Main Sequence G Type Stars - Habitable Simulation

The G-Type Stars described here are Main Sequence Stars on The H-R Diagram. They are very similar to our sun, Sol, forming a common spectral family. They are subdivided from G0 to G9. This article is based on data available from [www.pas.rochester.edu/~emamajek/EEM_dwarf_UBVIJHK_colors_Teff.txt here]. Additional parameters are calculated using the black body radiation formulas available at Math And Terraforming.

It is very important to remember that stars don't behave exactly as shown in the table. Each star has its own variations. Also, my calculations are based on the black body radiation formulas and they do not include flares and the Stellar Wind.

For each star model, parameters are compared to our own sun, Sol.

This article is dedicated for sci-fi writers, to have a better and close-up idea if a planet around a certain star can indeed be terraformed or not and at what cost. Please don't take it as a scientific work, it is just a simulation made with values that are much more easy to understand then dedicated scientific papers.

About the values[]

For all stars, the following parameters are calculated:

Main parameters:

Temperature (in degrees K, for our Sun, Sol it is 5778 K).
Mass: given in Solar masses
Radius: given in Solar radii
Bolometric Magnitude: includes all star's radiation, for Sol it is 4.81.
Visual magnitude: includes only visual light, for Sol it is 4.81.

Spectral parameters:

Main light spectra (for Sol, it is 577 nm). It helps us see if most light is emitted in red, blue, infrared or ultraviolet spectra.

Solar Constant - total energy output of the star: (Sol = 1)
Infrared light: (Sol = 1)
Red light: (Sol = 1)
Visible light: (Sol = 1)
Blue light: (Sol = 1)
Ultraviolet light: (Sol = 1)
Far UV light: (Sol = 1)

Habitable zone, based on light emissions:

Calculating the habitable zone, one must include four parameters:

Roche limit - below it, a star's gravity would tear apart any planet;
Solar constant - depends on distance from the star. For Earth, it is 1. Using Greenhouse Gases, it is possible to terraform a planet with a solar constant of 1/1000. By using Anti-Greenhouse Technology, it might be possible to terraform a planet with a solar constant of 20.
Light spectra - Plants on New Worlds need both red and blue light, which must be at least 1/1000 of what is on Earth. If either red or blue light fall below this limit, plants will not survive.
Toxic radiation include UV (especially far UV), X, gamma rays and ionized particle from the Stellar Wind. If toxic radiation is over 100 times higher then on Earth, Earth-like life is seriously threatened and atmosphere becomes too ionized and might be blown into space.

Further parameters:

Extended habitable zone (for Sol 0.223 to 31.6 AU): After applying all these constrains, one can determine the extended Habitable Zone, where greenhouse gasses or anti-greenhouse technology can bring temperature within acceptable boundaries, plants have enough red and blue light and toxic UV radiation is within acceptable limits.
Earth-like planet orbit: The distance of a Habitable Zone Planet or Earth-Like Planet (for Sol, 1 AU) is where a planet can exist without greenhouse gasses or anti greenhouse technology. It is listed if it fits within the extended habitable zone.
Tidal index: The star's tidal force on a planet in the extended habitable zone.
Orbital period: the orbital period of a star within the extended habitable zone.
Angular size: the size of the star as viewed from a planet in the habitable zone (Sol from Earth: 9.34). To see yourself how large a star would be as seen from a planet, draw a circle with the listed size in millimetres and look at it from a distance of one metre.

G0 Star[]

Main parameters:

Temperature: 5930
Mass: 1.06
Radius: 1.1
Bolometric magnitude: 4.42
Visual magnitude: 4.48

Spectral parameters:

Main light spectra: 536 (yellow)

Solar constant: 1.308
Infrared light: 1.253
Red light: 1.300
Visible light: 1.323
Blue light: 1.361
Ultraviolet light:1.687
Far UV light: 6.38

Habitable zone, based on light emissions:

Solar constant = 20: 0.256 AU
Solar constant = 1: 1.144 AU
Solar constant = 1/1000: 36.2 AU
Minimum red light: 36.1 AU
Minimum blue light: 36.9 AU
Roche limit: 0.00012 AU

Further parameters:

Extended habitable zone: 0.256 - 36.1 AU
Earth-like planet orbit: 1.144 AU
Tidal index: 0.000815 - 16.2
Tidal index for Earth-like planet: 0.810
Orbit period (days): 45.8 - 76800 (210 years)
Orbital period for Earth-like planet: 434 (1.2 years)
Angular size: 0.29 to 40.2
Angular size for Earth-like planet: 8.99.

G0 stars are very similar to the Sun, slightly bigger and brighter.

G1 Star[]

Main parameters:

Temperature: 5860
Mass: 1.03
Radius: 1.06
Bolometric magnitude: 4.55
Visual magnitude: 4.68

Spectral parameters:

Main light spectra: 542 (yellow)

Solar constant: 1.172
Infrared light: 1.145
Red light: 1.169
Visible light: 1.180
Blue light: 1.199
Ultraviolet light: 1.347
Far UV light: 2.74

Habitable zone, based on light emissions:

Solar constant = 20: 0.242 AU
Solar constant = 1: 1.083 AU
Solar constant = 1/1000: 34.3 AU
Minimum red light: 34.2 AU
Minimum blue light: 34.6 AU
Roche limit: 0.00012 AU

Further parameters:

Extended habitable zone: 0.242 - 34.2 AU
Earth-like planet orbit: 1.083 AU
Tidal index: 0.000881 - 17.58
Tidal index for Earth-like planet: 0.879
Orbit period (days): 42.8 - 71900 (197 years)
Orbital period for Earth-like planet: 405 (1.1 years)
Angular size: 0.29 to 40.9
Angular size for Earth-like planet: 9.15.

G1 stars are very similar to the Sun, slightly bigger and brighter.

G2 Star[]

Main parameters:

Temperature: 5770
Mass: 1.00
Radius: 1.012
Bolometric magnitude: 4.72
Visual magnitude: 4.80

Spectral parameters:

Main light spectra: 550 (yellow)

Solar constant: 1.020
Infrared light: 1.022
Red light: 1.020
Visible light: 1.019
Blue light: 1.018
Ultraviolet light: 1.006
Far UV light: 0.936

Habitable zone, based on light emissions:

Solar constant = 20: 0.226 AU
Solar constant = 1: 1.010 AU
Solar constant = 1/1000: 31.9 AU
Minimum red light: 31.9 AU
Minimum blue light: 31.9 AU
Roche limit: 0.00011 AU

Further parameters:

Extended habitable zone: 0.226 - 31.9 AU
Earth-like planet orbit: 1.010 AU
Tidal index: 0.000983 - 19.61
Tidal index for Earth-like planet: 0.980
Orbit period (days): 39.2 - 65800 (180 years)
Orbital period for Earth-like planet: 370 (1.0 years)
Angular size: 0.30 to 41.9
Angular size for Earth-like planet: 9.36.

Our sun, Sol, is listed as a G2 star. However, as one can see, Sol is a bit dimmer then the values listed here. This is a reminder for all of us that stars don't behave exactly as shown in tables.

G3 Star[]

Main parameters:

Temperature: 5720
Mass: 0.99
Radius: 1.002
Bolometric magnitude: 4.78
Visual magnitude: 4.87

Spectral parameters:

Main light spectra: 555 (yellow)

Solar constant: 0.974
Infrared light: 0.990
Red light: 0.976
Visible light: 0.969
Blue light: 0.958
Ultraviolet light: 0.880
Far UV light: 0.520

Habitable zone, based on light emissions:

Solar constant = 20: 0.221 AU
Solar constant = 1: 0.987 AU
Solar constant = 1/1000: 31.2 AU
Minimum red light: 31.2 AU
Minimum blue light: 31.0 AU
Roche limit: 0.00011 AU

Further parameters:

Extended habitable zone: 0.221 - 31.0 AU
Earth-like planet orbit: 0.987 AU
Tidal index: 0.001033 - 20.3
Tidal index for Earth-like planet: 1.016
Orbit period (days): 38.0 - 63200 (195 years)
Orbital period for Earth-like planet: 360 (1.1 years)
Angular size: 0.30 to 42.4
Angular size for Earth-like planet: 9.49.

G3 stars are very similar to our sun.

G4 Star[]

Main parameters:

Temperature: 5680
Mass: 0.985
Radius: 0.991
Bolometric magnitude: 4.83
Visual magnitude: 4.93

Spectral parameters:

Main light spectra: 559 (yellow)

Solar constant: 0.933
Infrared light: 0.959
Red light: 0.936
Visible light: 0.925
Blue light: 0.907
Ultraviolet light: 0.785
Far UV light: 0.321

Habitable zone, based on light emissions:

Solar constant = 20: 0.216 AU
Solar constant = 1: 0.966 AU
Solar constant = 1/1000: 30.5 AU
Minimum red light: 30.6 AU
Minimum blue light: 30.1 AU
Roche limit: 0.00011 AU

Further parameters:

Extended habitable zone: 0.216 - 31.0 AU
Earth-like planet orbit: 0.966 AU
Tidal index: 0.001085 - 21.1
Tidal index for Earth-like planet: 1.056
Orbit period (days): 36.9 - 60800 (166 years)
Orbital period for Earth-like planet: 349 (1.0 years)
Angular size: 0.31 to 42.9
Angular size for Earth-like planet: 9.59.

G4 stars are very similar to our sun.

G5 Star[]

Main parameters:

Temperature: 5660
Mass: 0.98
Radius: 0.977
Bolometric magnitude: 4.88
Visual magnitude: 4.98

Spectral parameters:

Main light spectra: 561 (yellow)

Solar constant: 0.897
Infrared light: 0.928
Red light: 0.900
Visible light: 0.888
Blue light: 0.867
Ultraviolet light: 0.728
Far UV light: 0.247

Habitable zone, based on light emissions:

Solar constant = 20: 0.212 AU
Solar constant = 1: 0.947 AU
Solar constant = 1/1000: 30.0 AU
Minimum red light: 30.0 AU
Minimum blue light: 29.5 AU
Roche limit: 0.00011 AU

Further parameters:

Extended habitable zone: 0.212 - 29.5 AU
Earth-like planet orbit: 0.947 AU
Tidal index: 0.001130 - 21.8
Tidal index for Earth-like planet: 1.092
Orbit period (days): 35.9 - 58900 (161 years)
Orbital period for Earth-like planet: 340 (0.9 years)
Angular size: 0.31 to 43.1
Angular size for Earth-like planet: 9.64.

G5 stars are very similar to our sun, slightly smaller.

G6 Star[]

Main parameters:

Temperature: 5600
Mass: 0.97
Radius: 0.949
Bolometric magnitude: 4.99
Visual magnitude: 4.10

Spectral parameters:

Main light spectra: 567 (yellow)

Solar constant: 0.820
Infrared light: 0.863
Red light: 0.824
Visible light: 0.806
Blue light: 0.778
Ultraviolet light: 0.596
Far UV light: 0.115

Habitable zone, based on light emissions:

Solar constant = 20: 0.202 AU
Solar constant = 1: 0.905 AU
Solar constant = 1/1000: 28.6 AU
Minimum red light: 28.7 AU
Minimum blue light: 27.9 AU
Roche limit: 0.00011 AU

Further parameters:

Extended habitable zone: 0.202 - 27.9 AU
Earth-like planet orbit: 0.905 AU
Tidal index: 0.001246 - 23.7
Tidal index for Earth-like planet: 1.183
Orbit period (days): 33.8 - 54600 (150 years)
Orbital period for Earth-like planet: 319 (0.9 years)
Angular size: 0.32 to 43.8
Angular size for Earth-like planet: 9.79.

G6 stars are very similar to our sun, slightly smaller.

G7 Star[]

Main parameters:

Temperature: 5550
Mass: 0.95
Radius: 0.927
Bolometric magnitude: 5.08
Visual magnitude: 5.2

Spectral parameters:

Main light spectra: 572 (yellow)

Solar constant: 0.762
Infrared light: 0.813
Red light: 0.766
Visible light: 0.745
Blue light: 0.712
Ultraviolet light: 0.504
Far UV light: 0.0599

Habitable zone, based on light emissions:

Solar constant = 20: 0.195 AU
Solar constant = 1: 0.873 AU
Solar constant = 1/1000: 27.6 AU
Minimum red light: 27.7 AU
Minimum blue light: 26.7 AU
Roche limit: 0.00011 AU

Further parameters:

Extended habitable zone: 0.195 - 26.7 AU
Earth-like planet orbit: 0.873 AU
Tidal index: 0.001335 - 24.9
Tidal index for Earth-like planet: 1.247
Orbit period (days): 32.3 - 51600 (141 years)
Orbital period for Earth-like planet: 305 (0.8 years)
Angular size: 0.32 to 44.4
Angular size for Earth-like planet: 9.93.

G7 stars are very similar to our sun, slightly smaller.

G8 Star[]

Main parameters:

Temperature: 5480
Mass: 0.94
Radius: 0.914
Bolometric magnitude: 5.16
Visual magnitude: 5.3

Spectral parameters:

Main light spectra: 580 (yellow)

Solar constant: 0.712
Infrared light: 0.777
Red light: 0.718
Visible light: 0.691
Blue light: 0.651
Ultraviolet light: 0.413
Far UV light: 0.0246

Habitable zone, based on light emissions:

Solar constant = 20: 0.189 AU
Solar constant = 1: 0.844 AU
Solar constant = 1/1000: 26.7 AU
Minimum red light: 26.8 AU
Minimum blue light: 25.5 AU
Roche limit: 0.00011 AU

Further parameters:

Extended habitable zone: 0.1888 - 25.5 AU
Earth-like planet orbit: 0.844 AU
Tidal index: 0.001444 - 26.4
Tidal index for Earth-like planet: 1.319
Orbit period (days): 30.9 - 48500 (141 years)
Orbital period for Earth-like planet: 292 (0.8 years)
Angular size: 0.33 to 45.2
Angular size for Earth-like planet: 10.12.

G8 stars are similar to our sun, but smaller. An Earth-like planet would experience significantly shorter year and stronger tides caused by its sun.

G9 Star[]

Main parameters:

Temperature: 5380
Mass: 0.9
Radius: 0.853
Bolometric magnitude: 5.39
Visual magnitude: 5.55

Spectral parameters:

Main light spectra: 590 (yellow)

Solar constant: 0.588
Infrared light: 0.660
Red light: 0.592
Visible light: 0.562
Blue light: 0.518
Ultraviolet light: 0.279
Far UV light: 0.00600

Habitable zone, based on light emissions:

Solar constant = 20: 0.171 AU
Solar constant = 1: 0.766 AU
Solar constant = 1/1000: 24.2 AU
Minimum red light: 24.3 AU
Minimum blue light: 22.8 AU
Roche limit: 0.00011 AU

Further parameters:

Extended habitable zone: 0.1713 - 22.8 AU
Earth-like planet orbit: 0.766 AU
Tidal index: 0.001736 - 30.6
Tidal index for Earth-like planet: 1.532
Orbit period (days): 27.3 - 41800 (141 years)
Orbital period for Earth-like planet: 258 (0.8 years)
Angular size: 0.35 to 46.5
Angular size for Earth-like planet: 10.40.

G9 stars are about half as luminous as our sun and slightly redder. We can clearly see that the Sun is not in the middle of G class. The Sun is more similar to cooler F class stars (like F8 or F9) then it is to a G9 star. This is because the spectral classes were initially made to include visible stars. The Sun was later linked to a position that would fit inside a spectral class and is not a model star used for classification.

Conclusion[]

G - type stars are similar stars to the Sun, having similar properties. The G class is the class of stars with the smallest diferences between them.