The small red dwarfRoss 248 will pass within 3.024 light years of Earth, becoming the closest star to the Sun.[11] It will recede after about 8,000 years, making first Alpha Centauri again and then Gliese 445 the nearest stars[11] (see timeline).
At some point in the next "several" hundred thousand years, the Wolf-Rayet starWR 104 is expected to explode in a supernova. It has been suggested that it may produce a gamma ray burst that could pose a threat to life on Earth should its poles be aligned 12° or lower towards Earth. The star's axis of rotation has yet to be determined with certainty.[22]
Earth will likely have undergone a supervolcanic eruption large enough to erupt 3,200 km3 of magma, an event comparable to the Toba supereruption 75,000 years ago.[18]
The star Gliese 710 will pass as close as 13,365 AU (0.2 light years to the Sun) before moving away. This will gravitationally perturb members of the Oort cloud, a halo of icy bodies orbiting at the edge of the Solar System, thereafter increasing the likelihood of a cometary impact in the inner Solar System.[28]
2 million
Estimated time required for coral reef ecosystems to physically rebuild and biologically recover from current human-caused ocean acidification.[29]
2 million+
The Grand Canyon will erode further, deepening slightly, but principally widening into a broad valley surrounding the Colorado River.[30]
Even without a mass extinction, by this time most current species will have disappeared through the background extinction rate, with many clades gradually evolving into new forms.[34] (However, without a mass extinction, there will now be an ecological crisis requiring millions of years of recovery).
50 million
Maximum estimated time before the moon Phobos collides with Mars.[35]
Estimated time until a gamma ray burst, or massive, hyperenergetic supernova, occurs within 6,500 light-years of Earth; close enough for its rays to affect Earth's ozone layer and potentially trigger a mass extinction, assuming the hypothesis is correct that a previous such explosion triggered the Ordovician–Silurian extinction event. However, the supernova would have to be precisely oriented relative to Earth to have any negative effect.[50]
The Sun's increasing luminosity begins to disrupt the carbonate–silicate cycle; higher luminosity increases weathering of surface rocks, which traps carbon dioxide in the ground as carbonate. As water evaporates from the Earth's surface, rocks harden, causing plate tectonics to slow and eventually stop. Without volcanoes to recycle carbon into the Earth's atmosphere, carbon dioxide levels begin to fall.[52] By this time, carbon dioxide levels will fall to the point at which C3 photosynthesis is no longer possible. All plants that utilize C3 photosynthesis (~99 percent of present-day species) will die.[53]
800 million
Carbon dioxide levels fall to the point at which C4 photosynthesis is no longer possible.[53] Free oxygen and ozone disappear from the atmosphere. Multicellular life dies out.[54]
The Sun's luminosity has increased by 10 percent, causing Earth's surface temperatures to reach an average of ~320 K (47 °C, 116 °F). The atmosphere will become a "moist greenhouse", resulting in a runaway evaporation of the oceans.[55] Pockets of water may still be present at the poles, allowing abodes for simple life.[56][57]
The Sun's increasing luminosity causes its circumstellar habitable zone to move outwards; as carbon dioxide increases in Mars's atmosphere, its surface temperature rises to levels akin to Earth during the ice age.[54][58]
2.3 billion
The Earth's outer core freezes, if the inner core continues to grow at its current rate of 1 mm per year.[59][60] Without its liquid outer core, the Earth's magnetic field shuts down,[61] and charged particles emanating from the Sun gradually deplete the atmosphere.[62]
2.8 billion
Earth's surface temperature, even at the poles, reaches an average of ~422 K (149 °C; 300 °F). At this point, life, now reduced to unicellular colonies in isolated, scattered microenvironments such as high-altitude lakes or subsurface caves, will completely die out.[52][63][注釈 4]
3 billion
Median point at which the Moon's increasing distance from the Earth lessens its stabilising effect on the Earth's axial tilt. As a consequence, Earth's true polar wander becomes chaotic and extreme.[64]
3.3 billion
One percent chance that Jupiter's gravity may make Mercury's orbit so eccentric as to collide with Venus, sending the inner Solar System into chaos and potentially leading to a planetary collision with Earth. Other possible scenarios include Mercury colliding with the Sun, being ejected from the Solar System, or colliding with Earth.[65]
3.5–4.5 billion
The amount of water vapour in the lower atmosphere increases to 40%. This, combined with the luminosity of the Sun reaching roughly 35–40% more than its present-day value, will result in Earth's atmosphere heating up and the surface temperature skyrocketing to roughly 1,600 K (1,330 °C; 2,420 °F), hot enough to melt surface rock.[66][67][68][69] This essentially will make the planet much like how Venus is today.[70]
Earth and Mars may become tidally locked with the expanding subgiant Sun.[58]
7.59 billion
The Earth and Moon are very likely destroyed by falling into the Sun, just before the Sun reaches the tip of its red giant phase and its maximum radius of 256 times the present day value.[76][注釈 5] Before the final collision, the Moon possibly spirals below Earth's Roche limit, breaking into a ring of debris, most of which falls to the Earth's surface.[77]
7.9 billion
The Sun reaches the tip of the red-giant branch of the Hertzsprung–Russell diagram, achieving its maximum radius of 256 times the present day value.[78] In the process, Mercury, Venus, very likely Earth, and possibly Mars are destroyed.[76]
During these times, it is possible that Saturn's moon Titan could achieve surface temperatures necessary to support life.[79]
8 billion
The Sun becomes a carbon-oxygen white dwarf with about 54.05 percent its present mass.[76][80][81][注釈 6] At this point, if somehow the Earth survives, temperatures on the surface of the planet, as well as other remaining planets in the Solar System, will begin to start dropping rapidly, due to the white dwarf Sun emitting much less energy than it does today.
If the Earth and Moon are not engulfed by the Sun, by this time they will become tidelocked, with each showing only one face to the other.[84][85] Thereafter, the tidal action of the Sun will extract angular momentum from the system, causing the lunar orbit to decay and the Earth's spin to accelerate.[86]
The cosmic microwave background cools from its current temperature of ~2.7 K to 0.3 K, rendering it essentially undetectable with current technology.[88]
450 billion
Median point by which the ~47 galaxies[89] of the Local Group will coalesce into a single large galaxy.[4]
800 billion
Expected time when the net light emission from the combined "Milkomeda" galaxy begins to decline as the red dwarf stars pass through their blue dwarf stage of peak luminosity.[90]
1012 (1 trillion)
Low estimate for the time until star formation ends in galaxies as galaxies are depleted of the gas clouds they need to form stars.[4]
The universe's expansion, assuming a constant dark energy density, multiplies the wavelength of the cosmic microwave background by 1029, exceeding the scale of the cosmic light horizon and rendering its evidence of the Big Bang undetectable. However, it may still be possible to determine the expansion of the universe through the study of hypervelocity stars.[87]
4x1012 (4 trillion)
Estimated time until the red dwarf star Proxima Centauri, the closest star to the Sun at a distance of 4.25 light-years, leaves the main sequence and becomes a white dwarf.[91]
1.2x1013 (12 trillion)
Estimated time until the red dwarf VB 10, as of 2016 the least massive main sequence star with an estimated mass of 0.075 M☉, runs out of hydrogen in its core and becomes a white dwarf.[92][93]
3×1013 (30 trillion)
Estimated time for stars (including the Sun) to undergo a close encounter with another star in local stellar neighborhoods. Whenever two stars (or stellar remnants) pass close to each other, their planets' orbits can be disrupted, potentially ejecting them from the system entirely. On average, the closer a planet's orbit to its parent star the longer it takes to be ejected in this manner, because it is gravitationally more tightly bound to the star.[94]
1014 (100 trillion)
High estimate for the time until normal star formation ends in galaxies.[4] This marks the transition from the Stelliferous Era to the Degenerate Era; with no free hydrogen to form new stars, all remaining stars slowly exhaust their fuel and die.[3]
Collisions between brown dwarfs will create new red dwarfs on a marginal level: on average, about 100 stars will be shining in what was once the Milky Way. Collisions between stellar remnants will create occasional supernovae.[4]
1015 (1 quadrillion)
Estimated time until stellar close encounters detach all planets in star systems (including the Solar System) from their orbits.[4]
By this point, the Sun will have cooled to five degrees above absolute zero.[95]
1019 to 1020 (10–100 quintillion)
Estimated time until 90%–99% of brown dwarfs and stellar remnants (including the Sun) are ejected from galaxies. When two objects pass close enough to each other, they exchange orbital energy, with lower-mass objects tending to gain energy. Through repeated encounters, the lower-mass objects can gain enough energy in this manner to be ejected from their galaxy. This process eventually causes the Milky Way to eject the majority of its brown dwarfs and stellar remnants.[4][96]
1020 (100 quintillion)
Estimated time until the Earth collides with the black dwarfSun due to the decay of its orbit via emission of gravitational radiation,[97] if the Earth is not ejected from its orbit by a stellar encounter or engulfed by the Sun during its red giant phase.[97]
1030
Estimated time until those stars not ejected from galaxies (1%–10%) fall into their galaxies' central supermassive black holes. By this point, with binary stars having fallen into each other, and planets into their stars, via emission of gravitational radiation, only solitary objects (stellar remnants, brown dwarfs, ejected planets, black holes) will remain in the universe.[4]
2×1036
The estimated time for all nucleons in the observable universe to decay, if the proton half-life takes its smallest possible value (8.2×1033 years).[98][99][注釈 7]
3×1043
Estimated time for all nucleons in the observable universe to decay, if the proton half-life takes the largest possible value, 1041 years,[4] assuming that the Big Bang was inflationary and that the same process that made baryons predominate over anti-baryons in the early Universe makes protons decay.[99][注釈 7] By this time, if protons do decay, the Black Hole Era, in which black holes are the only remaining celestial objects, begins.[3][4]
1065
Assuming that protons do not decay, estimated time for rigid objects, from free-floating rocks in space to planets, to rearrange their atoms and molecules via quantum tunneling. On this timescale, any discrete body of matter "behaves like a liquid" and becomes a smooth sphere due to diffusion and gravity.[97]
Estimated time until the central black hole of S5 0014+81, as of 2015 the most massive known with the mass of 40 billion solar masses, dissipates by the emission of Hawking radiation,[100] assuming zero angular momentum (non-rotating black hole). However, the black hole is on the state of accretion, so the time it takes may be longer than stated on the left.
1.7×10106
Estimated time until a supermassive black hole with a mass of 20 trillion solar masses decays by the Hawking process.[100] This marks the end of the Black Hole Era. Beyond this time, if protons do decay, the Universe enters the Dark Era, in which all physical objects have decayed to subatomic particles, gradually winding down to their final energy state in the heat death of the universe.[3][4]
10200
Estimated high time for all nucleons in the observable universe to decay, if they don't via the above process, through any one of many different mechanisms allowed in modern particle physics (higher-order baryon non-conservation processes, virtual black holes, sphalerons, etc.) on time scales of 1046 to 10200 years.[3]
101500
Assuming protons do not decay, the estimated time until all baryonic matter has either fused together to form iron-56 or decayed from a higher mass element into iron-56.[97] (see iron star)
Low estimate for the time until all objects exceeding the Planck mass[出典無効] collapse via quantum tunnelling into black holes, assuming no proton decay or virtual black holes.[97] On this vast timescale, even ultra-stable iron stars are destroyed by quantum tunnelling events. First iron stars of sufficient mass will collapse via tunnelling into neutron stars. Subsequently, neutron stars and any remaining iron stars collapse via tunnelling into black holes. The subsequent evaporation of each resulting black hole into sub-atomic particles (a process lasting roughly 10100 years) is on these timescales instantaneous.
Estimated time for a Boltzmann brain to appear in the vacuum via a spontaneous entropy decrease.[6]
High estimate for the time until all matter collapses into neutron stars or black holes, assuming no proton decay or virtual black holes,[97] which then (on these timescales) instantaneously evaporate into sub-atomic particles.
Because the total number of ways in which all the subatomic particles in the observable universe can be combined is ,[102][103] a number which, when multiplied by , disappears into the rounding error, this is also the time required for a quantum-tunnelled and quantum fluctuation-generated Big Bang to produce a new universe identical to our own, assuming that every new universe contained at least the same number of subatomic particles and obeyed laws of physics within the range predicted by string theory.[104]
By this point, halfway through the precessional cycle, Earth's axial tilt will be reversed, causing summer and winter to occur on opposite sides of Earth's orbit. This means that the seasons in the northern hemisphere, which experiences more pronounced seasonal variation due to a higher percentage of land, will be even more extreme, as it will be facing towards the Sun at Earth's perihelion and away from the Sun at aphelion.[145]
Comet C/1999 F1 (Catalina), one of the longest period comets known, returns to the inner solar system, after traveling in its orbit out to its aphelion 66,600 A.U. (1.05 light years) from the Sun and back.[155]
The Waste Isolation Pilot Plant, for nuclear weapons waste, is planned to be protected until this time, with a "Permanent Marker" system designed to warn off visitors through both multiple languages (the six UN languages and Navajo) and through pictograms.[161] (The Human Interference Task Force has provided the theoretical basis for United States plans for future nuclear semiotics.)
^ There is a roughly 1 in 100,000 chance that the Earth might be ejected into interstellar space by a stellar encounter before this point, and a 1 in 3 million chance that it will then be captured by another star. Were this to happen, life, assuming it survived the interstellar journey, could potentially continue for far longer.
^ This has been a tricky question for quite a while; see the 2001 paper by Rybicki, K. R. and Denis, C. However, according to the latest calculations, this happens with a very high degree of certainty.
^Based upon the weighted least-squares best fit on p. 16 of Kalirai et al. with the initial mass equal to a solar mass.
^ ab Around 264 half-lives. Tyson et al. employ the computation with a different value for half-life.
^Although listed in years for convenience, the numbers beyond this point are so vast that their digits would remain unchanged regardless of which conventional units they were listed in, be they nanoseconds or star lifespans.
^ Manually calculated from the fact that the calendars were 10 days apart in 1582 and grew further apart by 3 days every 400 years. 1 March AD 48900 (Julian) and 1 March AD 48901 (Gregorian) are both Tuesday. The Julian day number (a measure used by astronomers) at Greenwich mean midnight (start of day) is 19 581 842.5 for both dates.
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