Crom (47 Lupi c, P589)