History UsefulNotes / TheSolarSystem

20th Feb '17 4:28:00 PM ScorpiusOB1
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[[TakingYouWithMe The revenge of those protoplanets and other debris]] came four billion years ago in the form of a large number of them ending up in the inner Solar System, where they [[ColonyDrop pummeled to death]] the more or less formed terrestrial planets, scarring them with countless craters and causing quite a lot of damage to them[[note]]In the case of Earth, the heaviest impacts would have been enough to vaporize the oceans and even melt the crust in [[TabletopGame/Warhammer40000 Exterminatus]] fashion, wrapping the planet in an atmosphere of molten rock and water vapor for some time. It's not know if life had formed by then but if had it existed it would have been destroyed in the most violent collisions. Perhaps life formed several times, just to being destroyed again when a large impactor came crashing again, or it survived sheltered deep into Earth's crust or in the very deepest oceans. On a more positive note, it's thought those impacts brought still more water to Earth[[/note]]. This hellish rain may have lasted a few hundred million years, and was the last event of significance in the Solar System[[note]]On a more domestic scale, the remaining asteroids [[AsteroidMonster pummeled among themselves]] in the belt further reducing the population of large bodies and producing many smaller ones, and giant planets would have captured some of those floating rocks as moons (one of them ''very'' large -ask Neptune's Triton-). Venus, that could have been an Earth-like planet became the [[DeathWorld hellish world]] that is now because of its closeness to the Sun, and Mars being too small perhaps thanks to Jupiter's journey, lost its protecting magnetic field and with it most of its atmosphere and the liquid water it's now it had in those epochs[[/note]]. From there until now, little has happened in the Solar System in a global scale besides the occasional impact here and there of a stray asteroid or comet, the star passing across the Oort cloud[[note]]Ask [[https://en.wikipedia.org/wiki/Gliese_710 Gliese 710]][[/note]] sending a shower of comets to the inner Solar System, and a Sun that as it ages becomes more luminous[[note]]As it fuses the hydrogen on its core, the latter contracts increasing its temperature causing an increase of the fusion rate and thus of the released energy and so on. As there's no convection in the inner regions of the Sun, just the outermost ones, our star cannot use all of its nuclear fuel.[[/note]]


to:

[[TakingYouWithMe The revenge of those protoplanets and other debris]] came four billion years ago in the form of a large number of them ending up in the inner Solar System, where they [[ColonyDrop pummeled to death]] the more or less formed terrestrial planets, scarring them with countless craters and causing quite a lot of damage to them[[note]]In the case of Earth, the heaviest impacts would have been enough to vaporize the oceans and even melt the crust in [[TabletopGame/Warhammer40000 Exterminatus]] fashion, wrapping the planet in an atmosphere of molten rock and water vapor for some time. It's not know if life had formed by then but if had it existed it would have been destroyed in the most violent collisions. Perhaps life formed several times, just to being destroyed again when a large impactor came crashing again, or it survived sheltered deep into Earth's crust or in the very deepest oceans. On a more positive note, it's thought those impacts brought still more water to Earth[[/note]]. This hellish rain may have lasted a few hundred million years, and was the last event of significance in the Solar System[[note]]On a more domestic scale, the remaining asteroids [[AsteroidMonster [[AsteroidsMonster pummeled among themselves]] in the belt further reducing the population of large bodies and producing many smaller ones, and giant planets would have captured some of those floating rocks as moons (one of them ''very'' large -ask Neptune's Triton-). Venus, that could have been an Earth-like planet became the [[DeathWorld hellish world]] that is now because of its closeness to the Sun, and Mars being too small perhaps thanks to Jupiter's journey, lost its protecting magnetic field and with it most of its atmosphere and the liquid water it's now it known to have had in those epochs[[/note]]. From there until now, little has happened in the Solar System in a global scale besides the occasional impact here and there of a stray asteroid or comet, the star passing across the Oort cloud[[note]]Ask [[https://en.wikipedia.org/wiki/Gliese_710 Gliese 710]][[/note]] sending a shower of comets to the inner Solar System, and a Sun that as it ages becomes more luminous[[note]]As it fuses the hydrogen on its core, the latter contracts increasing its temperature causing an increase of the fusion rate and thus of the released energy and so on. As there's no convection in the inner regions of the Sun, just the outermost ones, our star cannot use all of its nuclear fuel.[[/note]]

16th Feb '17 8:38:25 PM dogman15
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Turning to nomenclature on a smaller scale, the New Horizons probe will reach Pluto and Charon in July 2015, giving cartographers at least two whole new worlds worth of craters, mountains, and other points of interest to name. Current plans are to name features after various underworld locations and their denizens, spacecraft and space scientists, explorers and their vessels (real and fictional), and artists and authors whose works have depicted exploration. [[http://www.ourpluto.org/ A page has been set up]] to allow people to vote for names to be submitted to the IAU for official use, so cast your vote for a real-life [[Series/{{Firefly}} Vallis Serenity]], [[Literature/WatershipDown Colles Watership]], and [[Series/BabylonFive Regio Z'ha'dum]]! [[note]]sorry, [[Franchise/StarTrek Trekkers]], but [[http://planetarynames.wr.usgs.gov/Feature/15133?__fsk=1962724877 there's already an Enterprise Rupes]] on Mercury.[[/note]][[note]]Sorry, voting was closed back on 24 April 2015[[/note]]

to:

Turning to nomenclature on a smaller scale, the New Horizons probe will reach reached Pluto and Charon in July 2015, giving cartographers at least two whole new worlds worth of craters, mountains, and other points of interest to name. Current plans are to name features after various underworld locations and their denizens, spacecraft and space scientists, explorers and their vessels (real and fictional), and artists and authors whose works have depicted exploration. [[http://www.ourpluto.org/ A page has been set up]] to allow people to vote for names to be submitted to the IAU for official use, so cast your vote for a real-life [[Series/{{Firefly}} Vallis Serenity]], [[Literature/WatershipDown Colles Watership]], and [[Series/BabylonFive Regio Z'ha'dum]]! [[note]]sorry, [[Franchise/StarTrek Trekkers]], but [[http://planetarynames.wr.usgs.gov/Feature/15133?__fsk=1962724877 there's already an Enterprise Rupes]] on Mercury.[[/note]][[note]]Sorry, voting was closed back on 24 April 2015[[/note]]
13th Feb '17 7:22:40 AM ScorpiusOB1
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As for the future, things will not change very much for the Solar System ''as a whole'' during the next five billion years[[note]]Some calculations simulations give a very small probability within that timeframe of either Mercury going haywire and being ejected of the Solar Sytem if it does not crash before into either Venus or Earth, or Mars colliding with Earth. Sleep well, it will ''not'' happen tomorrow. [[ParanoiaFuel We think]][[/note]]. Sure, the orbits of some moons such as Mars' Phobos or Neptune's Triton will decay and the latter will produce both a ''hell'' of a meteor shower and a splendid ring system around its planet, there will continue being the occasional asteroid/impact here and there, the occasional star passing too close and shaking the Oort Cloud sending comets to the inner Solar System, [[ArsonMurderAndJaywalking and the Earth becoming unhabitable]] because of a Sun that is brightening with time as described above but if we could see the Solar System by then it is expected we'd see something very similar to the current one[[note]OK, the Andromeda Galaxy and the Milky Way are expected to [[FusionDance merge]] around those ages and the Sun will end up on the outskirts of the newly-formed galaxy, if not thrown out to intergalactic space (it will come back much later, though), but unless we've ''very'' bad luck the collision will not affect us[[/note]].

to:

As for the future, things will not change very much for the Solar System ''as a whole'' during the next five billion years[[note]]Some calculations simulations give a very small probability within that timeframe of either Mercury going haywire and being ejected of the Solar Sytem if it does not crash before into either Venus or Earth, or Mars colliding with Earth. Sleep well, it will ''not'' happen tomorrow. [[ParanoiaFuel We think]][[/note]]. Sure, the orbits of some moons such as Mars' Phobos or Neptune's Triton will decay and the latter will produce both a ''hell'' of a meteor shower and a splendid ring system around its planet, there will continue being the occasional asteroid/impact here and there, the occasional star passing too close and shaking the Oort Cloud sending comets to the inner Solar System, [[ArsonMurderAndJaywalking and the Earth becoming unhabitable]] because of a Sun that is brightening with time as described above but if we could see the Solar System by then it is expected we'd see something very similar to the current one[[note]OK, one[[note]]OK, the Andromeda Galaxy and the Milky Way are expected to [[FusionDance merge]] around those ages and the Sun will end up on the outskirts of the newly-formed galaxy, if not thrown out to intergalactic space (it will come back much later, though), but unless we've ''very'' bad luck the collision will not affect us[[/note]].
13th Feb '17 7:19:20 AM ScorpiusOB1
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The Solar System was born more or less four thousand and a half billion years ago from the collapse of a large gas cloud, that as typical per the process of star formation fragmented into many smaller ones[[note]]There's strong evidence that one or several supernovae, the deaths of massive star, may have triggered this proces. It, as well as others, show that our Sun was born in a large star-forming region of the style of the [[https://en.wikipedia.org/wiki/Orion_Nebula Orion nebula]], forming part of a large star cluster (imagine the [[AlienSky star-studded sky in that epoch]]. Its brothers and sisters are somewhere in the Milky Way, perhaps even with planets where life has developed too[[/note]]. One of said fragments, as it collapsed, began spin faster flattening and taking a flying saucer-like shape. Its center, as it collapsed, became hotter and denser until hydrogen fusion began at its very center. The Sun was born[[note]]Our daystar was during those early epochs a very different one: larger, cooler, and more luminous during its contraction, covered by sunspots, and more active with strong flare activity. When hydrogen ignited, while less luminous than now, it kept said activity with sunspots and flares galore and a ''very'' powerful solar wind until a few million years later it calmed somewhat, especially said wind.

to:

The Solar System was born more or less four thousand and a half billion years ago from the collapse of a large gas cloud, that as typical per the process of star formation fragmented into many smaller ones[[note]]There's strong evidence that one or several supernovae, the deaths of massive star, may have triggered this proces. It, as well as others, show that our Sun was born in a large star-forming region of the style of the [[https://en.wikipedia.org/wiki/Orion_Nebula Orion nebula]], forming part of a large star cluster (imagine the [[AlienSky star-studded sky in that epoch]]. Its brothers and sisters are somewhere in the Milky Way, perhaps even with planets where life has developed too[[/note]]. One of said fragments, as it collapsed, began spin faster flattening and taking a flying saucer-like shape. Its center, as it collapsed, became hotter and denser until hydrogen fusion began at its very center. The Sun was born[[note]]Our daystar was during those early epochs a very different one: larger, cooler, and more luminous during its contraction, covered by sunspots, and more active with strong flare activity. When hydrogen ignited, while less luminous than now, it kept said activity with sunspots and flares galore and a ''very'' powerful solar wind until a few million years later it calmed somewhat, especially said wind.
wind.[[/note]]
13th Feb '17 7:17:33 AM ScorpiusOB1
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Galaxies as you surely know are large conglomerates of stuff we can see -stars (depending on the galaxy) of all types, gas, and dust[[note]]And in "dust" we include stuff such as planets, asteroids, comets... that while they outnumber in number stars one cannot say the same in what refers to their mass[[/note]]-, and other we cannot see but can be detected because of its gravitational influence -dark matter-[[note]]At least this is what most astronomers think.[[/note]].

Some history.

Believe it or not, but that galaxies are, well, galaxies is something known with certainly for less than a century. Even if the existence of a "small cloud in the constellation of Andromeda"[[note]]The famous Andromeda Galaxy, known for centuries as the "Andromeda Nebula"[[/note]] was known for centuries[[note]]Same for the Clouds of Magellan.[[/note]], and once the telescope was invented more of those clouds appeared galore they were considered as mere nebulae within the Milky Way with the exception of the Magellanic Clouds[[note]]Named so by the Portuguese explorer Ferdinand Magellan, who described them in the XVI century. However they were known since prehistoric times by people who lived in the Southern Hemisphere[[/note]], that were proved by telescopic observations to be galaxies of their own. Simply put, telescopes of the time lacked enough power to see them resolved into stars and it was not until TheRoaringTwenties. and later when it was proven without doubt those "nebulae" were actually something very different and much larger and more distant.


Classificating galaxies: putting order in the sky (or at least attempting that).

Of course with galaxies sprinkling the sky it was just matter of time astronomers decided to classify them. The most known of the schemes used to classify galaxies is the one developed by the American astronomer Edwin Powell Hubble[[note]]Yes, his name is where the name of that famous space telescope comes from[[/note]], and its a testament to its usefulness how despite having been expanded and somewhat tweaked it's still in use. On it Hubble classified galaxies into the following types:

Elliptical galaxies.

Elliptical galaxies are, well, galaxies that look more or less elliptical. Its actual shape range is an ellipsoid more or less flattened, from almost spherical to a football (rugby)-shaped system. They're also systems usually predominantly composed of old low-mass stars, giving them a yellow-orange hue on color images, usually with very little -if any- star formation, interstellar dust or (cold) gas[[note]]Hot gas, detectable thanks to its emission of X-Rays may be much more abundant[[/note]]. They're subclassified depending of how elongated they appear from E0 (spherical) to E7 (very elongated; above it a galaxy would become unstable and would puff up)[[note]]However, some flattened ellipticals can look spherical seen from certain angles[[/note]].

That's, however, the unique properties they've in common: ellipticals have the widest range of mass, sizes, and luminosities of all galaxies from tiny systems so faint that are outshined ''even by luminous stars'' (read: standard red giants), are very hard to detect, and are thought to be composed almost entirely dark matter to humongous galaxies tens of times more luminous than ours -which already is a good-sized one- whose haloes may extend up to millions of light-years away, that are considered the largest and most luminous ones known. Dinamically they show also a large variety: in the most massive ellipticals the stars move in random orbits around the center ("boxy ellipticals". Think on a swarm of angry bees), while moderately luminous ones have what seems to be a disk of stars embedded in the center ("disky ellipticals") and finally at least some of the less luminous ones have most, if not all, the stars in a disk -these systems are common on galaxy clusters-. Density also varies a lot: the already mentioned very low-luminosity systems -just as the haloes of those very luminous galaxies- are so scattered that are very difficult to see, and some recently discovered similar galaxies take that UpToEleven, being as large as our galaxy but of so low surface brightness that needed very powerful telescopes[[note]]Those galaxies were found on rich galaxy clusters, and that may hold clues to their origins[[/note]], and in the opposite side we've compact ellipticals (most, if not all of them, of low luminosity) where stars are so tightly packed (some recently discovered systems take this also UpToEleven, being considered ultracompact) that from our perspective may look star-like[[note]]M32, a satellite galaxy of the Andromeda Galaxy, is the nearest and best studied of those compact systems[[/note]]. Massive (often supermassive) black holes are usually found in the centers of most ellipticals of moderate luminosity upwards and specially the most luminous systems are typically hosts to large populations of globular clusters[[note]]Densely packed clusters of usually old stars. They are also present in other galaxy types, not just ellipticals[[/note]] (up to thousands or even more).

How did elliptical galaxies form?. Current understanding shows that their origins are very varied: the less luminous systems are expected to be what remains of the numerous low-mass irregular galaxies (see entry below for them) that formed in the earliest moments of the Universe and that [[FusionDance coalesced]] to form large ones as ours. These systems were originally gas-rich, but their weak gravity would not allow them to hold the gas that would be blown apart either by supernovae and/or interactions with nearby, more massive galaxies. No gas means no new stars, so as time passed by and stars died away just low-mass ones would remain. "Disky" low-luminosity elliptical galaxies are expected to have suffered a similar fate, except that their gas was blown away by interactions with the hot, low-density, gas expected to fill the intergalactic space in rich galaxy clusters -plus in some cases interactions with other galaxies of the cluster ("galaxy harassment") would warp them giving an elliptical look-, and talking about harassment the compact and ultracompact may be all what remains of a considerably larger away that was threshed away by a much larger one[[note]]Gravitational interactions would have funneled gas to the center of the doomed galaxy, feeding a powerful starburst that would have produced those tightly packed stars[[/note]].

Going upwards in mass, however, mergers are expected to be responsible of the origin of moderately luminous ellipticals and up. Things begin when two gas-rich spiral galaxies collide and distort themselves forming in the process a whole lot of stars and clusters, including massive ones that will become globular clusters in the future, and when they merge funneling gas to the center where once the gas is both exhausted by even stronger star formation activity and carried away by supernovae and strong stellar winds -or even a quasar-, a dense disk of stars within the elliptical's main body is unveiled. Later they continue when two or more of said "disky" ellipticals collide and merge again -with no or very little available gas there will be very few or no star formation, hence a "dry merger"- destroying said disks and forming a "boxy" one. In rich galaxy clusters, the pile-up continues and eventually a humongous elliptical galaxy forms, usually in the center[[note]]If we fast-forward in time, those galaxies will keep growing [[/note]].




Virgo: the nearest galaxy cluster.

The closest large agrupation of galaxies to us is the Virgo Cluster[[note]]Named so because it's in the constellation of Virgo, the Maiden.[[/note]]. It's estimated it contains around 2,000 galaxies[[note]]Most of these galaxies are dwarf ellipticals, however[[/note]], with a mass of around 1 quadrillion solar masses[[note]]And as large that it may be it's not a particularly massive cluster.[[/note]]. Its center is estimated to lie at a distance of 50-55 million light-years from the Milky Way.

Virgo contains all the things one could expect on a galaxy cluster: a giant elliptical galaxy on its center, galaxies of all sizes and types from dwarf to giant ones, hot gas that fills the intergalactic space, and lots of dark matter.

Probably the most conspicuous galaxy on Virgo is Messier 87, the already mentioned giant galaxy placed at its center[[note]]But not the brightest, that honor goes to Messier 49[[/note]]


While from our perspective looks very roughly spherical, improved studies of the distances to its galaxies show it's actually a large filament that points more or less towards our position in the sky.












Steady state

Another issue with this theory is that if it was true we'd see everywhere and not just at high redshifts galaxies in all their evolutionary stages, from pristine gas clouds to others in quasar mode and/or bursting with countless young stars, and finally mature systems as ours. They'd have just hydrogen and not heavier elements, as just the former is being formed ''ex-nihilo'', but all systems observed to date have hydrogen ''and'' helium in agreement with the Big Bang theory. Even with an expanding Universe carrying away the old galaxies some legacy of them should be visible beyond as a cosmic microwave background very different as the real one (see also [[Quasi-Steady_State_Cosmology|below]]), including with some luck systems much older than ours.


==How theories might be disproved==
Although cosmological theories and hypotheses in general are difficult to disprove, strong evidence against them might be found. Maybe five years or more after the James Webb space telescope and the Atacama long baseline radio-scopes are fully functional, expected to be about 2024, cosmological models of an older or infinite-age universe would predict that they will have found at the farthest observable distances some old, very large and red appearing elliptical and spiral galaxies, maybe with observably high metallicity. This would be strong evidence that the universe is much older and that the Big Bang model would likely be wrong. On the other hand, if only small young, blue-appearing galaxies with minimal metallicity were instead observed at these farthest distances (with no old appearing large galaxies), then all theories and hypothesis proposing an older or infinite age universe seemingly would also most likely be wrong — which would include nearly all of the alternative cosmologies above.

Another issue comes from the [[Drake_Equation#Fermi_paradox|Fermi paradox]]. With an infinite ''and'' infinitely old Universe, no matter how rare would be for an advanced civilization to appear and expand elsewhere; having an eternity, '''a whole lot''' of them would have appeared and even if any of those civilizations had not come here before or contacted with us, [[https://en.wikipedia.org/wiki/Kardashev_scale|the evidences of their existence]] would be detectable elsewhere.


===The evidence is already there, but we can't detect it===
The possibilities range from a [[conspiracy theory|government conspiracy]] to withhold contact to messages/media that are quite literally too "alien" for us to perceive. (''e.g.'' Our own era of pumping out vast quantities of easily-decoded AM audio and video may only run about a hundred years, as broadcasting shifts to digital encoding with the frequency spectrum of white noise if you don't know what's encoded in it. Other possibilities include those hypothetical aliens not broadcasting in the frequencies where we're looking for them, not ''broadcasting'' but instead sending highly focused (and less expensive in energetic terms but much harder to detect) transmissions, and more especulative ideas such as them not using radio waves but instead lasers and even other methods such as neutrinos or stuff that we may not even know that exists as "hyperspace" or "wormholes" (assuming those things ''existed at all'', that is.)

13th Feb '17 7:16:12 AM ScorpiusOB1
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As for the future, things will not change very much for the Solar System ''as a whole'' during the next five billion years[[note]]Some calculations simulations give a very small probability within that timeframe of either Mercury going haywire and being ejected of the Solar Sytem if it does not crash before into either Venus or Earth, or Mars colliding with Earth. Sleep well, it will ''not'' happen tomorrow. [[ParanoiaFuel We think]][[/note]]. Sure, the orbits of some moons such as Mars' Phobos or Neptune's Triton will decay and the latter will produce both a ''hell'' of a meteor shower and a splendid ring system around its planet, there will be the occasional asteroid/impact here and there, the occasional star passing too close[[note]]Ask [[https://en.wikipedia.org/wiki/Gliese_710 Gliese 710]][[/note]] will shake the Oort Cloud sending comets to the inner Solar System, [[ArsonMurderAndJaywalking and the Earth will become unhabitable]] as the Sun is becoming more luminous as it ages but if we could see the Solar System by then it is expected we'd see something very similar to the current one[[note]]OK, the Andromeda Galaxy and the Milky Way are expected to [[FusionDance merge]] around those ages and the Sun will end up on the outskirts of the newly-formed galaxy, if not thrown out to intergalactic space (it will come back much later, though), but unless we've ''very'' bad luck the collision will not affect us[[/note]].
Five billion years was not chosen at random for the fate of our Solar System is tightly tied to the one of its most massive body: the Sun. By that epoch it will have run out of hydrogen at its center and things will become interesting, so let's fast forward to the year [[TimeAbyss 7,590,000,000 AD]]. In that year our familiar Sun will be in [[OneWingedAngel full red giant-mode]]: a bloated and distorted star with a surface temperature having dropped to half of what it had in our epoch, thousands of times more luminous and more than two hundred times larger than our daystar[[note]]Why?. Hydrogen is intensely fusing around the small, hydrogen-exhausted, dense core of inert helium, that as it contracted caused first the hydrogen surrounding it to start fusing, and later as temperatures increased to fuse more and more intensely[[/note]], and so big that has lost more than a quarter of its mass carried away by strong solar winds, something that has caused the planet's orbits to wide, but not enough to avoid searing hot temperatures or worse[[note]]For the details: Mercury and Venus are history, having been engulfed millions of years before by the expanding Sun but not before having been roasted to Hell and back -and Venus having lost its atmosphere (poor Venus, she cannot catch a break)-. Earth, with no atmosphere to speak of and [[DeathWorld with a surface temperature of more than one thousand five hundred degrees Celsius]], is a LethalLavaLand precariously clinging to its orbit under an angry Sun that fills a whole lot of its sky and is very likely doomed to suffer the same fate than the two innermost planets. Mars is another LethalLavaLand that (we think) will survive the ordeal. Of the giant planets, temperatures will vary between the searing hot ones of Jupiter (higher than those at Mercury, but at least it could manage to accrete ''some'' (it will certainly ''not'' capture enough to be significant, much less to become a star) of the matter expelled by the Sun) and the rather Earth-like ones of Neptune, with their icy moons looking like huge comets, evaporating under the intense sunlight and probably after for a time their surfaces had melt giving pressure cooker-like conditions to the rocky surfaces below all that ice in some cases as Europa or Ganymede. The smallest bodies -asteroids and comets-, even as far as the Kuiper Belt, not only will have to contend with the intense heat but also with the mess caused to their orbits by the mass loss of the dying Sun, meaning that some of them will be ejected out of the Solar System and others will either crash with the remaining planets or into the Sun[[/note]]. It will also be the time when the Sun will suffer a dramatic transformation: the dense, inert helium core will ignite and will produce for a few seconds ''as much energy as an entire galaxy''. While this looks like a supernova, that energy will actually just be used to re-expand the core and nothing of that will be seen at its surface -in fact, with the Sun's innards expanding to fuse helium stably it will release less energy and will collapse back to a much smaller and less luminous star a bit more hot than its red giant past (somewhat more than four thousand degrees Celsius), but still quite luminous (forty-fifty times more) and large (ten times larger) compared with its past long-lived incarnation[[note]]Whatever remains of the inner Solar System -perhaps only Mars- will be hotter than Mercury. Farther away, Jupiter will enjoy Earth-like temperatures and even farther our things will freeze again. Meanwhile, asteroids and the like will keep their dance of death[[/note]]. Unfortunately for the Sun helium, fusing to produce carbon and oxygen, is a worse fuel than hydrogen and even if helium burning its supported by some hydrogen fusing around the core will run out of it in just a hundred million years and then the Sun will face a similar crisis to the one it faced when it ran out of hydrogen. Only this time said crisis will be fatal.
As happened with hydrogen before, helium will begin to fuse around an inert contracting core of carbon and oxygen. Further out, hydrogen will fuse to helium and as the core contracts it will "squeeze" those two burning shells causing them to fuse with force. The result is that the Sun will become again -in just twenty million years compared to the considerably longer time it needed to expand for the first time- a huge and luminous red giant suffering even stronger mass loss but, as helium burning under those extreme conditions is ''highly'' sensitive to the temperature[[note]]It scales as the temperature ''to the fortieth power''. Guess how nasty would be even small variations[[/note]], [[ClippedWingAngel an unstable one]]. Each hundred thousand years, the Sun will convulse suffering a pulse caused by a runaway helium ignition that will increase its luminosity as well as it radius just to contract and having things starting again. Those violent pulses will increase even more the already heavy mass loss as mentioned before, and by the fourth one all that will remain of the Sun will be the ''extremely'' hot -one hundred thousand degrees Celsius- and dense, as it has contracted to the size of the Earth, carbon-oxygen core half as massive as the Sun is now: a white dwarf. If the Sun is luminous enough, its ultraviolet radiation will cause the matter that ejected before to fluoresce as a beautiful [[https://en.wikipedia.org/wiki/Planetary_nebula planetary nebula]], that will however be short-lived as a few thousand years later both the gases will be rarefied and far away enough and the white dwarf's ultraviolet radiation will fade away as it begins to cool to stop shining. All that will remain to the dead white dwarf Sun is to keep cooling over [[TimeAbyss many billions of years]] until it will fade into oblivion as a black dwarf -or, if you prefer it, as a big and dense diamond as all those carbon will crystalize during said cooling-[[note]]No, we have not forgotten the planets and all that other stuff. Things will be as during the red giant stage, but this time ''harder'', as the Sun's convulsions will cause severe variations of temperature and will be pummeled by the matter expelled in the pulses. The worst, however, will come because of that severe mass drain with the Solar System becoming an even more of a mess with many small bodies, and perhaps even planets, having their orbits more or less dislocated with all that means -collisions either among them or the Sun, things being flung out, etc-. Said mess is expected to continue into the planetary nebula and white dwarf stages (it's conceivable its UV flux will be more or less nasty for the orbiting bodies), and whatever survives the ordeal -odds are that Jupiter at the very least- will see the dark, cold, veil of an endless night being put over it. The end... or is it?. [[TimeAbyss Time will keep going on]], and stars passing too close will begin to strip the dead Sun of its remaining retinue of planets. It has been estimated that in a ''quadrillion'' (ten to the fifteenth) years, it will have lost all of them.[[/note]]

to:

Galaxies as you surely know are large conglomerates of stuff we can see -stars (depending on the galaxy) of all types, gas, and dust[[note]]And in "dust" we include stuff such as planets, asteroids, comets... that while they outnumber in number stars one cannot say the same in what refers to their mass[[/note]]-, and other we cannot see but can be detected because of its gravitational influence -dark matter-[[note]]At least this is what most astronomers think.[[/note]].

Some history.

Believe it or not, but that galaxies are, well, galaxies is something known with certainly for less than a century. Even if the existence of a "small cloud in the constellation of Andromeda"[[note]]The famous Andromeda Galaxy, known for centuries as the "Andromeda Nebula"[[/note]] was known for centuries[[note]]Same for the Clouds of Magellan.[[/note]], and once the telescope was invented more of those clouds appeared galore they were considered as mere nebulae within the Milky Way with the exception of the Magellanic Clouds[[note]]Named so by the Portuguese explorer Ferdinand Magellan, who described them in the XVI century. However they were known since prehistoric times by people who lived in the Southern Hemisphere[[/note]], that were proved by telescopic observations to be galaxies of their own. Simply put, telescopes of the time lacked enough power to see them resolved into stars and it was not until TheRoaringTwenties. and later when it was proven without doubt those "nebulae" were actually something very different and much larger and more distant.


Classificating galaxies: putting order in the sky (or at least attempting that).

Of course with galaxies sprinkling the sky it was just matter of time astronomers decided to classify them. The most known of the schemes used to classify galaxies is the one developed by the American astronomer Edwin Powell Hubble[[note]]Yes, his name is where the name of that famous space telescope comes from[[/note]], and its a testament to its usefulness how despite having been expanded and somewhat tweaked it's still in use. On it Hubble classified galaxies into the following types:

Elliptical galaxies.

Elliptical galaxies are, well, galaxies that look more or less elliptical. Its actual shape range is an ellipsoid more or less flattened, from almost spherical to a football (rugby)-shaped system. They're also systems usually predominantly composed of old low-mass stars, giving them a yellow-orange hue on color images, usually with very little -if any- star formation, interstellar dust or (cold) gas[[note]]Hot gas, detectable thanks to its emission of X-Rays may be much more abundant[[/note]]. They're subclassified depending of how elongated they appear from E0 (spherical) to E7 (very elongated; above it a galaxy would become unstable and would puff up)[[note]]However, some flattened ellipticals can look spherical seen from certain angles[[/note]].

That's, however, the unique properties they've in common: ellipticals have the widest range of mass, sizes, and luminosities of all galaxies from tiny systems so faint that are outshined ''even by luminous stars'' (read: standard red giants), are very hard to detect, and are thought to be composed almost entirely dark matter to humongous galaxies tens of times more luminous than ours -which already is a good-sized one- whose haloes may extend up to millions of light-years away, that are considered the largest and most luminous ones known. Dinamically they show also a large variety: in the most massive ellipticals the stars move in random orbits around the center ("boxy ellipticals". Think on a swarm of angry bees), while moderately luminous ones have what seems to be a disk of stars embedded in the center ("disky ellipticals") and finally at least some of the less luminous ones have most, if not all, the stars in a disk -these systems are common on galaxy clusters-. Density also varies a lot: the already mentioned very low-luminosity systems -just as the haloes of those very luminous galaxies- are so scattered that are very difficult to see, and some recently discovered similar galaxies take that UpToEleven, being as large as our galaxy but of so low surface brightness that needed very powerful telescopes[[note]]Those galaxies were found on rich galaxy clusters, and that may hold clues to their origins[[/note]], and in the opposite side we've compact ellipticals (most, if not all of them, of low luminosity) where stars are so tightly packed (some recently discovered systems take this also UpToEleven, being considered ultracompact) that from our perspective may look star-like[[note]]M32, a satellite galaxy of the Andromeda Galaxy, is the nearest and best studied of those compact systems[[/note]]. Massive (often supermassive) black holes are usually found in the centers of most ellipticals of moderate luminosity upwards and specially the most luminous systems are typically hosts to large populations of globular clusters[[note]]Densely packed clusters of usually old stars. They are also present in other galaxy types, not just ellipticals[[/note]] (up to thousands or even more).

How did elliptical galaxies form?. Current understanding shows that their origins are very varied: the less luminous systems are expected to be what remains of the numerous low-mass irregular galaxies (see entry below for them) that formed in the earliest moments of the Universe and that [[FusionDance coalesced]] to form large ones as ours. These systems were originally gas-rich, but their weak gravity would not allow them to hold the gas that would be blown apart either by supernovae and/or interactions with nearby, more massive galaxies. No gas means no new stars, so as time passed by and stars died away just low-mass ones would remain. "Disky" low-luminosity elliptical galaxies are expected to have suffered a similar fate, except that their gas was blown away by interactions with the hot, low-density, gas expected to fill the intergalactic space in rich galaxy clusters -plus in some cases interactions with other galaxies of the cluster ("galaxy harassment") would warp them giving an elliptical look-, and talking about harassment the compact and ultracompact may be all what remains of a considerably larger away that was threshed away by a much larger one[[note]]Gravitational interactions would have funneled gas to the center of the doomed galaxy, feeding a powerful starburst that would have produced those tightly packed stars[[/note]].

Going upwards in mass, however, mergers are expected to be responsible of the origin of moderately luminous ellipticals and up. Things begin when two gas-rich spiral galaxies collide and distort themselves forming in the process a whole lot of stars and clusters, including massive ones that will become globular clusters in the future, and when they merge funneling gas to the center where once the gas is both exhausted by even stronger star formation activity and carried away by supernovae and strong stellar winds -or even a quasar-, a dense disk of stars within the elliptical's main body is unveiled. Later they continue when two or more of said "disky" ellipticals collide and merge again -with no or very little available gas there will be very few or no star formation, hence a "dry merger"- destroying said disks and forming a "boxy" one. In rich galaxy clusters, the pile-up continues and eventually a humongous elliptical galaxy forms, usually in the center[[note]]If we fast-forward in time, those galaxies will keep growing [[/note]].




Virgo: the nearest galaxy cluster.

The closest large agrupation of galaxies to us is the Virgo Cluster[[note]]Named so because it's in the constellation of Virgo, the Maiden.[[/note]]. It's estimated it contains around 2,000 galaxies[[note]]Most of these galaxies are dwarf ellipticals, however[[/note]], with a mass of around 1 quadrillion solar masses[[note]]And as large that it may be it's not a particularly massive cluster.[[/note]]. Its center is estimated to lie at a distance of 50-55 million light-years from the Milky Way.

Virgo contains all the things one could expect on a galaxy cluster: a giant elliptical galaxy on its center, galaxies of all sizes and types from dwarf to giant ones, hot gas that fills the intergalactic space, and lots of dark matter.

Probably the most conspicuous galaxy on Virgo is Messier 87, the already mentioned giant galaxy placed at its center[[note]]But not the brightest, that honor goes to Messier 49[[/note]]


While from our perspective looks very roughly spherical, improved studies of the distances to its galaxies show it's actually a large filament that points more or less towards our position in the sky.












Steady state

Another issue with this theory is that if it was true we'd see everywhere and not just at high redshifts galaxies in all their evolutionary stages, from pristine gas clouds to others in quasar mode and/or bursting with countless young stars, and finally mature systems as ours. They'd have just hydrogen and not heavier elements, as just the former is being formed ''ex-nihilo'', but all systems observed to date have hydrogen ''and'' helium in agreement with the Big Bang theory. Even with an expanding Universe carrying away the old galaxies some legacy of them should be visible beyond as a cosmic microwave background very different as the real one (see also [[Quasi-Steady_State_Cosmology|below]]), including with some luck systems much older than ours.


==How theories might be disproved==
Although cosmological theories and hypotheses in general are difficult to disprove, strong evidence against them might be found. Maybe five years or more after the James Webb space telescope and the Atacama long baseline radio-scopes are fully functional, expected to be about 2024, cosmological models of an older or infinite-age universe would predict that they will have found at the farthest observable distances some old, very large and red appearing elliptical and spiral galaxies, maybe with observably high metallicity. This would be strong evidence that the universe is much older and that the Big Bang model would likely be wrong. On the other hand, if only small young, blue-appearing galaxies with minimal metallicity were instead observed at these farthest distances (with no old appearing large galaxies), then all theories and hypothesis proposing an older or infinite age universe seemingly would also most likely be wrong — which would include nearly all of the alternative cosmologies above.

Another issue comes from the [[Drake_Equation#Fermi_paradox|Fermi paradox]]. With an infinite ''and'' infinitely old Universe, no matter how rare would be for an advanced civilization to appear and expand elsewhere; having an eternity, '''a whole lot''' of them would have appeared and even if any of those civilizations had not come here before or contacted with us, [[https://en.wikipedia.org/wiki/Kardashev_scale|the evidences of their existence]] would be detectable elsewhere.


===The evidence is already there, but we can't detect it===
The possibilities range from a [[conspiracy theory|government conspiracy]] to withhold contact to messages/media that are quite literally too "alien" for us to perceive. (''e.g.'' Our own era of pumping out vast quantities of easily-decoded AM audio and video may only run about a hundred years, as broadcasting shifts to digital encoding with the frequency spectrum of white noise if you don't know what's encoded in it. Other possibilities include those hypothetical aliens not broadcasting in the frequencies where we're looking for them, not ''broadcasting'' but instead sending highly focused (and less expensive in energetic terms but much harder to detect) transmissions, and more especulative ideas such as them not using radio waves but instead lasers and even other methods such as neutrinos or stuff that we may not even know that exists as "hyperspace" or "wormholes" (assuming those things ''existed at all'', that is.)


The Solar System was born more or less four thousand and a half billion years ago from the collapse of a large gas cloud, that as typical per the process of star formation fragmented into many smaller ones[[note]]There's strong evidence that one or several supernovae, the deaths of massive star, may have triggered this proces. It, as well as others, show that our Sun was born in a large star-forming region of the style of the [[https://en.wikipedia.org/wiki/Orion_Nebula Orion nebula]], forming part of a large star cluster (imagine the [[AlienSky star-studded sky in that epoch]]. Its brothers and sisters are somewhere in the Milky Way, perhaps even with planets where life has developed too[[/note]]. One of said fragments, as it collapsed, began spin faster flattening and taking a flying saucer-like shape. Its center, as it collapsed, became hotter and denser until hydrogen fusion began at its very center. The Sun was born[[note]]Our daystar was during those early epochs a very different one: larger, cooler, and more luminous during its contraction, covered by sunspots, and more active with strong flare activity. When hydrogen ignited, while less luminous than now, it kept said activity with sunspots and flares galore and a ''very'' powerful solar wind until a few million years later it calmed somewhat, especially said wind.

While that happened in the center, things were considerably more active in the surrounding disk. While the countless grains of matter that formed it were in full FusionDance forming larger ones that would fuse to form even larger ones and so on, the heat of the contracting core vaporized low-melting point compounds as water or methane and the like of those coalescing bodies too close, that were able to condense only further out, meaning the inner Solar System would be composed of low-mass (proto)planets formed of metal and rocks. In the outside, with those volatile compounds safe from vaporization, things happened at a considerably faster pace and much larger core bodies formed that began to accrete gas from the surrounding in a runaway process that stopped both by the disk running out of matter and the Sun's strong winds blowing away the remaining gas and dust, leaving behind the major planets of the Solar System[[note]]Jupiter needed just three million years to form, Saturn likely a similar amount of time, and Uranus and Neptune longer. Had this happened later, Saturn would have been a more massive planet. Same especially for Uranus and Neptune, that were unable to grow beyond much more than their original cores. Oh, the largest moons of the outer planets are thought to have been formed in disks surrounding the giant planets, imitating the way planets had formed around the Sun[[/note]]

It was by then when the real planetary dance began. While those protoplanets of the inner Solar System were gravitationally interacting until they began to smash among themselves[[note]]At slower pace than what happened in the outer Solar System. Our Moon was formed in one of said collisions, between the proto-Earth and another Mars-sized body, Pluto's Charon could have been formed in a similar way, and similar collisions are expected to have been suffered by the other terrestrial planets. And instead of Mercury, Venus, Earth, and Mars at first could have formed large terrestrial bodies similar to those "super-Earths" found in tightly orbits around other stars (keep reading on)[[/note]], both gravitational interactions between the large planets and the many remaining planet-building blocks caused them to migrate from their original orbits, closer to the Sun than now. While Saturn, Neptune, and Uranus moved outwards[[note]]Yes, Neptune and Uranus: in said migration the two exchanged positions taking their current order[[/note]] Jupiter moved ''inwards'', messing so much with the protoplanets existing in what is now the asteroid belt that, where a large planet could have been formed, remained only what would amount comparatively speaking to detritus, either expelling it to the cold outer reaches or the Solar System, forming the Kupiter belt and the Oort Cloud or even ejecting outside it[[note]]It was not only Jupiter's fault. The other major planets had something to say too[[/note]], and would have kept approaching until it reached a very close orbit around the Sun had not gravitational interactions with Saturn caused it to move outwards to its present position[[note]]Different computer models suggest also Jupiter not only could have messed up with those hypothetical inner Super-Earths, causing them to crash among themselves or with the Sun with the current terrestrial planets forming from the [[ShatteredWorld remaining debris of those collisions]], but also that a fifth lage planet would have been ejected by Jupiter and/or another sent to the cold, outer regions of the Solar System. On a more positive note, Jupiter could have sent inward water-rich planetesimals, that would have been quite handy for the water content of the future Earth. As ScienceMarchesOn, expect some if not all of the ideas about planetary migration described there being changed in the future[[/note]]. Uranus and Neptune would also have played havoc with the remaining protoplanets of the Solar System's outer regions where they orbited scattering it even further out.

[[TakingYouWithMe The revenge of those protoplanets and other debris]] came four billion years ago in the form of a large number of them ending up in the inner Solar System, where they [[ColonyDrop pummeled to death]] the more or less formed terrestrial planets, scarring them with countless craters and causing quite a lot of damage to them[[note]]In the case of Earth, the heaviest impacts would have been enough to vaporize the oceans and even melt the crust in [[TabletopGame/Warhammer40000 Exterminatus]] fashion, wrapping the planet in an atmosphere of molten rock and water vapor for some time. It's not know if life had formed by then but if had it existed it would have been destroyed in the most violent collisions. Perhaps life formed several times, just to being destroyed again when a large impactor came crashing again, or it survived sheltered deep into Earth's crust or in the very deepest oceans. On a more positive note, it's thought those impacts brought still more water to Earth[[/note]]. This hellish rain may have lasted a few hundred million years, and was the last event of significance in the Solar System[[note]]On a more domestic scale, the remaining asteroids [[AsteroidMonster pummeled among themselves]] in the belt further reducing the population of large bodies and producing many smaller ones, and giant planets would have captured some of those floating rocks as moons (one of them ''very'' large -ask Neptune's Triton-). Venus, that could have been an Earth-like planet became the [[DeathWorld hellish world]] that is now because of its closeness to the Sun, and Mars being too small perhaps thanks to Jupiter's journey, lost its protecting magnetic field and with it most of its atmosphere and the liquid water it's now it had in those epochs[[/note]]. From there until now, little has happened in the Solar System in a global scale besides the occasional impact here and there of a stray asteroid or comet, the star passing across the Oort cloud[[note]]Ask [[https://en.wikipedia.org/wiki/Gliese_710 Gliese 710]][[/note]] sending a shower of comets to the inner Solar System, and a Sun that as it ages becomes more luminous[[note]]As it fuses the hydrogen on its core, the latter contracts increasing its temperature causing an increase of the fusion rate and thus of the released energy and so on. As there's no convection in the inner regions of the Sun, just the outermost ones, our star cannot use all of its nuclear fuel.[[/note]]


As for the future, things will not change very much for the Solar System ''as a whole'' during the next five billion years[[note]]Some calculations simulations give a very small probability within that timeframe of either Mercury going haywire and being ejected of the Solar Sytem if it does not crash before into either Venus or Earth, or Mars colliding with Earth. Sleep well, it will ''not'' happen tomorrow. [[ParanoiaFuel We think]][[/note]]. Sure, the orbits of some moons such as Mars' Phobos or Neptune's Triton will decay and the latter will produce both a ''hell'' of a meteor shower and a splendid ring system around its planet, there will be continue being the occasional asteroid/impact here and there, the occasional star passing too close[[note]]Ask [[https://en.wikipedia.org/wiki/Gliese_710 Gliese 710]][[/note]] will shake close and shaking the Oort Cloud sending comets to the inner Solar System, [[ArsonMurderAndJaywalking and the Earth will become becoming unhabitable]] as the because of a Sun that is becoming more luminous brightening with time as it ages described above but if we could see the Solar System by then it is expected we'd see something very similar to the current one[[note]]OK, one[[note]OK, the Andromeda Galaxy and the Milky Way are expected to [[FusionDance merge]] around those ages and the Sun will end up on the outskirts of the newly-formed galaxy, if not thrown out to intergalactic space (it will come back much later, though), but unless we've ''very'' bad luck the collision will not affect us[[/note]].
Five billion years was not chosen at random for the fate of our Solar System is tightly tied to the one of its most massive body: the Sun. By that epoch it will have run out of hydrogen at its center and things will become interesting, so let's fast forward to the year [[TimeAbyss 7,590,000,000 AD]]. AD]][[note]]After core hydrogen exhaustion, the Sun will take its time to become a red giant -one and a half billion years still as something not very different of our current daystar -but more luminous- followed by seven hundred million years as a cooler and larger, but not more luminous subgiant star, and finally roughly six hundred million years to go full red giant. Stellar evolution takes usually its time -and remember that these are theoretical calculations, so while the basic picture will be more or less the same given numbers may somewhat change as ScienceMarchesOn-[[/note]]. In that year our familiar Sun will be in [[OneWingedAngel full red giant-mode]]: a bloated and distorted star with a surface temperature having dropped to half of what it had has in our epoch, thousands of times more luminous and more than two hundred times larger than our daystar[[note]]Why?. daystar[[note]]Why if there's no more hydrogen in the core?. Hydrogen is intensely fusing instead around the small, hydrogen-exhausted, dense core of inert helium, that as it contracted caused first the hydrogen surrounding it to start fusing, and later as temperatures increased because of said contraction to fuse more and more intensely[[/note]], intensely. At least, since the process will take so much time it has been calculated that temperatures will be Earth-like (the so-called "habitable zone") for some hundred million years in places as Mars or further out (Jupiter). Perhaps life will manage to appear there, even if it had little time to evolve.[[/note]], and so big that has lost more than a quarter of its mass carried away by strong solar winds, something that has caused the planet's orbits to wide, but not enough to avoid searing hot temperatures or worse[[note]]For the details: Mercury and Venus are history, having been engulfed millions of years before by the expanding Sun but not before having been roasted to Hell and back -and Venus having lost its atmosphere (poor Venus, she cannot catch a break)-. Earth, with no atmosphere to speak of and [[DeathWorld with a surface temperature of more than one thousand five hundred degrees Celsius]], is a LethalLavaLand precariously clinging to its orbit under an angry Sun that fills a whole lot of its sky and is very likely doomed to suffer the same fate than the two innermost planets. Mars is another LethalLavaLand that (we think) will survive the ordeal. Of the giant planets, temperatures will vary between the searing hot ones of Jupiter (higher than those at Mercury, but at least it could manage to accrete ''some'' (it will certainly ''not'' capture enough to be significant, much less to become a star) of the matter expelled by the Sun) and the rather Earth-like ones of Neptune, with their icy moons looking like huge comets, evaporating under the intense sunlight and probably after for a time their surfaces had melt have melted as temperature screamed upwards and liquid water vaporized giving pressure cooker-like conditions hellish, worse than Venus-like conditions, to the rocky surfaces below all that ice in some cases as Europa or Ganymede. The smallest bodies -asteroids and comets-, even as far as the Kuiper Belt, not only will have to contend with the intense heat but also with the mess caused to their orbits by the mass loss of the dying Sun, meaning that some of them will be end being ejected out of the Solar System and others will either crash with the remaining planets or into the Sun[[/note]]. It will also be the time when the Sun will suffer a dramatic transformation: the dense, inert helium core will ignite and will produce for a few seconds ''as much energy as an entire galaxy''. galaxy'' in what astronomers know as the "helium flash". While this looks like a supernova, that energy will actually just be used to re-expand the core and nothing of that will be seen at its surface -in fact, with the Sun's innards expanding to fuse helium stably it will release less energy and will collapse back to a much smaller and less luminous star a bit more hot than its red giant past (somewhat more than four thousand degrees Celsius), but still quite luminous (forty-fifty times more) and large (ten times larger) compared with its past long-lived incarnation[[note]]Whatever incarnation requiring several thousand years to become that[[note]]Whatever remains of the inner Solar System -perhaps only Mars- will be hotter than Mercury. Farther away, Jupiter will enjoy Earth-like temperatures and even farther our things will freeze again. Meanwhile, asteroids and the like will keep their dance of death[[/note]]. Unfortunately for the Sun helium, fusing to produce carbon and oxygen, is a worse fuel than hydrogen and even if helium burning its supported by some hydrogen fusing around the core our star will run out of it in just a hundred million years and then the Sun will face a similar crisis to the one it faced when it ran out of hydrogen.hydrogen there. Only this time said crisis will be fatal.
As happened with hydrogen before, helium will begin to fuse around an inert contracting inert, contracting, core of carbon and oxygen. oxygen[[note]]In vain; the Sun is too small to reach the temperatures and densities to fuse carbon[[/note]]. Further out, hydrogen will fuse keep fusing to helium and as the core contracts it will "squeeze" those two burning shells causing them to fuse with more force. The result is that the Sun will become again -in just twenty million years compared to the considerably longer time (more than two billion years, see above) it needed to expand for the first time- a huge and luminous red giant suffering even stronger mass loss but, as helium burning under those extreme conditions is ''highly'' sensitive to the temperature[[note]]It scales as the temperature ''to the fortieth power''. Guess how nasty would be even small variations[[/note]], [[ClippedWingAngel an unstable one]]. Each hundred thousand years, the Sun will convulse suffering a pulse caused by a runaway helium shell burning ignition that will increase its luminosity as well as it radius just to contract when it stops and having things starting again. Those violent pulses will increase even more the already heavy mass loss as mentioned before, and by the fourth one all that will remain of the Sun will be the ''extremely'' hot -one hundred thousand degrees Celsius- and dense, as it has contracted to the size of the Earth, carbon-oxygen core half as massive as the Sun is now: a white dwarf. If the Sun is luminous enough, its ultraviolet radiation will cause the matter that ejected before to fluoresce as a beautiful [[https://en.wikipedia.org/wiki/Planetary_nebula planetary nebula]], that will however be short-lived as a few thousand years later both the gases will be rarefied and far away enough and the white dwarf's ultraviolet radiation will fade away as it begins to cool to stop shining. All that will remain to the dead white dwarf Sun is to keep cooling over [[TimeAbyss many billions of years]] until it will fade into oblivion as a black dwarf -or, if you prefer it, as a big and dense diamond as all those carbon will crystalize during said cooling-[[note]]No, we have not forgotten the planets and all that other stuff. Things will be as during the previous red giant stage, but this time ''harder'', as the Sun's convulsions will cause severe variations of temperature on them and will be pummeled by the matter expelled in the pulses. The worst, however, will come because of that severe mass drain with the Solar System becoming an even more of a mess with many small bodies, and perhaps even planets, having their orbits more or less dislocated with all that means -collisions either among them or the Sun, things being flung out, etc-. Said mess is expected to continue into the planetary nebula and white dwarf stages (it's conceivable its UV flux during the planetary nebula phase will be more or less nasty for the orbiting bodies), and whatever survives the ordeal -odds are that Jupiter at the very least- will see the dark, black, incredibly cold, veil of an endless night being put over it. The end... or is it?. [[TimeAbyss Time will keep going ticking on]], and stars the very occasional star passing too close will begin to strip the dead Sun of more or less of its remaining retinue of planets.orbiting bodies. It has been estimated that in a ''quadrillion'' (ten to the fifteenth) years, it will have lost all of them.[[/note]]
9th Feb '17 4:41:13 PM ScorpiusOB1
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!!Formation will come soon.

As for the future, things will not change very much for the Solar System ''as a whole'' during the next five billion years[[note]]Some calculations simulations give a very small probability within that timeframe of either Mercury going haywire and being ejected of the Solar Sytem if it does not crash before into either Venus or Earth, or Mars colliding with Earth. Sleep well, it will ''not'' happen tomorrow. [[ParanoiaFuel We think]][[/note]]. Sure, the orbits of some moons such as Mars' Phobos or Neptune's Triton will decay and the latter will produce both a ''hell'' of a meteor shower and a splendid ring system around its planet, there will be the occasional asteroid/impact here and there, the occasional star passing too close[[note]]Ask [[https://en.wikipedia.org/wiki/Gliese_710 Gliese 710]][[/note]] will shake the Oort Cloud sending comets to the inner Solar System, [[ArsonMurderAndJaywalking and the Earth will become unhabitable]] as the Sun is becoming more luminous as it ages but if we could see the Solar System by then it is expected we'd see something very similar to the current one[[note]OK, the Andromeda Galaxy and the Milky Way are expected to [[FusionDance merge]] around those ages and the Sun will end up on the outskirts of the newly-formed galaxy, if not thrown out to intergalactic space (it will come back much later, though), but unless we've ''very'' bad luck the collision will not affect us[[/note]].

to:

!!Formation will come soon.


As for the future, things will not change very much for the Solar System ''as a whole'' during the next five billion years[[note]]Some calculations simulations give a very small probability within that timeframe of either Mercury going haywire and being ejected of the Solar Sytem if it does not crash before into either Venus or Earth, or Mars colliding with Earth. Sleep well, it will ''not'' happen tomorrow. [[ParanoiaFuel We think]][[/note]]. Sure, the orbits of some moons such as Mars' Phobos or Neptune's Triton will decay and the latter will produce both a ''hell'' of a meteor shower and a splendid ring system around its planet, there will be the occasional asteroid/impact here and there, the occasional star passing too close[[note]]Ask [[https://en.wikipedia.org/wiki/Gliese_710 Gliese 710]][[/note]] will shake the Oort Cloud sending comets to the inner Solar System, [[ArsonMurderAndJaywalking and the Earth will become unhabitable]] as the Sun is becoming more luminous as it ages but if we could see the Solar System by then it is expected we'd see something very similar to the current one[[note]OK, one[[note]]OK, the Andromeda Galaxy and the Milky Way are expected to [[FusionDance merge]] around those ages and the Sun will end up on the outskirts of the newly-formed galaxy, if not thrown out to intergalactic space (it will come back much later, though), but unless we've ''very'' bad luck the collision will not affect us[[/note]].
9th Feb '17 4:39:24 PM ScorpiusOB1
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Added DiffLines:

!Past and future
!!Formation will come soon.

As for the future, things will not change very much for the Solar System ''as a whole'' during the next five billion years[[note]]Some calculations simulations give a very small probability within that timeframe of either Mercury going haywire and being ejected of the Solar Sytem if it does not crash before into either Venus or Earth, or Mars colliding with Earth. Sleep well, it will ''not'' happen tomorrow. [[ParanoiaFuel We think]][[/note]]. Sure, the orbits of some moons such as Mars' Phobos or Neptune's Triton will decay and the latter will produce both a ''hell'' of a meteor shower and a splendid ring system around its planet, there will be the occasional asteroid/impact here and there, the occasional star passing too close[[note]]Ask [[https://en.wikipedia.org/wiki/Gliese_710 Gliese 710]][[/note]] will shake the Oort Cloud sending comets to the inner Solar System, [[ArsonMurderAndJaywalking and the Earth will become unhabitable]] as the Sun is becoming more luminous as it ages but if we could see the Solar System by then it is expected we'd see something very similar to the current one[[note]OK, the Andromeda Galaxy and the Milky Way are expected to [[FusionDance merge]] around those ages and the Sun will end up on the outskirts of the newly-formed galaxy, if not thrown out to intergalactic space (it will come back much later, though), but unless we've ''very'' bad luck the collision will not affect us[[/note]].
Five billion years was not chosen at random for the fate of our Solar System is tightly tied to the one of its most massive body: the Sun. By that epoch it will have run out of hydrogen at its center and things will become interesting, so let's fast forward to the year [[TimeAbyss 7,590,000,000 AD]]. In that year our familiar Sun will be in [[OneWingedAngel full red giant-mode]]: a bloated and distorted star with a surface temperature having dropped to half of what it had in our epoch, thousands of times more luminous and more than two hundred times larger than our daystar[[note]]Why?. Hydrogen is intensely fusing around the small, hydrogen-exhausted, dense core of inert helium, that as it contracted caused first the hydrogen surrounding it to start fusing, and later as temperatures increased to fuse more and more intensely[[/note]], and so big that has lost more than a quarter of its mass carried away by strong solar winds, something that has caused the planet's orbits to wide, but not enough to avoid searing hot temperatures or worse[[note]]For the details: Mercury and Venus are history, having been engulfed millions of years before by the expanding Sun but not before having been roasted to Hell and back -and Venus having lost its atmosphere (poor Venus, she cannot catch a break)-. Earth, with no atmosphere to speak of and [[DeathWorld with a surface temperature of more than one thousand five hundred degrees Celsius]], is a LethalLavaLand precariously clinging to its orbit under an angry Sun that fills a whole lot of its sky and is very likely doomed to suffer the same fate than the two innermost planets. Mars is another LethalLavaLand that (we think) will survive the ordeal. Of the giant planets, temperatures will vary between the searing hot ones of Jupiter (higher than those at Mercury, but at least it could manage to accrete ''some'' (it will certainly ''not'' capture enough to be significant, much less to become a star) of the matter expelled by the Sun) and the rather Earth-like ones of Neptune, with their icy moons looking like huge comets, evaporating under the intense sunlight and probably after for a time their surfaces had melt giving pressure cooker-like conditions to the rocky surfaces below all that ice in some cases as Europa or Ganymede. The smallest bodies -asteroids and comets-, even as far as the Kuiper Belt, not only will have to contend with the intense heat but also with the mess caused to their orbits by the mass loss of the dying Sun, meaning that some of them will be ejected out of the Solar System and others will either crash with the remaining planets or into the Sun[[/note]]. It will also be the time when the Sun will suffer a dramatic transformation: the dense, inert helium core will ignite and will produce for a few seconds ''as much energy as an entire galaxy''. While this looks like a supernova, that energy will actually just be used to re-expand the core and nothing of that will be seen at its surface -in fact, with the Sun's innards expanding to fuse helium stably it will release less energy and will collapse back to a much smaller and less luminous star a bit more hot than its red giant past (somewhat more than four thousand degrees Celsius), but still quite luminous (forty-fifty times more) and large (ten times larger) compared with its past long-lived incarnation[[note]]Whatever remains of the inner Solar System -perhaps only Mars- will be hotter than Mercury. Farther away, Jupiter will enjoy Earth-like temperatures and even farther our things will freeze again. Meanwhile, asteroids and the like will keep their dance of death[[/note]]. Unfortunately for the Sun helium, fusing to produce carbon and oxygen, is a worse fuel than hydrogen and even if helium burning its supported by some hydrogen fusing around the core will run out of it in just a hundred million years and then the Sun will face a similar crisis to the one it faced when it ran out of hydrogen. Only this time said crisis will be fatal.
As happened with hydrogen before, helium will begin to fuse around an inert contracting core of carbon and oxygen. Further out, hydrogen will fuse to helium and as the core contracts it will "squeeze" those two burning shells causing them to fuse with force. The result is that the Sun will become again -in just twenty million years compared to the considerably longer time it needed to expand for the first time- a huge and luminous red giant suffering even stronger mass loss but, as helium burning under those extreme conditions is ''highly'' sensitive to the temperature[[note]]It scales as the temperature ''to the fortieth power''. Guess how nasty would be even small variations[[/note]], [[ClippedWingAngel an unstable one]]. Each hundred thousand years, the Sun will convulse suffering a pulse caused by a runaway helium ignition that will increase its luminosity as well as it radius just to contract and having things starting again. Those violent pulses will increase even more the already heavy mass loss as mentioned before, and by the fourth one all that will remain of the Sun will be the ''extremely'' hot -one hundred thousand degrees Celsius- and dense, as it has contracted to the size of the Earth, carbon-oxygen core half as massive as the Sun is now: a white dwarf. If the Sun is luminous enough, its ultraviolet radiation will cause the matter that ejected before to fluoresce as a beautiful [[https://en.wikipedia.org/wiki/Planetary_nebula planetary nebula]], that will however be short-lived as a few thousand years later both the gases will be rarefied and far away enough and the white dwarf's ultraviolet radiation will fade away as it begins to cool to stop shining. All that will remain to the dead white dwarf Sun is to keep cooling over [[TimeAbyss many billions of years]] until it will fade into oblivion as a black dwarf -or, if you prefer it, as a big and dense diamond as all those carbon will crystalize during said cooling-[[note]]No, we have not forgotten the planets and all that other stuff. Things will be as during the red giant stage, but this time ''harder'', as the Sun's convulsions will cause severe variations of temperature and will be pummeled by the matter expelled in the pulses. The worst, however, will come because of that severe mass drain with the Solar System becoming an even more of a mess with many small bodies, and perhaps even planets, having their orbits more or less dislocated with all that means -collisions either among them or the Sun, things being flung out, etc-. Said mess is expected to continue into the planetary nebula and white dwarf stages (it's conceivable its UV flux will be more or less nasty for the orbiting bodies), and whatever survives the ordeal -odds are that Jupiter at the very least- will see the dark, cold, veil of an endless night being put over it. The end... or is it?. [[TimeAbyss Time will keep going on]], and stars passing too close will begin to strip the dead Sun of its remaining retinue of planets. It has been estimated that in a ''quadrillion'' (ten to the fifteenth) years, it will have lost all of them.[[/note]]
12th Jan '17 8:38:45 PM The_Glorious_SOB
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* UsefulNotes/{{Uranus}}: It had been detected by astronomers as early as 1690[[note]]John Flamsteed thought it was a star and named it "34 Tauri"; that designation was therefore available for [[Creator/JossWhedon a certain talespinner]] to apply to [[{{Series/Firefly}} the star system at the heart of his one of his 'Verses]].[[/note]], but Sir William Herschell actually identified it as a planet in 1789. It is named after the Greek god of the sky.[[note]]Yes, really, [[UranusIsShowing you adolescents]].[[/note]] It's 4 times the diameter of the Earth, which is still less than half the diameter of Jupiter. Seen as minty green in color observed from Earth by early telescopes, close-up observation showed it's more pale blue. It's denser than Jupiter and Saturn with a higher proportion of methane, ammonia and water. Uranus is even colder than Neptune. Voyager 2 passed by it in 1986 and observed few distinct clouds, [[ScienceMarchesOn but later observations from Earth have revealed more]]. It has a set of coal-black rings (discovered in 1977) and is tilted 98 degrees on its axis--each pole spends 42 years in light and 42 in darkness. Scientists have reason to believe it's on its unique side-ways tilt due to a massive impact that depleted it's internal core temperature. Also known for being the planet which the ''[[Franchise/StarTrek Enterprise]]'' circles while [[UranusIsShowing wiping out Klingons]].

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* UsefulNotes/{{Uranus}}: It had been detected by astronomers as early as 1690[[note]]John Flamsteed thought it was a star and named it "34 Tauri"; that designation was therefore available for [[Creator/JossWhedon a certain talespinner]] to apply to [[{{Series/Firefly}} the star system at the heart of his one of his 'Verses]].[[/note]], but Sir William Herschell actually identified it as a planet in 1789. It is named after the Greek god of the sky.[[note]]Yes, really, [[UranusIsShowing you adolescents]].[[/note]] It's 4 times the diameter of the Earth, which is still less than half the diameter of Jupiter. Seen as minty green in color observed from Earth by early telescopes, close-up observation showed it's more pale blue. It's denser than Jupiter and Saturn with a higher proportion of methane, ammonia and water. Uranus is even colder than Neptune. Voyager 2 passed by it in 1986 and observed few distinct clouds, [[ScienceMarchesOn but later observations from Earth have revealed more]]. It has a set of coal-black rings (discovered in 1977) and is tilted 98 degrees on its axis--each pole spends 42 years in light and 42 in darkness. Scientists have reason to believe it's on its unique side-ways tilt due to a massive impact that depleted it's its internal core temperature. Also known for being the planet which the ''[[Franchise/StarTrek Enterprise]]'' circles while [[UranusIsShowing wiping out Klingons]].
22nd Nov '16 1:40:18 AM harharhar
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* Last but not least, in January 2016 a group of astronomers have suggested that the eccentric orbits of several large Kuiper Belt Objects (see the Detached Object category of small solar system bodies listed further down) could be explained by the presence of a ninth planet, that would be a bit smaller in mass than Neptune or Uranus, two to four times larger than Earth, and that would orbit the Sun in a highly eccentric and inclined orbit that would take many thousands of years to complete never approaching at less than around seven times the Sun-Neptune distance. Please note, however, that despite the claims of "a new planet discovered" there's at best just indirect proof of its existence and it's an entirely hypothetical object until it's finally imaged[[note]]Not something that will be easy, mind you, with ''millions'' of stars and galaxies of similar brightness to that planet if it existed at all[[/note]].

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* Last but not least, in January 2016 a group of astronomers have suggested that the eccentric orbits of several large Kuiper Belt Objects (see the Detached Object category of small solar system bodies listed further down) could be explained by the presence of [[https://en.wikipedia.org/wiki/Planet_Nine a ninth planet, planet]] (so-called [[ExactlyWhatItSaysOnTheTin Planet Nine]]), that would be a bit smaller in mass than Neptune or Uranus, two to four times larger than Earth, and that would orbit the Sun in a highly eccentric and inclined orbit that would take many thousands of years to complete never approaching at less than around seven times the Sun-Neptune distance.distance[[note]]At its farthest, Neptune is 30-something AU away from the sun; Planet's Nine's nearest distance to the sun is predicted to be about ''200 AU''[[/note]]. Please note, however, that despite the claims of "a new planet discovered" there's at best just indirect proof of its existence and it's an entirely hypothetical object until it's finally imaged[[note]]Not something that will be easy, mind you, with ''millions'' of stars and galaxies of similar brightness to that planet if it existed at all[[/note]].



** [[https://en.wikipedia.org/wiki/Planet_Nine Planet Nine]][[note]]Listed here for convenience as this thing is theoretically far more massive than anything else in the outer edges of the solar system[[/note]]: This hypothetical large planet far, far away from the sun[[note]]At its farthest, Neptune is 30-something AU away from the sun; Planet's Nine's nearest distance to the sun is predicted to be about ''200 AU''[[/note]] is suspected to be responsible for the positionings and orbits of the Trans-Neptunian Objects. It has yet to be visually detected.
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