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Planetary Spin Calculator

This web page and the maths associated with this calculator are copyright protected by
Keith Dixon-Roche {© 14/03/17}

Terminology

1) Gravitational energy is the same as potential energy. As this web page deals with Newtonian mechanics only the term gravitational energy will be deployed.

2) Suffixes apply as follows:
'ₒ' = satellite orbit; '₁' = force-centre; '₂' = satellite; '₃' = secondary satellite

3) Refer to our Planetary Spin web page on for a detailed breakdown of the maths used in this calculator

Planetary System (Fig 1)

Planetary system
Fig 1. Planetary System

Planetary spin refers to the angular rotation (spin-rate) induced in a celestial satellite in orbit around a force-centre, such as a star or planet.

The body being investigated is a satellite
(e.g. as sun, planet or moon)

Its force-centre is a galactic star, solar sun or planet

Its secondary satellite(s) is a planet or moon

What Is Planetary Spin?

It is the spin rate of a force-centre or satellite. It has both [angular] velocity and direction.

Whilst it is not part of Newtonian mechanics, the energy that generates spin is found in Isaac Newton's laws of motion.

What Are Spin Energies?

Spin energy is the rotational energy inducing spin in a satellite.

Orbital Energy (Eₒ)

Assuming no other [energy] influences, gravitational energy will ensure that a satellite orbiting a force-centre will always present the same face to its force-centre causing it to spin at an angular velocity (ωₒ) with the same period as its orbital period

Force-Centre Energy (E₁)

This is the rotational energy induced in a satellite due to its own orbital kinetic energy, which varies with its distance from its force-centre according to Isaac Newton's inverse-square relationship. This energy will cause a satellite to rotate in the opposite direction to ωₒ

This energy can be found in Newton's output data for the satellite

Force-Centre Energy (E₃)

This is the rotational energy induced in a satellite by its own secondary satellites and will cause a satellite to rotate in the same direction as the secondary satellite's orbit. Its magnitude is dependent upon the relative angle between the satellite's orbital plane and that of its secondary satellites.

This energy can be found from the [sum of] Newton's output data for the orbit of each of the secondary satellite(s)

Moons or No Moons!

Apart from Mars, all the planets in our solar system possess spin energy from secondary satellite(s) at least a thousand times greater than that induced by the satellite's own kinetic energy. This is why Venus rotates in the opposite direction to the other planets; it has no secondary satellites to overcome the influence of E₁

Mars is a very special case because it appears to be hollow. The influence of its secondary satellites is only 2.5 times greater than E₁. Phobos actually rotates faster than its force-centre (Mars), which must be due to Mars' unusually low 'Δ' value

Example Calculation 1

Mercury & Venus have no moons, so we shall calculate the spin in both planets (Fig 2 shows the calculation for Venus)

Property units Mercury Venus
Newton Calculation
m₁ kg 1.9885E+30 1.9885E+30
m₂ kg 3.30110E+23 4.86737E+24
r₂ m 2439700 6051800
T₂ s 7600522 19413907
m 4.60012E+10 1.07477E+11
E₁⁽¹⁾ J 5.76563E+23 2.51533E+23
Spin Calculation
m₂ kg 3.30110E+23 4.86737E+24
r₂ m 2439700 6051800
Δ₂ 0.812863 0.68118
T₂ s 7600522 19413907
θ ° 0 (no moons) 0 (no moons)
E₁ J 5.76563E+23 2.51533E+23
E₃ J 0 (no moons) 0 (no moons)
J₂ kg.m² 5.19309E+35 3.3086276E+37
E₂ J 3.99116E+23 -1.48128E+24
ω₂ ᶜ/s 1.2398E-06 -2.99233E-07
Planetary spin in planets with no moons
1) output data from Newton for the satellites (Mercury and Venus)

Planetary spin in the planet Venus
Fig 2. Angular Velocity Calculation for the Planet Venus

Example Calculation 2

Neptune is a little more complicated as it has many moons, three of which orbit in the opposite direction (retrograde) to Neptune's own orbit (prograde)

Neptune's Moon E₃ (J)
Naiad -1.41526E+25
Thalassa -2.72711E+25
Despina -1.30039E+26
Galatea -2.20708E+26
Larissa -2.30921E+26
S/2004 N 1 -1.63551E+23
Proteus -1.44926E+27
Triton -2.05897E+29 x -1
Nereid 1.12539E+26
Halimede 2.56883E+21
Laomedeia 1.15675E+22
Sao 4.34646E+21
Neso 1.84075E+22 x -1
Psamathe 1.80844E+21 x -1
ΣE₃ 2.0393706E+29 #
Planetary spin energies calculated using the Newton calculator

Property units Neptune
Newton Calculation
m₁ kg 1.9885E+30
m₂ kg 1.024134E+26
r₂ m 24622000
T₂ s 5200329600
m 4444450000000
E₁⁽¹⁾ J 2.09361E+21
Spin Calculation
m₂ kg 1.0241340E+26
r₂ m 24622000
Δ₂ 0.0374096
T₂ s 5200329600
θ ° 23.8
E₁ J 2.09361E+21
E₃ J 2.039371E+29 #
J₂ kg.m² 3.4756E+37
E₂ J 2.03937E+29
ω₂ ᶜ/s 1.0833E-04
Planetary spin in the planet Neptune
1) output data from Newton for the satellite (Neptune)

 

Planetary spin in the planet Neptune
Fig 3. Angular Velocity Calculation for the Planet Neptune

Delta Value (Δ)

The delta value of any satellite or force-centre is the factor that must be applied to its radius in order to accurately define its polar moment of intertia, which can be used to define its structure using Core Pressure theory

Planetary Spin Calculator - Technical Help

Units

You may use whatever units you like (except: time must be in seconds and angles must be in degrees), but you will get out whatever you enter, so be consistent.

Input Data

The two available calculation options allow you to input either:
Δ₂: the delta value of the satellite to calculate its angular velocity (ω₂)
or
ω₂: the angular velocity of the satellite to calculate its delta value (Δ₂)

m₂: mass of the satellite

r₂: volumetric radius of the satellite

T₂: orbital period of the satellite [seconds]

θ: angle between the orbital plane of the satellite and that of its secondary satellites [degrees]

E₁: the energy induced into the satellite by its force-centre. This value may be obtained from CalQlata's Newton calculator from a calculation of the satellite itself

E₃: the total (ΣE₃) energy induced into the satellite by all of its secondary satellites. This value may be obtained by summing-up the individual E₃ energy values for each of the secondary satellites, which can be found using Newton

Output Data

ω₂: the angular velocity of the satellite; if the satellite's delta value (Δ₂) was entered
or
Δ₂: the delta value of the satellite; if the satellite's angular velocity (ω₂) was entered

J₂: polar moment of inertia of the satellite

E₂: total spin energy generating ω₂

Applicability

This calculator can be used for any satellite orbiting a force-centre

Accuracy

This calculator is as accurate as Newton's own laws of motion

Further Reading

You will find further reading on this subject in reference publications(55, 61, 62 & 64)