Arella's Home



Arella's planet is fictitious, but her star isn't. Her world circles HD 172051 (also called HIP 91438) about 43 light years from here.

Mass 1.721030 kg (0.865 Sol)
Mean radius 626753 km (0.90 Sol)
Temperature 5638K
Life span 1.62x1010 years
Age 4.3x109 years
Spectral type G5V
Apparent mag 5.85
Metallicity [Fe/H] 0.21 dex
Constellation Sagittarius
Right ascension 18h 38m 53.4005s
Declination -21o 03' 06.7368"
Local Brightness 121291 lux (0.95 Sol)

Arella lives on a large moon called Amphitrite. It orbits a gas giant called Serel. Amphitrite is just large enough to hold an atmosphere and has a gravity around 2/3 of Earth's. It orbits close enough to Serel to be tidally locked, so Arella always sees Serel looming large in her sky.


Mean radius 4332 km (0.68 Earth)
Surface area 2.358108 km2 (0.462 Earth)
Volume 3.4051011 km3 (0.314 Earth)
Mass 1.7371024 kg (0.29 Earth)
Mean density 5.1 g/cm3
Surface gravity 6.176 m/s2 (0.63 g)
Day Length 33.6 Earth hours
Orbit radius 478720 km
Orbital period 33.6 Earth hours
Escape velocity 7.315 km/s
Albedo 0.26
Atmos. Press 0.93 earth
Land % 0.2%
Max elevation 97m
Obliquity 0.11 deg


Mean radius 94380 km (1.35 Jupiter)
Surface area 1.121011 km2 (1.82 Jupiter)
Volume 3.521015 km3 (2.45 Jupiter)
Mass 4.4371027 kg (2.34 Jupiter)
Mean density 1.26 g/cm3
Surface gravity 33.245 m/s2 (3.39 g)
Day Length 11.63 earth hours
Orbit radius 1.30152x108 km (0.87au)
Orbital period 318.7 Earth days, 227.6 Amphitrite days
Escape velocity 79.217 km/s
Albedo 0.49
Angle in sky 22.3 deg (44.6 Earth Moon widths)


Amphitrite is tidally locked so Serel stays put in the sky. The side of Amphitrite that faces Serel experiences a daily 2.08 hr eclipse. The following two plots show a typical eclipse, here at 20deg longitude. The second is a log plot that show a typical visual response to light levels. As Serel's phase approaches full at night, light levels increase. A full Serel casts over 2000 lux on Amphitrite's surface.

The side of facing Serel recieves less total illumination as shown in the following two plots.


Amphitrite started out with 12% land cover. Land species evolved. Plate tectonics ended. Later, hominid species evolved. Land erosion reduced land coverage and continents sank below the sea. Some land species, including the hominids, successfully made the transition back to water before their land completely disappeared beneath the sea.

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Copyright 2017-2018 by David White

This page last updated 24-Jan-2018