The Outer Space Portal
Introduction
Outer space, or simply space, is the expanse that exists beyond Earth’s atmosphere and between celestial bodies. It contains ultra-low levels of particle densities, constituting a near-perfect vacuum of predominantly hydrogen and helium plasma, permeated by electromagnetic radiation, cosmic rays, neutrinos, magnetic fields and dust. The baseline temperature of outer space, as set by the background radiation from the Big Bang, is 2.7 kelvins (−270 °C; −455 °F).
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. Local concentrations of matter have condensed into stars and galaxies. Intergalactic space takes up most of the volume of the universe, but even galaxies and star systems consist almost entirely of empty space. Most of the remaining mass-energy in the observable universe is made up of an unknown form, dubbed dark matter and dark energy.
Outer space does not begin at a definite altitude above Earth’s surface. The Kármán line, an altitude of 100 km (62 mi) above sea level, is conventionally used as the start of outer space in space treaties and for aerospace records keeping. Certain portions of the upper stratosphere and the mesosphere are sometimes referred to as “near space“. The framework for international space law was established by the Outer Space Treaty, which entered into force on 10 October 1967. This treaty precludes any claims of national sovereignty and permits all states to freely explore outer space. Despite the drafting of UN resolutions for the peaceful uses of outer space, anti-satellite weapons have been tested in Earth orbit.
The concept that the space between the Earth and the Moon must be a vacuum was first proposed in the 17th century after scientists discovered that air pressure decreased with altitude. The immense scale of outer space was grasped in the 20th century when the distance to the Andromeda Galaxy was first measured. Humans began the physical exploration of space later in the same century with the advent of high-altitude balloon flights. This was followed by crewed rocket flights and, then, crewed Earth orbit, first achieved by Yuri Gagarin of the Soviet Union in 1961. The economic cost of putting objects, including humans, into space is very high, limiting human spaceflight to low Earth orbit and the Moon. On the other hand, uncrewed spacecraft have reached all of the known planets in the Solar System. Outer space represents a challenging environment for human exploration because of the hazards of vacuum and radiation. Microgravity has a negative effect on human physiology that causes both muscle atrophy and bone loss. (Full article…)
Selected article
A planet is a celestial body orbiting a star or stellar remnant that is massive enough to be rounded by its own gravity, not massive enough to cause thermonuclear fusion, and has cleared its neighbouring region of planetesimals. The planets were originally seen as a divine presence; as emissaries of the gods. As scientific knowledge advanced, the human perception of the planets changed over time, incorporating a number of disparate objects. On 24 August 2006, the IAU officially adopted a resolution defining planets within the Solar System. Copernicus suggested that the planets orbited the Sun, and this view was supported by Galileo after the development of the telescope. By careful analysis of the observation data, Johannes Kepler found their orbits to be not circular, but elliptical. Since 1992, through the discovery of hundreds of extrasolar planets, scientists are beginning to observe similar features throughout the Milky Way Galaxy. Planets are generally divided into two main types: large, low-density gas giants and smaller, rocky terrestrials. As of 23 April 2026, 6,416 known extrasolar planets (in 4,809 planetary systems and 1,061 multiple planetary systems) are listed in the Extrasolar Planets Encyclopaedia, ranging from the size of gas giants to that of terrestrial planets. Additionally, the IAU accepts five dwarf planets: Ceres, Pluto (originally classified as the Solar System’s ninth planet), Makemake, Haumea and Eris. No extrasolar dwarf planets have been detected.
Selected picture
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Kepler’s Supernova Credit: NASAThis Supernova remnant of Kepler’s Supernova (SN 1604) is made up of the materials left behind by the gigantic explosion of a star. There are two possible routes to this end: either a massive star may cease to generate fusion energy in its core, and collapse inward under the force of its own gravity, or a white dwarf star may accumulate material from a companion star until it reaches a critical mass and undergoes a similar collapse. In either case, the resulting supernova explosion expels much or all of the stellar material with great force. -
Earth “The Blue Marble“ is a famous photograph of Earth. NASA officially credits the image to the entire Apollo 17 crew — Eugene Cernan, Ronald Evans and Jack Schmitt — all of whom took photographic images during the mission. Apollo 17 passed over Africa during daylight hours and Antarctica is also illuminated. The photograph was taken approximately five hours after the spacecraft’s launch, while en route to the Moon. Apollo 17, notably, was the last manned lunar mission; no humans since have been at a range where taking a “whole-Earth” photograph such as “The Blue Marble” would be possible. -
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Image credit: Dave JarvisAn illustration of relative astronomical orders of magnitude, starting with the terrestrial planets of the Solar System in image 1 (top left) and ending with the largest known star, VY Canis Majoris, at the bottom right. The biggest celestial body in each image is shown on the left of the next frame. -
A timed exposure of the first Space Shuttle mission, STS-1. The shuttle Columbia stands on launch pad A at Kennedy Space Center, the night before launch. The objectives of the maiden flight were to check out the overall Shuttle system, accomplish a safe ascent into orbit and to return to Earth for a safe landing. -
Mercury is the smallest and closest to the Sun of the eight planets in the Solar System. It has no known natural satellites. The planet is named after the Roman deity Mercury, the messenger to the gods. -
Photo credit: NASAThe Eagle Nebula (also known as Messier Object 16, M16 or NGC 6611) is a young open cluster of stars. The nebula is an active region of star formation. Light from the bright, hot, young stars near the centre of the cluster illuminate the clouds of hydrogen gas and dust still collapsing to form new stars.
As projected on the sky, the Eagle Nebula lies in the constellation of Serpens Cauda. In three dimensions, it is relatively close to the Solar System being some 7,000 light years away on the edge of the Sagittarius Arm, the next nearest spiral arm towards the centre of the Milky Way.
In fact, when the picture is not coloured, is only red colored, the “Eagle” can be seen as a dark spot in the center of the nebula. -
A TRACE image of sunspots on the surface, or photosphere, of the sun from September 2002, is taken in the far ultraviolet on a relatively quiet day for solar activity. However, the image still shows a large sunspot group visible as a bright area near the horizon. Although sunspots are relatively cool regions on the surface of the sun, the bright glowing gas flowing around the sunspots have a temperature of over one million °C (1.8 million °F). The high temperatures are thought to be related to the rapidly changing magnetic field loops that channel solar plasma.
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Image credit: United States Geological SurveyA composite image of Olympus Mons on Mars, the tallest known volcano and mountain in the Solar System. This image was created from black-and-white imagery from the USGS‘s Mars Global Digital Image Mosaic and color imagery acquired from the 1978 visit of Viking 1. -
Space Shuttle Atlantis launch plume The launch of Space Shuttle Atlantis on STS-98, February 7 2001, at sunset. The sun is behind the camera, and the shape of the plume is cast across the vault of the sky, intersecting the rising full moon. The top portion of the plume is bright because it is illuminated directly by the sun; the lower portions are in the Earth’s shadow. After launch, the shuttle must engage in a pitch and roll program so that the vehicle is below the external tank and SRBs, as evidenced in the plume trail. The vehicle climbs in a progressively flattening arc, because achieving low orbit requires much more horizontal than vertical acceleration. -
Photo credit: Mars Reconnaissance OrbiterFalse-color Mars Reconnaissance Orbiter image of a side of the Chasma Boreale, a canyon in the polar ice cap of the Planum Boreum (north pole of Mars). Light browns are layers of surface dust, greys and blues are layers of water and carbon dioxide ice. Regular geometric cracking is indicative of higher concentrations of water ice.
The Planum Boreum’s permanent ice cap has a maximum depth of 3 km (1.9 mi). It is roughly 1200 km (750 mi) in diameter, an area equivalent to about 1½ times the size of Texas. The Chasma Boreale is up to 100 km (62.5 mi) wide and features scarps up to 2 km (1.25 mi) high. For a comparison, the Grand Canyon is approximately 1.6 km (1 mi) deep in some places and 446 km (279 mi) long but only up to 24 km (15 mi) wide. -
Orion Nebula A composite photo of the Orion Nebula, the closest region of star formation to Earth. It is composed of 520 separate images and NASA calls it “one of the most detailed astronomical images ever produced”. The nebula is located below Orion‘s Belt and is visible to the naked eye at night. It is one of the most scrutinized and photographed objects in the night sky, and is among the most intensely-studied celestial features. -
Planet Mars Credit: NASAMars, the fourth planet from the Sun, is named after the Roman god of war because of its blood red color. Mars has two small, oddly-shaped moons, Phobos and Deimos, named after the sons of the Greek god Ares. At some point in the future Phobos will be broken up by gravitational forces. The atmosphere on Mars is 95% carbon dioxide. In 2003 methane was also discovered in the atmosphere. Since methane is an unstable gas, this indicates that there must be (or have been within the last few hundred years) a source of the gas on the planet. -
Photo credit: Harrison SchmittAstronaut Eugene Cernan makes a short test drive of the lunar rover (officially, Lunar Roving Vehicle or LRV) during the early part of the first Apollo 17 extravehicular activity. The LRV was only used in the last three Apollo missions, but it performed without any major problems and allowed the astronauts to cover far more ground than in previous missions. All three LRVs were abandoned on the Moon. -
The Day the Earth Smiled refers to the date July 19, 2013, on which the Cassini spacecraft turned to image Saturn, its entire ring system, and the Earth from a position where Saturn eclipsed the Sun. Cassini imaging team leader and planetary scientist Carolyn Porco called for all the world’s people to reflect on humanity’s place in the cosmos, to marvel at life on Earth, and to look up and smile in celebration. The final mosaic, shown here, was released four months later and includes planets Earth, Mars, and Venus, and a host of Saturnian moons. -
Color-composite image of the Pleiades from the Digitized Sky Survey Credit: NASA, ESA, AURA/Caltech, Palomar ObservatoryThe Pleiades (also known as M45 or the Seven Sisters) is an open cluster in the constellation of Taurus. It is among the nearest to the Earth of all open clusters, probably the best known and certainly the most striking to the naked eye. -
Photo credit: New Horizons probeAn animation of an eruption by the Tvashtar Paterae volcanic region on the innermost of Jupiter‘s Galilean moons, Io. The ejecta plume is 330 km (205 mi) high, though only its uppermost half is visible in this image, as its source lies over the moon’s limb on its far side. This animation consists of a sequence of five images taken by NASA‘s New Horizons probe on March 1, 2007, over the course of eight minutes from 23:50 UTC. -
Photograph credit: NASA / JPL / Space Science InstituteThe Cassini–Huygens space-research project involved a collaboration between NASA, the European Space Agency, and the Italian Space Agency to send a probe to study the planet Saturn and its system, including its rings and its natural satellites.
This natural-color mosaic image, combining thirty photographs, was taken by the Cassini orbiter over the course of approximately two hours on 23 July 2008 as it panned its wide-angle camera across Saturn and its ring system as the planet approached equinox. Six moons are pictured in the panorama, with the largest, Titan, visible at the bottom left. -
Image credit: SeavAn animated image showing the apparent retrograde motion of Mars in 2003 as seen from Earth. All the true planets appear to periodically switch direction as they cross the sky. Because Earth completes its orbit in a shorter period of time than the planets outside its orbit, we periodically overtake them, like a faster car on a multi-lane highway. When this occurs, the planet will first appear to stop its eastward drift, and then drift back toward the west. Then, as Earth swings past the planet in its orbit, it appears to resume its normal motion west to east. -
NGC 4414 is an unbarred spiral galaxy about 62 million light-years away in the constellation Coma Berenices. It is a flocculent spiral galaxy, with short segments of spiral structure but without the dramatic well-defined spiral arms of a grand design spiral. NGC 4414 is a very isolated galaxy, with no signs of past interactions with other galaxies. -
Neptune is the eighth and farthest known planet from the Sun in the Solar System. In the Solar System, it is the fourth-largest planet by diameter, the third-most-massive planet and the densest giant planet. Neptune is 17 times the mass of Earth, slightly more massive than its near-twin Uranus. Neptune is denser and physically smaller than Uranus because its greater mass causes more gravitational compression of its atmosphere. Neptune orbits the Sun once every 164.8 years at an average distance of 30.1 au (4.5 billion km; 2.8 billion mi). It is named after the Roman god of the sea and has the astronomical symbol ♆, a stylised version of the god Neptune’s trident.
This picture of Neptune was taken by NASA‘s Voyager 2 spacecraft in 1989, at a range of 4.4 million miles (7.1 million kilometres) from the planet, approximately four days before closest approach. The photograph shows the Great Dark Spot, a storm about the size of Earth, in the centre, while the fast-moving bright feature nicknamed the “Scooter” and the Small Dark Spot can be seen on the western limb. These clouds were seen to persist for as long as the spacecraft’s cameras could resolve them. -
Photo: Yuri Beletsky, ESOA laser shoots towards the centre of the Milky Way from the Very Large Telescope facility in Chile, to provide a laser guide star, a reference point in the sky for the telescope’s adaptive optics (AO) system. AO technology improves the performance of optical systems by reducing the effect of atmospheric distortion. AO was first envisioned by Horace W. Babcock in 1953, but did not come into common usage until advances in computer technology during the 1990s made the technique practical.
Space-related portals
General images
The following are images from various outer space-related articles on Wikipedia.
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Voyager 1 is the first artificial object to reach the interstellar medium. (from Interstellar medium) -
Spatial density of space debris by altitude according to ESA MASTER-2001, without debris from the Chinese ASAT and 2009 collision events (from Space debris) -
Cosmic dust of the Andromeda Galaxy as revealed in infrared light by the Spitzer Space Telescope. (from Cosmic dust) -
A dusty trail from the early Solar System to carbonaceous dust today. (from Cosmic dust) -
The diversity found in the different types and scales of astronomical objects make the field of study increasingly specialized. (from Outline of space science) -
Tupan Patera on Jupiter’s moon Io (from Space exploration) -
Gabbard diagram of almost 300 pieces of debris from the disintegration of the five-month-old third stage of the Chinese Long March 4 booster on 11 March 2000 (from Space debris) -
Timeline of the expansion of the universe, where space is represented schematically at each time by circular sections. On the left, the dramatic expansion of inflation; at the center, the expansion accelerates (artist’s concept; neither time nor size are to scale) (from Outer space) -
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Surface of Mars by the Spirit rover (2004) (from Space exploration) -
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 (edges) and gegenschein (center), which is visually crossed by the Milky Way (from Outer space) -
Astronaut Piers Sellers during the third spacewalk of STS-121, a demonstration of orbiter heat shield repair techniques (from Outline of space science) -
The famous Earthrise photo, the first of its kind taken by a human (from Outer space) -
Artistic image of a rocket lifting from a Saturn moon (from Space exploration) -
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 (from Outer space) -
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. -
View from International Space Station, showing the yellow-green airglow of Earth’s ionosphere with the Milky Way in the background. (from Outer space) -
This light-year-long knot of interstellar gas and dust resembles a caterpillar. (from Interstellar medium) -
Illustration of a satellite breaking up into multiple pieces at higher altitudes (from Space debris) -
Atmospheric attenuation in dB/km as a function of frequency over the EHF band. Peaks in absorption at specific frequencies are a problem, due to atmosphere constituents such as water vapor (H2O) and carbon dioxide (CO2). (from Interstellar medium) -
Three-dimensional structure in Pillars of Creation. (from Interstellar medium) -
Debris impacts on Mir's solar panels degraded their performance. The damage is most noticeable on the panel on the right, which is facing the camera with a high degree of contrast. Extensive damage to the smaller panel below is due to impact with a Progress spacecraft rather than space debris. (from Space debris) -
Known orbit planes of Fengyun-1C debris one month after the weather satellite’s disintegration by the Chinese ASAT (from Space debris) -
A laser-guided observation of the Milky Way Galaxy at the Paranal Observatory in Chile in 2010 (from Outline of space science)
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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 (from Outer space) -
A proposed timeline of the origin of space, from physical cosmology (from Outline of space science)
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Concept for a space-based solar power system to beam energy down to Earth (from Outer space) -
Space Shuttle Endeavour had a major impact on its radiator during STS-118. The entry hole is about 5.5 mm (0.22 in), and the exit hole is twice as large. (from Space debris) -
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Debris density in low Earth orbit (from Space debris) -
Spatial density of LEO space debris by altitude, according to 2011 a NASA report to the United Nations Office for Outer Space Affairs (from Space debris) -
Apollo 16 LEM Orion, the Lunar Roving Vehicle and astronaut John Young (1972) (from Space exploration) -
Gabbard diagram of debris from the disintegration of the third stage of a Chinese Long March 4 booster (from Space debris)
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Because of the hazards of a vacuum, astronauts must wear a pressurized space suit while outside their spacecraft. -
The original Magdeburg hemispheres (left) used to demonstrate Otto von Guericke’s vacuum pump (right) -
Collision on Launch Avoidance lead to delayed spacecraft launches to avoid potential conjunctions/collisions during launch. Seen here is a Collision Avoidance analysis that mandated a four-minute delay for the launch of SPADEX in 2024. (from Space debris) -
Saudi officials inspect a crashed PAM-D module in January 2001. (from Space debris) -
Space debris identified as WT1190F, burning up in a fireball over Sri Lanka (from Space debris) -
South is up in the first image of Earth taken by a person, probably by Bill Anders (during the 1968 Apollo 8 mission) (from Outer space) -
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View of an orbital debris hole made in the panel of the Solar Max satellite (from Space debris) -
Illustration of Earth’s atmosphere gradual transition into outer space (from Outer space) -
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Major elements of 200 stratospheric interplanetary dust particles. (from Cosmic dust) -
Crew quarters on Zvezda, the base ISS crew module (from Space exploration) -
Objects in Earth orbit including fragmentation debris, November 2020, NASA: ODPO (from Space debris) -
Astronaut Buzz Aldrin had a personal Communion service when he first arrived on the surface of the Moon. (from Space exploration) -
Infographic showing the space debris situation in different kinds of orbits around Earth (from Space debris) -
Distribution of Matter in a cubic section of the universe. The blue fiber-like structures represent matter, while the empty regions show the cosmic voids (from Outer space) -
For the first time, the NASA / ESA / Canadian Space Agency / James Webb Space Telescope has observed the chemical signature of carbon-rich dust grains at redshift z ≈ 7, which is roughly equivalent to one billion years after the birth of the Universe, this observation suggests exciting avenues of investigation into both the production of cosmic dust and the earliest stellar populations in our Universe. (from Cosmic dust) -
A computer-generated animation by the European Space Agency representing space debris in low earth orbit at the current rate of growth compared to mitigation measures being taken (from Space debris) -
Delta-v’s in km/s for various orbital maneuvers (from Space exploration) -
Smooth chondrite interplanetary dust particle. (from Cosmic dust) -
Concept art for a NASA Vision mission (from Space exploration) -
NASA computer-generated image of growth of space debris (from Space debris) -
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Porous chondrite dust particle (from Cosmic dust) -
First television image of Earth from space, taken by TIROS-1 (1960) (from Space exploration) -
A MESSENGER image from 18,000 km showing a region about 500 km across (2008) (from Space exploration) -
Comet 103P/Hartley (2010) (from Space exploration) -
Apollo Command Service Module in lunar orbit (from Space exploration) -
Structure of galactic space of the Milky Way, as viewed from the Solar System, with dark nebulas (white text) and star clouds (black text) labeled (from Outer space) -
Map showing the Sun located near the edge of the Local Interstellar Cloud and Alpha Centauri about 4 light-years away in the neighboring G-Cloud complex (from Interstellar medium) -
Growth of tracked objects in orbit and related events; efforts to manage outer space global commons have so far not reduced the total amount of debris or the growth of objects in orbit. (from Space debris) -
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The distribution of ionized hydrogen (known by astronomers as H II from old spectroscopic terminology) in the parts of the Galactic interstellar medium visible from the Earth’s northern hemisphere as observed with the Wisconsin Hα Mapper (Haffner et al. 2003). (from Interstellar medium) -
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The Long Duration Exposure Facility (LDEF) is an important source of information on small-particle space debris. (from Space debris) -
After reentry, Delta 2 second stage pieces were found in South Africa. (from Space debris) -
Model of a Russian Vostok spacecraft (from Space exploration) -
Perseverance’s backshell sitting upright on the surface of Jezero Crater (from Space debris) -
A micrometeoroid left this crater on the surface of Space Shuttle Challenger‘s front window on STS-7. (from Space debris) -
A computer-generated map of objects orbiting Earth, as of 2005. About 95% are debris, not working artificial satellites (from Outer space) -
Bow shock formed by the magnetosphere of the young star LL Orionis (center) as it collides with the Orion Nebula flow -
Earth and the Moon as seen from cislunar space on the 2022 Artemis 1 mission (from Outer space) -
Vanguard 1 is expected to remain in orbit until at least the year 2250. (from Space debris) -
Zodiacal light caused by cosmic dust. (from Cosmic dust) -
Reconstruction of solar activity over 11,400 years. Period of equally high activity over 8,000 years ago marked. (from Space climate) -
Interstellar medium and astrosphere meeting (from Interstellar medium) -
Newton’s cannonball, an illustration of how objects can “fall” in a curve around the planet (from Outer space) -
Baker–Nunn cameras were widely used to study space debris. (from Space debris) -
Artist’s impression of dust formation around a supernova explosion. (from Cosmic dust) -
Astronomers used the James Webb Space Telescope to image the warm dust around a nearby young star, Fomalhaut, to study the first asteroid belt ever seen outside the Solar System in infrared light. (from Cosmic dust)
Did you know (auto-generated)
- … that, for the Space 220 Restaurant, Disney reached out to NASA engineers to understand what a space elevator might look like?
- … that some severe environmental impacts of the invasion of Ukraine can be seen from space?
- … that the space industry of India has supported the launch of more than 100 domestic satellites and more than 300 foreign satellites?
- … that Nature’s Fynd, producer of microbe-based meat substitutes, is working with NASA to develop a bioreactor for use in space travel?
- … that Louis W. Roberts was among the highest ranking African-American space program staff at NASA while the Apollo program was underway?
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