Outer space

[1] It contains ultra-low levels of particle densities, constituting a near-perfect vacuum[2] of predominantly hydrogen and helium plasma, permeated by electromagnetic radiation, cosmic rays, neutrinos, magnetic fields and dust.

[3] The plasma between galaxies is thought to account for about half of the baryonic (ordinary) matter in the universe, having a number density of less than one hydrogen atom per cubic metre and a kinetic temperature of millions of kelvins.

[20] According to the Big Bang theory, the very early universe was an extremely hot and dense state about 13.8 billion years ago[21] which rapidly expanded.

[22] Matter that remained following the initial expansion has since undergone gravitational collapse to create stars, galaxies and other astronomical objects, leaving behind a deep vacuum that forms what is now called outer space.

[55] The lithopanspermia hypothesis suggests that rocks ejected into outer space from life-harboring planets may successfully transport life forms to another habitable world.

A conjecture is that just such a scenario occurred early in the history of the Solar System, with potentially microorganism-bearing rocks being exchanged between Venus, Earth, and Mars.

[60] Rapid decompression can rupture eardrums and sinuses, bruising and blood seep can occur in soft tissues, and shock can cause an increase in oxygen consumption that leads to hypoxia.

The Crew Altitude Protection Suit (CAPS), a fitted elastic garment designed in the 1960s for astronauts, prevents ebullism at pressures as low as 2 kilopascals (0.3 psi).

Exposure to high-energy, ionizing cosmic rays can result in fatigue, nausea, vomiting, as well as damage to the immune system and changes to the white blood cell count.

[71] On a round-trip Mars mission lasting three years, a large fraction of the cells in an astronaut's body would be traversed and potentially damaged by high energy nuclei.

[73] The transition between Earth's atmosphere and outer space lacks a well-defined physical boundary, with the air pressure steadily decreasing with altitude until it mixes with the solar wind.

[80] The Kármán line, established by the Fédération Aéronautique Internationale, and used internationally by the United Nations,[16] is set at an altitude of 100 km (62 mi) as a working definition for the boundary between aeronautics and astronautics.

[97] Low Earth orbit overlaps the inner Van Allen radiation belt, a toroidal region composed primarily of high energy protons.

These plasmas form a medium from which storm-like disturbances powered by the solar wind can drive electrical currents into the Earth's upper atmosphere.

The solar wind is a continuous stream of charged particles emanating from the Sun which creates a very tenuous atmosphere (the heliosphere) for billions of kilometers into space.

[124] Interplanetary space extends out to the heliopause where the influence of the galactic environment starts to dominate over the magnetic field and particle flux from the Sun.

These atoms are ejected into the interstellar medium by stellar winds or when evolved stars begin to shed their outer envelopes such as during the formation of a planetary nebula.

[134] The cataclysmic explosion of a supernova propagates shock waves of stellar ejecta outward, distributing it throughout the interstellar medium, including the heavy elements previously formed within the star's core.

Large regions of higher density matter known as molecular clouds allow chemical reactions to occur, including the formation of organic polyatomic species.

[146][148][149] When gas falls from the filamentary structures of the WHIM into the galaxy clusters at the intersections of the cosmic filaments, it can heat up even more, reaching temperatures of 108 K and above in the so-called intracluster medium (ICM).

[156] In 1648, his brother-in-law, Florin Périer, repeated the experiment on the Puy de Dôme mountain in central France and found that the column was shorter by three inches.

He extended the Copernican heliocentric cosmology to the concept of an infinite universe filled with a substance he called aether, which did not resist the motion of heavenly bodies.

It was replaced by Albert Einstein's theory of special relativity, which holds that the speed of light in a vacuum is a fixed constant, independent of the observer's motion or frame of reference.

[174] American physicists Ralph Alpher and Robert Herman predicted 5 K for the temperature of space in 1948, based on the gradual decrease in background energy following the then-new Big Bang theory.

They allow relay of long-range communications like television, provide a means of precise navigation, and permit direct monitoring of weather conditions and remote sensing of the Earth.

The latter role serves a variety of purposes, including tracking soil moisture for agriculture, prediction of water outflow from seasonal snow packs, detection of diseases in plants and trees, and surveillance of military activities.

[185] Satellites make use of the significantly reduced drag in space to stay in stable orbits, allowing them to efficiently span the whole globe, compared to for example stratospheric balloons or high-altitude platform stations, which have other benefits.

This is evidenced by the spectacular pictures sent back by the Hubble Space Telescope, allowing light from more than 13 billion years ago—almost to the time of the Big Bang—to be observed.

Proposed concepts for addressing this issue include, fully reusable launch systems, non-rocket spacelaunch, momentum exchange tethers, and space elevators.

For example, the Daedalus Project study, which proposed a spacecraft powered by the fusion of deuterium and helium-3, would require 36 years to reach the "nearby" Alpha Centauri system.

Being essentially empty, outer space allows the earliest (redder) galaxies to be viewed without obstruction, as in the Webb's First Deep Field image.
An artist's concept of the expanding universe opening up from the viewer's left, facing the viewer in a 3/4 pose.
Timeline of the expansion of the universe , where visible space is represented by the circular sections. At left, a dramatic expansion occurs in the inflationary epoch , and at the center, the expansion accelerates . Neither time nor size are to scale.
A wide field view of outer space as seen from Earth's surface at night. The interplanetary dust cloud is visible as the horizontal band of zodiacal light , including the false dawn [ 29 ] (edges) and gegenschein (center), which is visually crossed by the Milky Way
The lower half shows a blue planet with patchy white clouds. The upper half has a man in a white spacesuit and maneuvering unit against a black background.
Because of the hazards of a vacuum, astronauts must wear a pressurized space suit while outside their spacecraft.
Illustration of Earth's atmosphere gradual transition into outer space
Conventional anti-satellite weapons such as the SM-3 missile remain legal under the law of armed conflict , even though they create hazardous space debris
A computer-generated map of objects orbiting Earth, as of 2005. About 95% are debris, not working artificial satellites [ 104 ]
Earth and the Moon as seen from cislunar space on the 2022 Artemis 1 mission
Near-Earth space showing the low-Earth (blue), medium Earth (green), and high Earth (red) orbits. The last extends beyond the radius of geosynchronous orbits
At lower left, a white coma stands out against a black background. Nebulous material streams away to the top and left, slowly fading with distance.
The sparse plasma (blue) and dust (white) in the tail of comet Hale–Bopp are being shaped by pressure from solar radiation and the solar wind, respectively.
Patchy orange and blue nebulosity against a black background, with a curved orange arc wrapping around a star at the center.
Bow shock formed by the magnetosphere of the young star LL Orionis (center) as it collides with the Orion Nebula flow
Structure of the Universe
Large-scale matter distribution in a cubic section of the universe. The blue fiber-like structures represent the matter, and the empty regions in between represent the cosmic voids of the intergalactic medium
A glass display case holds a mechanical device with a lever arm, plus two metal hemispheres attached to draw ropes.
The original Magdeburg hemispheres (left) used to demonstrate Otto von Guericke's vacuum pump (right)
South is up in the first image of Earth taken by a person, [ 175 ] probably by Bill Anders (during the 1968 Apollo 8 mission)
The International Space Station is an orbiting laboratory for space applications and habitability. Visible in the background is yellow-green airglow of Earth's ionosphere and the interstellar field of the Milky Way.
Concept for a space-based solar power system to beam energy down to Earth [ 190 ]