History UsefulNotes / TheSolarSystem

** UsefulNotes/TheMoon (AKA, Luna): Our nearest neighbor, and the only celestial body beyond Earth that has been explored by humans in person ([[UsefulNotes/ConspiracyTheories allegedly]]). It is theorized that the Moon is the left over debris from [[EarthShatteringKaboom a giant impact event]] with a proto-Earth and a Mars' sized object called Theia. Another theory holds that both Theia and the proto-Earth were completely destroyed by the impact, then the debris coalesced to form Earth and the Moon. Or even that they collided ''twice'' before ending up in their current forms. The Moon is a very unusual object (while not the largest moon in the solar system, relative to the size of its planet it's enormous) and the high angular momentum of the Earth-Moon system is even more unusual, and dramatic events were needed to bring it into existence. It's also Tidal Locked, which means it's in a synchronous rotation with Earth, such that the same face is always pointing towards the Earth at all times. This is not as remarkable or unusual as it may appear[[note]]Pluto and Charon experience the same phenomenon[[/note]].

Despite years and years of ScienceFiction stories about planets around other suns, we actually lacked any real scientific proof of them until the early 1990's when exoplanets were first detected by their wobble on their parent star. Until then, it was quite possible that our solar system was simply a fluke. For example, one theory on the formation of our solar system, "Tidal Theory" - 1917, was that a passing star came close to our sun, drawing a filament of solar matter out of it which coalesced into the planets. Wiki/{{Wikipedia}} has a page on those theories [[https://en.wikipedia.org/wiki/History_of_Solar_System_formation_and_evolution_hypotheses here]] if you are interested.

** [[https://en.wikipedia.org/wiki/90377_Sedna Sedna]]: Almost certainly the sixth dwarf planet. Its orbit is so distant that it never comes within 46 AU of Neptune (which for the record is more than 1.5 times distance between Neptune and the sun) and thus no planet's gravity exerts any influence on it. Its orbit is also extremely elliptical (its closest approach to the sun is 76 AU while the furthest it gets is 936 AU), something that is normally caused by interaction with Neptune and thus causing renewed speculation that a large planet must exist beyond Neptune's orbit. Its orbital period is estimated to be ''11,400 years'', while it's only physically observable from Earth for 25 years of its orbit. This means astronomers were ''very'' lucky to find it.

As happened with hydrogen before, helium will begin to fuse around an inert, contracting, core of carbon and oxygen[[note]]In vain; the Sun is too small to reach the temperatures and densities to fuse carbon[[/note]]. Further out, hydrogen will 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 at least 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 the four largest planets at the very least- will see the black, incredibly cold, veil of an endless night being put over it. The end... or is it?. [[TimeAbyss Time will keep ticking on]], and the very occasional star passing too close will strip the dead Sun of more or less of its remaining retinue of orbiting bodies. It has been estimated that in a ''quadrillion'' (ten to the fifteenth) years, it will have lost all of them.[[/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]][[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 has in our epoch, thousands of times more luminous and more than two hundred times larger than our 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. 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 of 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, maybe up to being totally vaporized in the cases of those composed almost of ice as the moons of Saturn, and probably after their surfaces have melted as temperature screamed upwards and had liquid oceans for a time, said water vaporized giving hellish, worse than Venus-like conditions, to the rocky surfaces below all that ice in some cases as Europa, Ganymede, or Titan before it was lost to space. The smallest bodies -asteroids and comets-, even as far as the Kuiper Belt, not only 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 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'' 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 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 there. Only this time said crisis will be fatal.

[[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 [[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 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]]

You'll often hear, particularly when concerning the ''Voyager'' probes, that they have reached the "edge" of the Solar System; originally this meant moving beyond Pluto's orbit, a definition that now feels very "last century". Now, it generally means when the "atmosphere" generated by the Sun is pushed back by the atmosphere of interstellar space (a point called the heliopause). And while yes, the space beyond the heliopause is technically the same as the space between stars, it is NOWHERE NEAR the edge of the Sun's gravitational influence, which is a thousand times farther out. In fact, the Sun's influence doesn't "end". Rather, it merges with its closest neighbors, including Alpha Centauri. In other words, you're not out of the Solar System til you're in another one.

* UsefulNotes/{{Venus}}: sometimes referred to as Earth's sister planet due to their similar sizes. It has an extremely dense atmosphere (surface pressure is 90 bars, compared to 1 on Earth) and can reach a surface temperature of 470 °C/870 °F (although at the top of Maxwell Montes, almost 7 miles above the average surface level, it's "only" 380 °C/716 °F and 60 bars). The culprit for all this? The greenhouse effect--90 atmospheres of carbon dioxide with some helping of other greenhouse gases will be quite hot. [[note]]"An Estimate of the Surface Temperature of Venus Independent of Passive Microwave Radiometry" by one [[Creator/CarlSagan C. Sagan]] gives it at ~700K in 1967.[[/note]] Volcanoes on Earth have belched out the same amount, [[SealedEvilInACan but it ended up trapped in carbonate rock]]. Venus also started with the same amount of water as the earth had, but it was vaporized (300 atmospheres worth) and created a [[UpToEleven super greenhouse effect]] with temperatures in the ''thousands'' of degrees. [[note]]This plus the slow rotation probably wrecked any chance at plate tectonics; instead of plates constantly sliding against each other, [[LethalLavaLand there seems to be intermittent vulcanism punctuated by extreme periods of volcanic activity replacing much of the surface every billion years or so]].[[/note]] Eventually the water molecules dissociated into hydrogen and oxygen and escaped into space, leaving Venus high and dry. Interestingly, the zone between 50 and 65 kilometers above the surface has pressures and temperatures right around Earth normal. Add to that the fact that an 80/20 nitrogen/oxygen mix would act like a lifting gas and [[Film/TheEmpireStrikesBack Cloud City]] would be right at home. It oddly rotates in the ''opposite direction'' to most other planets. Due to Venus being mythologically associated with femininity, by convention all geographic features there are named after women or female entities, except for Maxwell Montes and Alpha and Beta Regio. [[note]]These features were first detected by ground-based radar in the mid-1960s; Alpha and Beta Regio were the first two terrain features to be isolated, and Maxwell Montes was named after James Clerk Maxwell, the formulator of the theory and equations of electromagnetism that ultimately led to the invention of radar.[[/note]] There is some argument over whether the proper adjective is 'Venusian', 'Venerean', or 'Cytherean'.

* UsefulNotes/{{Jupiter}}: The largest of them all, and thus fittingly named after the Roman God of Gods. Of course, [[OlderThanTheyThink the Romans named it that long before they had any idea just how big it was]]. Jupiter is ''vast'', often referred to as a "failed brown dwarf" and while not as dense as Earth, it has a magnetic field some 20,000 times stronger than our world does. Jupiter is... ''odd'', and by extension makes our solar system unusual. Gas giants have the tendency to migrate inwards towards their stars, becoming "hot jupiters". This happened in our system, and it would have [[Music/MileyCyrus come in like a wrecking ball...]] until the formation of Saturn. Saturn pulled Jupiter outwards, allowing the rocky terrestrial worlds to form. Jupiter has been described as a cosmic vacuum [[BigBrotherInstinct protecting us from comets and other asteroids]] that would otherwise [[TheEndOfTheWorldAsWeKnowIt obliterate all life on Earth]].

* UsefulNotes/TheSun (Popularly formally named in ScienceFiction as '''Sol'''): The star of the show, literally and figuratively. About 99.9% of all the mass in the Solar system is in the sun. Our Sun is a wonderfully stable one, unusually so even for a G-type, which is beneficial for us. Other stars big and small often emit dangerous-to-life x-ray flares. She has [[BeautyMark the odd sunspot here and there too]], and thank goodness, last time our Sun didn't, we experienced an ice age. Rather than red dwarfs, that shine out mostly infrared light, she emits a lot of light on the visible spectrum, [[ThePowerOfTheSun which is just great for photosynthesising plants]]. She does emit ultraviolet radiation too, [[EmbarrassinglyPainfulSunburn so put on that sunblock before you step outside]]. Sadly, all good things must come to an end. The Sun is already 4.6 billion years old, and when it uses up too much of its Hydrogen reserves, it'll get hotter and hotter, until becoming a humongous Red Giant that'll no doubt swallow up the inner planets along with Earth. [[/index]]

Turning to nomenclature on a smaller scale, the New Horizons probe 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]]

The official IAU definition for fictional names of features on Pluto is items from global underworld mythos, leading to the use of [[Literature/TheLordOfTheRings Balrog Macula]] and [[Creator/HPLovecraft Cthulhu Regio]]. Most features are named for real astronomers (Tombaugh Regio, a.k.a. "Pluto's Heart"), real explorers (Hillary Montes and Norgay Montes), and real spacecraft (Sputnik Planum, Voyager Terra).

The official IAU definition for fictional names of features on Charon is items and milestones of "fictional space".[[note]]Charon ''was'' discovered in 1978, which was arguably the heyday of science fiction on TV.[[/note]] With that one, the ''New Horizons'' team is really going to town. [[Franchise/StarTrek Vulcan Planum]] (with [[Creator/LeonardNimoy Spock Crater]]), [[Series/DoctorWho Gallifrey Macula]], [[Franchise/{{Alien}} Ripley Crater and Nostromo Chasma]], Anime/{{Macross}} and [[Series/{{Firefly}} Serenity Chasmae]], [[Franchise/StarWars Organa, Skywalker and Vader Craters]]...

* Other theories on planetary-mass bodies beyond the orbit of Neptune include [[https://bit.ly/whatsbeyondNeptune a moderately-sized tenth planet and a]] [[https://www.bibliotecapleyades.net/sumer_anunnaki/esp_sumer_annunaki22.htm dead star]].

Most of these and their associated moons are named after characters from Myth/ClassicalMythology; the planets themselves have Roman/Latin names, but the moons are more variable.

** UsefulNotes/TheMoonsOfUranus (The Bard [[AC:InSpace]]): Fittingly for an English-discovered planet, Uranus' moons are all named after characters from Creator/WilliamShakespeare. Two of the original five received names from Creator/AlexanderPope's ''Literature/TheRapeOfTheLock''.

->'''Mercury''' was near the sun so Janet dropped by - but the mercury on Mercury was much too high.\\

'''Earth''' looked exciting, Kind of green and inviting, So Janet thought she'd give it a go. But the creatures on that planet looked so very weird to Janet. She didn't even stop to say "hello".\\

'''Pluto''', little Pluto is the farthest planet from the sun

[[caption-width-right:350:[[MyFriendsAndZoidberg Ignore Pluto.]] [[PlutoIsExpendable It's not a planet anymore.]] Also, [[YouCannotGraspTheTrueForm definitely not to Scale]]]]

-->--''WesternAnimation/SchoolhouseRock'', "[[https://www.youtube.com/watch?v=MGgajx1pGPU Interplanet Janet]]"[[note]]Released before the [=IAU=]'s redefinition of a planet and before the Voyager probes had visited the outer planets, explaining why their descriptions are rather light on info.[[/note]]

The official IAU definition for fictional names of features on Pluto is items from global underworld mythos, leading to the use of [[Franchise/TheLordOfTheRings Balrog Macula]] and [[Creator/HPLovecraft Cthulhu Regio]]. Most features are named for real astronomers (Tombaugh Regio, a.k.a. "Pluto's Heart"), real explorers (Hillary Montes and Norgay Montes), and real spacecraft (Sputnik Planum, Voyager Terra).

* UsefulNotes/TheSun: The star of the show, literally and figuratively. About 99.9% of all the mass in the Solar system is in the sun. Our Sun is a wonderfully stable one, unusually so even for a G-type, which is beneficial for us. Other stars big and small often emit dangerous-to-life x-ray flares. She has [[BeautyMark the odd sunspot here and there too]], and thank goodness, last time our Sun didn't, we experienced an ice age. Rather than red dwarfs, that shine out mostly infrared light, she emits a lot of light on the visible spectrum, [[ThePowerOfTheSun which is just great for photosynthesising plants]]. She does emit ultraviolet radiation too, [[EmbarrassinglyPainfulSunburn so put on that sunblock before you step outside]]. Sadly, all good things must come to an end. The Sun is already 4.6 billion years old, and when it uses up too much of its Hydrogen reserves, it'll get hotter and hotter, until becoming a humongous Red Giant that'll no doubt swallow up the inner planets along with Earth. [[/index]]

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, [[BreadEggsMilkSquick 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]].
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]][[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 has in our epoch, thousands of times more luminous and more than two hundred times larger than our 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. 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 their surfaces have melted as temperature screamed upwards and liquid water vaporized giving 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 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 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'' 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 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 there. 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[[note]]In vain; the Sun is too small to reach the temperatures and densities to fuse carbon[[/note]]. Further out, hydrogen will 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 black, incredibly cold, veil of an endless night being put over it. The end... or is it?. [[TimeAbyss Time will keep ticking on]], and the very occasional star passing too close will strip the dead Sun of more or less of its remaining retinue of orbiting bodies. It has been estimated that in a ''quadrillion'' (ten to the fifteenth) years, it will have lost all of them.[[/note]]

The official IAU definition for fictional names of features on Charon is items and milestones of "fictional space".[[note]]Charon ''was'' discovered in 1978, which was arguably the heyday of science fiction on TV.[[/note]] With that one, the ''New Horizons'' team is really going to town. [[Franchise/StarTrek Vulcan Planum]] (with [[Creator/LeonardNimoy Spock Crater]]), [[Series/DoctorWho Gallifrey Macula]], [[Franchise/{{Alien}} Ripley Crater and Nostromo Chasma]], Manga/{{Macross}} and [[Series/{{Firefly}} Serenity Chasmae]], [[Franchise/StarWars Organa, Skywalker and Vader Craters]]...

The official IAU definition for fictional names of features on Pluto is items from global underworld mythos, leading to the use of [[Series/TheLordOfTheRings Balrog Macula]] and [[Creator/HPLovecraft Cthulhu Regio]]. Most features are named for real astronomers (Tombaugh Regio, a.k.a. "Pluto's Heart"), real explorers (Hillary Montes and Norgay Montes), and real spacecraft (Sputnik Planum, Voyager Terra).

* UsefulNotes/{{Jupiter}}: The largest of them all, and thus fittingly named after the Roman God of Gods. Of course, [[OlderThanTheyThink the Romans named it that long before they had any idea just how big it was]]. Jupiter is ''vast'', often referred to as a "failed brown dwarf" and while not as dense as Earth, it has a magnetic field some 20,000 times stronger than our world does. Jupiter is... ''odd'', and by extension makes our solar system unusual. Gas giants have the tendency to migrate inwards towards their stars, becoming "hot jupiters". This happened in our system, and it would have come in like a wrecking ball... until the formation of Saturn. Saturn pulled Jupiter outwards, allowing the rocky terrestrial worlds to form. Jupiter has been described as a cosmic vacuum [[BigBrotherInstinct protecting us from comets and other asteroids]] that would otherwise [[TheEndOfTheWorldAsWeKnowIt obliterate all life on Earth]].

* [[UsefulNotes/DwarfPlanets Pluto]]– Charon[[note]](along with four smaller moons--Nix, Hydra, Kerberos, and Styx)[[/note]][[note]]Charon's status is itself a subject of debate. It is currently classified as Pluto's largest natural satellite, but the IAU has yet to clearly define what a natural satellite is. Some argue that because the Pluto-Charon barycenter lies in the empty space between the two bodies, Charon should be classified as a dwarf planet.[[/note]]

!!Dwarf Planets

* [[http://en.wikipedia.org/wiki/Pluto Pluto]]–[[http://en.wikipedia.org/wiki/Charon_(moon) Charon]][[note]](along with four smaller moons--Nix, Hydra, Kerberos, and Styx)[[/note]][[note]]Charon's status is itself a subject of debate. It is currently classified as Pluto's largest natural satellite, but the IAU has yet to clearly define what a natural satellite is. Some argue that because the Pluto-Charon barycenter lies in the empty space between the two bodies, Charon should be classified as a dwarf planet.[[/note]]
* [[http://en.wikipedia.org/wiki/Haumea_(dwarf_planet) Haumea]][[note]](it has two moons--Hi'iaka and Namaka)[[/note]]
* [[http://en.wikipedia.org/wiki/Makemake_(dwarf_planet) Makemake]]
* [[http://en.wikipedia.org/wiki/Eris_(dwarf_planet) Eris]][[note]](it is accompanied by a single known moon, Dysnomia)[[/note]][[note]]When first discovered, it was nicknamed [[Series/XenaWarriorPrincess Xena]]. No, Dysnomia was never referred to in any official context as "[[{{Sidekick}} Gabrielle]]".[[/note]]

Look at the page image for ConvenientlyClosePlanet. That's just the Earth–moon system to scale. The planets are much, much farther apart than this.

** [[http://en.wikipedia.org/wiki/Comet_Halley Halley's Comet]]: The best-known of all comets, because it's large enough to be seen from Earth and (unlike most large-ish comets) has an orbital period short and predictable enough that the average human has at least one opportunity in their lifetime to see it.

** UsefulNotes/TheMoon(AKA, Luna): Our nearest neighbor, and the only celestial body beyond Earth that has been explored by humans in person ([[UsefulNotes/ConspiracyTheories allegedly]]). It is theorized that the Moon is the left over debris from [[EarthShatteringKaboom a giant impact event]] with a proto-Earth and a Mars' sized object called Theia. Another theory holds that both Theia and the proto-Earth were completely destroyed by the impact, then the debris coalesced to form Earth and the Moon. Or even that they collided ''twice'' before ending up in their current forms. The Moon is a very unusual object (while not the largest moon in the solar system, relative to the size of its planet it's enormous) and the high angular momentum of the Earth-Moon system is even more unusual, and dramatic events were needed to bring it into existence. It's also Tidal Locked, which means it's in a synchronous rotation with Earth, such that the same face is always pointing towards the Earth at all times. This is not as remarkable or unusual as it may appear.

** UsefulNotes/TheMoon: Our nearest neighbor, and the only celestial body beyond Earth that has been explored by humans in person ([[UsefulNotes/ConspiracyTheories allegedly]]). It is theorized that the Moon is the left over debris from [[EarthShatteringKaboom a giant impact event]] with a proto-Earth and a Mars' sized object called Theia. Another theory holds that both Theia and the proto-Earth were completely destroyed by the impact, then the debris coalesced to form Earth and the Moon. Or even that they collided ''twice'' before ending up in their current forms. The Moon is a very unusual object (while not the largest moon in the solar system, relative to the size of its planet it's enormous) and the high angular momentum of the Earth-Moon system is even more unusual, and dramatic events were needed to bring it into existence.