This is what Eurystheus may look like assuming its mass is minimum and temperature at its equilibrium
Date November 17, 2005
Discoverers Goździewski et al.
Detection method Radial velocity
Site McDonald Observatory
Name & designations
Pronunciation /'yu•rēs•fē•yis/
Adjective Eurysthian
Planet numbers P163, 14 Herculis P2,
Hercules P3, Tarandus P13,
2005 P35, 2005 Her-2,
2005 Tar-4
Star designations 14 Herculis c, 11 Tarandi c,
BF 2110 c, PH 11 c,
P1 Herculis c, P1 Tarandi c,
HD 145675 c, HIP 79248 c,
Gliese 614 c, SAO 45933 c
System 14 Herculis
Constellation Hercules
Caelregio Tarandus
Right ascension 16h 10m 24.31s (242.601 31°)
Declination +43° 49' 03.5" (+43.817 64°)
Distance 17.570 pc (57.307 ly)
Orbital characteristics
Semimajor axis 6.856 489 AU (1 025.716 2 Gm)
Periastron 6.827 689 AU (1 021.407 7 Gm)
Apastron 6.885 289 AU (1 030.024 6 Gm)
Eccentricity 0.004 200 4
Orbital circumference 43.080 45 AU (6 444.744 Gm)
Orbital area 147.689 50 AU² (3 305 220.6 Gm²)
Orbital period 6 906.351 036 d (18.908 558 62 yr)
Avg. velocity 10.837 km/s (2.278 AU/yr)
Max. velocity 10.860 km/s (2.283 AU/yr)
Min. velocity 10.814 km/s (2.274 AU/yr)
Direction of orbit
relative to star's rotation
Inclination 26.510° to ecliptic
−7.738° to star's equator
10.239° to invariable plane
Argument of periastron 41.250°
Longitude of ascending node 184.999°
Longitude of periastron 226.249°
Angular separation 390.232 mas
Observing the parent star
Mean angular star size 0.069 91° (4.195')
Max. angular star size 0.070 21° (4.212')
Min. angular star size 0.069 62° (4.177')
Mean star magnitude −21.946
Max. star magnitude −21.955
Min. star magnitude −21.937
Bulk characteristics
Mean radius 0.970 27 RJ (67.863 Mm)
Equatorial radius 0.955 26 EJ (68.258 Mm)
Polar radius 1.002 32 PJ (67.073 Mm)
Mean circumference 426.397 Mm
Equatorial circumference 428.879 Mm
Polar circumference 421.432 Mm
Surface area 0.942 25 SJ (57 869 Mm²)
Volume 0.914 64 VJ (1.309 0 × 106 Mm³)
Flattening 0.017 47 (1:57.257)
Angular diameter 51.637 μas
Mass 4.680 561 MJ
Reciprocal mass
relative to star
Density 6.789 g/cm³
Gravitational influence
Surface gravity 13.112 g (128.59 m/s²)
Weight on Eurystheus
(150 lb on Earth)
1 967 lb
Standard gravitational parameter 5.930 × 108 km³/s²
Escape velocity 132.19 km/s
Hill radius 326.692 LD (125.580 0 Gm)
Roche limit
(3 g/cm3 satellite)
0.292 03 LD (112.257 Mm)
Stationary orbit 0.436 83 LD (167.918 Mm)
Stationary velocity 50.188 km/s (11.281 LD/d)
Rotation characteristics
Rotation period 8.213 2 h (0.342 218 d)
Rotation velocity 14.505 km/s (43.83°/h)
Direction of rotation
relative to orbit
Axial tilt 80.801°
Longitude of vernal equinox 25.114°
North pole right ascension 20h 50m 27s (312.612°)
North pole declination +37° 59' 42" (+37.995°)
North polar constellation Cygnus
North polar caelregio Avis
South pole right ascension 08h 50m 27s (132.612°)
South pole declination −37° 59' 42" (−37.995°)
South polar constellation Vela
South polar caelregio Malus
Thermal characteristics
Surface temperature 239 K (−34°C, −30°F, 430°R)
Mean irradiance 16.6 W/m² (0.012 2 I)
Irradiance at periastron 16.8 W/m² (0.012 3 I)
Irradiance at apastron 16.5 W/m² (0.012 1 I)
Albedo 0.828 (bond), 0.846 (geom.)
Scale height 23.77 km
Surface density 0.433 g/m³
Molar mass 2.70 g/mol
Composition 92.074% hydrogen (H2)
5.813% helium (He)
2.819% water (H2O)
437 ppm methane (CH4)
379 ppm ammonia (NH3)
173 ppm benzene (C6H6)
43.5 ppm ethane (C2H6)
31.9 ppm hydrogen deuteride (HD)
2.52 ppm
1.88 ppb argon (Ar)
133 ppt neon (Ne)
Water (H2O)
Dipole strength 783 μT (7.83 G)
Magnetic moment 3.45 × 1020 T•m³
Dipole tilt 1.49°
Satellite system
Number of moons 148
Number of rings 23

Eurystheus (14 Herculis c, P163) is an exoplanet which orbits the yellow-orange K-type main sequence star 14 Herculis, meaning the star is smaller, cooler and thus dimmer than our Sun. It is approximately 57 light-years or 18 parsecs from Earth towards the constellation Hercules in the caelregio Tarandus.

Eurystheus is a gas giant several times more massive than Jupiter and orbits further from the star than Jupiter is to the Sun.

Eurystheus is named after the king of Tiryns, one of three Mycenaean strongholds in the Argolid in Greek mythology.

Discovery and chronology Edit

Eurystheus was discovered on November 17, 2005 by a team of astronomers led by Krzysztof Goździewski. The team used the spectrometer mounted on the telescope in McDonald Observatory in Texas and found that this star has a long-term trend in addition to the inner planet Cerenytis discovered seven years prior. Less than a year later on November 2, 2006, Eurystheus was confirmed.

Eurystheus is the 156th exoplanet discovered overall, 130th since 2000, and 35th in 2005. Eurystheus is the 3rd exoplanet discovered in the constellation Hercules (2nd in 2005) and 13th in the caelregio Tarandus (4th in 2005). Since Eurystheus is the second planet discovered in the 14 Herculis system, the planet receives the designations 14 Herculis c (a is not used because the parent star uses this letter to reduce confusion) and 14 Herculis P2. Note that the chronology does not include speculative brown dwarfs (objects with minimum masses below 13 MJ but with speculative true masses above 13 MJ).

Orbit and rotation Edit

Orbit Edit

Eurystheus is located near the middle of the Jovian orbit (which is a classification of orbit) as it orbits the star at an average distance of 6.86 AU (1 AU is the average distance between the Earth and the Sun). If we place this planet in our solar system, it would orbit between the orbits of Jupiter and Saturn. Eurystheus has an almost perfectly circular orbit with an eccentricity of 0.004. Despite the Eurystheus' wide orbit, the orbital distance can only vary by about 0.06 AU from the star. The planet takes 18.91 years or nearly 227 months to make one complete trip around the star at an average velocity of 2.28 AU/yr or 10.8 km/s. Eurystheus is in a 4:1 resonance with the inner known planet Cerenytis.

Parent star observation and irradiance Edit

Viewed from Eurystheus, the parent star would appear to be 83 times fainter than the Sun seen from Earth. The parent star has a magnitude −21.95 compared to −26.74 for the Sun's magnitude viewed from Earth. Viewed from Eurystheus, the parent star would have an angular diameter of 4.2' on average, which is 17 the angular diameter of the full moon we see every month.

Eurystheus receives 17 watts worth of energy per square meter from the parent star compared 1368 W/m² for Earth.

Rotation Edit

Eurystheus rotates very rapidly, even more rapid than the fastest rotator in the solar system, Jupiter. It takes just 8.2 hours to make one complete turn, similar to the period of Cerenytis. A year on Eurystheus lasts 20181 Eurystheus days, which is 55.10 times longer than a year on Earth. Even more stranger is that the planet rotates on its side like Uranus. The planet tilts 80.8° to the plane of its orbit, which is almost perpendicular to its orbit. The planet's north pole points to the constellation Cygnus (in Avis), while the south pole points to the constellation Vela (in Malus).

Structure and composition Edit

Mass and size Edit

Eurystheus is massive, 4.68 times more massive than Jupiter, the most massive planet in our solar system. It is classified as super-Jupiter in the planetary mass classification scheme. Even though this planet is much more massive than Jupiter, it is slightly smaller than Jupiter, meaning that Eurystheus must be very dense, has very strong gravity, and has very high escape velocity. Even though Eurystheus is denser than Earth (6.8 vs. 5.5 g/cm³), the densest planet in our solar system, it would still be a gas giant with no solid surface.

This planet is more spherical than any giant planet in our solar system with a flattening of 0.01747. The equatorial radius is 68,258 km while the polar radius is 67,073 km. Using these three datas, its mean radius is calculated to be 67,863 km, actually twice as close to its equatorial radius than its polar radius.

Gravitational influence Edit

The gravitational force of Eurystheus is over 13 times stronger than Earth's. So if you weigh 150 pounds on Earth, you would weigh 1967 pounds or almost a ton on Eurystheus. So a person standing on Eurystheus would weigh nearly as much as a small car parked on Earth! To escape this planet, it would need to go more than twice as fast as required to escape Jupiter and 12 times faster than is required to escape Earth.

Since the gravity of this planet is so strong, the roche limit lies relatively far from the planet at 1.65 planetary radii. Eurystheus has a very large hill sphere, with its boundary lying at 1850 times the radius of the planet or 327 LD. The stationary orbit lies nearly 60% further out than roche limit. The orbital velocity at stationary orbit is calculated to be 50.2 km/s or 31.2 mi/s. Since the planet takes 8.2 hours to rotate, then a moon would also take 8.2 hours to orbit the planet at stationary orbit.

Interior Edit

Below Eurystheus' outer envelope (atmosphere), the weight of all the gases pressing down produce a tremendous pressure. That pressure allow hydrogen and helium to condense in the upper mantle despite the higher temperatures deeper down. In the middle mantle lies liquid metallic hydrogen where hydrogen can conduct electricity under even greater pressure heated beyond its critical point. In the lower mantle, there is narrow layer of solid metallic hydrogen. At the center lies an ultra-dense core of rock and metal with a mass 86 Earth masses, roughly 5.8% the total mass of the planet. The temperature of the core is estimated to be 113,400 K (113,100°C, 203,700°F) and an estimated pressure 489 GPa.

Atmosphere Edit

Like all gas giants, Eurystheus' atmosphere composes mostly of hydrogen (92%), with helium (5.8%) and water (2.8%) making up most of the rest. Eurystheus contains trace amounts of other gases, including methane and ammonia. Ethane makes up 43 parts per million of the atmosphere. Unlike most gas giants and common on terrestrial planets, the atmosphere contains argon but at a concentration of 2 parts per billion.

Eurystheus contains banded clouds of ammonia and water and this planet would appear as orange and white stripes from space. The ammonia clouds are in the cooler upper deck and water clouds in the warmer lower deck. The temperature of this planet is 239 K (−34°C, −30°F), which is far warmer than its equilibrium temperature of 85 K (−188°C, −307°F) due to its high mass and density that produces a lot of internal heating. This planet radiates four times the amount of energy than it receives from the parent star. There are thousands of jet streams and zonal jets, which can produce violent long-lasting storms and high winds, even more violent than Jupiter's.

Magnetic field Edit

This planet has a very strong magnetic field, about 7.83 gauss, which is 25 times stronger than Earth's.

That powerful magnetic field is produced by the movements of metallic hydrogen in its interior caused by the planet's rotation. This mechanism is well known as dynamo effect. The magnetic field blocks most of stellar and cosmic radiation from reaching the planet, but occasionally it can produce beautiful, vivid aurorae when the stellar radiation got caught in the magnetic field lines and move towards their poles where it interact with the planet's upper atmosphere (ionosphere). Its magnetic field is so strong that occasional auroral display are often more brilliant than aurorae on Earth.

Moons and rings Edit

Eurystheus has a big family of 148 moons, several of them larger than our Moon. The largest moon has mass 23.7 Lunar masses (0.291 Earth masses) and has diameter 2.871 DL (6,198 miles, 9,974 kilometers). There are six moons bigger than our Moon and one of these is larger than Mars. 14 moons have diameters between 1000 miles and 2000 miles, 49 have diameters between 100 and 1000 miles and 79 have diameters less than 100 miles.

Eurystheus has 23 rings. The rings are made mainly of dusts and boulders, and little ice.

Future studies Edit

The probability that Eurystheus will transit 14 Herculis can be a slim 0.29% chance, but it is speculated that Eurystheus will not transit since I speculated that the inclination is 27°. Eurystheus can be studied effectively using astrometry or direct imaging. The planet can be studied using astrometry using Gaia, James Webb Space Telescope (JWST), Space Interoferometry Mission (SIM), or even the current Hubble Space Telescope (HST) guidance sensor. The astrometry can constrain the inclination and thus calculate the exact mass. The direct imaging can see what the planet may really look like. The direct imaging can constrain the size of this planet like transit method. 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.

Astronomers may eventually use astroseismology to study the interior, including the extent, features and compositions by layers. Using the spectrometer 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 Doppler shifts, which in turn rotation period can then be calculated.

In orbit around the planet, moons can be detected using the transit across the planet, detecting the wobble of the planet, or even direct imaging. Rings can also be detected using just two methods: transit or direct imaging.

Eurystheus can further be studied using the JWST's successor: ATLAST, due to launch between 2025–35.

Related links Edit