|Neidon as seen from orbit.|
|Planet of Kerbol|
|Semi-major axis||409 355 191 706 m [Note 1]|
|Apoapsis||414 577 213 080 m [Note 1]|
|Periapsis||404 133 170 332 m [Note 1]|
|Orbital inclination||1.27 °|
|Argument of periapsis||0 °|
|Longitude of the ascending node||259 °|
|Mean anomaly||2.272 rad (at 0s UT)|
|Sidereal orbital period||1 519 864 480 s|
|70 364 d 0 h 34 m 40 s|
|Synodic orbital period||9259616.3 s|
|Orbital Velocity||1 671 to 1 714 m/s|
|Equatorial radius||2 145 000 m|
|Equatorial Circumference||13 477 432 m|
|Surface area||5.7818185×1013 m2|
|Standard gravitational parameter||1.4167882×1013 m3/s2|
|Density||5 135.0303 kg/m3|
|Surface gravity||3.08 m/s2 (0.314 g)|
|Escape velocity||3 634.58 m/s|
|Sidereal rotation period||40 250.000 s|
|1 d 5 h 10 m 50 s|
|Solar day||40 251.066 s|
|1 d 5 h 10 m 51.1 s|
|Sidereal rotational velocity||334.84 m/s|
|Synchronous orbit||6 201.27 km|
|Sphere of influence||4.4157238×109 m [Note 1]|
|Atmosphere present||✓ Yes|
|Atmospheric Pressure||607.950 kPa|
|Atmospheric height||260 000 m|
|Temperaturemin||-222.19 °C 50.96 K|
|Temperaturemax||-183.15 °C 90 K|
|Oxygen present||× No|
Neidon is an ice giant and the ninth planet of the Kerbol system. It is the third planet added in the Outer Planets Mod and is the Neptune analog for Kerbal Space Program. The planet is an attractive target to visit because of the deep blue and purple colors, however its distance makes it a difficult place to visit. Neidon also has two moons: Thatmo, and Nissee.. It also has a procedural system of asteroids if Custom Asteroids is installed. As with the other gas giants, it is not possible to land on Neidon - instead, the craft is simply destroyed.
Neidon's great distance from Kerbol reduces solar panel output to under 0.11% of that at Kerbin, so bringing extra solar panels or an alternative power source (e.g. RTGs) for missions to Neidon and its moons is recommended.
|“|| Due to its distance from Kerbin, it wasn't until fairly recently that Kerbalkind discovered the Kerbol system's most distant planet. At first scientists thought Neidon might be a purple, rocky planet like Eve, but they quickly realized they were in fact looking at an ice giant similar to Urlum.|
— Kerbal Astronomical Society
Neidon has a very cold, dense atmosphere that extends to an altitude of 260,000 meters and has an average molecular mass of 2.8 g/mol. This indicates a composition of mostly hydrogen (80%) and helium (19%), and a small amount of methane may contribute to the color. The upper atmosphere also has traces of hydrocarbons, carbon monoxide, and carbon dioxide.
Like all other atmospheres in the game, Neidon's atmosphere fades exponentially as altitude increases. The scale height varies with altitude. The pressure-altitude profile is globally constant and independent of temperature. The following table gives the atmospheric pressure at various altitudes above the datum level.
|Altitude (m)||Pressure (Pa)||Pressure (atm)|
|10 000||446 822||4.410|
|20 000||312 958||3.089|
|30 000||208 184||2.055|
|40 000||133 036||1.313|
|50 000||83 115||0.820|
|60 000||51 560||0.509|
|70 000||31 904||0.315|
|80 000||19 819||0.196|
|90 000||12 157||0.120|
|100 000||7 406||0.073|
|120 000||2 714||0.027|
|140 000||1 024||0.010|
Judging by density and planet models, it's interesting to note that the atmosphere in game is only the outer layer. At sea-level the atmosphere of a realistic planet would start to gradually become liquid until it reached the icy mantle. This is also true for Urlum.
Temperatures and Atmospheric Layers
There appears to be several layers in Neidon's atmosphere - a Troposphere, where temperatures decrease with altitude, and a Stratosphere, where temperatures increase with altitude. The boundary between the troposphere and stratosphere is called the Tropopause, and occurs at an altitude of 25 km. There is also a Thermosphere which begins around 100 km and extends out to 160 km.
Aerobraking into Neidon's orbit from a high-speed interplanetary intercept is possible but it is very difficult to achieve due to rapid and often destructive aerodynamic heating. A successful aerocapture requires a properly designed spacecraft, with a large ablator mass and a low ballistic coefficient, and precise periapsis targeting. The required periapsis altitude depends on the spacecraft's drag characteristics and its approach velocity. The margins for error are extremely small.
You could also use parachutes in Neidon's atmosphere to slow your spacecraft down.
From the average density of the planet, it's possible to estimate models for its composition. One model suggests a solid core - likely iron (radius of 128.7 km) - surrounded by a mantle made of ices (water, ammonia, and methane with a radius of 645.3 km). The outer atmospheric layer begins to liquefy and harden to pressures that destroy any spacecraft. From the outer layer to the ice mantle could be 1,372.8 km.
The deep purple and blue color could be due to methane in the atmosphere, which absorbs red light.
There is an extremely tilted magnetic field that indicates a magnetosphere that may be formed by convective fluids in the icy mantle or lower atmospheric regions, similar to Urlum.
With certain graphical modifications installed, Neidon has rotating clouds. By observing the rotation of these clouds, wind speeds can be estimated to vary between 325 to 600 m/s, the fastest wind speeds in the game.
Neidon only has two natural satellites, each with a very inclined orbit:
- Thatmo, an icy moon, has a very thin atmosphere and a retrograde orbit.
- Nissee, a rocky moon, has a highly inclined and eccentric orbit.
Synchronous Orbits around any of the Neidonean moons are impossible, as they all lie outside the Sphere of Influence of the moons, as is common with tidally locked bodies.
Neidon has a total of eight (atmosphere and space-only) biomes.
|5×||260 000 m (above the atmosphere)|
|10×||260 000 m (above the atmosphere)|
|50×||260 000 m (above the atmosphere)|
|100×||260 000 m (above the atmosphere)|
|1 000×||321 750 m|
|10 000×||643 500 m|
|100 000×||1 287 000 m|