Crom

Crom (47 Lupi c, P589) 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.

Crom is the middermost of the three known planets in 47 Lupi system. Crom is an three times the size of the Earth. It is a midplanet massing 14.4 es. The planet takes nearly four weeks to orbit the star in a 5:4 tidal lock ratio.

is named after, a in pre-Christian Ireland, reputedly  with , whose worship is said to have been ended by.

Discovery and chronology
Crom 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 Crom. This wobble is relatively weak, which implies that all three orbiting planets are low-mass, either super-Earths or midplanets. Crom is one of 41 planets announced on September 12, 2011 and one of 84 found in that month, the monthly record.

Crom is the 581$⊕$ exoplanet discovered overall, 555$⊕$ since 2000, 201$⊕$ since 2010, and 93$⊕$ in 2011. It is the 5$⊕$ exoplanet discovered in the constellation Lupus (3$⊕$ in 2011) and 51$⊕$ exoplanet discovered in the caelregio Simianus (5$⊕$ in 2011). Since Crom is the second planet discovered in the 47 Lupi system, the planet receives the designations 47 Lupi c (a is not used because the parent star uses this letter to reduce confusion) and 47 Lupi P2. Note that the chronology does not include planets that are speculatively s.

Orbit
Crom orbits the star at an of 0.865 s or 0.178, about two times closer to the star than  is to the Sun. Crom has a semi-circular orbit with an eccentricity of 0.158. The planet takes 2.383 s or 27.58 days to orbit the star at an of 14.78 AU/yr (70.3 km/s, 43.7 mi/s). Irpa is in a 5:2 with the innermost known planet Irpa and 1:4 resonance with the outermost known planet Prima.

Parent star observation and irradiance
Viewed from Crom, 47 Lupi would have a −30.51, over 32 times brighter than the Sun seen from Earth. However, observers on Crom would not see light from 47 Lupi the same time as it emits, but it takes 89 seconds for light emitted from 47 Lupi to reach the planet. The parent star would have an of 3.12° on average, 6 times the angular diameter of the  we sometimes see at night.

Since the planet orbits at only about one-sixth the Earth-Sun distance, Crom receives about 30 times more energy from its star than Earth receives from the Sun. The planet absorbs 87% of the incoming energy.

Rotation
Crom is, meaning the planet rotates every time when the planet orbits the star. Since the planet takes 27.58 days to orbit the star, then it would take 27.58 days to rotate once on its axis. So the year on Crom lasts exactly 1 day compared to 366 Earth days in an Earth year. The planet tilts 19.6° to the plane of its orbit, which is three quarters of the Earth's tilt of 23.4°. None of the planet's poles point to bright star. The north pole points to the constellation (subdivision of the caelregio Tarandus) while the south pole points to  (in Felis).

Mass and size
Crom is a midplanet, massing 14.4 es, more massive than but less massive than. Crom is three times the size of the Earth with the radius of nearly 20 s. Still Crom is a little bit smaller than Uranus and Neptune, corresponding that this planet is around twice the density of either s.

Gravitational influence
The acceleration due to gravity is 15.7 m/s², which is 60% stronger than 9.8 m/s² acceleration due to Earth's gravity. So if you weigh 150 on Earth, you would weigh 240 pounds on Crom, similar to the weight of a professional football player on Earth!

Based on its periastron distance and the mass ratio between planet and star, Crom's radius is calculated to be about 1.5. Within the hill sphere is where the orbit of satellites would be stable, outside 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 0.062 LD. Denser moons would be required to orbit closer to the planet in order to break up, because denser moons are stronger and often have stronger gravity. A moon with the same density as Earth's would have to orbit within 0.051 LD in order to tear apart by tidal forces. Because Crom rotates so slowly, taking 22.07 days to complete a rotation because of the tidal forces of the star confining it to a 5:4 tidal lock ratio, 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 22.07 days, is calculated to be 2.4 LD, compared to nearly 0.1 LD 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 2.91 g/cm³, Crom has crust underneath deep oceans of water, mantle of exotic forms of water ice, lower mantle of diamond, and rocky core. Crom has similar structure to Tamar orbiting around 61 Virginis because these planets have similar densities. With the of 598 K (325°C, 617°F, 1077°R), it is too hot to have normal liquid water on its surface but cool enough to have exotic form of liquid water under heavy pressure. All of the planet's surface is covered by liquid water with an estimated depth of 677 kilometers or 421 miles, a 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 6152 km or 3823 mi and a pressure 32.1. The lower mantle composes of with the radius of 4125 km or 2563 mi and a pressure 61.7 MPa. At the center of this planet is a hot rocky core with a temperature of 6600 K and a pressure 1.15 GPa. The core has a radius of 8141 km or 5059 mi.

Diamond abundance
In its lower mantle, Crom has an estimated 76 million times more diamond than Earth has! There would be enough diamond to build cities covering about 75% the surface area of this planet with every building and appliances made of diamond!

Atmosphere
Crom has atmosphere about the thickness of the  and about 22 times thicker than. About half of all gases in the atmosphere is. Helium makes up the same portion of the atmosphere as oxygen on Earth, while there are as much  as Earth's.  makes up one-quarter the proportion of Earth's.  makes up 3.5% of the atmosphere, compared to 1% for Earth's depending on. makes up 356, identical to the concentration of CO$⊕$ in Earth's atmosphere in 1993 and slightly less than approximately 400 ppm for Earth's atmosphere at present.

Clouds are virtually nonexistent on Crom because there are no chemicals suitable for cloud formation at the temperature of around 600 K.

Magnetic field
Crom has an extremely weak, about 230 millionths of a or 23 s, which is about 1300 times weaker than. The reason for its weakness is because the planet rotates so slowly because it is partially locked to its star. Because the magnetic field is so weak, stellar radiation and cosmic rays bombard the surface almost constantly.

Moons and rings
Crom has no moons nor rings.

Transits
It is speculated that Crom will not transit since Crom's orbit is slanted diagonally. If Crom does transit, its signal can be found with some effort as Crom takes 27.6 days to orbit the star. 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 Crom 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 extremely difficult because it orbits only 0.18 AU (within the glare of its star). The between the planet and the star is 12 s.  (to be launched between 2025–35) may be able to image Crom 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 Crom can reliably be detected while the planet transit its star if it does so.

Related links

 * Irpa (47 Lupi b, P588)
 * Prima (47 Lupi d, P590)