Date August 7, 2005
Discoverers Butler et al.
Detection method Doppler spectroscopy
Site Lick Observatory
Name & designations
Pronunciation /'dē•nō/
Adjective Deinian
Planet numbers P153, HD 11964 P2,
Cetus P5, Hippocampus P20,
2005 P25, 2005 Cet-3,
2005 Hip-5
Star designations PH 119 b, P4 Ceti b,
P15 Hippocampi b,
HD 11964 b, HIP 9094 b,
Gliese 81.1 Ab, GJ 9063 Ab,
SAO 148123 b
System HD 11964
Constellation Cetus
Caelregio Hippocampus
Right ascension 01h 57m 09.61s (29.290 03°)
Declination −10° 14' 32.7" (−10.242 43°)
Distance 32.850 pc (107.142 ly)
Orbital characteristics
Semimajor axis 3.171 757 AU (474.488 1 Gm)
Periastron 3.042 550 AU (455.159 0 Gm)
Apastron 3.300 965 AU (493.817 3 Gm)
Eccentricity 0.040 736 8
Orbital circumference 19.922 70 AU (2 980.393 Gm)
Orbital area 31.578 33 AU² (706 707.9 Gm²)
Orbital period 1 945.003 591 d (5.325 129 61 yr)
Avg. velocity 17.795 km/s (3.741 AU/yr)
Max. velocity 18.154 km/s (3.817 AU/yr)
Min. velocity 17.429 km/s (3.664 AU/yr)
Direction of orbit
relative to star's rotation
Inclination 9.145° to line of sight
1.558° to star's equator
−4.111° to invariable plane
Argument of periastron 154.897°
Longitude of ascending node 252.710°
Longitude of periastron 47.607°
Angular separation 96.554 mas
Observing the parent star
Mean angular star size 0.163 06° (9.784')
Max. angular star size 0.169 99° (10.199')
Min. angular star size 0.156 68° (9.401')
Mean star magnitude −25.226
Max. star magnitude −25.316
Min. star magnitude −25.139
Bulk characteristics
Mean radius 0.976 11 RJ (68.272 Mm)
Equatorial radius 0.962 39 EJ (68.768 Mm)
Polar radius 1.005 40 PJ (67.279 Mm)
Mean circumference 428.963 Mm
Equatorial circumference 432.080 Mm
Polar circumference 422.728 Mm
Surface area 0.953 59 SJ (58 566 Mm²)
Volume 0.931 20 VJ (1.332 7 × 106 Mm³)
Flattening 0.021 80 (1:45.87)
Angular diameter 27.785 μas
Mass 3.812 451 MJ
Reciprocal mass
relative to star
Density 5.432 g/cm³
Gravitational influence
Surface gravity 10.553 g (103.49 m/s²)
Weight on Deino
(150 lb on Earth)
1 583 lb
Standard gravitational parameter 4.830 × 108 km³/s²
Escape velocity 118.95 km/s
Hill radius 126.276 LD (48.540 4 Gm)
Roche limit
(3 g/cm3 satellite)
0.272 74 LD (104.839 Mm)
Stationary orbit 0.358 49 LD (137.802 Mm)
Stationary velocity 48.433 km/s (10.886 LD/d)
Rotation characteristics
Rotation period 7.444 01 h (0.310 167 d)
Rotation velocity 16.123 km/s (48.36 °/h)
Direction of rotation
relative to orbit
Axial tilt 5.577°
Longitude of vernal equinox 136.006°
North pole right ascension 09h 53m 35s (148.397°)
North pole declination +04° 09' 11" (+4.153°)
North polar constellation Sextans
North polar caelregio Felis
South pole right ascension 21h 53m 35s (328.397°)
South pole declination −04° 09' 11" (−4.153°)
South polar constellation Aquarius
South polar caelregio Hippocampus
Thermal characteristics
Surface temperature 370 K (97°C, 206°F, 666°R)
Mean irradiance 106 W/m² (0.077 4 I)
Irradiance at periastron 115 W/m² (0.084 1 I)
Irradiance at apastron 97.7 W/m² (0.071 5 I)
Albedo 0.734 (bond), 0.750 (geom.)
Scale height 9.09 km
Surface density 0.797 g/m³
Molar mass 2.42 g/mol
Composition 92.692% hydrogen (H2)
5.477% helium (He)
1.287% water (H2O)
0.443% methane (CH4)
697 ppm hydrogen sulfide (H2S)
3.38 ppb ammonia (NH3)
281 ppb hydrogen deuteride (HD)
132 ppb propane (C3H8)
87.7 ppb neon (Ne)
552 ppt phosphine (PH3)
Dipole strength 1.15 mT (11.5 G)
Magnetic moment 2.88 × 1021 T•m³
Dipole tilt 0.33°
Satellite system
Number of moons 74
Number of rings 20

Deino (HD 11964 b, P153) is a planet which orbits the yellow G-type main sequence star HD 11964, meaning the star has just ran out of hydrogen fuel in its core. The star is considerably larger but cooler and lot more luminous than our Sun, located 107 light-years or 33 parsecs from Earth towards the constellation Cetus in the caelregio Hippocampus.

Deino is four times more massive than Jupiter, but similar in size. It orbits a bit closer to the star than Jupiter with an orbital period of 64 months (5.3 years).

Deino (the dread) is named after one of the sisters in Graeae in Greek mythology.

Discovery and chronology Edit

Deino was discovered on August 7, 2005 by a team of astronomers led by Paul Butler. The team used the spectrometer mounted on the telescope in Lick Observatory and found that this star wobble caused by planets. On that same day, the second planet Scylla was also announced. However, Deino wasn't fully confirmed until May 27, 2007.

Deino is the 146th exoplanet discovered overall, 120th since 2000, and 25th in 2005. Deino is also the 5th exoplanet discovered in the constellation Cetus (3rd in 2005) and 20th exoplanet discovered in the caelregio Hippocampus (5th in 2005). Deino is the second planet discovered in the HD 11964 system, despite its designation HD 11964 b (a is not used because the parent star uses this letter to reduce confusion). More accurately, this planet is also designated HD 11964 P2. However, at the time of its discovery, this planet was designated HD 11964 c. 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

Deino takes 168 megaseconds (5.33 years) to orbit eccentrically around the star at an average distance of 15.38 microparsecs (3.172 astronomical units). During one point of its orbit, Deino can be as close to the star as 14.75 μpc (3.043 AU) or as far away as 16.00 μpc (3.301 AU). The planet moves at an average velocity of 17.80 km/s and it varies from 17.43 to 18.15 km/s during its orbit. It's speculated inclination is 9° to line of sight (1.55° to star's equator). The argument of periastron is 102°, which is the angle between periastron and ascending node. The longitude of ascending node is 253° counterclockwise from the origin of longitude at First Point of Aries as seen from north. Adding argument of periastron and longitude of ascensing node yields 408° in longitude of periastron, but since it is more than 360°, we subtract that number and finished with 48°.

Parent star observation and irradiance Edit

When viewing HD 11964 from one of its moons since this planet is a gas giant with no solid surface, that sun would appear to be four times dimmer than the Sun as seen from Earth, corresponding to its apparent magnitude −25.23. The angular diameter of HD 11964 as seen from Deino is 0.163°, which is one-third the angular diameter of the full moon and sun as seen from Earth, because Deino orbits nearly 3.2 times farther away from the star than Earth to the Sun.

Deino receives an average of 106 W/m² of irradiance compared to 1368 W/m² for Earth and 51 W/m² for Jupiter.

Rotation Edit

Deino takes 7 hours, 26 minutes, and 38 seconds to rotate once on its axis, which is nearly one-third of an Earth day. The rotation velocity is 16.36 km/s, 10.17 mi/s, 58902 kph, or 36600 mph. This planet rotates in the same direction as its revolution. Deinian year lasts 6255 Deinian days, compared to Earth year that lasts 366 Earth days. The tilt of this planet is such that its north pole points to the Earth's northern equatorial constellation Sextans (in Felis), while the south pole points to the Earth's southern equatorial constellation Aquarius (in Hippocampus).

Structure and composition Edit

Mass and size Edit

Using the speculated inclination, its speculated true mass for Deino is 3.8125 MJ or 1211.7 M. This planet had a minimum mass 0.6059 MJ or 192.6 M. It is classified as super-Jupiter in the planetary mass classification scheme. This planet has mean radius of 67.520 megameters, which is slightly smaller than Jupiter. Deino has density 5.432 g/cm³, which is slightly less dense than Earth. Its flattening is 0.0218, one-third that of Jupiter's.

Gravitational influence Edit

Deino has gravitational force 1059 times stronger than Earth's and four times that of Jupiter's. The object falling to the planet accelerates at 103 m/s² or 340 ft/s². If you weigh 150 pounds on Earth, you would weigh 1583 pounds on Deino.

The roche limit, where a 3 g/cm³ moon tear apart by tidal forces, is 0.273 lunar distances (105 megameters), which is 1.54 planetary radii. The hill radius, the boundary where the gravitational influence of the planet is identical to the star, is 126.28 lunar distances (48.54 gigameters), which is 711 times the radius of the planet. The stationary orbit, where the satellite's orbital period is identical to the rotation period of the planet, analogous to the Earth's geostationary orbit, is 137.8 Mm, which is 2.00 planetary radii and one-third the Earth-Moon distance. The stationary velocity, the orbital velocity at stationary orbit, is 48.4 km/s or 30.1 mi/s. Since the planet takes 7.4 hours to rotate, then a moon would take 7.4 hours to orbit the planet at stationary orbit.

Interior Edit

Below Deino's 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 middle mantle, the temperature is 34,000 K (33,800°C, 60,800°F) and a pressure 820 GPa. In the lower mantle, there is a narrow layer of solid metallic hydrogen at a pressure of 2.2 TPa and temperature 40,800 K (40,500°C, 73,000°F). At the center lies a core of rock and metal with a mass 23 Earth masses, roughly 1.9% the total mass of the planet. The temperature of the core is estimated to be 43,300 K (43,000°C, 77,400°F) and an estimated pressure 6.7 TPa.

Atmosphere Edit

Deino's atmosphere composes about 92.7% hydrogen and 5.5% helium, along with trace amounts of other gases, including water vapor and methane but no ammonia. The atmosphere also contains small amounts of hydrogen sulfide (rotten egg gas) at 697 ppm.

Deino contains water clouds and the planet appears light gray from space. The water clouds are in the cooler upper deck and sulfur clouds in the warmer lower deck. Heat from its interior raises the temperature from 135 K (−138°C or −217°F) to 370 K (97°C or 206°F). This planet radiates about same amount of heat as it receives from the star, because the star is over four times more luminous than our Sun, plus the planet orbits 61% closer to HD 11964 than Jupiter to the Sun. Like Jupiter, there are hundreds of jet streams and zonal jets, which can produce storms and high winds.

Magnetic field Edit

This planet has a very strong magnetic field, at around 11.54 gauss. It is 2.65 times more powerful than Jupiter's and 37.46 times more powerful than Earth's. Because of the very strong magnetic field, Deino can have frequent and vivid auroras when the stellar activity is high or from nearby moons.

Moons and rings Edit

Deino has 74 moons and it has 20 dusty rings. The largest moon has mass 12.1 Lunar masses (0.149 Earth masses) and has diameter 1.911 Lunar diameters (4,125 miles, 6,638 kilometers), which is more massive and about the size of Mars. There are five other moons that are bigger than our Moon, six with diameters between 1000 miles and the diameter of our Moon, and 22 have diameters between 100 and 1000 miles. All the rest (40) are less than 100 miles in diameter.

Future studies Edit

The method will use to study Deino might be direct imaging using the space telescopes like the James Webb Space Telescope (JWST) to see what this planet actually looks like. The speculated inclination is 171°, which is almost face-on, which of course does not allow transits. The inclination of Deino's orbit shall be constrained using astrometry from Gaia, James Webb Space Telescope (JWST), or Space Interoferometry Mission (SIM). However, the inclination could be constrained sooner using the ground-based telescopes or the Hubble Space Telescope (HST) guidance sensor. Determining the inclination is important for determining its actual mass.

The direct imaging can constrain the size of this planet. After knowing its size, density and surface gravity can then be calculated. Using the density of the planet, astronomers can probe the interior and estimate the mass and size of the core. Astronomers will also study the mantle and its temperature of the core using astroseismology. Using the spectrometer mounted on the JWST, it can constrain its temperature and study the atmospheric chemical makeup. Using the same method, the rotation rate can also be constrained using Doppler shifts. Using the rotation rate and circumference of the planet (calculated using 2π radius), 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.

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

Related links Edit