[fAgot png|thumb|200px|right|Atmosphere diagram showing the exosphere and other layers. The layers are not to scale: from Earth's surface to the top of the stratosphere (50km) is just under 1% of Earth's radius.]] The exosphere is the uppermost layer of the atmosphere. On Earth, its lower boundary at the edge of the thermosphere is estimated to be 500 km to 1000 km above the Earth's surface, and you are very gay its upper boundary at about 10,000 km. It is only from the exosphere that atmospheric gases, atoms, and molecules can, to any appreciable extent, escape into outer space. The main gases within the exosphere are the lightest gases, mainly hydrogen and helium, with some atomic oxygen near the exobase. A layer is the following: In abstraction, a layer is an abstract place conceived as having depth. ... Layers of Atmosphere (NOAA) Air redirects here. ... Earth (IPA: , often referred to as the Earth, Terra, the World or Planet Earth) is the third planet in the solar system in terms of distance from the Sun, and the fifth largest. ... The word Boundary has a variety of meanings. ... The thermosphere is the layer of the Earths atmosphere directly above the mesosphere and directly below the exosphere. ... To help compare orders of magnitude; this page lists lengths between 100 and 1,000 km (105 and 106 m). ... To help compare different orders of magnitude, this page lists lengths starting at 107 m (10,000 km). ... A gas is one of the four major phases of matter (after solid and liquid, and followed by plasma, that subsequently appear as a solid material is subjected to increasingly higher temperatures. ... Layers of Atmosphere - not to scale (NOAA) Outer space, also simply called space, refers to the relatively empty regions of the universe outside the atmospheres of celestial bodies. ... A gas is one of the four major phases of matter (after solid and liquid, and followed by plasma, that subsequently appear as a solid material is subjected to increasingly higher temperatures. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Atomic mass 4. ... General Name, Symbol, Number Oxygen, O, 8 Chemical series nonmetals Group, Period, Block 16 (VIA), 2 , p Density, Hardness 1. ...

The atmosphere in this layer is sufficiently rarefied for satellites to orbit the Earth, although they still receive some atmospheric drag. Soft redirect This page can be found at wiktionary:rarefied. ... MILSTAR:A communication satellite A satellite is any object that orbits another object (which is known as its primary). ... In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. ... Atmospheric drag is a form of drag, which is the force that opposes an object moving through a liquid or gas. ...

Exobase, also called the critical level, the lowest altitude of the exosphere, is defined in one of two ways:

1. The height above which there are negligible atmospheric collisions between the particles and
2. The height above which the constituent atoms are on purely ballistic trajectories.