|Jool as seen from orbit.|
|Planet of Kerbol|
|Semi-major axis||68 773 560 320 m [Note 1]|
|Apoapsis||72 212 238 387 m [Note 1]|
|Periapsis||65 334 882 253 m [Note 1]|
|Orbital inclination||1.304 °|
|Argument of periapsis||0 °|
|Longitude of the ascending node||52 °|
|Mean anomaly||0.1 rad (at 0s UT)|
|Sidereal orbital period||104 661 432 s|
|4 845 d 2 h 37 m 12.1 s|
|Synodic orbital period||10090901.7 s|
|Orbital Velocity||3 927 to 4 341 m/s|
|Equatorial radius||6 000 000 m|
|Surface area||4.5238934×1014 m2|
|Standard gravitational parameter||2.8252800×1014 m3/s2|
|Density||4 678.7834 kg/m3|
|Surface gravity||7.85 m/s2 (0.8 g)|
|Escape velocity||9 704.43 m/s|
|Sidereal rotation period||36 000.000 s|
|1 d 4 h 0 m 0 s|
|Solar day||36 012.387 s|
|1 d 4 h 0 m 12.4 s|
|Sidereal rotational velocity||1 047.2 m/s|
|Synchronous orbit||15 010.46 km|
|Sphere of influence||2.4559852×109 m[Note 1]|
|Atmosphere present||✓ Yes|
|Atmospheric Pressure||1 519.88 kPa|
|Scale height||31 000 m|
|Atmospheric height||200 000 m|
|Temperaturemin||-73.15 °C 200 K|
|Temperaturemax||-73.15 °C 200 K|
|Oxygen present||× No|
Jool is a gas giant and the sixth planet of the Kerbol star system. It is the Jupiter analog for Kerbal Space Program. Aside from Kerbol, Jool has the largest diameter and greatest mass of all celestial bodies. While its distance from Kerbin makes it difficult to reach, it is one of the most appealing targets for missions due to its large and complex system of five moons: Laythe, Vall, Tylo, Bop, and Pol. It was possible to land and plant flags on Jool before v0.23. Before 0.23, the craft won't stop at an altitude of 0, instead it will continue descending until it gets to -250 m. At this point anything that hits this altitude at any speed will be completely destroyed.
|“|| Jool is particularly known for being a rather large, predominantly green planet. Kerbalkind has longed to visit it since it was first spotted in the sky. Philosophers reason that the swirling green planet must be a really nice place to visit, on account of its wholesome coloration.
If you look at Jool through a telescope, it is fuzzy.
— Kerbal Astronomical Society
Jool has an extremely dense, cold atmosphere with a mass of approximately 8.8×1019 kilograms, a datum level pressure of 1519.875 kilopascals (15 atmospheres), and a depth of 200,000 meters. Compared to the atmosphere of Kerbin, Jool's atmosphere has 1875 times the mass, 15 times the surface pressure, and nearly 3 times the depth. At an altitude of 96,378 m on Jool, the atmospheric pressure is the same as at sea level on Kerbin (1 atm).
The average molecular weight of Jool air is 2.8 g/mol, and its adiabatic index is 1.43. Although the composition of Jool's atmosphere is unknown, these values suggest that it consists mostly of hydrogen and helium. The molar mass of Jool's atmosphere is comparable to the real life planets Uranus and Neptune. Because of the low molar weight, Jool air at the datum level is only about 2 times as dense as Kerbin air at sea level.
Like all other atmospheres in the game, Jool's atmosphere fades exponentially as altitude increases. The scale height varies with altitude, which is a change from pre-1.0 versions of the game. 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)|
|0||1 519 875||15.000|
|10 000||1 072 480||10.585|
|20 000||817 125||8.064|
|30 000||658 008||6.494|
|40 000||520 935||5.141|
|50 000||405 932||4.006|
|60 000||311 385||3.073|
|70 000||234 855||2.318|
|80 000||173 901||1.716|
|90 000||126 082||1.244|
|100 000||88 960||0.878|
|110 000||60 095||0.593|
|120 000||37 045||0.366|
|130 000||19 870||0.196|
|140 000||12 750||0.126|
|150 000||10 000||0.099|
|160 000||7 221||0.071|
|170 000||4 524||0.045|
|180 000||2 216||0.022|
Air temperatures decrease as altitude increases up to an elevation of about 123 km, were the coldest atmospheric temperatures are found. A gradual warming begins above 123 km. At an altitude of 194 km there begins a very rapid increase in temperature, suggesting the presence of a thermosphere.
Air temperatures vary with latitude and time of day. At the datum level (elevation = 0) the temperature is a globally constant -73 °C. As the altitude increases, latitudinal and diurnal temperature variations are observed, becoming more pronounced with increasing altitude. At an altitude of 123.45 km, temperatures at the equator vary between a nighttime low of -129 °C and a daytime high of -122 °C. At this same altitude over the poles, the temperature varies between -185 °C and -181 °C. Since Jool has no axial tilt, there are no seasonal temperature variations.
Aerobraking into Jool orbit from a high-speed interplanetary intercept is possible but, since version 1.0.3, 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.
Parachutes work very effectively in Jool's dense atmosphere.
Jool has no solid surface to land on; descending spacecraft will explode when they reach the altitude of -250 m. The message "... collided with Cloud" will be displayed in the mission summary. The game may glitch out and corrupt the save. Prior to version 0.23, it was possible to land on a solid surface, though spacecraft were inevitably and invariably devoured by the Kraken.
If a kerbonaut is put on EVA, he will not be destroyed, making one-way sacrificial landings possible. However, as seen near the end of this video, the kerbonaut will start to glitch out and shake uncontrollably. This only happens on 4× time warp. The game will later glitch and the Hell Kraken will strike. Unless you restart the game, Kerbin's atmosphere will be missing but it is unknown if this still happens.
This glitch, while most common on Jool, is not unique to Jool, and can even be experienced on Kerbin in extreme situations; for example, going on EVA from a high speed spaceplane as it takes off can occasionally cause this, or it can even, although much more rarely, happen in less extreme situations as simple as sliding slowly on the Mun. If you do experience this outside of Jool, it is very difficult to replicate, which is why recordings of this are so rare.
|Rotational/Inertial transition||1 000 000 m|
|5×||200 000 m (above the atmosphere)|
|10×||200 000 m (above the atmosphere)|
|50×||200 000 m (above the atmosphere)|
|100×||200 000 m (above the atmosphere)|
|1 000×||300 000 m|
|10 000×||600 000 m|
|100 000×||1 200 000 m|
Jool has five natural satellites, each with an orbit well-aligned with Jool's orbital plane:
Laythe, Vall, and Tylo are in a Laplace resonance, with orbital periods of 1:2:4 respectively. Despite the fact that the moons can easily eclipse both each other and Jool, they do not.
Synchronous Orbits around any of the Joolian moons are impossible, as they all lie outside the Sphere of Influence of the moons, as is common with tidally locked bodies.
- → See also: Images of Jool
- Jool has roughly the same equatorial radius as the planets Earth and Venus.
- The sunsets and sunrises on Jool are a shade of yellowish brown.
- Like Jool's moons, Jupiter's three nearest moons, Io, Europa, and Ganymede, have a Laplace resonance of 1:2:4.
- Jool, Laythe and Tylo all have a surface gravity of 7.85 m/s² (≃ 0.8 g)
- The green gas which composes Jool could be chlorine.
- The barometric, gravitational and temperature measurements taken as close to 0 meters altitude are roughly 14.9785 atm, 0.785 m/s2, 989.45 °C, respectively.
- Despite not having a surface, the game files that contain what the Kerbals say in the different reports/observations (ScienceDefs.cfg) also contains some reports while landed on the surface of Jool.
- “Kerbal Space Program: Planting a Flag on Jool” by Dahud Lefthanded in version 0.20
- Added a new, more distant moon named Pol.
- Initial Release