Ino is a so-called "blue Jupiter" due to its appearance and size
Date November 27, 2009
Discoverers Guenther et al.
Detection method Radial velocity
Site Karl Schwarzschild Observatory
Name & designations
Pronunciation /'ī•nō/
Adjective Inian
Planet numbers P375, 30 Arietis B P1, Aries P7,
Araneus P45, 2009 P69,
2009 Ari-2, 2009 Arn-9
Star designations BF 363 b, PH 306 b,
P4 Arietis b, P37 Arani b,
Arietis b, 30 Arietis Bb,
28 Arani Bb, HD 16232 b,
HIP 12184 b, SAO 75470 b
System 30 Arietis B
Constellation Aries
Caelregio Araneus
Right ascension 02h 36m 57.74s (39.240 59°)
Declination +24° 38' 53.0" (+24.648 06°)
Distance 40.787 pc (133.030 ly)
Orbital characteristics
Semimajor axis 0.983 467 AU (147.124 6 Gm)
Periastron 0.699 495 AU (104.642 9 Gm)
Apastron 1.267 440 AU (189.606 3 Gm)
Eccentricity 0.288 746 2
Orbital circumference 6.083 18 AU (910.030 Gm)
Orbital area 2.909 15 AU² (65 105.32 Gm²)
Orbital period 335.082 947 d (0.917 406 98 yr)
Avg. velocity 31.540 km/s (6.631 AU/yr)
Max. velocity 35.805 km/s (7.528 AU/yr)
Min. velocity 26.599 km/s (5.592 AU/yr)
Direction of orbit
relative to star's rotation
Inclination 49.768° to line of sight
−2.179° to star's equator
−1.422° to invariable plane
Argument of periastron 307.189°
Longitude of ascending node 24.939°
Longitude of periastron 332.128°
Angular separation 24.118 mas
Observing the parent star
Mean angular star size 0.615 14° (36.908')
Max. angular star size 0.864 86° (51.892')
Min. angular star size 0.477 32° (28.639')
Mean star magnitude −27.562
Max. star magnitude −28.302
Min. star magnitude −27.011
Bulk characteristics
Mean radius 1.097 57 RJ (76.767 Mm)
Equatorial radius 1.079 14 EJ (77.110 Mm)
Polar radius 1.136 92 PJ (76.080 Mm)
Mean circumference 482.340 Mm
Equatorial circumference 484.497 Mm
Polar circumference 478.026 Mm
Surface area 1.205 75 SJ (74 052 Mm²)
Volume 1.324 00 VJ (1.894 9 × 106 Mm³)
Flattening 0.013 42 (1:74.53)
Angular diameter 25.169 μas
Mass 12.945 677 MJ
Reciprocal mass
relative to star
Density 12.972 g/cm³
Gravitational influence
Surface gravity 28.341 g (277.93 m/s²)
Weight on Ino
(150 lb on Earth)
4 251 lb
Standard gravitational parameter 1.640 × 109 km³/s²
Escape velocity 206.71 km/s
Hill radius 43.571 LD (16.748 8 Gm)
Roche limit
(3 g/cm3 satellite)
0.409 92 LD (157.573 Mm)
Stationary orbit 0.361 24 LD (138.860 Mm)
Stationary velocity 87.284 km/s (19.618 LD/d)
Rotation characteristics
Rotation period 4.318 55 h (0.179 940 d)
Rotation velocity 31.164 km/s (83.36°/h)
Direction of rotation
relative to orbit
Axial tilt 0.001°
Longitude of vernal equinox 201.850°
North pole right ascension 12h 18m 16s (184.569°)
North pole declination −03° 00' 46" (−3.013°)
North polar constellation Virgo
North polar caelregio Noctua
South pole right ascension 00h 18m 16s (4.569°)
South pole declination +03° 00' 46" (+3.013°)
South polar constellation Pisces
South polar caelregio Hippocampus
Thermal characteristics
Surface temperature 655 K (382°C, 719°F, 1179°R)
Mean irradiance 2 759 W/m² (2.017 I)
Irradiance at periastron 5 453 W/m² (3.987 I)
Irradiance at apastron 1 661 W/m² (1.215 I)
Albedo 0.136 (bond), 0.144 (geom.)
Scale height 6.81 km
Surface density 0.397 g/m³
Molar mass 2.26 g/mol
Composition 97.463% hydrogen (H2)
1.177% helium (He)
0.811% methane (CH4)
0.387% water (H2O)
84.0 ppm sulfur dioxide (SO2)
607 ppm hydrogen chloride (HCl)
570 ppm carbon monoxide (CO)
432 ppm hydrogen deuteride (HD)
7.11 ppb phosphorus pentachloride (PCl5)
42.3 ppb disulfur dichloride (S2Cl2)
Dipole strength 11.8 mT (118 G)
Magnetic moment 4.37 × 1022 T•m³
Dipole tilt 9.97°
Satellite system
Number of moons 308
Number of rings 88

Ino (30 Arietis Bb, P375) is a planet which orbits the yellow-white F-type main sequence star 30 Arietis B, meaning the star is larger, hotter and thus brighter than our Sun. It is approximately 133 light-years or 41 parsecs away towards the constellation Aries in the caelregio Araneus.

Ino has a very similar orbital distance from the star as Earth from the Sun, although Ino is hotter than Earth because the parent star is more luminous than our Sun and the planet is emitting heat from its interior.

Ino is named after the queen of Thebes in Greek mythology. This planet had a former name Pontus after a historical Greek region on the southern coast of Black Sea where it is now modern-day northeastern Turkey.

Discovery and chronology Edit

Ino was discovered on November 27, 2009 (which was on Black Friday) using a precise radial velocity method from echelle spectrograph installed in Alfred-Jensch telescope in Karl Schwarzschild Observatory. Eike Guenther was the discoverer.

Ino is the 368th extrasolar planet discovered overall, 342nd since 2000, and 70th in 2009. It is also the 7th exoplanet discovered in the constellation Aries (2nd in 2009) and 45th in the caelregio Araneus (9th in 2009). Ino is the first and only planet discovered in the 30 Arietis B system, hence the designations 30 Arietis Bb (a is not used because the parent star uses this letter to reduce confusion) and 30 Arietis B P1. 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

Ino takes 29 megaseconds or 11 months to revolve around the star in a prograde direction at an average velocity of 31.54 km/s or 19.60 mi/s, which is slightly faster than Earth's. Ino orbits at 4.77 microparsecs (μpc) or 147 gigameters (Gm) from the star, which is similar to the distance between Earth and the Sun, but its orbital eccentricity is much higher. At periastron, the planet's closest distance to the star is 3.39 μpc or 105 Gm, which is slightly closer to the star than Venus to the Sun. At apastron, the planet's farthest distance to the star is 6.14 μpc or 189 Gm, which is half-way between the orbits of Earth and Mars. The circumference of its orbit is 29.49 μpc or 910 Gm, which is 2π average radius. The area of its orbit, that is, the area of space inside the planet's orbit, is 68.38 μpc² or 65105 Gm². The inclination of its orbit is about 50°.

Parent star observation and irradiance Edit

As viewed from the planet, the star appears to be two times brighter than the Sun as seen from Earth. Although since the planet's orbit is eccentric, the brightness of the star as seen from Ino changes. At periastron, the star appears to be twice as bright as the average apparent brightness while at apastron would appear to be 60% as bright. The apparent diameter of the star is 20% larger than the full moon and sun as seen from Earth. Like apparent brightness, the apparent diameter of the star also changes throughout its orbit because of its high eccentricity. At periastron, the star would appear to be 41% larger than its average value while at apastron, the star would appear to be 78% as large.

Because the planet orbits at similar distance from 30 Arietis B as Earth is from the Sun, Ino should receive similar irradiance as Earth's, but it is not the case because 30 Arietis B emits twice as much energy than the Sun over the same timespan. This corresponds that Ino receives twice as much energy per square meter as Earth's. Because Ino orbits so eccentrically which causes distance from the star to vary considerably, so does irradiance. At periastron, the planet receives twice the average energy per square meter while at apastron, it receives just 60% of the average energy.

Rotation Edit

Ino takes a fast 4.3 hours to rotate in the same direction is its orbit once on its axis and tilts 0° to the plane of its orbit. Since Ino is not tilted on its axis, each day and night always last 2.3 hours. The tilt of this planet is such that both poles point to the Earth's equatorial constellations: Virgo (in Noctua) for the north pole, and Pisces (in Hippocampus) for the south pole.

Structure and composition Edit

Mass and size Edit

Ino has mass 12.95 Jupiter masses or 4115 Earth masses, which is extremely close to the boundary between planets and brown dwarfs at 13.00 Jupiter masses or 4132 Earth masses. In the planetary mass classification, Ino is a super-Jupiter. Its mean radius is 1.10 times that of Jupiter or 76 megameters, meaning at a distance of 41 parsecs, this planet has an angular diameter of 2516 microarcseconds, six billionth the size of the full moon. It can fit 1749 Earths inside Ino! Since Ino is much more massive and only slightly bigger than Jupiter, this planet is very dense and has very strong gravity. The density of this planet is close to 13 g/cm³, which is over twice as dense as Earth and nearly 10 times denser than Jupiter.

Gravitational influence Edit

The gravitational strength on Ino is more than 28 times stronger than Earth's, nearly 11 times stronger than Jupiter's, and stronger than even our Sun by 1.5%. The surface gravity is derived from dividing its mass by square of its radius, meaning if this planet is bigger, then its gravitational field would be weaker. If you weigh 150 pounds on Earth, you'll weigh 4251 pounds or over 2 tons on Ino.

Since the gravity and tidal forces of Ino are so strong, the maximum distance from the planet where a 3 g/cm³ moon tear apart by tidal forces, called its roche limit, stretches very far from the planet. The roche limit is 41% the Earth–Moon distance at 2.05 planetary radii or 158 megameters. The hill radius is 107 times as distant as the roche limit at roughly 1634 gigameters. Ino's gravitational field is so strong that moons would have to orbit within the roche limit in order for a moon to always face the same side of the planet. However, a moon can be at that orbit without tearing apart by tidal forces as long as its density is at least 4 g/cm³. If it is in its stationary orbit, it would have an orbital speed of 87.3 km/s or 54.2 mi/s. Since the planet takes 4.3 hours to rotate, then a moon would take 4.3 hours to orbit the planet at stationary orbit.

Interior Edit

Below its outer envelope lies mantle of pressurized hydrogen, below it lies liquid hydrogen and helium, below it lies liquid metallic hydrogen, and then solid metallic hydrogen. At the planet's center lies a rocky/metallic core with a temperature about 94,000°C or 169,000°F, much higher than Jupiter's due to its high mass. Ino has the interior structure similar to Jupiter and Saturn.

Atmosphere Edit

The main gases of the atmosphere are hydrogen and helium as well as trace amounts of methane, water, sulfur dioxide, hydrogen chloride, hydrogen deuteride, phosphorus pentachloride, and disulfur dichloride. The equilibrium temperature of this planet, based on it orbital distance and parent star's luminosity, is 31°C or 88°F, but the surface temperature (1-bar layer) is over 380°C or nearly 720°F. This unexpectedly high temperature is caused by a great deal of internal heating caused by its strong gravitational contraction. At that temperature, there are no chemicals suitable for the formation of clouds.

Since there are no clouds on Ino, there are no storms, but winds may still blow. The winds on the planet may reach as high as 3000 mph (5000 kph) due to its very rapid rotation and high temperature. Most of the winds are powered by internal heating since the planet radiates three times more heat from the interior than it receives from 30 Arietis B.

Magnetic field Edit

Ino has a magnetic field far more powerful than Jupiter's, the planet with the strongest magnetic field in our solar system. This planet has a magnetic field strength of 118 Gauss, compared to 4.28 Gauss for Jupiter and 0.307 for Earth.

That powerful magnetic field is produced by its rapid rotation that causes very fast movements of liquid metallic hydrogen in the mantle that produces electric currents. This magnetic field can stretch up to 45 AU, which is longer than the average distance between the Sun and Pluto. The center of the magnetic field is not at the physical center of the planet, but it is offset by about 8 megameters.

Moons and rings Edit

Ino is so massive that there are over 300 moons with diameters at least 1 km or more. Most moons are tiny, but some are large. The largest moon has mass 0.81 Earth masses and has a thick carbon dioxide-rich atmosphere with a liquid water and possibly microbial life. The second largest has mass 0.33 Earth masses and it is a barren world and volcanic. The third largest has about the size of Mars with surface pockmarked with craters. There are seven moons that are larger and more massive than our Moon. Ino has a faint ring system leftover from the formation of the planet and its moons over 900 million years ago.

Future studies Edit

Ino is speculated that it does not transit the star because the orbital plane is speculated not to be edge-on. The inclination of this planet places halfway between face-on and edge-on. However if Ino does transit 30 Arietis B (which only occurs when the orbital inclination is close to 90°), then its inclination, true mass, radius (which can calculate derivative properties like density and surface gravity using mass), temperature, and other parameters can be constrained as well as studying its atmosphere and looking for moons and rings in orbit. If Ino does not transit its star, then this planet can be studied by direct imaging or astrometry instead. Finding planets with direct imaging orbiting as close as 1 AU from the star is difficult because the glare of its star prevents astronomers from seeing close-orbiting planets. But in 2010, there is a new direct imaging instrument, called vortex coronagraph, that can detect and characterize planets as close to their stars as 1 AU (right where Ino orbits). On the otherhand, Gaia shall study the astrometry of this planet and a thousand others, constraining their inclinations. Once inclination is known, it will determine whether this object is actually a planet or a brown dwarf.