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78-656: The specific design of TMGs varies between different space agencies and different suits, though they all serve the same purpose. Outside a Liquid Cooling and Ventilation Garment , pressure bladder, and restraint layer, the TMG for the A7L suit worn on the Moon and during the Skylab Program began with a layer of neoprene -coated nylon ripstop . This was the innermost layer of protection from micrometeoroids. Next, thermal radiation protection

156-506: A G-type main-sequence star . The largest objects that orbit the Sun are the eight planets . In order from the Sun, they are four terrestrial planets ( Mercury , Venus , Earth and Mars ); two gas giants ( Jupiter and Saturn ); and two ice giants ( Uranus and Neptune ). All terrestrial planets have solid surfaces. Inversely, all giant planets do not have a definite surface, as they are mainly composed of gases and liquids. Over 99.86% of

234-517: A planetary nebula , returning some of the material that formed the Sun—but now enriched with heavier elements like carbon—to the interstellar medium . Astronomers sometimes divide the Solar System structure into separate regions. The inner Solar System includes Mercury, Venus, Earth, Mars, and the bodies in the asteroid belt . The outer Solar System includes Jupiter, Saturn, Uranus, Neptune, and

312-408: A diameter of about 250 km (160 mi) and is one of the few minor planets possessing a ring system. Beyond the orbit of Neptune lies the area of the " trans-Neptunian region ", with the doughnut-shaped Kuiper belt, home of Pluto and several other dwarf planets, and an overlapping disc of scattered objects, which is tilted toward the plane of the Solar System and reaches much further out than

390-415: A few meters to hundreds of kilometers in size. Many asteroids are divided into asteroid groups and families based on their orbital characteristics. Some asteroids have natural satellites that orbit them , that is, asteroids that orbit larger asteroids. The asteroid belt occupies a torus-shaped region between 2.3 and 3.3 AU from the Sun, which lies between the orbits of Mars and Jupiter. It

468-676: A means for advocating for and/or engaging in activities related to outer space , exploitation of space systems, and space exploration . The listings summarize all countries and regional authorities that have established space agencies. The listings established a comparative summary of demonstrated capabilities across the countries that have invested in the pursuit of space-based objectives. Government space agency organizations are established with objectives that include national prestige, exploitation of remote sensing information, communications, education, and economic development. These agencies tend to be civil in nature (vs military) and serve to advance

546-402: A reference is included to that program's first demonstration of the technical capacity or capability to meet the defined objective. The fifth listing identifies countries that are considering or are developing space agency organizations but have not ratified formation or operation as of yet. Note as well that the demonstrated capabilities represent the national (or regional) capacity to achieve

624-565: A relationship between these orbital distances, like the Titius–Bode law and Johannes Kepler's model based on the Platonic solids , but ongoing discoveries have invalidated these hypotheses. Some Solar System models attempt to convey the relative scales involved in the Solar System in human terms. Some are small in scale (and may be mechanical—called orreries )—whereas others extend across cities or regional areas. The largest such scale model,

702-530: A science payload from a sub-orbital or orbital mission. Several space agencies, both national and international, have demonstrated all four of those capabilities. 2013 (NADA) 2023 (NATA) This group of agencies have developed or are developing launch infrastructure including space launch sites, suborbital launch technology, orbital launch systems, and reusable hardware technologies. This group of agencies have developed advanced technological capabilities required for travel and study of other heavenly bodies within

780-532: A shell surrounding the inert helium, and the energy output will be greater than at present. The outer layers of the Sun will expand to roughly 260 times its current diameter, and the Sun will become a red giant . Because of its increased surface area, the surface of the Sun will be cooler (2,600 K (4,220 °F) at its coolest) than it is on the main sequence. The expanding Sun is expected to vaporize Mercury as well as Venus, and render Earth and Mars uninhabitable (possibly destroying Earth as well). Eventually,

858-413: A small fraction of the solar nebula, the terrestrial planets could not grow very large. The giant planets (Jupiter, Saturn, Uranus, and Neptune) formed further out, beyond the frost line, the point between the orbits of Mars and Jupiter where material is cool enough for volatile icy compounds to remain solid. The ices that formed these planets were more plentiful than the metals and silicates that formed

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936-612: A technological progression in complexity and capacity that historically aligned to the developments that occurred during the 20th century space race between the United States and the Soviet Union. It is not intended to offer that this is the only path to advanced space faring status; variations and adaptations are expected and are likely to occur based on the technological capabilities that are available to today as opposed to 50 or more years ago. For each identified "Demonstrated capability"

1014-417: Is 30 AU from the Sun. With a few exceptions, the farther a planet or belt is from the Sun, the larger the distance between its orbit and the orbit of the next nearest object to the Sun. For example, Venus is approximately 0.33 AU farther out from the Sun than Mercury, whereas Saturn is 4.3 AU out from Jupiter, and Neptune lies 10.5 AU out from Uranus. Attempts have been made to determine

1092-409: Is a great ring of debris similar to the asteroid belt, but consisting mainly of objects composed primarily of ice. It extends between 30 and 50 AU from the Sun. It is composed mainly of small Solar System bodies, although the largest few are probably large enough to be dwarf planets. There are estimated to be over 100,000 Kuiper belt objects with a diameter greater than 50 km (30 mi), but

1170-428: Is a small chance that another star will pass through the Solar System in the next few billion years. Although this could destabilize the system and eventually lead millions of years later to expulsion of planets, collisions of planets, or planets hitting the Sun, it would most likely leave the Solar System much as it is today. The Sun's main-sequence phase, from beginning to end, will last about 10 billion years for

1248-606: Is maintained from the US defence budget, whereas ESA's money is used for developing the European Galileo positioning system. For European contributors to ESA, the national budgets shown include also their contributions to ESA. Eight government space agencies, the United States (NASA), China (CNSA), France (CNES), Germany (DLR), India (ISRO), Italy (ASI), Japan (JAXA) and Russia (Roscosmos), have annual budgets of more than one billion US dollars . Solar System The Solar System

1326-412: Is no "gap" as seen between the size of Earth and of Neptune (with a radius 3.8 times as large). As many of these super-Earths are closer to their respective stars than Mercury is to the Sun, a hypothesis has arisen that all planetary systems start with many close-in planets, and that typically a sequence of their collisions causes consolidation of mass into few larger planets, but in case of the Solar System

1404-464: Is strong consensus among astronomers that five members of the Kuiper belt are dwarf planets . Many dwarf planet candidates are being considered, pending further data for verification. The scattered disc, which overlaps the Kuiper belt but extends out to near 500 AU, is thought to be the source of short-period comets. Scattered-disc objects are believed to have been perturbed into erratic orbits by

1482-475: Is the gravitationally bound system of the Sun and the objects that orbit it. It formed about 4.6 billion years ago when a dense region of a molecular cloud collapsed, forming the Sun and a protoplanetary disc . The Sun is a typical star that maintains a balanced equilibrium by the fusion of hydrogen into helium at its core , releasing this energy from its outer photosphere . Astronomers classify it as

1560-430: Is the Solar System's star and by far its most massive component. Its large mass (332,900 Earth masses ), which comprises 99.86% of all the mass in the Solar System, produces temperatures and densities in its core high enough to sustain nuclear fusion of hydrogen into helium. This releases an enormous amount of energy , mostly radiated into space as electromagnetic radiation peaking in visible light . Because

1638-468: Is thought to be remnants from the Solar System's formation that failed to coalesce because of the gravitational interference of Jupiter. The asteroid belt contains tens of thousands, possibly millions, of objects over one kilometer in diameter. Despite this, the total mass of the asteroid belt is unlikely to be more than a thousandth of that of Earth. The asteroid belt is very sparsely populated; spacecraft routinely pass through without incident. Below are

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1716-446: Is white Ortho-Fabric, made with a blend of Gore-Tex , Kevlar , and Nomex . This layer can withstand temperatures from −300 to 300 °F (−180 to 150 °C). The outer layer provides both micrometeoroid and thermal protection, by reflecting most of the sun's thermal radiation. List of space agencies Government space agencies are established by governments of countries or regional groupings of countries to establish

1794-489: The Milky Way galaxy. The Solar System formed at least 4.568 billion years ago from the gravitational collapse of a region within a large molecular cloud . This initial cloud was likely several light-years across and probably birthed several stars. As is typical of molecular clouds, this one consisted mostly of hydrogen, with some helium, and small amounts of heavier elements fused by previous generations of stars. As

1872-627: The Roscosmos State Corporation for Space Activities (Roscosmos) of Russia, the Indian Space Research Organisation (ISRO), and the China National Space Agency (CNSA). The space agency listings are segregated to enable identification of subsets of the complete list that have advanced to higher levels or technical or programmatic proficiency in accordance with the following: The four listings identify

1950-489: The Solar System . These involve the capacity to leave the local area around the planet Earth for lunar and/or missions to other bodies in the Solar System. As of February 2023, six (6) countries/agencies have achieved objectives necessary to be listed here. This category is formed by agencies that operate and construct satellites in extraterrestrial environments, but do not have the capability to transport those satellites to

2028-608: The Sweden Solar System , uses the 110-meter (361-foot) Avicii Arena in Stockholm as its substitute Sun, and, following the scale, Jupiter is a 7.5-meter (25-foot) sphere at Stockholm Arlanda Airport , 40 km (25 mi) away, whereas the farthest current object, Sedna , is a 10 cm (4 in) sphere in Luleå , 912 km (567 mi) away. At that scale, the distance to Proxima Centauri would be roughly 8 times further than

2106-449: The asteroid belt (between Mars's and Jupiter's orbit) and the Kuiper belt (just outside Neptune's orbit). Six planets, seven dwarf planets, and other bodies have orbiting natural satellites , which are commonly called 'moons'. The Solar System is constantly flooded by the Sun's charged particles , the solar wind , forming the heliosphere . Around 75–90 astronomical units from the Sun,

2184-494: The frost line , and it lies at roughly five times the Earth's distance from the Sun. The planets and other large objects in orbit around the Sun lie near the plane of Earth's orbit, known as the ecliptic . Smaller icy objects such as comets frequently orbit at significantly greater angles to this plane. Most of the planets in the Solar System have secondary systems of their own, being orbited by natural satellites called moons. All of

2262-419: The fusor stars in the Milky Way . The Sun is a population I star , having formed in the spiral arms of the Milky Way galaxy. It has a higher abundance of elements heavier than hydrogen and helium (" metals " in astronomical parlance) than the older population II stars in the galactic bulge and halo . Elements heavier than hydrogen and helium were formed in the cores of ancient and exploding stars, so

2340-528: The grand tack hypothesis suggests that a final inward migration of Jupiter dispersed much of the asteroid belt, leading to the Late Heavy Bombardment of the inner planets. The Solar System remains in a relatively stable, slowly evolving state by following isolated, gravitationally bound orbits around the Sun. Although the Solar System has been fairly stable for billions of years, it is technically chaotic , and may eventually be disrupted . There

2418-427: The heliosphere , which spans much of the Solar System. Along with light , the Sun radiates a continuous stream of charged particles (a plasma ) called the solar wind . This stream spreads outwards at speeds from 900,000 kilometres per hour (560,000 mph) to 2,880,000 kilometres per hour (1,790,000 mph), filling the vacuum between the bodies of the Solar System. The result is a thin , dusty atmosphere, called

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2496-554: The interplanetary medium , which extends to at least 100 AU . Activity on the Sun's surface, such as solar flares and coronal mass ejections , disturbs the heliosphere, creating space weather and causing geomagnetic storms . Coronal mass ejections and similar events blow a magnetic field and huge quantities of material from the surface of the Sun. The interaction of this magnetic field and material with Earth's magnetic field funnels charged particles into Earth's upper atmosphere, where its interactions create aurorae seen near

2574-421: The magnetic poles . The largest stable structure within the heliosphere is the heliospheric current sheet , a spiral form created by the actions of the Sun's rotating magnetic field on the interplanetary medium. The inner Solar System is the region comprising the terrestrial planets and the asteroids . Composed mainly of silicates and metals, the objects of the inner Solar System are relatively close to

2652-566: The pre-solar nebula collapsed, conservation of angular momentum caused it to rotate faster. The center, where most of the mass collected, became increasingly hotter than the surroundings. As the contracting nebula spun faster, it began to flatten into a protoplanetary disc with a diameter of roughly 200 AU and a hot, dense protostar at the center. The planets formed by accretion from this disc, in which dust and gas gravitationally attracted each other, coalescing to form ever larger bodies. Hundreds of protoplanets may have existed in

2730-470: The Kuiper belt. The entire region is still largely unexplored . It appears to consist overwhelmingly of many thousands of small worlds—the largest having a diameter only a fifth that of Earth and a mass far smaller than that of the Moon—composed mainly of rock and ice. This region is sometimes described as the "third zone of the Solar System", enclosing the inner and the outer Solar System. The Kuiper belt

2808-510: The Moon is from Earth. If the Sun–Neptune distance is scaled to 100 metres (330 ft), then the Sun would be about 3 cm (1.2 in) in diameter (roughly two-thirds the diameter of a golf ball), the giant planets would be all smaller than about 3 mm (0.12 in), and Earth's diameter along with that of the other terrestrial planets would be smaller than a flea (0.3 mm or 0.012 in) at this scale. Besides solar energy,

2886-462: The Solar System is a measure of the total amount of orbital and rotational momentum possessed by all its moving components. Although the Sun dominates the system by mass, it accounts for only about 2% of the angular momentum. The planets, dominated by Jupiter, account for most of the rest of the angular momentum due to the combination of their mass, orbit, and distance from the Sun, with a possibly significant contribution from comets. The radius of

2964-545: The Solar System is home to the giant planets and their large moons. The centaurs and many short-period comets orbit in this region. Due to their greater distance from the Sun, the solid objects in the outer Solar System contain a higher proportion of volatiles such as water, ammonia, and methane, than planets of the inner Solar System because their lower temperatures allow these compounds to remain solid, without significant sublimation . The four outer planets, called giant planets or Jovian planets, collectively make up 99% of

3042-457: The Solar System stands out in lacking planets interior to the orbit of Mercury. The known Solar System lacks super-Earths , planets between one and ten times as massive as the Earth, although the hypothetical Planet Nine , if it does exist, could be a super-Earth orbiting in the edge of the Solar System. Uncommonly, it has only small terrestrial and large gas giants; elsewhere planets of intermediate size are typical—both rocky and gas—so there

3120-523: The Solar System's mass is in the Sun and nearly 90% of the remaining mass is in Jupiter and Saturn. There is a strong consensus among astronomers that the Solar System has at least nine dwarf planets : Ceres , Orcus , Pluto , Haumea , Quaoar , Makemake , Gonggong , Eris , and Sedna . There are a vast number of small Solar System bodies , such as asteroids , comets , centaurs , meteoroids , and interplanetary dust clouds . Some of these bodies are in

3198-400: The Solar System, created by heat and light pressure from the early Sun; those objects closer to the Sun, which are more affected by heat and light pressure, are composed of elements with high melting points. Objects farther from the Sun are composed largely of materials with lower melting points. The boundary in the Solar System beyond which those volatile substances could coalesce is known as

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3276-406: The Sun by the outer planets, and are expected to become comets or be ejected out of the Solar System. While most centaurs are inactive and asteroid-like, some exhibit cometary activity, such as the first centaur discovered, 2060 Chiron , which has been classified as a comet (95P) because it develops a coma just as comets do when they approach the Sun. The largest known centaur, 10199 Chariklo , has

3354-455: The Sun compared to around two billion years for all other subsequent phases of the Sun's pre- remnant life combined. The Solar System will remain roughly as it is known today until the hydrogen in the core of the Sun has been entirely converted to helium, which will occur roughly 5 billion years from now. This will mark the end of the Sun's main-sequence life. At that time, the core of the Sun will contract with hydrogen fusion occurring along

3432-495: The Sun fuses hydrogen at its core, it is a main-sequence star. More specifically, it is a G2-type main-sequence star , where the type designation refers to its effective temperature . Hotter main-sequence stars are more luminous but shorter lived. The Sun's temperature is intermediate between that of the hottest stars and that of the coolest stars. Stars brighter and hotter than the Sun are rare, whereas substantially dimmer and cooler stars, known as red dwarfs , make up about 75% of

3510-422: The Sun is 0.0047 AU (700,000 km; 400,000 mi). Thus, the Sun occupies 0.00001% (1 part in 10 ) of the volume of a sphere with a radius the size of Earth's orbit, whereas Earth's volume is roughly 1 millionth (10 ) that of the Sun. Jupiter, the largest planet, is 5.2 AU from the Sun and has a radius of 71,000 km (0.00047 AU; 44,000 mi), whereas the most distant planet, Neptune,

3588-403: The Sun is growing brighter; early in its main-sequence life its brightness was 70% that of what it is today. The temperature, reaction rate , pressure, and density increased until hydrostatic equilibrium was achieved: the thermal pressure counterbalancing the force of gravity. At this point, the Sun became a main-sequence star. Solar wind from the Sun created the heliosphere and swept away

3666-472: The Sun twice for every three times that Neptune does, or once for every two. The classical belt consists of objects having no resonance with Neptune, and extends from roughly 39.4 to 47.7 AU. Members of the classical Kuiper belt are sometimes called "cubewanos", after the first of their kind to be discovered, originally designated 1992 QB 1 , (and has since been named Albion); they are still in near primordial, low-eccentricity orbits. Currently, there

3744-499: The Sun; the radius of this entire region is less than the distance between the orbits of Jupiter and Saturn. This region is within the frost line , which is a little less than 5 AU from the Sun. The four 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 silicates —which form their crusts and mantles —and metals such as iron and nickel which form their cores . Three of

3822-565: The astronomical sense (chemical compounds with melting points of up to a few hundred kelvins such as water, methane, ammonia, hydrogen sulfide , and carbon dioxide . ) Icy substances comprise the majority of the satellites of the giant planets and small objects that lie beyond Neptune's orbit. The centaurs are icy, comet-like bodies whose semi-major axes are longer than Jupiter's and shorter than Neptune's (between 5.5 and 30 AU). These are former Kuiper belt and scattered disc objects (SDOs) that were gravitationally perturbed closer to

3900-615: The benefits of exploitation and/or exploration of space. Government agencies span the spectrum from ancient organizations with small budgets to mature national or regional enterprises such as the National Aeronautics and Space Administration (NASA) of the United States, the European Space Agency (ESA) which coordinates for more than 20 constituent countries, the Japan Aerospace Exploration Agency (JAXA),

3978-402: The bodies in the Kuiper belt . Since the discovery of the Kuiper belt, the outermost parts of the Solar System are considered a distinct region consisting of the objects beyond Neptune . The principal component of the Solar System is the Sun, a G-type main-sequence star that contains 99.86% of the system's known mass and dominates it gravitationally. The Sun's four largest orbiting bodies,

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4056-410: The collisions caused their destruction and ejection. The orbits of Solar System planets are nearly circular. Compared to many other systems, they have smaller orbital eccentricity . Although there are attempts to explain it partly with a bias in the radial-velocity detection method and partly with long interactions of a quite high number of planets, the exact causes remain undetermined. The Sun

4134-432: The core will be hot enough for helium fusion; the Sun will burn helium for a fraction of the time it burned hydrogen in the core. The Sun is not massive enough to commence the fusion of heavier elements, and nuclear reactions in the core will dwindle. Its outer layers will be ejected into space, leaving behind a dense white dwarf , half the original mass of the Sun but only the size of Earth. The ejected outer layers may form

4212-518: The date when it was terminated. Additionally, the strategic nature of many space programs result in cooperation between civil agency and military organizations to meet unique staff and technical proficiencies required to support space programs given the geographic expanse required to ensure successful operation. As of 2024, nearly 80 different government space agencies are in existence, including more than 70 national space agencies and several international agencies. Initial competencies demonstrated include

4290-413: The descriptions of the three largest bodies in the asteroid belt. They are all considered to be relatively intact protoplanets , a precursor stage before becoming a fully-formed planet (see List of exceptional asteroids ): Hilda asteroids are in a 3:2 resonance with Jupiter; that is, they go around the Sun three times for every two Jovian orbits. They lie in three linked clusters between Jupiter and

4368-496: The desired orbit/trajectory/landing spot. As far as we know as of the 10th May 2024, five space agencies have achieved the requirements to be listed here: This small group of countries/space agencies have demonstrated the highest technological capacity with systems and solutions that support human spaceflight along with the ancillary technological capabilities to support human activity in orbit and/or on extraterrestrial bodies. The missions identified (and personnel when appropriate) are

4446-441: The early Solar System, but they either merged or were destroyed or ejected, leaving the planets, dwarf planets, and leftover minor bodies . Due to their higher boiling points, only metals and silicates could exist in solid form in the warm inner Solar System close to the Sun (within the frost line ). They would eventually form the rocky planets of Mercury, Venus, Earth, and Mars. Because these refractory materials only comprised

4524-449: The first generation of stars had to die before the universe could be enriched with these atoms. The oldest stars contain few metals, whereas stars born later have more. This higher metallicity is thought to have been crucial to the Sun's development of a planetary system because the planets formed from the accretion of "metals". The region of space dominated by the Solar magnetosphere is

4602-412: The first successful accomplishments of each activity. The annual budgets listed are the official budgets of national space agencies available in public domain. The budgets are not normalized to the expenses of space research in different countries, i.e. higher budget does not necessarily mean more activity or better performance in space exploration. Budget could be used for different projects: e.g. GPS

4680-407: The four inner planets (Venus, Earth, and Mars) have atmospheres substantial enough to generate weather; all have impact craters and tectonic surface features, such as rift valleys and volcanoes. Asteroids except for the largest, Ceres, are classified as small Solar System bodies and are composed mainly of carbonaceous , refractory rocky and metallic minerals, with some ice. They range from

4758-409: The funding and nomination of candidates to serve as astronauts, cosmonauts, or taikonauts with the countries/organizations executing human spaceflight solutions. Other demonstrated capabilities include the operation of a satellite (e.g. a communications or remote sensing system) largely developed and/or delivered by a third party, the domestic development of a satellite system, and the capacity to recover

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4836-441: The giant planets, account for 99% of the remaining mass, with Jupiter and Saturn together comprising more than 90%. The remaining objects of the Solar System (including the four terrestrial planets, the dwarf planets, moons, asteroids , and comets) together comprise less than 0.002% of the Solar System's total mass. The Sun is composed of roughly 98% hydrogen and helium, as are Jupiter and Saturn. A composition gradient exists in

4914-566: The gravitational influence of Neptune's early outward migration . Most scattered disc objects have perihelia within the Kuiper belt but aphelia far beyond it (some more than 150 AU from the Sun). SDOs' orbits can be inclined up to 46.8° from the ecliptic plane. Some astronomers consider the scattered disc to be merely another region of the Kuiper belt and describe scattered-disc objects as "scattered Kuiper belt objects". Some astronomers classify centaurs as inward-scattered Kuiper belt objects along with

4992-454: The identified objective. These listings do not attempt to determine which programs were uniquely or solely funded by the space agency itself. For each listing, the short name or acronym identified is the English version, with the native language version below. The date of the founding of the space agency is the date of first operations where applicable. If the space agency is no longer running, then

5070-415: The larger moons orbit their planets in prograde direction, matching the direction of planetary rotation; Neptune's moon Triton is the largest to orbit in the opposite, retrograde manner. Most larger objects rotate around their own axes in the prograde direction relative to their orbit, though the rotation of Venus is retrograde. To a good first approximation, Kepler's laws of planetary motion describe

5148-491: The largest natural satellites are in synchronous rotation , with one face permanently turned toward their parent. The four giant planets have planetary rings, thin discs of tiny particles that orbit them in unison. As a result of the formation of the Solar System , planets and most other objects orbit the Sun in the same direction that the Sun is rotating. That is, counter-clockwise, as viewed from above Earth's north pole. There are exceptions, such as Halley's Comet . Most of

5226-422: The level of cosmic-ray penetration in the Solar System varies, though by how much is unknown. The zone of habitability of the Solar System is conventionally located in the inner Solar System, where planetary surface or atmospheric temperatures admit the possibility of liquid water . Habitability might be possible in subsurface oceans of various outer Solar System moons. Compared to many extrasolar systems,

5304-443: The main asteroid belt. Trojans are bodies located within another body's gravitationally stable Lagrange points : L 4 , 60° ahead in its orbit, or L 5 , 60° behind in its orbit. Every planet except Mercury and Saturn is known to possess at least 1 trojan. The Jupiter trojan population is roughly equal to that of the asteroid belt. After Jupiter, Neptune possesses the most confirmed trojans, at 28. The outer region of

5382-400: The mass orbiting the Sun. All four giant planets have multiple moons and a ring system, although only Saturn's rings are easily observed from Earth. Jupiter and Saturn are composed mainly of gases with extremely low melting points, such as hydrogen, helium, and neon , hence their designation as gas giants . Uranus and Neptune are ice giants , meaning they are largely composed of 'ice' in

5460-402: The orbits of objects around the Sun. These laws stipulate that each object travels along an ellipse with the Sun at one focus , which causes the body's distance from the Sun to vary over the course of its year. A body's closest approach to the Sun is called its perihelion , whereas its most distant point from the Sun is called its aphelion . With the exception of Mercury, the orbits of

5538-464: The planets are nearly circular, but many comets, asteroids, and Kuiper belt objects follow highly elliptical orbits. Kepler's laws only account for the influence of the Sun's gravity upon an orbiting body, not the gravitational pulls of different bodies upon each other. On a human time scale, these perturbations can be accounted for using numerical models , but the planetary system can change chaotically over billions of years. The angular momentum of

5616-415: The primary characteristic of the Solar System enabling the presence of life is the heliosphere and planetary magnetic fields (for those planets that have them). These magnetic fields partially shield the Solar System from high-energy interstellar particles called cosmic rays . The density of cosmic rays in the interstellar medium and the strength of the Sun's magnetic field change on very long timescales, so

5694-507: The remaining gas and dust from the protoplanetary disc into interstellar space. Following the dissipation of the protoplanetary disk , the Nice model proposes that gravitational encounters between planetisimals and the gas giants caused each to migrate into different orbits. This led to dynamical instability of the entire system, which scattered the planetisimals and ultimately placed the gas giants in their current positions. During this period,

5772-404: The solar wind is halted, resulting in the heliopause . This is the boundary of the Solar System to interstellar space . The outermost region of the Solar System is the theorized Oort cloud , the source for long-period comets , extending to a radius of 2,000–200,000 AU . The closest star to the Solar System, Proxima Centauri , is 4.25 light-years (269,000 AU) away. Both stars belong to

5850-480: The terrestrial inner planets, allowing them to grow massive enough to capture large atmospheres of hydrogen and helium, the lightest and most abundant elements. Leftover debris that never became planets congregated in regions such as the asteroid belt, Kuiper belt, and Oort cloud. Within 50 million years, the pressure and density of hydrogen in the center of the protostar became great enough for it to begin thermonuclear fusion . As helium accumulates at its core,

5928-456: The total mass of the Kuiper belt is thought to be only a tenth or even a hundredth the mass of Earth. Many Kuiper belt objects have satellites, and most have orbits that are substantially inclined (~10°) to the plane of the ecliptic. The Kuiper belt can be roughly divided into the " classical " belt and the resonant trans-Neptunian objects . The latter have orbits whose periods are in a simple ratio to that of Neptune: for example, going around

6006-430: Was provided by five layers of aluminized PET film ( Mylar ), alternating with four layers of nonwoven Dacron , which provided thermal spacing, followed by two layers of aluminized polyimide Kapton film and Beta cloth marquisette laminate. The outermost layer of PTFE ( Teflon )-coated filament Beta cloth was non-flammable and provided abrasion protection from the notoriously abrasive lunar dust . This layer

6084-565: Was supplemented with Teflon abrasion patches at the knees and other areas. The construction of the TMG on the EMU suits in use on the Space Shuttle and International Space Station differs somewhat from the construction of the Apollo/Skylab TMG. The EMU TMG includes seven layers of aluminized Mylar laminated with Dacron, rather than five, and eliminates the use of Kapton. The outermost layer

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