Tylo

	Tylo
	Tylo as seen from orbit.
	Moon of Jool
	Orbital Characteristics
Semi-major axis	68 500 000 m
Apoapsis	68 500 000 m
Periapsis	68 500 000 m
Orbital eccentricity	0
Orbital inclination	0.025 °
Argument of periapsis	0 °
Longitude of the ascending node	0 °
Mean anomaly	3.14 rad (at 0s UT)
Sidereal orbital period	211 926 s
	9 d 4 h 52 m 6.4 s
Synodic orbital period	212 356.4 s
Orbital velocity	2 031 m/s
Longest time eclipsed	5 917 s
	Physical Characteristics
Equatorial radius	600 000 m
Equatorial circumference	3 769 911 m
Surface area	4.5238934×1012 m2
Mass	4.2332127×1022 kg
Standard gravitational parameter	2.8252800×1012 m3/s2
Density	46 787.273 kg/m3
Surface gravity	7.85 m/s2 (0.8 g)
Escape velocity	3 068.81 m/s
Sidereal rotation period	211 926.36 s
	9 d 4 h 52 m 6.4 s
Sidereal rotational velocity	17.789 m/s
Synchronous orbit	Outside sphere of influence
Sphere of influence	10 856 518 m
	Atmospheric Characteristics
Atmosphere present	No
	Scientific multiplier
Surface	12
Splashed	N/A
Near space	10
Outer space	8
Recovery	8
	↑ 1.0 1.1 1.2 1.3 The distances are given from the body's center, not from the surface (unlike ingame) ;

Tylo is the largest moon of Jool and the Kerbol System, and the largest celestial body without an atmosphere. It is the analog for Ganymede. It is the third moon from Jool, is the same diameter as Kerbin, and is tidally locked. Tylo orbits Jool in roughly nine days. Synchronous orbits around Tylo are impossible, as they would lie far outside of its SOI at a radius of 14,758,067 meters.

Tylo is a relatively difficult target to visit. Its gravity is similar to Kerbin's, but without an atmosphere, there is no way to aerobrake, and a large amount of fuel must be used to land and take off. However, due to its large gravity well, Tylo is ideal for a gravity assist to enter or leave the Jool system with minimal fuel consumption.

According to former developer NovaSilisko, Tylo was planned to be made into a high-contrasting body like Saturn's moon Iapetus.^[1]

In-game Description

“

Tylo was the first moon of Jool to be discovered by the Kerbal Astronomical Society. After many failed attempts to take a flawless picture of Jool to hang on the office walls, it was finally discovered that the wandering white smear was indeed a moon.

Scientists speculate that the view from the surface with Laythe, Vall and Jool overhead must be “quite something”.''

— Kerbal Astronomical Society

”

Topography

Tylo has a rocky surface. It has a varying elevation between 0 meters (Tylo baseline height) and peaks of more than 11290 meters. Tylo's surface looks similar to that of Mün, but has much fewer impact craters (especially on the side facing away from Jool) and is more uneven.

Due to the coloring of the surface of Tylo, it is likely that it is covered in a rhyolite layer of rock, nickel, a little cobalt, and some sort of ice and dust spread by meteorite impacts but as there is no official way to determine the composition of the moon this is only hypothetical. This explains why Tylo has a rather bright and white surface.

Because it is very large in comparison to other moons, it is unlikely that it is a captured planet. For a planet of this size, Jool would have to be much larger and denser to produce a large and strong enough gravitational well. It is unknown why Tylo hasn't formed an atmosphere.

Because of its high gravity and lack of an atmosphere, Tylo is very hard to land on and reach orbit from. However, low altitude orbits at high speeds can be achieved for these same reasons.

Biomes

Tylo has 9 Biomes. It mostly consists of generic Low-, Mid- and Highlands with some Mara and Minor Craters scattered in between. There are four distinct Craters. Previously three of these Craters were simply named Major Crater, the reason for this oddity not being known.

Biome list

Tylo In-game biome map as of 1.2

Highlands
Midlands
Lowlands
Mara
Minor Craters
Gagarin Crater
Grissom Crater
Galileio Crater
Tycho Crater

Science

Tylo has the second-highest science multipliers in the game. The only orbit with a higher multiplier is the sun and the only surface with a better multiplier is that of Eve. Unfortunately Tylo has no atmosphere, which means that there is one less zone to conduct experiments in and that some experiments do not work at all. That means that it is only the second most science-rich Joolian moon after Laythe.

Reference Frames

Time warp	Minimum Altitude
1×	Any
5×	30 000 m
10×	30 000 m
50×	60 000 m
100×	120 000 m
1 000×	240 000 m
10 000×	480 000 m
100 000×	600 000 m

Trivia

Kerbin has the same equatorial radius as Tylo (600,000m) yet Tylo's surface gravity is much lower than Kerbin. This is most likely because Tylo is composed of lower density matter.
Tylo is one of the few bodies in the solar system with almost totally manually-created colors (i.e., it uses a color map instead of procedural coloration). It only has a tenuous coat of a height-based darkening, and some simple noise. The only other manually-colored objects in the game are the Mun and Jool.
The Gagarin crater on Tylo was most likely named after Yuri Gagarin, the first man in space.
The Grissom crater on Tylo was most likely named after Virgil "Gus" Grissom, the second American in space.
The Galileo crater on Tylo was most likely named after Galileo Galilei who is widely considered to be the inventor of the telescope.
The Tycho crater on Tylo was most likely named after Tycho Brahe who helped overturn a belief in favor of the heliocentric theory.
Using systematic designation Tylo would be designated Jool I.
There are two known Easter eggs on Tylo.

Spoiler:

One is Carl Sagan's face (which is now broken) on a mountain and the other is a cave-like underground formation. The cave-like formation used to be below the surface, but as of 1.3 it is back at the surface and is visible from low orbit