This article is both about the M-Type Stars along Main Sequence Stars and the M - type Brown Dwarfs, on The H-R Diagram. These objects are dimmer then our sun, Sol and are subdivided from M0 to M9. M - type stars are brighter, above M7, while the hot M - type brown dwarfs are found at M8 or below. There is a small gap, where it is difficult to certainly say if an object is a dim star or a brown dwarf. M - type stars are the most common type of stars in the Universe and are known to host planets. So, studying them is very important. 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 5500 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)
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.
M0 Star[]
Main parameters:
- Temperature: 3850
- Mass: 0.57
- Radius: 0.588
- Bolometric magnitude: 7.65
- Visual magnitude: 8.8
Spectral parameters:
Main light spectra: 825 (infrared)
- Solar constant: 0.1023
- Infrared light: 0.1916
- Red light: 0.0891
- Visible light: 0.0621
- Blue light: 0.0353
- Ultraviolet light: 0.000522
Habitable zone, based on light emissions:
- Solar constant = 20: 0.0715 AU
- Solar constant = 1: 0.320 AU
- Solar constant = 1/1000: 10.11 AU
- Minimum red light: 9.44 AU
- Minimum blue light: 5.94 AU
- Roche limit: 0.000085 AU
Further parameters:
- Extended habitable zone: 0.0715 - 5.94 AU
- Earth-like planet orbit: 0.320 AU
- Tidal index: 0.01616 - 111.5
- Tidal index for Earth-like planet: 5.57
- Orbit period (days): 9.25 - 7000 (19 years)
- Orbital period for Earth-like planet: 87.4
- Angular size: 0.93 to 76.8
- Angular size for Earth-like planet: 17.18.
Already for M0 stars, light spectra switches from red to infrared, which means that even red light is not in too high amount, while blue light is far dimmer. Despite the fact that greenhouse gasses can allow a planet as far as 10 AU to be terraformed, plants, without an artificial source of light, cannot survive beyond 6 AU. Any inner or Earth-like planet would be tidal locked.
M1 Star[]
Main parameters:
- Temperature: 3660
- Mass: 0.5
- Radius: 0.501
- Bolometric magnitude: 8.22
- Visual magnitude: 9.64
Spectral parameters:
Main light spectra: 868 (infrared)
- Solar constant: 0.0638
- Infrared light: 0.1284
- Red light: 0.0526
- Visible light: 0.0346
- Blue light: 0.01797
- Ultraviolet light: 0.000138
Habitable zone, based on light emissions:
- Solar constant = 20: 0.0564 AU
- Solar constant = 1: 0.253 AU
- Solar constant = 1/1000: 7.99 AU
- Minimum red light: 7.26 AU
- Minimum blue light: 4.24 AU
- Roche limit: 0.000079 AU
Further parameters:
- Extended habitable zone: 0.0565 - 4.24 AU
- Earth-like planet orbit: 0.253 AU
- Tidal index: 0.0278 - 156.8
- Tidal index for Earth-like planet: 7.84
- Orbit period (days): 6.93 - 4500 (12 years)
- Orbital period for Earth-like planet: 65.5
- Angular size: 1.10 to 82.9
- Angular size for Earth-like planet: 18.53.
The environment around M1 stars has more infrared and less blue light. There is only little UV light, which can affect photodisintegration of certain substances on the ground.
M2 Star[]
Main parameters:
- Temperature: 3560
- Mass: 0.44
- Radius: 0.446
- Bolometric magnitude: 8.59
- Visual magnitude: 10.21
Spectral parameters:
Main light spectra: 892 (infrared)
- Solar constant: 0.0465
- Infrared light: 0.0973
- Red light: 0.0371
- Visible light: 0.0236
- Blue light: 0.0116
- Ultraviolet light: 0.0000616
Habitable zone, based on light emissions:
- Solar constant = 20: 0.0482 AU
- Solar constant = 1: 0.216 AU
- Solar constant = 1/1000: 6.82 AU
- Minimum red light: 6.09 AU
- Minimum blue light: 3.41 AU
- Roche limit: 0.000075 AU
Further parameters:
- Extended habitable zone: 0.0482 - 3.41 AU
- Earth-like planet orbit: 0.216 AU
- Tidal index: 0.0378 - 189.1
- Tidal index for Earth-like planet: 9.46
- Orbit period (days): 5.83 - 3470 (9.5 years)
- Orbital period for Earth-like planet: 55.1
- Angular size: 1.22 to 86.4
- Angular size for Earth-like planet: 19.32.
The environment around M3 stars has more infrared and less blue light. An Earth-like planet would orbit the star at half of Mercury's orbit and would most likely be tidal locked. Because of the lack of blue light, any Earth-like planet would not give the same agricultural output like Earth does.
M3 Star[]
Main parameters:
- Temperature: 3430
- Mass: 0.37
- Radius: 0.361
- Bolometric magnitude: 9.21
- Visual magnitude: 11.15
Spectral parameters:
Main light spectra: 926 (infrared)
- Solar constant: 0.0273
- Infrared light: 0.0600
- Red light: 0.0207
- Visible light: 0.0126
- Blue light: 0.00577
- Ultraviolet light: 0.0000182
Habitable zone, based on light emissions:
- Solar constant = 20: 0.0369 AU
- Solar constant = 1: 0.1651 AU
- Solar constant = 1/1000: 5.22 AU
- Minimum red light: 4.55 AU
- Minimum blue light: 2.40 AU
- Roche limit: 0.000069 AU
Further parameters:
- Extended habitable zone: 0.0369 - 2.40 AU
- Earth-like planet orbit: 0.165 AU
- Tidal index: 0.0641 - 271
- Tidal index for Earth-like planet: 13.57
- Orbit period (days): 4.26 - 2233 (6.1 years)
- Orbital period for Earth-like planet: 40.3
- Angular size: 1.40 to 91.4
- Angular size for Earth-like planet: 20.4.
Most M3 stars are known to lack massive flares, as do dimmer M - type stars. Their habitable zones are small and close to the stellar body.
M4 Star[]
Main parameters:
- Temperature: 3210
- Mass: 0.23
- Radius: 0.274
- Bolometric magnitude: 10.1
- Visual magnitude: 12.61
Spectral parameters:
Main light spectra: 989 (infrared)
- Solar constant: 0.01287
- Infrared light: 0.0310
- Red light: 0.00880
- Visible light: 0.00490
- Blue light: 0.001967
- Ultraviolet light: 0.00000234
Habitable zone, based on light emissions:
- Solar constant = 20: 0.0254 AU
- Solar constant = 1: 0.113 AU
- Solar constant = 1/1000: 3.588 AU
- Minimum red light: 2.97 AU
- Minimum blue light: 1.40 AU
- Roche limit: 0.000054 AU
Further parameters:
- Extended habitable zone: 0.0254 - 1.403 AU
- Earth-like planet orbit: 0.1134 AU
- Tidal index: 0.1169 - 357
- Tidal index for Earth-like planet: 17.9
- Orbit period (days): 3.08 - 1264 (3.4 years)
- Orbital period for Earth-like planet: 29.1
- Angular size: 1.83 to 100.9
- Angular size for Earth-like planet: 22.57.
It is known that M4 stars are flare stars. However, some of them, like Barnard's Star, are far more stable and can support a habitable planet, while others are eruptive.
M5 Star[]
Main parameters:
- Temperature: 3060
- Mass: 0.162
- Radius: 0.196
- Bolometric magnitude: 11.4
- Visual magnitude: 14.15
Spectral parameters:
Main light spectra: 1038 (infrared)
- Solar constant: 0.00571
- Infrared light: 0.01459
- Red light: 0.00358
- Visible light: 0.001859
- Blue light: 0.000674
- Ultraviolet light: 0.000000318
Habitable zone, based on light emissions:
- Solar constant = 20: 0.0169 AU
- Solar constant = 1: 0.0755 AU
- Solar constant = 1/1000: 2.39 AU
- Minimum red light: 1.89 AU
- Minimum blue light: 0.82 AU
- Roche limit: 0.000045 AU
Further parameters:
- Extended habitable zone: 0.0169 - 0.821 AU
- Earth-like planet orbit: 0.0755 AU
- Tidal index: 0.240 - 568
- Tidal index for Earth-like planet: 28.4
- Orbit period (days): 1.991 - 675 (1.8 years)
- Orbital period for Earth-like planet: 18.83
- Angular size: 2.23 to 108.5
- Angular size for Earth-like planet: 24.2.
Most M5 stars are eruptive, flare stars. Their flares erode atmospheres around their planets and can cause overheating to any terraformed planet. Still, for those stars who have rare flare activity, terraforming might be possible. Flares have a devastating effect on any Inner Planet, so, habitable zone should be limited inwards to the orbit of an Earth-like planet (if flare activity even allows that).
M6 Star[]
Main parameters:
- Temperature: 2810
- Mass: 0.102
- Radius: 0.137
- Bolometric magnitude: 12.19
- Visual magnitude: 16.32
Spectral parameters:
Main light spectra: 1130 (infrared)
- Solar constant: 0.00216
- Infrared light: 0.00613
- Red light: 0.001127
- Visible light: 0.000515
- Blue light: 0.000154
- Ultraviolet light: 0.0000000211
Habitable zone, based on light emissions:
- Solar constant = 20: 0.0104 AU
- Solar constant = 1: 0.0464 AU
- Solar constant = 1/1000: 1.469 AU
- Minimum red light: 1.062 AU
- Minimum blue light: 0.392 AU
- Roche limit: 0.000036 AU
Further parameters:
- Extended habitable zone: 0.01039 - 0.392 AU
- Earth-like planet orbit: 0.0465 AU
- Tidal index: 0.664 - 945
- Tidal index for Earth-like planet: 47.2
- Orbit period (days): 1.210 - 280
- Orbital period for Earth-like planet: 11.45
- Angular size: 3.27 to 123.2
- Angular size for Earth-like planet: 27.6.
Nearly all known M6 stars are eruptive flare stars. Any terraformed planet would be boiled during a massive flare event, with almost if not all life brought to extinction. Some stars are known to blow flares almost continuously, while others are known to blow superflares, increasing their luminosity even a thousand times in a matter of less then a minute. Whatever planet is to be terraformed around such a star, it must be out, close to the outer end of the extended habitable zone.
M7 Star[]
Main parameters:
- Temperature: 2680
- Mass: 0.09
- Radius: 0.12
- Bolometric magnitude: 12.61
- Visual magnitude: 17.7
Spectral parameters:
Main light spectra: 1185 (infrared)
- Solar constant: 0.001437
- Infrared light: 0.00431
- Red light: 0.000667
- Visible light: 0.000282
- Blue light: 0.000075
- Ultraviolet light: 4.44E-09
Habitable zone, based on light emissions:
- Solar constant = 20: 0.00848 AU
- Solar constant = 1: 0.0379 AU
- Solar constant = 1/1000: 1.199 AU
- Minimum red light: 0.817 AU
- Minimum blue light: 0.274 AU
- Roche limit: 0.000034 AU
Further parameters:
- Extended habitable zone: 0.00848 - 0.274 AU
- Earth-like planet orbit: 0.0379 AU
- Tidal index: 1.201 - 1253
- Tidal index for Earth-like planet: 62.6
- Orbit period (days): 0.949 - 174.3
- Orbital period for Earth-like planet: 8.98
- Angular size: 4.10 to 132.3
- Angular size for Earth-like planet: 29.6.
The dim M7 stars are known to be highly eruptive, blowing powerful flares all the time. It is highly unlikely that a planet around such stars can be somehow terraformed and sustain Earth-like life.
M8 Object[]
Main parameters:
- Temperature: 2570
- Mass: 0.085
- Radius: 0.114
- Bolometric magnitude: 12.95
- Visual magnitude: 18.6
Spectral parameters:
Main light spectra: 1236 (infrared)
- Solar constant: 0.001144
- Infrared light: 0.00360
- Red light: 0.000473
- Visible light: 0.000187
- Blue light: 0.0000445
- Ultraviolet light: 1.21E-09
Habitable zone, based on light emissions:
- Solar constant = 20: 0.00756 AU
- Solar constant = 1: 0.038 AU
- Solar constant = 1/1000: 1.069 AU
- Minimum red light: 0.688 AU
- Minimum blue light: 0.211 AU
- Roche limit: 0.000033 AU
Further parameters:
- Extended habitable zone: 0.00756 - 0.211 AU
- Earth-like planet orbit: 0.0338 AU
- Tidal index: 1.910 - 1487
- Tidal index for Earth-like planet: 74.3
- Orbit period (days): 0.823 - 121.3
- Orbital period for Earth-like planet: 7.79
- Angular size: 5.05 to 140.9
- Angular size for Earth-like planet: 31.5.
Objects included in M8 are both very dim stars and very bright brown dwarfs. These objects are prone to massive flares, rendering their planets uninhabitable. Earth-like planets would be exposed to major tidal stress and would experience strong volcanism. Any inner planet would be scourged by flares.
M9 Brown Dwarf[]
Main parameters:
- Temperature: 2380
- Mass: 0.079
- Radius: 0.102
- Bolometric magnitude: 13.54
- Visual magnitude: 19.17
Spectral parameters:
Main light spectra: 1335 (infrared)
- Solar constant: 0.000727
- Infrared light: 0.00248
- Red light: 0.000238
- Visible light: 0.0000815
- Blue light: 0.0000158
- Ultraviolet light: 9.45E-11
Habitable zone, based on light emissions:
- Solar constant = 20: 0.00603 AU
- Solar constant = 1: 0.0270 AU
- Solar constant = 1/1000: 0.853 AU
- Minimum red light: 0.487 AU
- Minimum blue light: 0.126 AU
- Roche limit: 0.000032 AU
Further parameters:
- Extended habitable zone: 0.00603 - 0.126 AU
- Earth-like planet orbit: 0.0270 AU
- Tidal index: 5.01 - 2170
- Tidal index for Earth-like planet: 109
- Orbit period (days): 0.608 - 57.8
- Orbital period for Earth-like planet: 5.75
- Angular size: 7.59 to 158.1
- Angular size for Earth-like planet: 35.3.
The hottest brown dwarfs, often included into the M9 spectral subclass, have, at least in theory, a habitable zone. While very hot brown dwarfs are known to have occasional flares, these flares are by far not as violent as those of most M - type stars. Any close-orbiting planets would face powerful tidal forces. They emit only small amounts of blue light, dramatically limiting their outer limit of the habitable zone. Inner planets, if they do exist, must experience extreme tidal forces.
The bright M - type are the most likely of all brown dwarfs to host a habitable zone planet because their habitable zones are far larger.
Conclusion[]
The M - type class is the most diverse of all spectral classes. The most massive members of this group (M0 to M3) are brighter and have larger habitable zones, while the least massive stars (M5 to M8) are known to be eruptive and mostly unlikely to support a planet suitable for terraforming. The smallest members of the group (M9) are not stars at all but brown dwarfs.