Sooloo's Guide to Celestial Bodies

One of the most popular works granted to the Terran people by the Ooloonoo was Sooloo's Guide to Celestial Bodies. It contains useful bits of information about stars, planet types, asteroids, comets and various hazards a traveler may encounter among the stars.

## Star Types

Most stars belong to a range of categories known as "Main Sequence Stars". These stars fuse hydrogen into helium in their cores and possess a consistent position on the stellar color spectrum of visible light. 90% of the stars in the Milky Way galaxy are main sequence stars.

### **Main Sequence Stars**

#### Class O (blue-white)

An extremely rare main-sequence star. These stars are also known as blue hypergiants. Due to their high mass, O-type stars end their lives rather quickly in violent supernova explosions, resulting in black holes or neutron stars.

#### Class B (blue-white)

The large class B main-sequence stars are very bright and blue. Although somewhat rare, the luminosity of these stars make them among the most visible to the naked eye.

#### Class A (blue)

These relatively young white or bluish-white main-sequence stars are typically among the most visible to the naked eye. They are large and rotate very quickly, but will eventually evolve into slower and cooler red giants.

#### Class F (green)

F-type stars are fairly large and sometimes referred to as yellow-white dwarves. Although they often emit significant amounts of UV radiation, their wide habitable zones have a good chance of supporting life-bearing worlds.

#### Class G (yellow)

Often referred to as yellow dwarves, G-type stars actually range in color from white to slightly yellow. Although their lifespans are shorter than K-type stars, worlds inside the habitable zone of a G star often enjoy optimal conditions for the development of life.

#### Class K (orange)

These main-sequence stars, sometimes referred to as orange dwarves, are a fairly common sight. They are stable on the main-sequence for up to 30 billion years, meaning that worlds orbiting a K-type star have a longer than average window to evolve life.

#### Class M (red)

The most common stars in the universe, often referred to as red dwarves. Their low luminosity means they are difficult to observe with the naked eye from afar. Although they typically have an extremely long lifespan, red dwarves emit almost no UV light resulting in unfavorable conditions for most forms of life.

### **Non-Main Sequence Stars**

#### Black Hole

Typically formed as a result of the collapse of a very massive star at the end of its life cycle, black holes have extremely strong gravity fields that prevent anything - including light - from escaping once the event horizon has been crossed.

#### Neutron Star

These incredibly dense stellar remnants are sometimes created when a massive star suffers a rapid collapse and explodes in a supernova. Although their diameter is typically as little as ten kilometers, their mass is many times greater than an average G-type star. The gravitational waves and radiation emitted by Neutron Stars must be carefully navigated around.

#### Pulsar

Pulsars are highly magnetized neutron stars that emit beams of electromagnetic radiation. As the star rotates, the radiation beam is only visible when it is pointing directly at the observer. This results in a very precise interval of pulses, which sometimes is so exact that it can be used to measure the passage of time with extreme accuracy.

#### White Dwarf

A white dwarf is a small, very dense, hot star that is made mostly of carbon. These faint stars are what remains after a red giant star loses its outer layers. Their nuclear cores are depleted. They will eventually lose their heat and become a cold, dark black dwarf.

#### Black Dwarf

Stars that die but do not have the mass to create novae instead shed mass as they slowly cool, becoming dark inert black dwarfs.

#### Brown Dwarf

Brown dwarfs are substellar objects that lack the mass to sustain hydrogen fusion. Roughly the size of large gas giants, they have a much greater density. Their low luminosity and comparatively small heat generation means that planets orbiting them are unlikely to support life.

#### Red Supergiant

With a large radius and comparatively low surface temperature, red giants are stars of moderate mass in a late stage of stellar evolution. Their expanded stellar atmosphere and high luminosity make for distant habitable zone orbits.

## Planet Types

A planet is an astronomical body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, is not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals. There are a number of shared characteristics that have lead to a system of planetary classification.

### **Common Planet Types**

There are several basic categories most planets can be grouped into based upon several shared characteristics; such as common elements present, tectonic activity, and atmospheric composition.

#### **Telluric World**

These planets are small and rocky, usually possessing an atmosphere, climate, liquid water, and frequently some form of life. A variety of biomes can potentially be found on telluric worlds, some as diverse as Terra, others consisting of a single planet-wide biome.

##### Alpine World

A frigid mountainous world with a nitrogen-oxygen atmosphere. Snow covers the mountaintops and frozen-over lakes dot the valleys. The poles are big, and significant water deposits can be found permanently frozen as glacial ice. However, the planet experiences seasonal variations and the equatorial band is covered by vegetation. A stable biosphere exists but vegetation is mostly limited to mosses and lichens.

##### Arid World

Rocky world dominated by dry, arid plains covered by a nitrogen-oxygen atmosphere. The small hydrosphere allows for brief wet seasons, but aside from a few ubiquitous grasses vegetation is largely concentrated around shallow oases and forested polar regions.

##### Hydrocarbon World

Hydrocarbon Worlds are planets with huge deposits of hydrocarbons (considered common) and have light quantaties of the base metal tantalum and trace amounts of bismuth. They often support life. Effectively, they are Water Worlds with hydrocarbon compounds instead of water.

##### Water World

Rocky planets covered by 50-90% water with a nitrogen-oxygen atmosphere. Landmasses are separated by oceans, with large climate variations depending on latitude and precipitation.

#### **Barren World**

Barren and rocky worlds with a thin or non-existent atmosphere. The surface is covered in meteor impact craters and are usually completely devoid of life.

##### Carbide World

Carbide Worlds are rich in carbon, a common element. These worlds offer extremely low yields for mining operations and rarely contain life.

##### Dust World

Dust Worlds have light deposits of bismuth, aluminum, and potassium. They appear red from space and have a dark red surface with blotches of pink and brown. Their surface is composed of silicate and metal oxides. Their thin atmosphere occasionally supports minimal ecosystems.

##### Metallic World

Metallic Worlds are rich in all sorts of metals, including precious metals, corrosives, and base metals. When they are hot enough, they appear red-orange from space, and have a heavily-cratered yellow and orange surface. If they are not so hot, they appear gray from space, with a shiny cratered gray surface. Usually found in the first or second orbital position, these worlds are the cores of burnt planets, occasionally having a dangerously high gravity and magnetism, and usually prone to lightning storms.

##### Selenic World

Selenic Worlds are dry, dusty worlds that feature base metals like selenium, calcium, and aluminum. They appear grey from space and have a heavily cratered grey surface.

#### **Crystalline World**

These are rocky planets with composition primarily of crystalline nature. Usually geologically stable, these worlds have a thin or non-existent atmosphere and very low temperatures, precluding the existence of complex life.

##### Frozen World

Rocky world covered in a thick layer of permanently frozen ice, often water. A strange form of hydro-volcanism can be found on these worlds with volcanoes of ice spouting plumes of liquid water.

##### Pellucid World

Distinctive from a distance with their glittering gem-like surface. We are still not sure how these crystalline planets form. Most seem to have relatively little to no atmosphere but whatever process forms them also leaves a great deal of residual radioactivity. These worlds can be exploited for rare resources. However, great care must be taken due to their latent toxicity which is hostile to most common forms of life.

#### **Toxic World**

A rocky planet with a thick atmosphere that is lethal to most known higher forms of life.

##### Corrosive World

Planets with high quantities of corrosives - acids, bases, and/or oxidizers. The surface is usually pitted and jagged with little variation.

##### Poison World

These planets have vast deposits of cyanic, flouric, halogen or other compounds poisonous to higher forms of life, often in the forms in clouds and in liquid oceans.

##### Primordial World

These planets are large and rocky, composed of a core of metal and a crust of silicate. Their atmosphere is composed of a super-thick layer of carbon dioxide at extremely hot temperatures. These planets often experience very active volcanism.

##### Radioactive World

These worlds are rich with radioactive materials, such as uranium, francium, and astatine. Large exposed veins of radioactive ores scatter a landscape scoured by massive storms of radioactive dust. The sheer volume of radioactive decay happening within the crust of these planets creates instability and strange tectonics.

### **Other Planetary Types**

Some few planets types are unique and cannot be grouped into categories. These planets are either lacking enough diversity to be included as another category or are created through an artificial process.

#### **Molten World**

Rocky world that is scorching hot. The atmosphere is thin or non-existent, and lava from the interior flows freely due to constant volcanic eruptions. These planets have a very thin crust, and experience extremely frequent earthquakes as a result of the motion of the mantle. This type of planet cannot sustain organic life.

#### **Hell World**

Hell worlds do not occur naturally. They are created in the wake of the Xeltek. Once Xeltek portals are constructed and activated, the previous planet is radically altered. The atmosphere is flooded with corrosive pollutants and greenhouse gases. The seas are poisoned and eventually all life dies or becomes horrifically mutated. Hell Worlds are hot, toxic, radioactive, violently tectonic and teeming with hostile life.

#### **Gas Giant**

Gaseous planet with an atmosphere primarily composed of hydrogen and helium surrounding a dense core. Gas giants often have several rocky moons.

#### **Ice Giant**

Gaseous planet with an atmosphere primarily composed of methane and ammonia surrounding a dense core. Ice giants often have several rocky moons.

## Other Celestial Terrain

### **Asteroid**

Thought to be the shattered remnants of planetesimals, these bodies are too small to become rounded by their own gravity and often share an orbital path or field with many others. Occasionally, a rogue asteroid can be captured by a planet's gravity, becoming a moonlet.

Asteroids appear in three major categories, based upon their primary composition. Stony asteroids are composed primarily of silicates. Metallic asteroids are mostly made of heavy metals. Crystalline asteroids are covered in crystalline outcroppings, sometimes water ice.

### **Comet**

A comet is an icy, small body that, when passing close to a star, warms and begins to release gases in a process called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. Comets usually have highly eccentric elliptical orbits, and they have a wide range of orbital periods, ranging from several years to potentially several millions of years.

### **Nebula**

These large accumulations of interstellar gas and dust tend to have fewer habitable planets within them, but the celestial bodies within nebulae also have a significantly higher chance of yielding rare minerals that can be difficult to find anywhere else.

The ionized particles of these vast clouds interfere with the operation of sensors and weapons targeting and guidance systems. Travel and combat in this terrain is consequently usually at much slower speeds and closer range.

### **Spaceborne Life-Forms**

Space is vast and almost entirely empty. But that tiny fraction that is not contains an incredible amount of diversity, including organisms that live their entire lifespans in the void. Well known examples are the void cloud, asteroid burrowers, and stellar drakes.