|Date||December 14, 2009|
|Discoverers||Vogt et al.|
|Detection method||Radial velocity|
|Site|| Keck Observatory,|
|Name & designations|
|Planet numbers|| P379, 61 Virginis P2,|
Virgo P17, Noctua P40,
2009 P73, 2009 Vir-7,
|Star designations|| 61 Virginis c, 134 Noctae c,|
BF 4505 c, PH 309 c,
P12 Virginis c, P29 Noctae c,
HD 115617 c, HIP 64924 c,
HR 5019 c, Gliese 506 c,
SAO 157844 c
|Right ascension||13h 18m 24.31s (199.601 31°)|
|Declination||−18° 18' 40.3" (−18.311 20°)|
|Distance||8.555 pc (27.903 ly)|
|Semimajor axis||0.217 824 AU (32.586 0 Gm)|
|Periastron||0.187 792 AU (28.093 3 Gm)|
|Apastron||0.247 856 AU (37.078 7 Gm)|
|Eccentricity||0.137 871 8|
|Orbital circumference||1.363 85 AU (204.030 Gm)|
|Orbital area||0.147 636 AU² (3 304.03 Gm²)|
|Orbital period||38.021 137 d)|
|Avg. velocity||62.320 km/s (13.102 AU/yr)|
|Max. velocity||66.477 km/s (13.976 AU/yr)|
|Min. velocity||57.864 km/s (12.165 AU/yr)|
| Direction of orbit|
relative to star's rotation
|Inclination|| 76.133° to ecliptic|
1.855° to star's equator
11.455° to invariable plane
|Argument of periastron||340.628°|
|Longitude of ascending node||256.010°|
|Longitude of periastron||236.638°|
|Angular separation||25.461 mas|
|Observing the parent star|
|Mean angular star size||2.322 66° (139.359')|
|Max. angular star size||2.694 10° (161.646')|
|Min. angular star size||2.041 23° (122.474')|
|Mean star magnitude||−29.807|
|Max. star magnitude||−30.129|
|Min. star magnitude||−29.526|
|Mean radius||3.459 1 R⊕ (22.038 Mm)|
|Equatorial radius||3.462 4 E⊕ (22.083 Mm)|
|Polar radius||3.452 4 P⊕ (21.946 Mm)|
|Mean circumference||138.467 Mm|
|Equatorial circumference||138.754 Mm|
|Polar circumference||137.891 Mm|
|Surface area||11.965 0 S⊕ (6 102.9 Mm²)|
|Volume||41.387 V⊕ (44 831 Mm³)|
|Flattening||0.006 24 (1:160.3)|
|Angular diameter||34.438 μas|
|Mass||18.745 1 M⊕|
| Reciprocal mass|
relative to star
|Surface gravity||1.567 g (15.36 m/s²)|
| Weight on Tamar|
(150 lb (1 wa) on Earth)
|235 lb (1.57 wa)|
|Standard gravitational parameter||7.472 × 106 km³/s²|
|Escape velocity||26.04 km/s|
|Hill radius||2.052 LD (0.788 8 Gm)|
| Roche limit|
(3 g/cm3 satellite)
|0.067 95 LD (26.121 Mm)|
|Stationary orbit||2.997 22 LD (1 152.127 Mm)|
|Stationary velocity||2.527 km/s (0.568 LD/d)|
|Rotation period||811.117 6 h (33.796 566 d)|
|Rotation velocity||171 kph (0.44°/h)|
| Direction of rotation|
relative to orbit
|Longitude of vernal equinox||169.025°|
|North pole right ascension||19h 12m 37s (288.156°)|
|North pole declination||+21° 20' 24" (+21.340°)|
|North polar constellation||Vulpecula|
|North polar caelregio||Testudo|
|South pole right ascension||07h 12m 37s (108.156°)|
|South pole declination||−21° 20' 24" (−21.340°)|
|South polar constellation||Canis Major|
|South polar caelregio||Araneus|
|Surface temperature||487 K (214°C, 418°F, 877°R)|
|Mean irradiance||21 605 W/m² (15.798 I⊕)|
|Irradiance at periastron||29 068 W/m² (21.255 I⊕)|
|Irradiance at apastron||16 687 W/m² (12.202 I⊕)|
|Albedo||0.127 (bond), 0.138 (geom.)|
|Scale height||32.55 km|
|Volume||48.927 ae (204.88 Mm³)|
|Total mass||7.295 atmu (37.49 Eg)|
|Surface pressure||0.017 3 atm (1.76 kPa, 0.255 psi)|
|Surface density||0.183 g/m³|
|Molar mass||7.32 g/mol|
|Composition|| 60.776% hydrogen (H2)|
18.328% helium (He)
13.539% nitrogen (N2)
4.024% water (H2O)
1.865% oxygen (O2)
1.432% methane (CH4)
316 ppm nitric oxide (NO)
175 ppm argon (Ar)
137 ppm carbon monoxide (CO)
43.7 ppm ammonia (NH3)
21.1 ppm krypton (Kr)
3.56 ppm carbon dioxide (CO2)
866 ppb xenon (Xe)
|Dipole strength||0.622 nT (6.22 μG)|
|Magnetic moment||7.50 × 1013 T•m³|
|Number of moons||0|
|Number of rings||0|
Tamar (61 Virginis c, P379) is a planet which orbits the yellow G-type main sequence star 61 Virginis, which is similar to our Sun. It is approximately 28 light-years or 9 parsecs from Earth towards the constellation Virgo in the caelregio Noctua.
Tamar is in the middle of the known three-planet 61 Virginis system. Tamar is an ocean planet with all the surface covered in oceans of water hundreds of miles deep. It is a midplanet with 22 times the mass of Earth.
Discovery and chronology Edit
Tamar was discovered on December 14, 2009 by a team of astronomers led by Steven Vogt. The team used the HIRES spectrometer mounted on the Keck Telescope in Hawaii and the Anglo-Austrialian Telescope in New South Wales, Australia and found that the star 61 Virginis has three periodic variations in the spectrum. This implies evidence for a three-planet system around 61 Virginis, including Tamar.
Tamar is the 372nd exoplanet discovered overall, 346th since 2000, and 74th in 2009. Tamar is the 17th exoplanet discovered in the constellation Virgo (7th in 2009) and 40th exoplanet discovered in the caelregio Noctua (12th in 2009). Since Tamar is the second planet discovered in the 61 Virginis system, the planet receives the designations 61 Virginis c (a is not used because the parent star uses this letter to reduce confusion) and 61 Virginis 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
Tamar orbits the star at an average distance of 0.2178 AU (1 AU is the average distance between the Earth and the Sun) or 32.59 Gm (million km), nearly two times closer to the star than Mercury is to the Sun. Tamar has a semi-circular orbit with an eccentricity of 0.1379. Tamar's orbit varies from 0.1878 AU (28.09 Gm) to 0.2479 AU (37.08 Gm). The planet takes just 38 days, 5.4 weeks or 3.3 megaseconds to make one complete trip around the star at an average velocity of 62.3 km/s, 38.7 mi/s, or 13.1 AU/yr. Tamar is in a 4:13 resonance with the outermost known planet Tuonetar and 9:1 resonance with the innermost planet Devana.
Parent star observation and irradiance Edit
Viewed from Tamar, the parent star would have a magnitude −29.81 compared to −26.74 for the magnitude of the Sun seen from Earth. Observed from Tamar, 61 Virginis would appear to be 17 times brighter than the Sun seen from Earth. Viewed from Tamar, the parent star would have an angular diameter of 2.3° on average, which is 4.6 times the angular diameter of the full moon we sometimes see at night.
Tamar receives nearly 15.8 times more energy from the star than Earth receives from the Sun, 21,605 W/m² vs. 1,368 W/m².
Tamar is in a 9:8 tidal lock ratio, meaning the planet rotates nine times every time when the planet orbits the star eight times. Since the planet takes 38.021 days to orbit the star, then it would take 33.797 days to rotate once on its axis. So the year on Tamar lasts exactly 1.125 days compared to 366 Earth days in an Earth year. The planet tilts 6.2° to the plane of its orbit, which is a quarter of the Earth's tilt of 23.4°. The planet's north pole points to the constellation Vulpecula (in Testudo), while the south pole points to the constellation Canis Major (in Araneus).
Structure and composition Edit
Mass and size Edit
Tamar is an intermediate-mass planet, massing 18.75 Earth masses, classifying it as midplanet in the planetary mass classification scheme. Tamar is 9% more massive than Neptune and 29% more massive than Uranus. The size of this planet is 3.46 Earth radii, corresponding to the density of 2.50 g/cm³, meaning that it is less than half the density of Earth.
Gravitational influence Edit
The gravitational force of Tamar is 57% stronger than Earth's. So if you weigh 150 pounds (1 wame) on Earth, you would weigh 235 pounds (1.57 wames) on Tamar, which is about the weight of an average professional football player on Earth!
Tamar has the hill sphere radius of just 35.79 planetary radii. The satellite's orbit within the hill sphere is stable while the orbit outside of hill sphere is unstable. The roche limit of Tamar is 1.19 planetary radii. If a 3 g/cm³ satellite orbits within a roche limit, it would tear apart by tidal forces. Denser moons would withstand greater tidal forces and orbiting closer to the planet would be required to tear apart. Tamar's stationary orbit, analogous to the Earth's geostationary orbit, is located at a distance of 52.17 planetary radii. Stationary orbit is an orbit where its orbital period is synchronous with the planet's rotation period. Since the planet takes 30.417 days to rotate once on its axis, then a moon in stationary orbit would also take 30.417 days to orbit the planet, that's very similar to the orbital period of the Moon in orbit around the Earth. So a moon would always present the same face to the planet and the observer on the moon appears that the planet never rotate while observer on the planet's surface appears that the moon always hang in the sky and never move.
With the density of 2.51 g/cm³, Tamar has the layers of rock, diamond and exotic forms of water. With the surface temperature of 487 K (214°C, 418°F), it is too hot to have normal liquid water on its surface but cool enough to have exotic form of liquid water under pressure. All of the planet's surface is covered by liquid water with an estimated depth of 873 kilometers or 543 miles. The upper mantle composes of the exotic form of water called ice VII or "hot ice" with the radius of 5398 km or 3354 mi and a pressure 0.36 GPa. The lower mantle composes of diamond with the radius of 6204 km or 3855 mi and a pressure 0.89 GPa. At the center of this planet is a carbon-iron core with a temperature of 7100 K (6800°C, 12300°F) and a pressure 1.57 GPa. The core has a radius of 9563 km or 5942 mi.
Diamond abundance Edit
The diamond just mentioned are found in the lower mantle underneath the layer of "hot ice" in the upper mantle. Tamar has an estimated 260 million times more diamond than Earth has! There would be enough diamond to build a city planet the size of this planet with every building and appliances made of diamond!
Tamar has a thin atmosphere three times thicker than Mars' and 55.5 times thinner than Earth's. The atmosphere is made of 61% hydrogen, 18% helium, 14% nitrogen, 4% water, 2% oxygen, and 1% methane. Clouds are virtually nonexistent.
Magnetic field Edit
Tamar has an extremely weak magnetic field, about six millionths of a gauss, which is 50,000 times weaker than Earth's. A possible reason for its weakness is because the planet rotates so slowly caused by the tidal forces of the nearby star.
Moons and rings Edit
Because Tamar orbits so close to its star and the small hill sphere, Tamar has no moons nor rings. But if moons actually exist, they have to orbit within 21⁄6 LD from the planet or they will flung off into space.
Future studies Edit
It is speculated that Tamar will not transit since I speculated that the inclination is 56.1°. Studying Tamar using the direct imaging would not be a reliable option since the planet orbits way too close to the glare of its star. The planet can best be studied using astrometry using Gaia, James Webb Space Telescope (JWST), or Space Interoferometry Mission (SIM). The astrometry can constrain the inclination and thus calculate the exact mass.
Maybe ATLAST can reliably be used to directly image planets down to 0.01 AU from the sun-like stars. The direct imaging can see what Tamar 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 and true mass calculated using 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 ATLAST, a tenuous atmosphere and the surface can be studied.
In orbit around the planet, moons and rings can be detected (if they exist) using the transit across the planet, detecting the wobble of the planet, or even direct imaging.