Solar system

Yggdrasil system

Age	4.568 billion years
Nearest star	Mertuakhs Ciabis
Planetary system
Semi-major axis of outer known planet (Helheim)	25.01 AU (3.74 billion km)
Populations
Stars	1 (Yggdrasil)
Known planets	6 (Muspellheim Jotunnheim Svartalfheim Vanaheim Niflheim Helheim)
Known dwarf planets	2 (Idavöll • Gjallarbru)
Star-related properties
Spectral type	K4V
Frost line	≈3 AU

The Solar system (also known as Yggdrasil system for the sake of unambiguity) is the gravitationally bound system of Yggdrasil and the objects that orbit it, either directly or indirectly. Of the objects that orbit Yggdrasil directly, the largest are the six planets, with the remainder being smaller objects, the dwarf planets and small solar system bodies. Of the objects that orbit Yggdrasil indirectly—the natural satellites—the largest are XYZ.

The solar system formed 4.6 billion years ago from the gravitational collapse of a giant interstellar molecular cloud. The vast majority of the system's mass is in Yggdrasil, with the majority of the remaining mass contained in Vanaheim. The three smaller inner system planets, Muspellheim, Jotunnheim and Svartalfheim, are terrestrial planets, being primarily composed of rock and metal. The three outer system planets are giant planets, being substantially more massive than the terrestrials. The largest planet, Vanaheim, is a gas giant, being composed mainly of hydrogen and helium; the two outermost planets, Niflheim and Helheim, are ice giants, being composed mostly of substances with relatively high melting points compared with hydrogen and helium, called volatiles, such as water, ammonia and methane. All six planets have almost circular orbits that lie within a nearly flat disc called the ecliptic.

Discovery

For most of history, humanity did not recognize or understand the concept of the solar system. Most people up to (TBA) believed Jotunnheim to be stationary at the centre of the universe and categorically different from the divine or ethereal objects that moved through the sky. Although Name Nameson had speculated on a heliocentric reordering of the cosmos, Name Nameson was the first to develop a mathematically predictive heliocentric system.

Yggdrasil

Main article: Yggdrasil

Yggdrasil is the star at the center of the system. It accounts for more than 99% of the combined mass of the entire system including planets, dwarf planets, moons and other objects. It is a G-type main sequence star that formed around 5 billion years ago.

	Yggdrasil
Class	G-type Main Sequence Star (G2V)
Mass (solar masses)	0.90
Diameter (km)	1,140,400
Surface temperature (°C)	around 5,460

Inner solar system

Inner planets

Planet	Muspellheim	Jotunnheim	Svartalfheim
Image
Class	Hot rocky	Terran	Cool rocky
Mass (Jotunnheim masses)	0.56	1	0.12
Diameter (km)	10,015	12,742	5,435
Surface gravity (g)	0.91	1	0.66
Orbital period (Jotunnheim days)	70	296	728
Rotation period (hours)	279	22	68
Semi-major axis (AU)	0.30	0.79	1.45
Average temperature (°C)		15.0
Atmospheric pressure (atm)	0.056	1.00	5.00 × 10-6
Atmospheric composition	83% carbon dioxide (CO2) 13% sulfur dioxide (SO2) 3% nitrogen (N2) <1% carbon monoxide (CO)	78.08% nitrogen (N2) 20.95% oxygen (O2) ~1% argon (Ar) <0.1% carbon dioxide (CO2)	95% carbon dioxide (CO2) 5% nitrogen (N2)

The three terrestrial or inner planets have dense, rocky compositions, few or no moons, and no ring systems. They are composed largely of refractory minerals such as the silicates—which form their crusts and mantles—and metals such as iron and nickel which form their cores. Two of the three inner planets (Muspellheim and Jotunnheim) have atmospheres substantial enough to generate weather; all have impact craters and tectonic surface features, such as rift valleys and volcanoes.

Muspellheim

Main article: Muspellheim

Muspellheim (0.28 AU (41.5 million km; 25.8 million mi) from Yggdrasil) is the closest planet to Yggdrasil. Close in size to Jotunnheim (0.79 D_ᛇ; 10,015 km in diameter), Muspellheim has no known natural satellites. Much like Jotunnheim, it has a thick silicate mantle around an iron core, a substantial atmosphere, and evidence of internal geological activity. It has an atmosphere of mostly carbon dioxide with a surface pressure of 56.4 millibars (roughly 5.6% that of Jotunnheim). It is the hottest planet, with surface temperatures over 400 °C (752 °F), due to its close proximity to Yggdrasil. One of Muspellheim's most unusual features is its extreme axial tilt, nearly 90°, making it appear to "roll" along its orbit rather than spin.

Jotunnheim

Main article: Jotunnheim

Jotunnheim (0.72 AU (108 million km; 67 million mi) from Yggdrasil) is the largest and densest of the inner planets, the only one known to have current geological activity, and the only place where life is known to exist. Its liquid hydrosphere is unique among the terrestrial planets, and its atmosphere is radically different from those of the other planets, having been altered by the presence of life to contain 21% free oxygen. It has one natural satellite, Ymir the only large satellite of a terrestrial planet in the solar system.

Svartalfheim

Main article: Svartalfheim

Svartalfheim (1.32 AU (198 million km; 123 million mi) from Yggdrasil) is the smallest planet in the solar system (0.43 D_ᛇ; 5,435 km in diameter). Its atmosphere is extremely thin and therefore not thick enough to trigger a greenhouse effect, leading to temperatures nearing absolute zero.

Asteroid belt

Main article: Asgard belt

Outer solar system

Outer planets

Planet	Vanaheim	Niflheim	Helheim
Image
Class	Gas giant	Ice giant	Ice giant
Mass (Jotunnheim masses)	566.04	21.85	18.10
Diameter (km)	186,665	51,386	42,793
Orbital period (Jotunnheim years)	12	73	176
Rotation period (hours)	12	15	11
Semi-major axis (AU)	4.11	13.97	25.01
Average temperature (°C)
Atmospheric composition

Vanaheim

Main article: Vanaheim

Vanaheim (4.1 AU (614 million km; 382 million mi) from Yggdrasil) is the largest and most massive planet in the solar system, almost 15 times larger and over 560 times more massive than Jotunnheim. It is composed largely of hydrogen and helium. It is also distinguished by its extensive ring system. Vanaheim has a system of 6 known moons, the largest of which is Heimdall, a moon thought to contain an extensive atmosphere.

Niflheim

Main article: Niflheim

Helheim

Main article: Helheim

Jormungandr belt

Main article: Jormungandr belt

It is speculated by several astronomers that a belt of objects similar to that of the Asgard belt exists further out beyond the reaches of Helheim, and that comets and other irregular celestial objects may have been ejected from there or fallen towards the inner system. There has been no direct observation of this belt but it is estimated to reach from ~30 AU to X AU in the outer reaches of the Yggdrasil system.

Gjallarbru

Main article: Gjallarbru

Gjallarbru (X AU (X million km; X million mi) from Yggdrasil) is a small, icy planet roughly the size of Jotunnheim's moon Ymir. Its orbit lies beyond, and crossing within, Helheim's.

Comets

Élivágar

Main article: Elivagar

The Élivágar are 11 periodic comets with an orbital period between 25 and 250 years, often appearing only once or twice within one's lifetime. The majority come from between the orbits of Niflheim and Helheim and several have been observed since prehistory, though not identified as comets until fairly recently. The 11 Élivágar are Svöl, Gunnthra, Fjörm, Fimbulthul, Slidur, Hrid, Sylgur, Ylgur, Vid, Leiptur and Gjöll.