Theory For the Braves of Heart: The Potential Threats to Earth from the Universe!

It is not inordinately question, in the traditional amateur astronomy literature of dangers that cosmic events would brought Earth. Largest threat asserted in the amateur community in the 1970s was that Sun was going to "fry" Earth, 5 billion years from now, becoming a red giant. Assertion of such threats is clearly contemporary and certainly reflects a passage to what may be called catastrophism. It looks like some wrong ways might have been taken at one moment, bringing astronomers to interest themselves into considerations which, until then, had always been left apart. Military space programs, on a other hand, aiming at monitoring nuclear explosions also brought to more interest in those domains as events such as NEOs or energetic explosions in the Universe might interfere. A additional explanation is that a new collective representation would have developed among the community of profesional astronomers. The neodarwinist, string theorecists, on a other hand, are the other proponents of catastrophism in astronomy with specific scenarios of how Earth might come to be destroyed by the forces in the Universe like: collisions between planets of the solar system due to the irregularities of the orbit of Mercury or the close flyby of a star; the Earth's rotation halting; the Earth elongated and destroyed between two black holes, or destroyed from inside by a small black hole dating back to the time when, after the Big Bang, numerous such black holes would have been formed; disparition of gravity; antimatter; a strangelet made from up, down and strange quarks; or the survenance of a collision between branes, those elements of the conception of the Universe like engaged into a eternal cycling course The following list is for the braves of heart, as it's showing the potential dangers linked to astronomy, we might elaborate a count of. And, beware! Those are just the threats coming from the Universe, astronomically speaking, as other, various, weather, geological, or others threats might be listed as well, further thrilling you!... As far closest threats are concerned, they are noted unaccurate should they have proved such

Apart Joking. Most Likely Catastrophic Events for Earth and Humans
Apart from the long list below of catastrophes lurking, from an astronomical point of view, in the Universe about Earth, here are (as taken from a list issued by the FOXNews Internet site in January 2009), the most likely catastrophes capable of hitting our planet, and ourselves:

• A Medium-Sized Asteroid Impact: apart from the Tunguska impact which destroyed acres of forest in Siberia by the beginning of the 20th century, it has been evidenced that more such medium-sized impactors have hit Earth, like near New York about 300 B.C., in eastern Canada about 11,000 B.C., or the famed Meteor Crater, 50,000 years ago. Such impactors are causing regional destructions only
  
• A Massive Volcanic Eruption: on an unknwon scale of time, massive volcanic events like those who created the Siberia and Indian Traps through spreading lava in every direction for hundred of miles,and releasing deadly gas, smoke and soot in the Earth' atmosphere during tens of thousands of years, would certainly brought to a mass extinction on the planet! Some lesser volcanic events of the kind are dangerous too, the most famed -and likely most to come- one, being the 'Yellowstone supervolcano', sitting atop a massive magma chamber, the eruption of which likely would kill any people living between the Rockies and the Appalachians. Some think that Yellowstone supervolcano next eruption is overdue as occurring each 600,000 years and the last one have occurred about 640,000 years ago, or, also, that the eruption would have global effects and not only in the sole USA. Such so-called 'supervolcanoes' are 6 of their kind nowadays with three located in the USA, one in the Yellowstone National Park in Wyoming, on in Long Valley, Calif., and one in Valles Caldera, N.M. Some catastrophic volcanism could also trigger major tectonic plate movement on the planet. On the other hand, a lesser, but major, volcanic eruption could occur within a lifetime, or hundreds of years from now and trigger one 'year without summer' for some areas of the world
  
• A Nuclear War: albeit the Cold War is over now and that no power in the world today has the thousands of warheads it would take for a 'nuclear winter', a new nuclear race between some new superpowers would bring to the same scenario. Such a global nuke war would husher amounts of dust, smoke and soot into the atmosphere, blocking Sun's light and causing a mass extinction. The post-nuclear radioactive particles falling back Earth would complete the destruction. The atmospheric soot further would also destroy the ozone layer
  
• A Black Hole Approaching our Solar System: with the orbits of the solar system distorted and the gravitational pulls disrupting Earth, the whole of the solar system would eventually get into orbit around the black hole, and swallowed. Some fear that large-power particles colliders, like the LHC recently opened in Geneva, Switzerland, might yield a black hole
  
• The Sun Turning a Red Giant: the Sun, in 5 billion years from now, is to turn into a red giant star, eventually engulfing the orbits of the planets until Mars. The beginnings of that end would lurk as soon as in one billion years from now, with the heat of the Sun beginning to already alter the Earth's climate
  
• Also Not Mere Speculation: a GRB located 30 light-years away and pointed in our direction with frying the atmosphere and global fires, a magnetic poles reversal forcing people using goggles and headgear or stay indoors, mind-altering agents manipulating people's brain, strangelets or vacuum instabilities tearing the fabric of space and fabricated by some science experiments, thinking, self-replicating or recursive self-improvement AI computers could ultimately create pandemonia or take control, a deadly contagion with sterilizating procedures now forgotten, or even a Internet collective, self-destructive bad idea are some other of the threats which may considered not a mere speculation altogether

Less Nature, More Societal! A study at the Oxford University in 2015 is listing the potential threats to Earth by order of probability, from the least to the larger, which much more societal than natural:

• A 5-kilometer accross asteroid enough to end civilisation 0.00013 percent
• Artificial intelligence taking over the world and sweeping humans out 0-10 percent
• A supervolcano bringing a volcanic winter 0.00003 percent
• A ecological collapse. probability: na
• Bad global governance. probability: n/a
• Global system collapse. probability: n/a
• A global pandemic 0.0001 percent
• A nuclear war 0.005 percent
• Extreme climate change 0.01 percent
• Synthetic biology with new super-organisms 0.01 percent
• Nanotechnology 0.01 percent

A list, by chronologicial order of what could threaten Earth, from the Universe!

• 2012 A.D.: due to the Earth axis' wobble which generates the precession about every 26,000 years, the Sun seems to be lining up each such intervall with the center of the Milky Way, at the time of winter solstice. This is now occurring next Dec. 21, 2012. Ancient Aztec texts, as studied by a 19th century Frenchman, Charles Etienne Brasseur de Bourbourg, a priest-turned-archaeologist, are predicting a doomsday for that day! Translated into some science, some galactic alignment could generate magnetic disturbances which could lead to a pole shift in a matter of day, or hours, changing the North to the South! Instead of being magnetic only, the pole shift would be a geophysical one, with the entire mantle of the Earth shifting, causing earthquakes or massive tsunamis threatening coastal cities. The fear of that day is also linked to the fact that the year 2012 is bound to be too, the year of the next solar maximum (UNACCURATE)
• Now or At a Undetermined Date: a coronal mass ejection (CME) coming from the Sun could annihilate all the power grids at Earth as it would need year for reconstruction. Satellites would also be affected as terrestrial societies which are more and more interconnected via the Internet would be seriously damaged
• 2027 A.D.: there is a 10 percent chance that a solar storm occurs, that will damage the world economy at the level of tens of trillions of dollars, comparable to the one in 1859, one of the largest on record which caused telegraph systems to fail worldwide
• 2036 A.D.: a NEO, which will have already passed near Earth on April 13th, 2029 and have had its trajectory modified during that first graze, presents the risk of a hit on April 13th, 2036, as the change in the orbit in 2029, will have placed it on an orbit onto which it might be captured into a keyhole by Earth, bringing it to a potential hit. More will be known by 2013, when the decision will be eventually made to send a mission to modify the orbit of the asteroid
• 100 years From Now: a tech-damaging solar superflare could (such events occur every few thousand years)
• 2600 A.D.: according to scientist Stephen Hawking, the Earth will become overcrowded, and increased energy consumption will turn Earth into a ball of fire because of the rising population and exponential consumption. He favors the Starshot Breakthrough journey to Alpha Centauri, also warning of the AI threat with a will of their own
• Between 100 Years and a Billion Years From Now: instead of a dynamo mechanism providing Earth with a magnetic field, it would be a Earth's center fission-based nuclear reactor which would yield it. This reactor would stop due to fuel's lack. Earth's magnetosphere would cease hence Earth's protection against solar radiations would be removed letting atmosphere exposed to erosion by solar wind. more details at NuclearPlanet.com (in English). A NASA Goddard Space Flight Center retired scientist stated (http://www.gsfc.nasa.gov/scienceques2002/20030103.htm) in January 2003 that even if magnetosphere was to disappear atmosphere would still protect Earth as it would be stripped by solar wind on a duration of some billion years only. He was supporting his views based on Venus retaining a very dense atmosphere despite lack of magnetic field and closeness to the Sun, or on Mars retaining one too though having no global magnetic field and a gravity one-third Earth's
• March, 16th, 2880 : asteroid 1950 DA, one kilometer in diameter, has one chance to 300 (highest probability; low probability: from 0 to 1 chance to 300) to hit Earth. March, 16th, 2880 is a Saturday. A computer simulation showed made in 2003 is showing that asteroid would hit in Atlantic Ocean and trigger 400ft high waves on USA East coast, 30-50 ft high on the European coasts. Asteroid is one kilometer in diameter. An object like Tunguska's (Siberia) in 1908, 100 to 160 ft wide, would destroy New-York. It is thought about how to deflect 1950 DA. We are left with some centuries ahead to get such technologies. more details about asteroids: "About NEOs"; more about 1950 DA see archives of the Science magazine, April, 5th 2002
• 2,500 Years From Now or undefined: Earth's magnetic field is flipping about each 300,000 years, reversing its polarity. Last time was 780,000 years ago. Recent studies are showing that Earth's magnetic field faded by 10 percent during last 150 years as north geomagnetic pole's motion is accelerating. This would not hint to field vanish and flip during next 2,500 years however but better to Earth's magnetic field being at onset of a so-called "excursion". Field would reverse and back, over a period of about 400 years. It would fade during this time lapse. South Atlantic anomaly is a region of the field already known as a place of a weakness, with effect on satellites and atmosphere. Such an excursion would surely have effects about Earth's climate and bring ecological changes on a global scale. A period of real reversal, which last during some thousands years would weaken the Earth's magnetosphere and expose more populations to the damaging effect of the solar and space radiations, heightening the number of cancers. Specialists also point to that that weakness of our magnetosphere also is concomitant to a weakness of the heliophere, that protective bubble of the Sun and the solar system. A geomagnetic flip would not momentarily leave Earth without the magnetic field that protects us from solar flares and coronal mass ejections from the Sun. A weaker field would certainly lead to a small increase in solar radiation on Earth as well as a beautiful display of aurora at lower latitudes but nothing deadly. Moreover, even with a weakened magnetic field, Earth's thick atmosphere also offers protection against the sun's incoming particles. There is no indication that Earth's magnetic field ever disappeared completely in the past. .
• Between 3,000 Years and Several Million Years From Now: Sun is currently in a thin galactic medium (0.3 particles per cm3). It might encounter a denser environment 3,000 years from now if one or two interstellar clouds, located between Sun and Proxima Centauri, really pass over us and several million years from now too as Sun might encounter another denser interstellar medium. Heliosphere, this bubble protecting solar system, would be more or less transformed and Earth more or less directly theatened. Traces of an increase of beryllium 1,060,000 and 33,000 years from now, are pointing to a modified galactic environment due to an increase of cosmic rays, a supernova shock-wave, and an encounter with a small dense piece of interstellar medium. Traces of more ancient supernova events are showing that a supernova explosion occurred less than 90 light-years away, 5 million years ago or that other supernovae yielded Pliocene-Pleistocene transition. Such supernovae almost certainly exploded in an interstellar cloud named "Sco-Cen", which is a feature of the local interstellar medium. It was then nearer to us than now and producing supernovae at an important rate. A recent study is showing that Local Bubble (Sun current interstellar medium) is inserted in an ensemble of bubbles and tunnels formed by supernovae explosions. Main feature of this network would be a vertical vent chimney evacuating hot gas from Milky Way. Sun is just in middle of this chimney. A wall of denser material is located at less than 200 light-years from us and it is unknown if it is moving towards us or away. Time range for all these questions is between 10,000 and 100,000 years or 2 or 3 times each billion years. When the Sun is crossing a dense interstellar dust cloud, this triggers a period of glaciation as such giant molecular clouds allowdust to accumulate into Earth's atmosphere. A resulting dust layer hovering over the Earth would absorb and scater solar radiation, yet allowing heat to escape from our planet. This would lead to a runaway ice formation and snowball glaciations. At least two of four glaciations, 600 to 800 million years ago, were snowball glaciations. Collisions with dense dust clouds are rare. Even a moderately dense space cloud may be devastating however. Even if such a cloud can not compress the edge of the heliosphere down to the Earth's orbit, as dust particles continue to be deflected, a large flow of hydrogen, from space clouds, triggers the Sun to greatly increase its production of ionized cosmic rays. On the other hand as such a passage into an interstellar cloud might take as long as 500,000 years, Earth would be expected to endure at least one magnetice reversal. During such a reversal, ionized cosmic rays can enter Earth's magnetosphere instead of being deflected. Cosmic rays would destroy as much as 40 percent of the ozone layer (up to 80 percent above the poles). Uranium 235/238 is found in interstellar material originating in supernovae explosions. New studies revealed by late 2009 that interstellar clouds are strongly magnetized. Any run of the Sun run into one such cloud along its journey in the Milky Way, would have the strong magnetic fields compress the heliosphere even more than it is now (due to such a cloud, the so-called 'Local Fluff' being near the border of the heliosphere and compressing it already the way it is), allowing more cosmic rays to reach the inner solar system, and affecting the Earth's climate
• 7000 Years From Now: West Antarctica platforms are melting since 10 000 years as a natural process and this could lead to an increase of 4.8 meters of the sea level
• 9800 Years From Now: Barnard star, a very fast proper motion star, is closing Sun and becomes nearest star to it (3.8 light-years) surclassing Proxima Centauri (4.25 light-years). Effect of this is unknown. ESA's Gaia mission made a census by 2018 of more than 7 million Sun-like stars' trajectories and it found that 9 stars are going to get closer to our solar system than Proxima Centauri is, in the next 5 million years. 17 stars came that close in the past
• Some Thousand Years From Now: a new ice age could begin about 10,000 AD (and it has already begun nowaday) due to an Earth's orbit cycle. It would last 90,000 years yielding temperatures 3° C cooler than today. Another ice age is forecasted beginning 2,000 years from now only, yielding temperatures 0.5° C cooler than today's. Another date for the next ice age on Earth is 60,000 years from now with the less manking worrying about the greenhouse effect, the later the ice age occurring, or even not occurring on a timelapse of 300,000 years
• 27,000 Years From Now: Earth's orbit eccentricity cyclical variations are bringing orbit to change between a circle and an ellipse. A circular orbit is yielding a glaciation, an elliptic a warm era. Next circular phase hence glaciation is to occur 27,000 years from now. This is maybe linked to previous item
• 36,000 Years From Now: red dwarf Ross 248 is coming close to the Sun at no less than 3 light-years. Effects are unknown
• 50,000 Years From Now: the overall encounter rate of stars sending Oort Cloud's comets into the inner solar system is one every 50,000 years in average, as they would come closer than 30 trillion miles (kilometers). The effects of such a flurry of comets are unknown
• 100 000 Years From Now: stars in Sun's neighbourhood are moving in average at 30 km per second and are spaced each other between 5 and 6 light-years. A star grazing Sun might expel Earth from its orbit. Odds for such an event are one to 100,000 on a duration of 3.5 billion years. We would then become a wandering and lonely planet in deep space. One star is passing within a few light years from Sun once every 1 million years, within 560 billion miles (900 billion km) -near that is: 250 times Pluto's orbit, 0.15 light-year- once every 36 million years (i.e. very often), and within 3,000 AU (75 times Pluto's orbit, 0.05 light-year i.e. really close) once each 400 millions years (i.e. often). Most of such stars are red dwarfs. Main effect of such passages is to send Oort cloud comets into inner solar system. Planetary impacts then would increase during million years. Such a comets flurry may be yielded too by Milky Way mass concentrations tidal forces or by Sun encountering an interstellar cloud (see above at "Between 3,000 Years and Several Million Years From Now"). A closer star graze -about 900 AU, i.e. about a little more than Kuiper Belt- is unlikely and occurred once only since solar system beginning. Since Sun's birth we already circled Milky Way 20 times

  click for a view of red dwarfs close approaches

• Undefined From Now: WR 104, a Wolf-Rayet star about 8,000 light years away, could go supernova any day from tomorrow to 500,000 years from now and its light and GRB reaching Earth, as that will depended upon the star's rotation. That should cause a 50 percent increase in UVB radiation and a quarter of the protective ozone wiped out. And the same for the MY Camelopardalis binary two stars of which could merge and located at about 13,000 light-years from Earth
• Undefined From Now: one of gas giants planet might start an atomic process and become a star. This is positively excluded for Jupiter however. Gas giants Jupiter and Saturn are somehow more similar to Sun than Earth and surely are intermediate types between Sun and Earth. Temperature at Jupiter's center is 30 000° C only. Temperatures of 16 million degrees C at Sun's center. All giant planets, Uranus excepted, continue to emit energy however. This is based on the fact that they contracted on themselves as they formed and are still doing now at a feeble pace. Uranus and Neptune attracted less hydrogen and helium than Jupiter and Saturn did
• 1.35 Million Years From Now: red dwarf Gliese 710 (which presently is 64 light-years away in constellation Serpens, the Serpent) is passing at 1,243 billion of miles from the Sun. It becomes one of brightest stars in the sky at magnitude -2.7 or the equivalent of Mars at a opposition). On another hand as star will pass through Oort Cloud this will increase the rate of comets falling into inner solar system by 50% as about 12 naked-eye comets will appear in Earth's sky each year during 3-4 million years
• 2,250,000 Years From Now: Great Bear stars mainly belong to a cluster 30 x 18 light-years wide, located 75 light-years from us. It is moving towards us at 10 km per second with a loose ensemble of a hundreth of stars, 100 light-years radius. Our Sun itself is part of this ensemble, on its outskirts
• Unspecified From Now: as Sun is moving in the Milky Way, it might encounter a globular cluster. Globular clusters have orbits leading them to cross Milky Way's plane. There are 200 globular clusters. Many are concentrated near galactic center. Mean distance between stars of a globular cluster is some tenths of light-year (5 to 6 in the normal solar neighbourhood, 2 to 3 in an open cluster). Such passages of globular clusters in galactic plane may trigger gas clouds collapse leading to star formation
• 5 Million Years From Now: cluster Collinder 399 (constellation of the Little Fox), containing 40 stars, is passing near Sun. According to Hipparcos measures this cluster might be a mere asterism. Cluster however is linked to 10 clusters (of them the Pleiades). All have an identical motion. One cluster at least might be coming in our direction. Time elapsing clusters are tending to dismantle. Pleiades will scatter 250 millions years from now. Open clusters usually scatter on durations of hundreds of millions of years, as some rare ones may reach about 1 billion years in age!
• Unspecified From Now: magnetars, those powerful neutron stars in terms of magnetic field, are enduring significant surface quakes. Albeit of a tiny size compared to the star's, they can have damageable effects upon the Earth's magnetosphere like hinted to during such a event which occurred 50,000 light-years away from us. A blast occurring within 10 light-years of our planet would furtherfry Earth's ozone layer as the closest magnetar known is 13,000 light-years away. Only 32 magnetars are known in our Milky Way Galaxy as they might be more numerous
• 20 Million Years From Now (or unspecified from now): a medium-sized black hole, remainder of a swallowed dwarf galaxy as absorbed by our own Milky Way Galaxy could lie on the path of the Sun around the Milky Way
• 26 Million Years From Now (or earlier): it might that collisions with large asteroids like those which triggered mass extinctions along the Earth's geological history, occur each 26 millions years. With the last one having occurred by the end of the dinosaurs era, 70 millions years ago, we might be long overdue... Some think that such collisions waves are triggered by a dark, distant companion of the Sun, which periodically perturbs comets in the Oort Cloud, sending some into the inner solar system, as another theory is stating that this is due to the solar system as a whole moving in and out, at interval, of the Milky Way Galaxy plane. That last possibility, moreover, would trigger, above all, the move towards the inner solar system of 'dark' comets, which would have lost their water ice through evaporation and thus largely being undetected and dark. That would be such dark comets which would have triggered the impact craters seen at Earth, and not the NEOs
• 30 Million Years From Now: the so-called 'Smith's Cloud' likely launched from the outer regions of the galactic disk around 70 million years ago as it is now boomeranging back, and expected to plow into the Milky Way’s disk in about 30 million years, likely to ignite a spectacular burst of star formation, perhaps providing enough gas to make 2 millions. That should happen in the Perseus Arm of our Milky Way Galaxy, which is not that far from our solar system. That should also modify the aspect of the Milky Way
• 35 Million Years From Now: cluster IC 4665, 30 stars, linked to Collinder 399 (see above), is passing near Sun
• 50 Million Years From Now: a new unique continent alike to Pangea -an ancient unique continent at a moment of Earth's history- is appearing due to plate tectonics. 250 million years from now a new unique continent would exist, entirely surrounded by water
• 100 Million Years From Now: as Sun gets older, its luminosity is increasing (see below at "In a Few Hundreds Million Years From Now"), and increases greenhouse at Earth. Earth already endures an important temperature increase. Due to the gravitational attraction of Moon, on a other hand, day's length on Earth turned to 24 hours 38 minutes
• 100 or 200 Million Years From Now (or Unspecified): gamma-rays bursts (GRBs) are hyper-energy jets resulting from supernovae events. They occur too in our Milky Way and might harm Earth yielding a mass extinction. High-energy gamma-rays flow would deplete ozone and let deadly UV radiations reach the surface, leading to widespread cancers and disease. To be harmful such bursts should happen about 1,000 light-years from Earth and the beam directed us. Such occurrence is seen every 100 or 200 million years. Harmful high energy radiations are yielded by other sources. Powerful quasars e.g. are emitting such radiations. Even gamma-ray bursts occurring outside our Galaxy might be harmful. GRB bursts occur almost daily and are so powerful that they can be seen across billions of light-years. A gamma-ray burst could affect Earth in much the same way as a supernova but at much greater distance, and only if its jet is directly pointed our way. Astronomers estimate that a gamma-ray burst could affect Earth from up to 10,000 light-years away with each separated by about 15 million years, on average. As with impacts, our planet likely has already experienced such events over its long history. more about GRBs

->A More Scientist's Approach to Some Energetic, Stellar Events in the Universe!
The university in Topeka, Kansas, as part of NASA's Exobiology and Evolutionary Biology Program, is embarking, since 2009, into a comprehensive study of all the possibly damaging energetic, stellar events which could send deadly radiations down to the vicinity of the Earth. The team plans to look into the following energetic events:
. supernova, as a couple of those are exploding in our Galaxy every century and damages being possible within a 10-light-year radius of the explosion
. long-duration GRBs, which are flows of gamma-rays, as generated by hyped supernovae, ten times more powerful than a supernova and the GRB emitted along the dying star's axis. Their range is in the order of 6,500 light-years. Their rate in the Milky Way Galaxy is varying with time as they might have been boosted in the past when our Galaxy merged with younger, small galaxies, with less heavy elements in those. From that time on, there could exist ticking-time stellar bombs in our Galaxy. One can speculate than, on average, a GRB explodes in the Milky Way Galaxy every 10 million years
. short-duration GRBs, which are thought to be the merger of two neutron stars, are releasing less energy than the previous kind, but with the fraction of high-energy gamma rays higher. Short-duration GRBs are more likely to occur in mature galaxies, like our Milky Way Galaxy, where neutrons stars are numerous
. soft gamma-ray repeaters (SGRs) are emitted by neutron stars, supposedly when the super-dense surface of them is cracking. Their damage range to Earth is of 10 light-years only. In 2004, as a SGR exploded 50,000 light-years away from the Earth, the energy released was still strong enough to disrupt radio waves on Earth! Their occurrence rate is unknown

• 200 or 300 Million Years From Now: an important and dense cloud of matter located around Milky Way center is increasing in density. This will is trigger a burst of star formation. Such star will turn supernovae at the important rate of one supernova every year. Explosions will be too far away from Earth to be seen naked eye. Such a star burst could transform our Galaxy into a M 82-shaped galaxy. Milky Way would become a type Ir-II galaxy, an irregular galaxy of type II. M82 started its process of high rate star formation 20 to 50 million years ago. Such a star burst is happening happens every 500 million years as gas, as a natural process is attracted towards Galaxy center. The Milky Way's supermassive black hole would also trigger two polar jets. Such a episode in any case should not harm Earth albeit a large increase in the emission of X-rays might be potentially dangerous to any planet close to or on the line of emission
• 230 Million Years From Now: a stellar black hole passes at more than 1,000 light-years from Earth. This should not yield any danger. The collisions between a star and a black hole are not ruled out by astronomers. This stellar black hole is presently in Milky Way plane, 6,000 to 9,000 light-years away. Some 1 million stellar black holes are moving among Milky Way. Stellar black holes may be the ultimate result of a supernova event. Other potentially dangerous objets which are located in a radius of about 3,000 light-years from us are, for example, pulsars, mini-quasars, or supernovae remnants. A stellar-mass black hole passing along Neptune would significantly modify the Earth's orbit. A whopping 100,000,000 isolated black holes are likely lurking somewhere in our Milky Way Galaxy, and potentially much closer than the one thought to be nearest to our planet, located less than 3,000 lightyears away from Earth. Any passage could either disrupt Earth, or put NEOs on course to us
• 235 Million Years From Now: a group of stars comes to reach our solar system. Such passages may trigger gravitational consequences among the comets of the Oort Cloud or also other gravitational effects upon the Sun and the solar system
• Undefined From Now: places of high density dark matter might exist inside our Milky Way. Whether dark matter would be of the WIMPs kind (see at How is Matter Distributed in the Universe?) Earth's passage in such an environment would trigger genetic mutations (cancers, etc) and volcanism as Earth's core would heat. Interestingly Permian-Triassic extinction, 250 million years ago, might be a two-fold one matching such a passage. Dark matter would first act swiftly on living beings, then WIMPs geological interaction occur. Another mass extinction period, the Devonian extinction (364 million years ago) would too be a two-fold extinction
• A Few Hundred Million Years From Now: due to Sun increased luminosity and heat, and to a correlative increased greenhouse effect at Earth the latter is tens of degrees warmer. See, too, below at "1 Billion Years From Now"
• 250 Million Years From Now: a reassembly of the continents at Earth and the Sun increased luminosity are yielding a mass extinction of plant and animals life
• About 300 Million Years From Now: a loose cluster of stars is passing close to our solar system, which could trigger possible gravitational disturbances
• 500 Million Years From Now: mankind, animals, and plants do not exist anymore at Earth. Sun increased luminosity renders such forms of life impossible
• 670 Million Years From Now: should a supernova explode about 26 light-years from Earth, such an event would be harmful. Such an occurrence exists about every 670 million years. Gamma-rays reaching us during one year would erode 47 percent of ozone layer. Biosphere would endure significant and lasting damages. During a further 10 years and although ozone would have cured by itself, Earth would experiment a cosmic rays hammering. Such close supernovae explosions might have been at the origin of one or more mass extinctions during the last few hundreds million years (see, too, above at "between 3,000 years and several million years from now"). Main mass extinctions are: Ordovician ( 440 million years ago, 2/3 of all species), Devonian (360 million years ago, 60 percent of all species), Permian-Triassic (250 million years ago, 90 percent of any form of life), Triassic (220 million years ago, half of all species); Cretacious-Tertiary event (65 million years ago, dinosaurs and half of all other species). Ordovician extinction might have been triggered by a supernova explosion at 10,000 light-years from Earth (atmosphere was degraded by gamma-ray radiation and let pass ultraviolet radiation; atmosphere then became dark and triggered an ice age). Given the vastness of space and the long times between supernovae, astronomers can say with certainty that there is no threatening star close enough to hurt Earth. They estimate that, on average, about one or two supernovae explode each century in our Galaxy. Only those who would explode at less than 50 light-years away would hurt. X- and gamma-ray radiation would damage the ozone layer. At some wavelengths, just a 10 percent increase in ground-level UV could be lethal to some organisms, including phytoplankton near the ocean surface. Because these organisms form the basis of oxygen production on Earth and the marine food chain, any significant disruption to them could cascade into a planet-wide problem
• 750 Million Years From Now: Sagittarius dwarf galaxy is eventually swallowed by our Milky Way. This event is somehow similar to a galaxy encounter
• 1 Billion Years From Now: 'Active Galactic Nuclei,' or AGN are active galaxies with a strong star formation rate. Some may merge together. A large number of forecast mergers, which should occur 1 billion years from now, are located at less than 650 million light-years from us. Consequences of the merger between two AGNs are unknown
• 1 Billion Years From Now: Sun is now 11 percent brighter than now making Earth inhospitable. there is a moist greenhouse effect as all water is turned into water vapor. Day's length, due to Moon's gravity, on a other hand, increased to 30 hours and 23 minutes
• 2 to 3 Billion Years From Now: the pull of our Moon is changing the precession of equinoxes at Earth, yielding a larger inclination of Earth's polar axis, thus a climate change
• 3.5 Billion Years From Now: Sun is now 40 per cent brighter than now. Oceans evaporate completely; Earth becomes similar to Venus
• Between 1 Billion and 4 Billion Years From Now: the Milky Way might face the threat that it could collide with the Large Magellanic Cloud. It would head straight to the center of the Milky Way, unfolding over the course of billions of years. That could wake up the supermassive black hole there, as our Sun could be among the small fraction of stars getting lobbed from the Galaxy. The Milky Way would easily devour the smaller Large Magellanic Cloud and maintain its signature spiral shape, even if its insides will be all jumbled. The collision could also awaken dormant black holes or trigger cosmic radiation, not taking in account to send gaz and stars into the Milky Way's supermassive black hole having its size increased by 8 times or even changing it into a quasar. Scientists think that any risk to life on Earth however, is 'very unlikely'
• Between 3 to 4 Billion Years From Now: there is a one percent chance that a disruption of the orbits might lead to a collision between the Earth, Mercury, Mars, or Venus. The risk might be generated by Mercury, as there is a one percent chance that the elongation of the planet's orbit would increase due to gravitationel interaction by Jupiter, and slam into Venus'! Mercury would then be tossed out from the solar system, or slam into the Sun or Venus, at the least, as worst -less possible in terms of chance- scenarios would have the move destabilizing the inner solar system as a whole and Earth collided by Mercury, Mars, or Venus. The destabilization of Mercury would destabilize Mars which would graze Earth as Venus would eventually be disturbed and come to crash. Mars might be tossed out of the solar system too by the disruption! That is due to the general instability of the orbits in a solar system, with orbits slowly evolving, along eons, through gravitational tugs. The fact that the Sun is expected to swell and lose mass will add on a timespan of about 7 billion years. Encounters with large solar system's dwellers like Jupiter could also fling the ejected planets into entirely new orbits. Evidence of such notable evolutions are found in the exo-solar systems, which can be observed around other stars, as, further, the general relativity has an impact of the evolution. The collisions between planets could form new worlds of their own
• Between 5 and 7 Billion Years From Now: Sun has become a red giant; temperature at Earth's surface is of 212°F (100°C), with winds running at 6,200 miles par hour (10,000 km/h)! Earth is eventually vaporized as its orbit is encompassed by Sun expansion. The Earth, in the process of the Sun's swelling, might even be tossed out of the solar system by a passing nearby star, with a chance of one-in-100,000! Sun might expell a planetary nebula expanding at 15 miles per second, reaching us in 70 days. Two authors, Fred Adams, and NASA Gregory Laughlin propose a method to gradually stretch Earth's orbit up to 50% more in a few billion years. Earth orbit growth would match Sun luminosity increase. An asteroid or a comet (about 62 miles wide) with a path already Earth bound would be deviated by retrorockets so they pass nearer still Earth. This would yield Earth an effect similar to a gravity-assist flyby. Earth would be slightly pulled (about some miles) further from Sun. Intervening body would then head back to its aphelion regaining some orbital energy at Jupiter and Saturn. Operation would be repeated each 6,000 years. Operation is hazardous however: we could loose Moon, as Mars would have too to be moved further to make room Earth. At last such a passage of an object 10 times larger than one which killed dinosaurs, would occur at 10,000 miles Earth only presenting obvious collision risks. About this question, it has been said too that as Sun somehow would loose some of its gravity strength allowing Earth to naturally move away (mass loss at Sun should be of 20 percent). Another danger is that Sun in its red giant process might even become a stellar black hole. A last point on the question, at last, is that the transformation of the Sun into a red giant will bring too that the distance of the Moon to the Earth will be dramatically decreased, with an eventual close encounter crushing our satellite due to the gravitational tugs exerting on it
• 5 Billion Years From Now (or Between 6 to 8 Billion Years From Now) : our Milky Way is now colliding with M31, Andromeda galaxy. Main harmful consequence of such a collision is the merger of galactic black holes, triggering shock-waves, radiations, and gravitationel waves. Both galaxies would eventually turn into a single giant elliptical galaxy. Contrarily to what might be expected, such an encounter is not directly harmful to stars and planets -albeit a possibility remains that Earth be either ejected out, into the interstellar -or even intergalactic space, or moved into the supermassive black hole and destroyed. One unlikely but remotely possible outcome is that the Sun might be expelled from the resulting galaxy, or that the Earth orbit be disturbed by a stellar nearby passage. There is enough space between stars to avoid collision at this level. Stars very rarely collide with each other but as the galaxies entangle themselves, strong tidal effects produce new structures before settling into a stable arrangement after millions of year. Another harmful source however would result from other energetic phenomenons like an increase stars formation rate and a flurry of supernovae. The motion of the Andromeda Galaxy towards our Milky Way Galaxy began 2 billion years ago. The merger of two galaxies, further, may have the resulting supermassive black hole expelled from the resulting galaxy, and moving then in the void of the intergalactic space at speeds of the order of 6 million mph (9,6 million km/h), leaving the resulting, merged galaxy without a supermassive black hole at is center! Latest studies are showing, on the other hand, that the Triangulum galaxy will be spiraling into M31 at the time of the collision with the Milky Way galaxy. The Triangulum already had come close to M31 according to a 3-billion year cycle, and had been stripped of some stars at the time, which are now part of Andromeda! Those late studies are stressing that the collision between M31 and the Milky Way might occur as soon as by 3 billion years from now, as a final merger is to occur by 15 billion years from now! Each star in a galaxy enjoys a 590 million billions miles (950 million billons km), which constitutes a limit to the risks of collision as most of what would be felt by our solar system would be gravitational effects and a ejection outwards (upon a tidal tail), or inwards towards the Galaxy's nucleus. A collision between two galaxies unfolds on a duration of several hundreds of million years as, at the moment of the collision, both are moving at speeds of several hundreds of thousand mph. External arms of both the Milky Way and Andromeda galaxies should be deformed by strong gravitational tides as astronomers think there are 12 percent chance that our solar system be driven outside, in the tide trail of the Milky Way and 3 percent only into the Andromeda Galaxy proper. Further gravitational tides are increasing to 30 percent the odds the solar system be ejected out. Eventually, the merger between both galaxies will be complete after 7 billion years and becoming a giant elliptical galaxy, at the center of which a strong star formation process will have been engaged and making that galaxy a starbust galaxy, with a black hole at the center. Such violent interactions likely will push our solar system, in any case, into the halo of the elliptical, which might prove a relatively save haven, away from any radiation yielded
• 10 Billion Years From Now: Local Group's galaxies are merging into a giant elliptic galaxy. Local Group is the ensemble of galaxies immediately surrounding our Milky Way. Globular clusters of each galaxy survive merger. Mergers of galactic black holes occur too. Such energetic events trigger shock-waves and radiations
• 10 to 20 Billion Years From Now: Universe, dark energy stopping, might collapse back to a Big Crunch. Every form of matter and life is annihilated
• 20 Billion Years From Now: a recent theory, named "Big Rip theory" is stating that dark energy will increase at an ever expanding rate. This will rip apart anything bond by gravity, down to atomic level. Universe would end 20 billion years from now. Event's beginning will be at 1 billion years before the event proper: all galaxies then will have flown away and will be no more visible. 60 million years before Big Rip, Milky Way is ripped apart. 3 months before, solar system is ripped in turn. 30 minutes before the end, Earth itself which is exploding. Then atoms themselves, and atoms nuclei will be ripped in turn. Such a Big Rip is linked to real nature of dark energy, dark matter, gravity, and the cosmological constant. A recent study about dark energy by a Chandra team is pushing further such a fate as dark energy was found relatively steady however. Big Rip should not occur for at least the next few tens of billions of years
• 50 to 100 Billion Years From Now: some think that galaxies are receding from our Milky Way at an ever accelerating page. 50 to 100 billion years from now, they would excede light speed and reach an "event horizon". Such theories think that as soon as now we are no more able to see galaxies of redshift 2 (6-7 billion years away). Reaching their "event horizon", galaxies would just let by a "frozen image" of them. This image would eventually evaporate. Galaxies which are near our, Milky Way, or gravitationally bond to it -this would concern about a thousand galaxies- would be excepted of the phenomenon
• 26 or 52 Billion Years From Now (or 50 to 80 Billion Years): Milky Way, with Local Group, merge into Virgo cluster. This event yields energetic events due to galaxies collisions
• 27 Billion Years From Now: the dark energy makes that the expansion of the Universe gets the galaxy clusters close to us, like the Virgo Cluster for example, to get distant, and eventually disappear to our view!
• 100 Billion Years From Now: due to Earth-Moon interactions, day at Earth is now 47 present days long. Earth's and Moon's rotation, as Moon revolution about Earth are now equal
• 244 Billion Years From Now: Milky Way, with Local Group, is heading to a region called the Great Attractor. This region is located 300 million light-years from us -about ACO3627 cluster, or Norma cluster. Arriving in a region where a lot of galaxies will have moved will trigger energetic events due to galaxies collisions
• one quinquadragintillion years (10 followed by 138 zeros): should one day, the Higgs boson mass of 125 gigaelectronvolts be altered, a bubble of expanding negative energy, within which all the laws of physics would be disrupted, would expand and grow until it finally ingest the Universe