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. 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!...

• 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
• 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. There are some centuries ahead. 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 filed 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
• 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
• 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
• Some Thousand Years From Now: a new ice age could begin about 10,000 AD 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
• 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
• 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: 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 Million Years From Now: red dwarf Gliese 710 (which presently is 68 light-years away) is passing at 1 light-year or at less than 0.5 light-year from Sun. It becomes one of brightest stars in the sky at magnitude 0.6). On another hand as star will pass through Oort Cloud this will increase the rate of comets falling into inner solar system by 50%
• 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
• 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
• 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
• 100 or 200 Million Years From Now (or Unspecified): gamma-rays bursts (GRBs) might be 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. Recent studies are downplaying such risks however. 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
• 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
• 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. 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
• 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
• 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)
• 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: Sun is now 11 per cent brighter than now making Earth inhospitable. there is a moist greenhouse effect as all water is turned into water vapor
• 3.5 Billion Years From Now: Sun is now 40 per cent brighter than now. Oceans evaporate completely; Earth becomes similar to Venus
• 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. 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
• 5 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 and radiations. 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 ejected out, into the interstellar -or even intergalactic space. There is enough space between stars to avoid collision at this level. 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
• 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, said "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
• 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