What real star is most like Kerbol?

[Needles_10]

It may be a funny little question, but I have to ask. It would be interesting, seeing how many/how few stars are actually similar enough to Kerbol to be considered "Kerbol-like". I'm thinking of possibly writing a story about a manned voyage to Kerbol in a "Sleeper Ship" of some sort, using real-life stars and realistic plot-points. Do stars like Kerbol even exist? If so, which ones are they? So...what stars are similar to Kerbol? Let's find out. I'll try and compile a list.

Parameters

Kerbol-like Star Candidates

[Brotoro]

There are no real stars with the same radius and mass of Kerbol.

The text at the link you gave mentions the temperature and luminosity of Kerbol (as being determining factors for what type of star it is) but the values for temperature and luminosity are not given in the specifications. Do we know those values?

[rodion_herrera]

The radius of Kerbol is around 37% of our sun. According to a red dwarf type table, a red dwarf star with stellar class M4V has 39% radius of the sun, and its mass should be around 36% of the sun's. Here's where Kerbol gets wacky--if its mass is indeed 1.756E28, then doing this: (1.756E27/81.989E30)*100 we see that Kerbol's mass is only 0.88% of our sun, a far cry than the expected 36% mass that we expect from a red dwarf star having about 39% the radius of our sun. I guess squad set it up like this, because if their gravity simulation engine is tied to mass, then giving Kerbol the expected 36% mass of the sun will render interplanetary maneuvers very difficult due to the amount of Delta-V needed, not to mention that the orbits of the planets around Kerbol would be drastically affected--the won't look as they are in the game, perhaps there would even be no planets (ejections).

Edited June 1, 2013 by rodion_herrera

[Kerbface]

Yeah, it's just scaled down. I wouldn't try to base a realistic story on the current sizes in game.

[Needles_10]

Well...we seem to have a dilemma here.

The star does not have to be exactly like Kerbol. It may have parameters similar to that of Kerbol, but not necessarily all of them.

Better now? Star-hunt away!

[Brotoro]

Well... Assuming that the developers want Kerbin to have Earth-like surface conditions (which I assume is true because they gave it a surface acceleration due to gravity the same as Earth, and it has oceans and polar caps), we can assume that (once they get the clouds installed) it will have a similar albedo (percent of light reflected) and a similar greenhouse warming effect that Earth has. So, in order to have an Earth-like surface temperature with those conditions, it would need to have the same radiative equilibrium temperature that Earth has. Earth's radiative equilibrium temperature is about -17 degrees Celsius (yes...if not for the 32°C of greenhouse warming our atmosphere provides, Earth's oceans would be permanently frozen). The formula for the radiative temperature of a planet (Tp) is given by the formula:

Tp = Tsun * (1-Albedo)^(1/4) * SQRT[ Rsun / (2*D) ]

where Tsun is the temperature of the sun, Albedo is the percentage of light reflected (about 36% for Earth with its clouds), Rsun is the radius of the sun, and D is the distance of the planet from the sun. Rsun and D need to be in the same units. Tsun and Tp are in Kelvin. This formula works for our solar system as well as the Kerbol system, where Rsun is the radius of the star in question.

-17°C is 256.15 Kelvins

Using values from the Kerbal Celestials wiki (check my work), I get a temperature for Kerbol of 2612 Kelvins. This is the temperature of a red star (spectral class M).

The luminosity of a star is given by the formula:

L = 4 * pi * (Rsun)^2 * sigma * (Tsun)^4

where Rsun is the star's radius in meters, sigma is the stefan-boltzmann constant (5.67 x10^-8), Tsun is in Kelvins

And from that (again, somebody should check my work) I get a luminosity for Kerbol of 2.27 x10^24 Watts. This is 0.59% of our Sun's luminosity.

All of this points to Kerbol being a red dwarf star. The temperature is close to that of a spectral type M6 red dwarf. The luminosity is close to that of a spectral type M4 red dwarf. And the radius is about right for an M3 red dwarf.

Nearby examples of similar stars are Proxima Centauri (closest star to the Sun) and Barnard's star (4th closest star to the Sun). Our Galaxy is thick with these stars (they are by far the most common stars in our Galaxy).

The fly in the ointment, of course, is that the mass listed in the wiki for Kerbol (which I assume is accurate, since it is easily derived from the orbits of its planets), is only 0.88% of our Sun's mass, whereas red dwarf stars actually have masses that are considerably greater than that (M6 red dwarf = 10% solar mass. M4 red dwarf = 20% solar mass). Kerbol's mass is too small to support thermonuclear fusion in its core ...unless something funny is going on inside it...see "Magratheans" link below

[Cryocasm]

Well... Assuming that the developers want Kerbin to have Earth-like surface conditions (which I assume is true because they gave it a surface acceleration due to gravity the same as Earth, and it has oceans and polar caps), we can assume that (once they get the clouds installed) it will have a similar albedo (percent of light reflected) and a similar greenhouse warming effect that Earth has. So, in order to have an Earth-like surface temperature with those conditions, it would need to have the same radiative equilibrium temperature that Earth has. Earth's radiative equilibrium temperature is about -17 degrees Celsius (yes...if not for the 32°C of greenhouse warming our atmosphere provides, Earth's oceans would be permanently frozen). The formula for the radiative temperature of a planet (Tp) is given by the formula:

Tp = Tsun * (1-Albedo)^(1/4) * SQRT[ Rsun / (2*D) ]

where Tsun is the temperature of the sun, Albedo is the percentage of light reflected (about 36% for Earth with its clouds), Rsun is the radius of the sun, and D is the distance of the planet from the sun. Rsun and D need to be in the same units. Tsun and Tp are in Kelvin. This formula works for our solar system as well as the Kerbol system, where Rsun is the radius of the star in question.

-17°C is 256.15 Kelvins

Using values from the Kerbal Celestials wiki (check my work), I get a temperature for Kerbol of 2612 Kelvins. This is the temperature of a red star (spectral class M).

The luminosity of a star is given by the formula:

L = 4 * pi * (Rsun)^2 * sigma * (Tsun)^4

where Rsun is the star's radius in meters, sigma is the stefan-boltzmann constant (5.67 x10^-8), Tsun is in Kelvins

And from that (again, somebody should check my work) I get a luminosity for Kerbol of 2.27 x10^24 Watts. This is 0.59% of our Sun's luminosity.

All of this points to Kerbol being a red dwarf star. The temperature is close to that of a spectral type M6 red dwarf. The luminosity is close to that of a spectral type M4 red dwarf. And the radius is about right for an M3 red dwarf.

Nearby examples of similar stars are Proxima Centauri (closest star to the Sun) and Barnard's star (4th closest star to the Sun). Our Galaxy is thick with these stars (they are by far the most common stars in our Galaxy).

The fly in the ointment, of course, is that the mass listed in the wiki for Kerbol (which I assume is accurate, since it is easily derived from the orbits of its planets), is only 0.88% of our Sun's mass, whereas red dwarf stars actually have masses that are considerably greater than that (M6 red dwarf = 10% solar mass. M4 red dwarf = 20% solar mass). Kerbol's mass is too small to support thermonuclear fusion in its core ...unless something funny is going on inside it...see "Magratheans" link below

You could always deduce Kerbol's mass from the orbital speeds, Earth's being 27 km/s and Kerbin's being nearly 10 km/s. Using some percents, we find that Kerbol could fit into the red dwarf class. Its also possible to be a brown dwarf, considering its size compares to Jupiter.

[Brotoro]

You could always deduce Kerbol's mass from the orbital speeds, Earth's being 27 km/s and Kerbin's being nearly 10 km/s. Using some percents, we find that Kerbol could fit into the red dwarf class. Its also possible to be a brown dwarf, considering its size compares to Jupiter.

No. In order to calculate Kerbol's mass, you need to use Kepler's third law of planetary motion, as modified by Newton to include masses:

M = 4 * pi^2 * D^2 / ( G * P^3 )

Where D is the semi-major axis of the orbit of a planet orbiting Kerbol (in meters), P is the orbital period of that planet (in seconds), and G is the constant of universal gravitation (6.6726x10^-11). Then M is the mass of Kerbol in kg.

This calculation confirms the value given in the Kerbal Celestials wiki. So Kerbol has too little mass to support thermonuclear fusion even though its other parameters match it being a red dwarf star.

[Deadpangod3]

In terms of looks I say Barnards Star

*random wiki link*:

http://en.wikipedia.org/wiki/Barnard's_Star

Small, red, and cold...

FIND THE KERBALS!!!!!

[Cryocasm]

No. In order to calculate Kerbol's mass, you need to use Kepler's third law of planetary motion, as modified by Newton to include masses:

M = 4 * pi^2 * D^2 / ( G * P^3 )

Where D is the semi-major axis of the orbit of a planet orbiting Kerbol (in meters), P is the orbital period of that planet (in seconds), and G is the constant of universal gravitation (6.6726x10^-11). Then M is the mass of Kerbol in kg.

This calculation confirms the value given in the Kerbal Celestials wiki. So Kerbol has too little mass to support thermonuclear fusion even though its other parameters match it being a red dwarf star.

Well, given my explanation it can still provide for nuclear fusion, despite there being no serious math behind it. I am quite aware of nuclear physics and its obvious that such a body cannot sustain fusion and would most likely just float about space as a rotating mass of gas.

[Holo]

I once did the maths and calculated the equilibrium temperature of Kerbin to be ~-6 C