title: Planetary habitability

text: Under the auspices of SETI's Project Phoenix, scientists Margaret Turnbull and Jill Tarter developed the "HabCat" (or Catalogue of Habitable Stellar Systems) in 2002. The catalogue was formed by winnowing the nearly 120,000 stars of the larger Hipparcos Catalogue into a core group of 17,000 potentially habitable stars, and the selection criteria that were used provide a good starting point for understanding which astrophysical factors are necessary to habitable planets. According to research published in August 2015, very large galaxies may be more favorable to the formation and development of habitable planets than smaller galaxies, like the Milky Way galaxy.


title: Planetary habitability

text: However, what makes a planet habitable is a much more complex question than having a planet located at the right distance from its host star so that water can be liquid on its surface: various geophysical and geodynamical aspects, the radiation, and the host star's plasma environment can influence the evolution of planets and life, if it originated. Liquid water is a necessary but not sufficient condition for life as we know it, as habitability is a function of a multitude of environmental parameters


title: Planetary habitability

text: The spectral class of a star indicates its photospheric temperature, which (for main-sequence stars) correlates to overall mass. The appropriate spectral range for habitable stars is considered to be "late F" or "G", to "mid-K". This corresponds to temperatures of a little more than 7,000 K down to a little less than 4,000 K (6,700 °C to 3,700 °C); the Sun, a G2 star at 5,777 K, is well within these bounds. This spectral range probably accounts for between 5% and 10% of stars in the local Milky Way galaxy. "Middle-class" stars of this sort have a number of characteristics considered important to planetary habitability:


title: Planetary habitability

text: Whether fainter late K and M class red dwarf stars are also suitable hosts for habitable planets is perhaps the most important open question in the entire field of planetary habitability given their prevalence (habitability of red dwarf systems). Gliese 581 c, a "super-Earth", has been found orbiting in the "habitable zone" (HZ) of a red dwarf and may possess liquid water. However it is also possible that a greenhouse effect may render it too hot to support life, while its neighbor, Gliese 581 d, may be a more likely candidate for habitability. In September 2010, the discovery was announced of another planet, Gliese 581 g, in an orbit between these two planets. However, reviews of the discovery have placed the existence of this planet in doubt, and it is listed as "unconfirmed". In September 2012, the discovery of two planets orbiting Gliese 163 was announced. One of the planets, Gliese 163 c, about 6.9 times the mass of Earth and somewhat hotter, was considered to be within the habitable zone.


title: Planetary habitability

text: A recent study suggests that cooler stars that emit more light in the infrared and near infrared may actually host warmer planets with less ice and incidence of snowball states. These wavelengths are absorbed by their planets' ice and greenhouse gases and remain warmer.


title: Planetary habitability

text: A 2020 study found that about half of Sun-like stars could host rocky, potentially habitable planets. Specifically, they estimated with that, on average, the nearest habitable zone planet around G and K-type stars is about 6 parsecs away, and there are about 4 rocky planets around G and K-type stars within 10 parsecs (32.6 light years) of the Sun.


title: Planetary habitability

text: The habitable zone (HZ) is a shell-shaped region of space surrounding a star in which a planet could maintain liquid water on its surface. The concept was first proposed by astrophysicist Su-Shu Huang in 1959, based on climatic constraints imposed by the host star. After an energy source, liquid water is widely considered the most important ingredient for life, considering how integral it is to all life systems on Earth. However, if life is discovered in the absence of water, the definition of an HZ may have to be greatly expanded.


title: Planetary habitability

text: The inner edge of the HZ is the distance where runaway greenhouse effect vaporize the whole water reservoir and, as a second effect, induce the photodissociation of water vapor and the loss of hydrogen to space. The outer edge of the HZ is the distance from the star where a maximum greenhouse effect fails to keep the surface of the planet above the freezing point, and by condensation.


title: Planetary habitability

text: A "stable" HZ implies two factors. First, the range of an HZ should not vary greatly over time. All stars increase in luminosity as they age, and a given HZ thus migrates outwards, but if this happens too quickly (for example, with a super-massive star) planets may only have a brief window inside the HZ and a correspondingly smaller chance of developing life. Calculating an HZ range and its long-term movement is never straightforward, as negative feedback loops such as the CNO cycle will tend to offset the increases in luminosity. Assumptions made about atmospheric conditions and geology thus have as great an impact on a putative HZ range as does stellar evolution: the proposed parameters of the Sun's HZ, for example, have fluctuated greatly.


title: Planetary habitability

text: Second, no large-mass body such as a gas giant should be present in or relatively close to the HZ, thus disrupting the formation of Earth-size bodies. The matter in the asteroid belt, for example, appears to have been unable to accrete into a planet due to orbital resonances with Jupiter; if the giant had appeared in the region that is now between the orbits of Venus and Mars, Earth would almost certainly not have developed in its present form. However a gas giant inside the HZ might have habitable moons under the right conditions.


title: Planetary habitability

text: Changes in luminosity are common to all stars, but the severity of such fluctuations covers a broad range. Most stars are relatively stable, but a significant minority of variable stars often undergo sudden and intense increases in luminosity and consequently in the amount of energy radiated toward bodies in orbit. These stars are considered poor candidates for hosting life-bearing planets, as their unpredictability and energy output changes would negatively impact organisms: living things adapted to a specific temperature range could not survive too great a temperature variation. Further, upswings in luminosity are generally accompanied by massive doses of gamma ray and X-ray radiation which might prove lethal. Atmospheres do mitigate such effects, but their atmosphere might not be retained by planets orbiting variables, because the high-frequency energy buffeting these planets would continually strip them of their protective covering.


title: Planetary habitability

text: The Sun, in this respect as in many others, is relatively benign: the variation between its maximum and minimum energy output is roughly 0.1% over its 11-year solar cycle. There is strong (though not undisputed) evidence that even minor changes in the Sun's luminosity have had significant effects on the Earth's climate well within the historical era: the Little Ice Age of the mid-second millennium, for instance, may have been caused by a relatively long-term decline in the Sun's luminosity. Thus, a star does not have to be a true variable for differences in luminosity to affect habitability. Of known solar analogs, one that closely resembles the Sun is considered to be 18 Scorpii; unfortunately for the prospects of life existing in its proximity, the only significant difference between the two bodies is the amplitude of the solar cycle, which appears to be much greater for 18 Scorpii.


title: Planetary habitability

text: While the bulk of material in any star is hydrogen and helium, there is a significant variation in the amount of heavier elements (metals). A high proportion of metals in a star correlates to the amount of heavy material initially available in the protoplanetary disk. A smaller amount of metal makes the formation of planets much less likely, under the solar nebula theory of planetary system formation. Any planets that did form around a metal-poor star would probably be low in mass, and thus unfavorable for life. Spectroscopic studies of systems where exoplanets have been found to date confirm the relationship between high metal content and planet formation: "Stars with planets, or at least with planets similar to the ones we are finding today, are clearly more metal rich than stars without planetary companions." This relationship between high metallicity and planet formation also means that habitable systems are more likely to be found around stars of younger generations, since stars that formed early in the universe's history have low metal content.


title: Planetary habitability

text: Habitability indicators and biosignatures must be interpreted within a planetary and environmental context. Whether a planet will emerge as habitable depends on the sequence of events that led to its formation, which could include the production of organic molecules in molecular clouds and protoplanetary disks, delivery of materials during and after planetary accretion, and the orbital location in the planetary system. The chief assumption about habitable planets is that they are terrestrial. Such planets, roughly within one order of magnitude of Earth mass, are primarily composed of silicate rocks, and have not accreted the gaseous outer layers of hydrogen and helium found on gas giants. The possibility that life could evolve in the cloud tops of giant planets has not been decisively ruled out, though it is considered unlikely, as they have no surface and their gravity is enormous. The natural satellites of giant planets, meanwhile, remain valid candidates for hosting life.


title: Planetary habitability

text: In February 2011 the Kepler Space Observatory Mission team released a list of 1235 extrasolar planet candidates, including 54 that may be in the habitable zone. Six of the candidates in this zone are smaller than twice the size of Earth. A more recent study found that one of these candidates (KOI 326.01) is much larger and hotter than first reported. Based on the findings, the Kepler team estimated there to be "at least 50 billion planets in the Milky Way" of which "at least 500 million" are in the habitable zone.


title: Planetary habitability

text: In analyzing which environments are likely to support life, a distinction is usually made between simple, unicellular organisms such as bacteria and archaea and complex metazoans (animals). Unicellularity necessarily precedes multicellularity in any hypothetical tree of life, and where single-celled organisms do emerge there is no assurance that greater complexity will then develop. The planetary characteristics listed below are considered crucial for life generally, but in every case multicellular organisms are more picky than unicellular life.


title: Planetary habitability

text: Low-mass planets are poor candidates for life for two reasons. First, their lesser gravity makes atmosphere retention difficult. Constituent molecules are more likely to reach escape velocity and be lost to space when buffeted by solar wind or stirred by collision. Planets without a thick atmosphere lack the matter necessary for primal biochemistry, have little insulation and poor heat transfer across their surfaces (for example, Mars, with its thin atmosphere, is colder than the Earth would be if it were at a similar distance from the Sun), and provide less protection against meteoroids and high-frequency radiation. Further, where an atmosphere is less dense than 0.006 Earth atmospheres, water cannot exist in liquid form as the required atmospheric pressure, 4.56 mm Hg (608 Pa) (0.18 inch Hg), does not occur. In addition, a lessened pressure reduces the range of temperatures at which water is liquid.


title: Planetary habitability

text: Secondly, smaller planets have smaller diameters and thus higher surface-to-volume ratios than their larger cousins. Such bodies tend to lose the energy left over from their formation quickly and end up geologically dead, lacking the volcanoes, earthquakes and tectonic activity which supply the surface with life-sustaining material and the atmosphere with temperature moderators like carbon dioxide. Plate tectonics appear particularly crucial, at least on Earth: not only does the process recycle important chemicals and minerals, it also fosters bio-diversity through continent creation and increased environmental complexity and helps create the convective cells necessary to generate Earth's magnetic field.


title: Planetary habitability

text: "Low mass" is partly a relative label: the Earth is low mass when compared to the Solar System's gas giants, but it is the largest, by diameter and mass, and the densest of all terrestrial bodies. It is large enough to retain an atmosphere through gravity alone and large enough that its molten core remains a heat engine, driving the diverse geology of the surface (the decay of radioactive elements within a planet's core is the other significant component of planetary heating). Mars, by contrast, is nearly (or perhaps totally) geologically dead and has lost much of its atmosphere. Thus it would be fair to infer that the lower mass limit for habitability lies somewhere between that of Mars and that of Earth or Venus: 0.3 Earth masses has been offered as a rough dividing line for habitable planets. However, a 2008 study by the Harvard-Smithsonian Center for Astrophysics suggests that the dividing line may be higher. Earth may in fact lie on the lower boundary of habitability: if it were any smaller, plate tectonics would be impossible. Venus, which has 85% of Earth's mass, shows no signs of tectonic activity. Conversely, "super-Earths", terrestrial planets with higher masses than Earth, would have higher levels of plate tectonics and thus be firmly placed in the habitable range.


title: Planetary habitability

text: Exceptional circumstances do offer exceptional cases: Jupiter's moon Io (which is smaller than any of the terrestrial planets) is volcanically dynamic because of the gravitational stresses induced by its orbit, and its neighbor Europa may have a liquid ocean or icy slush underneath a frozen shell also due to power generated from orbiting a gas giant.


title: Planetary habitability

text: Saturn's Titan, meanwhile, has an outside chance of harbouring life, as it has retained a thick atmosphere and has liquid methane seas on its surface. Organic-chemical reactions that only require minimum energy are possible in these seas, but whether any living system can be based on such minimal reactions is unclear, and would seem unlikely. These satellites are exceptions, but they prove that mass, as a criterion for habitability, cannot necessarily be considered definitive at this stage of our understanding.


title: Planetary habitability

text: A larger planet is likely to have a more massive atmosphere. A combination of higher escape velocity to retain lighter atoms, and extensive outgassing from enhanced plate tectonics may greatly increase the atmospheric pressure and temperature at the surface compared to Earth. The enhanced greenhouse effect of such a heavy atmosphere would tend to suggest that the habitable zone should be further out from the central star for such massive planets.


title: Planetary habitability

text: Finally, a larger planet is likely to have a large iron core. This allows for a magnetic field to protect the planet from stellar wind and cosmic radiation, which otherwise would tend to strip away planetary atmosphere and to bombard living things with ionized particles. Mass is not the only criterion for producing a magnetic field—as the planet must also rotate fast enough to produce a dynamo effect within its core—but it is a significant component of the process.


title: Planetary habitability

text: The mass of a potentially habitable exoplanet is between 0.1 and 5.0 Earth masses. However it is possible for a habitable world to have a mass as low as 0.0268 Earth Masses. The radius of a potentially habitable exoplanet would range between 0.5 and 1.5 Earth radii.


title: Planetary habitability

text: As with other criteria, stability is the critical consideration in evaluating the effect of orbital and rotational characteristics on planetary habitability. Orbital eccentricity is the difference between a planet's farthest and closest approach to its parent star divided by the sum of said distances. It is a ratio describing the shape of the elliptical orbit. The greater the eccentricity the greater the temperature fluctuation on a planet's surface. Although they are adaptive, living organisms can stand only so much variation, particularly if the fluctuations overlap both the freezing point and boiling point of the planet's main biotic solvent (e.g., water on Earth). If, for example, Earth's oceans were alternately boiling and freezing solid, it is difficult to imagine life as we know it having evolved. The more complex the organism, the greater the temperature sensitivity. The Earth's orbit is almost perfectly circular, with an eccentricity of less than 0.02; other planets in the Solar System (with the exception of Mercury) have eccentricities that are similarly benign.


title: Planetary habitability

text: Habitability is also influenced by the architecture of the planetary system around a star. The evolution and stability of these systems are determined by gravitational dynamics, which drive the orbital evolution of terrestrial planets. Data collected on the orbital eccentricities of extrasolar planets has surprised most researchers: 90% have an orbital eccentricity greater than that found within the Solar System, and the average is fully 0.25. This means that the vast majority of planets have highly eccentric orbits and of these, even if their average distance from their star is deemed to be within the HZ, they nonetheless would be spending only a small portion of their time within the zone.


title: Planetary habitability

text: A planet's movement around its rotational axis must also meet certain criteria if life is to have the opportunity to evolve. A first assumption is that the planet should have moderate seasons. If there is little or no axial tilt (or obliquity) relative to the perpendicular of the ecliptic, seasons will not occur and a main stimulant to biospheric dynamism will disappear. The planet would also be colder than it would be with a significant tilt: when the greatest intensity of radiation is always within a few degrees of the equator, warm weather cannot move poleward and a planet's climate becomes dominated by colder polar weather systems.


title: Planetary habitability

text: If a planet is radically tilted, seasons will be extreme and make it more difficult for a biosphere to achieve homeostasis. The axial tilt of the Earth is higher now (in the Quaternary) than it has been in the past, coinciding with reduced polar ice, warmer temperatures and "less" seasonal variation. Scientists do not know whether this trend will continue indefinitely with further increases in axial tilt (see Snowball Earth).


title: Planetary habitability

text: The exact effects of these changes can only be computer modelled at present, and studies have shown that even extreme tilts of up to 85 degrees do not absolutely preclude life "provided it does not occupy continental surfaces plagued seasonally by the highest temperature." Not only the mean axial tilt, but also its variation over time must be considered. The Earth's tilt varies between 21.5 and 24.5 degrees over 41,000 years. A more drastic variation, or a much shorter periodicity, would induce climatic effects such as variations in seasonal severity.


title: Planetary habitability

text: The Earth's Moon appears to play a crucial role in moderating the Earth's climate by stabilising the axial tilt. It has been suggested that a chaotic tilt may be a "deal-breaker" in terms of habitability—i.e. a satellite the size of the Moon is not only helpful but required to produce stability. This position remains controversial.


title: Planetary habitability

text: In the case of the Earth, the sole Moon is sufficiently massive and orbits so as to significantly contribute to ocean tides, which in turn aids the dynamic churning of Earth's large liquid water oceans. These lunar forces not only help ensure that the oceans do not stagnate, but also play a critical role in Earth's dynamic climate.


title: Planetary habitability

text: Concentrations of radionuclides in rocky planet mantles may be critical for the habitability of Earth-like planets. Such planets with higher abundances likely lack a persistent dynamo for a significant fraction of their lifetimes, and those with lower concentrations may often be geologically inert. Planetary dynamos create strong magnetic fields which may often be necessary for life to develop or persist as they shield planets from solar winds and cosmic radiation. The electromagnetic emission spectra of stars could be used to identify those which are more likely to host habitable Earth-like planets. As of 2020, radionuclides are thought to be produced by rare stellar processes such as neutron star mergers.


title: Planetary habitability

text: Additional geological characteristics may be essential or major factors in the habitability of natural celestial bodies – including some that may shape the body's heat and magnetic field. Some of these are unknown or not well understood and being investigated by planetary scientists, geochemists and others.


title: Planetary habitability

text: It is generally assumed that any extraterrestrial life that might exist will be based on the same fundamental biochemistry as found on Earth, as the four elements most vital for life, carbon, hydrogen, oxygen, and nitrogen, are also the most common chemically reactive elements in the universe. Indeed, simple biogenic compounds, such as very simple amino acids such as glycine, have been found in meteorites and in the interstellar medium. These four elements together comprise over 96% of Earth's collective biomass. Carbon has an unparalleled ability to bond with itself and to form a massive array of intricate and varied structures, making it an ideal material for the complex mechanisms that form living cells. Hydrogen and oxygen, in the form of water, compose the solvent in which biological processes take place and in which the first reactions occurred that led to life's emergence. The energy released in the formation of powerful covalent bonds between carbon and oxygen, available by oxidizing organic compounds, is the fuel of all complex life-forms. These four elements together make up amino acids, which in turn are the building blocks of proteins, the substance of living tissue. In addition, neither sulfur (required for the building of proteins) nor phosphorus (needed for the formation of DNA, RNA, and the adenosine phosphates essential to metabolism) are rare.


title: Planetary habitability

text: Relative abundance in space does not always mirror differentiated abundance within planets; of the four life elements, for instance, only oxygen is present in any abundance in the Earth's crust. This can be partly explained by the fact that many of these elements, such as hydrogen and nitrogen, along with their simplest and most common compounds, such as carbon dioxide, carbon monoxide, methane, ammonia, and water, are gaseous at warm temperatures. In the hot region close to the Sun, these volatile compounds could not have played a significant role in the planets' geological formation. Instead, they were trapped as gases underneath the newly formed crusts, which were largely made of rocky, involatile compounds such as silica (a compound of silicon and oxygen, accounting for oxygen's relative abundance). Outgassing of volatile compounds through the first volcanoes would have contributed to the formation of the planets' atmospheres. The Miller–Urey experiment showed that, with the application of energy, simple inorganic compounds exposed to a primordial atmosphere can react to synthesize amino acids.


title: Planetary habitability

text: Even so, volcanic outgassing could not have accounted for the amount of water in Earth's oceans. The vast majority of the water—and arguably carbon—necessary for life must have come from the outer Solar System, away from the Sun's heat, where it could remain solid. Comets impacting with the Earth in the Solar System's early years would have deposited vast amounts of water, along with the other volatile compounds life requires, onto the early Earth, providing a kick-start to the origin of life.


title: Planetary habitability

text: Thus, while there is reason to suspect that the four "life elements" ought to be readily available elsewhere, a habitable system probably also requires a supply of long-term orbiting bodies to seed inner planets. Without comets there is a possibility that life as we know it would not exist on Earth.


title: Planetary habitability

text: One important qualification to habitability criteria is that only a tiny portion of a planet is required to support life, a so-called Goldilocks Edge or Great Prebiotic Spot. Astrobiologists often concern themselves with "micro-environments", noting that "we lack a fundamental understanding of how evolutionary forces, such as mutation, selection, and genetic drift, operate in micro-organisms that act on and respond to changing micro-environments." Extremophiles are Earth organisms that live in niche environments under severe conditions generally considered inimical to life. Usually (although not always) unicellular, extremophiles include acutely alkaliphilic and acidophilic organisms and others that can survive water temperatures above 100 °C in hydrothermal vents.


title: Planetary habitability

text: The discovery of life in extreme conditions has complicated definitions of habitability, but also generated much excitement amongst researchers in greatly broadening the known range of conditions under which life can persist. For example, a planet that might otherwise be unable to support an atmosphere given the solar conditions in its vicinity, might be able to do so within a deep shadowed rift or volcanic cave. Similarly, craterous terrain might offer a refuge for primitive life. The Lawn Hill crater has been studied as an astrobiological analog, with researchers suggesting rapid sediment infill created a protected microenvironment for microbial organisms; similar conditions may have occurred over the geological history of Mars.


title: Planetary habitability

text: Earth environments that "cannot" support life are still instructive to astrobiologists in defining the limits of what organisms can endure. The heart of the Atacama desert, generally considered the driest place on Earth, appears unable to support life, and it has been subject to study by NASA and ESA for that reason: it provides a Mars analog and the moisture gradients along its edges are ideal for studying the boundary between sterility and habitability. The Atacama was the subject of study in 2003 that partly replicated experiments from the Viking landings on Mars in the 1970s; no DNA could be recovered from two soil samples, and incubation experiments were also negative for biosignatures.


title: Planetary habitability

text: The two current ecological approaches for predicting the potential habitability use 19 or 20 environmental factors, with emphasis on water availability, temperature, presence of nutrients, an energy source, and protection from solar ultraviolet and galactic cosmic radiation.


title: Planetary habitability

text: Mesoplanets would be ideal for complex life, whereas hypopsychroplanets and hyperthermoplanets might only support extremophilic life.


title: Planetary habitability

text: The HEC uses the following terms to classify exoplanets in terms of mass, from least to greatest: asteroidan, mercurian, subterran, terran, superterran, neptunian, and jovian.


title: Planetary habitability

text: In determining the feasibility of extraterrestrial life, astronomers had long focused their attention on stars like the Sun. However, since planetary systems that resemble the Solar System are proving to be rare, they have begun to explore the possibility that life might form in systems very unlike our own.


title: Planetary habitability

text: Typical estimates often suggest that 50% or more of all stellar systems are binary systems. This may be partly sample bias, as massive and bright stars tend to be in binaries and these are most easily observed and catalogued; a more precise analysis has suggested that the more common fainter stars are usually singular, and that up to two thirds of all stellar systems are therefore solitary.


title: Planetary habitability

text: The separation between stars in a binary may range from less than one astronomical unit (AU, the average Earth–Sun distance) to several hundred. In latter instances, the gravitational effects will be negligible on a planet orbiting an otherwise suitable star and habitability potential will not be disrupted unless the orbit is highly eccentric (see Nemesis, for example). However, where the separation is significantly less, a stable orbit may be impossible. If a planet's distance to its primary exceeds about one fifth of the closest approach of the other star, orbital stability is not guaranteed. Whether planets might form in binaries at all had long been unclear, given that gravitational forces might interfere with planet formation. Theoretical work by Alan Boss at the Carnegie Institution has shown that gas giants can form around stars in binary systems much as they do around solitary stars.


title: Planetary habitability

text: One study of Alpha Centauri, the nearest star system to the Sun, suggested that binaries need not be discounted in the search for habitable planets. Centauri A and B have an 11 AU distance at closest approach (23 AU mean), and both should have stable habitable zones. A study of long-term orbital stability for simulated planets within the system shows that planets within approximately three AU of either star may remain rather stable (i.e. the semi-major axis deviating by less than 5% during 32 000 binary periods). The continuous habitable zone (CHZ for 4.5 billion years) for Centauri A is conservatively estimated at 1.2 to 1.3 AU and Centauri B at 0.73 to 0.74—well within the stable region in both cases.


title: Planetary habitability

text: Determining the habitability of red dwarf stars could help determine how common life in the universe might be, as red dwarfs make up between 70 and 90% of all the stars in the galaxy.


title: Planetary habitability

text: Astronomers for many years ruled out red dwarfs as potential abodes for life. Their small size (from 0.08 to 0.45 solar masses) means that their nuclear reactions proceed exceptionally slowly, and they emit very little light (from 3% of that produced by the Sun to as little as 0.01%). Any planet in orbit around a red dwarf would have to huddle very close to its parent star to attain Earth-like surface temperatures; from 0.3 AU (just inside the orbit of Mercury) for a star like Lacaille 8760, to as little as 0.032 AU for a star like Proxima Centauri (such a world would have a year lasting just 6.3 days). At those distances, the star's gravity would cause tidal locking. One side of the planet would eternally face the star, while the other would always face away from it. The only ways in which potential life could avoid either an inferno or a deep freeze would be if the planet had an atmosphere thick enough to transfer the star's heat from the day side to the night side, or if there was a gas giant in the habitable zone, with a habitable moon, which would be locked to the planet instead of the star, allowing a more even distribution of radiation over the planet. It was long assumed that such a thick atmosphere would prevent sunlight from reaching the surface in the first place, preventing photosynthesis.


title: Planetary habitability

text: This pessimism has been tempered by research. Studies by Robert Haberle and Manoj Joshi of NASA's Ames Research Center in California have shown that a planet's atmosphere (assuming it included greenhouse gases CO and HO) need only be , for the star's heat to be effectively carried to the night side. This is well within the levels required for photosynthesis, though water would still remain frozen on the dark side in some of their models. Martin Heath of Greenwich Community College, has shown that seawater, too, could be effectively circulated without freezing solid if the ocean basins were deep enough to allow free flow beneath the night side's ice cap. Further research—including a consideration of the amount of photosynthetically active radiation—suggested that tidally locked planets in red dwarf systems might at least be habitable for higher plants.


title: Planetary habitability

text: Size is not the only factor in making red dwarfs potentially unsuitable for life, however. On a red dwarf planet, photosynthesis on the night side would be impossible, since it would never see the sun. On the day side, because the sun does not rise or set, areas in the shadows of mountains would remain so forever. Photosynthesis as we understand it would be complicated by the fact that a red dwarf produces most of its radiation in the infrared, and on the Earth the process depends on visible light. There are potential positives to this scenario. Numerous terrestrial ecosystems rely on chemosynthesis rather than photosynthesis, for instance, which would be possible in a red dwarf system. A static primary star position removes the need for plants to steer leaves toward the sun, deal with changing shade/sun patterns, or change from photosynthesis to stored energy during night. Because of the lack of a day-night cycle, including the weak light of morning and evening, far more energy would be available at a given radiation level.


title: Planetary habitability

text: Red dwarfs are far more variable and violent than their more stable, larger cousins. Often they are covered in starspots that can dim their emitted light by up to 40% for months at a time, while at other times they emit gigantic flares that can double their brightness in a matter of minutes. Such variation would be very damaging for life, as it would not only destroy any complex organic molecules that could possibly form biological precursors, but also because it would blow off sizeable portions of the planet's atmosphere.


title: Planetary habitability

text: For a planet around a red dwarf star to support life, it would require a rapidly rotating magnetic field to protect it from the flares. A tidally locked planet rotates only very slowly, and so cannot produce a geodynamo at its core. The violent flaring period of a red dwarf's life cycle is estimated to only last roughly the first 1.2 billion years of its existence. If a planet forms far away from a red dwarf so as to avoid tidal locking, and then migrates into the star's habitable zone after this turbulent initial period, it is possible that life may have a chance to develop. However, observations of the 7 to 12-billion year old Barnard's Star showcase that even old red dwarfs can have significant flare activity. Barnard's Star was long assumed to have little activity, but in 1998 astronomers observed an intense stellar flare, showing that it is a flare star.


title: Planetary habitability

text: Red dwarfs have one advantage over other stars as abodes for life: far greater longevity. It took 4.5 billion years before humanity appeared on Earth, and life as we know it will see suitable conditions for 1 to 2.3 more. Red dwarfs, by contrast, could live for trillions of years because their nuclear reactions are far slower than those of larger stars, meaning that life would have longer to evolve and survive.


title: Planetary habitability

text: While the likelihood of finding a planet in the habitable zone around any specific red dwarf is slight, the total amount of habitable zone around all red dwarfs combined is equal to the total amount around Sun-like stars given their ubiquity. Furthermore, this total amount of habitable zone will last longer, because red dwarf stars live for hundreds of billions of years or even longer on the main sequence. However, combined with the above disadvantages, it is more likely that red dwarf stars would remain habitable longer to microbes, while the shorter-lived yellow dwarf stars, like the Sun, would remain habitable longer to animals.


title: Planetary habitability

text: Recent research suggests that very large stars, greater than ~100 solar masses, could have planetary systems consisting of hundreds of Mercury-sized planets within the habitable zone. Such systems could also contain brown dwarfs and low-mass stars (~0.1–0.3 solar masses). However the very short lifespans of stars of more than a few solar masses would scarcely allow time for a planet to cool, let alone the time needed for a stable biosphere to develop. Massive stars are thus eliminated as possible abodes for life.


title: Planetary habitability

text: However, a massive-star system could be a progenitor of life in another way – the supernova explosion of the massive star in the central part of the system. This supernova will disperse heavier elements throughout its vicinity, created during the phase when the massive star has moved off of the main sequence, and the systems of the potential low-mass stars (which are still on the main sequence) within the former massive-star system may be enriched with the relatively large supply of the heavy elements so close to a supernova explosion. However, this states nothing about what types of planets would form as a result of the supernova material, or what their habitability potential would be.


title: Planetary habitability

text: In a review of the factors which are important for the evolution of habitable Earth-sized planets, Lammer et al. proposed a classification of four water-dependent habitat types:


title: Planetary habitability

text: Class I habitats are planetary bodies on which stellar and geophysical conditions allow liquid water to be available at the surface, along with sunlight, so that complex multicellular organisms may originate.


title: Planetary habitability

text: Class II habitats include bodies which initially enjoy Earth-like conditions, but do not keep their ability to sustain liquid water on their surface due to stellar or geophysical conditions. Mars, and possibly Venus are examples of this class where complex life forms may not develop.


title: Planetary habitability

text: Class III habitats are planetary bodies where liquid water oceans exist below the surface, where they can interact directly with a silicate-rich core.


title: Planetary habitability

text: Along with the characteristics of planets and their star systems, the wider galactic environment may also impact habitability. Scientists considered the possibility that particular areas of galaxies (galactic habitable zones) are better suited to life than others; the Solar System in which we live, in the Orion Spur, on the Milky Way galaxy's edge is considered to be in a life-favorable spot:


title: Planetary habitability

text: Thus, relative isolation is ultimately what a life-bearing system needs. If the Sun were crowded amongst other systems, the chance of being fatally close to dangerous radiation sources would increase significantly. Further, close neighbors might disrupt the stability of various orbiting bodies such as Oort cloud and Kuiper belt objects, which can bring catastrophe if knocked into the inner Solar System.


title: Planetary habitability

text: While stellar crowding proves disadvantageous to habitability, so too does extreme isolation. A star as metal-rich as the Sun would probably not have formed in the very outermost regions of the Milky Way given a decline in the relative abundance of metals and a general lack of star formation. Thus, a "suburban" location, such as the Solar System enjoys, is preferable to a Galaxy's center or farthest reaches.


title: Planetary habitability

text: While most investigations of extraterrestrial life start with the assumption that advanced life-forms must have similar requirements for life as on Earth, the hypothesis of other types of biochemistry suggests the possibility of lifeforms evolving around a different metabolic mechanism. In "Evolving the Alien", biologist Jack Cohen and mathematician Ian Stewart argue astrobiology, based on the Rare Earth hypothesis, is restrictive and unimaginative. They suggest that Earth-like planets may be very rare, but non-carbon-based complex life could possibly emerge in other environments. The most frequently mentioned alternative to carbon is silicon-based life, while ammonia and hydrocarbons are sometimes suggested as alternative solvents to water. The astrobiologist Dirk Schulze-Makuch and other scientists have proposed a Planet Habitability Index whose criteria include "potential for holding a liquid solvent" that is not necessarily restricted to water.


title: Planetary habitability

text: More speculative ideas have focused on bodies altogether different from Earth-like planets. Astronomer Frank Drake, a well-known proponent of the search for extraterrestrial life, imagined life on a neutron star: submicroscopic "nuclear molecules" combining to form creatures with a life cycle millions of times quicker than Earth life. Called "imaginative and tongue-in-cheek", the idea gave rise to science fiction depictions. Carl Sagan, another optimist with regards to extraterrestrial life, considered the possibility of organisms that are always airborne within the high atmosphere of Jupiter in a 1976 paper. Cohen and Stewart also envisioned life in both a solar environment and in the atmosphere of a gas giant.


title: Planetary habitability

text: "Good Jupiters" are gas giants, like the Solar System's Jupiter, that orbit their stars in circular orbits far enough away from the habitable zone not to disturb it but close enough to "protect" terrestrial planets in closer orbit in two critical ways. First, they help to stabilize the orbits, and thereby the climates of the inner planets. Second, they keep the inner stellar system relatively free of comets and asteroids that could cause devastating impacts. Jupiter orbits the Sun at about five times the distance between the Earth and the Sun. This is the rough distance we should expect to find good Jupiters elsewhere. Jupiter's "caretaker" role was dramatically illustrated in 1994 when Comet Shoemaker–Levy 9 impacted the giant.


title: Planetary habitability

text: However, the evidence is not quite so clear. Research has shown that Jupiter's role in determining the rate at which objects hit Earth is significantly more complicated than once thought.


title: Planetary habitability

text: The role of Jupiter in the early history of the Solar System is somewhat better established, and the source of significantly less debate. Early in the Solar System's history, Jupiter is accepted as having played an important role in the hydration of our planet: it increased the eccentricity of asteroid belt orbits and enabled many to cross Earth's orbit and supply the planet with important volatiles such as water and carbon dioxide. Before Earth reached half its present mass, icy bodies from the Jupiter–Saturn region and small bodies from the primordial asteroid belt supplied water to the Earth due to the gravitational scattering of Jupiter and, to a lesser extent, Saturn. Thus, while the gas giants are now helpful protectors, they were once suppliers of critical habitability material.


title: Planetary habitability

text: In contrast, Jupiter-sized bodies that orbit too close to the habitable zone but not in it (as in 47 Ursae Majoris), or have a highly elliptical orbit that crosses the habitable zone (like 16 Cygni B) make it very difficult for an independent Earth-like planet to exist in the system. See the discussion of a stable habitable zone above. However, during the process of migrating into a habitable zone, a Jupiter-size planet may capture a terrestrial planet as a moon. Even if such a planet is initially loosely bound and following a strongly inclined orbit, gravitational interactions with the star can stabilize the new moon into a close, circular orbit that is coplanar with the planet's orbit around the star.


title: Planetary habitability

text: A supplement to the factors that support life's emergence is the notion that life itself, once formed, becomes a habitability factor in its own right. An important Earth example was the production of molecular oxygen gas () by ancient cyanobacteria, and eventually photosynthesizing plants, leading to a radical change in the composition of Earth's atmosphere. This environmental change is called the Great Oxygenation Event. This oxygen proved fundamental to the respiration of later animal species. The Gaia hypothesis, a scientific model of the geo-biosphere pioneered by James Lovelock in 1975, argues that life as a whole fosters and maintains suitable conditions for itself by helping to create a planetary environment suitable for its continuity. Similarly, David Grinspoon has suggested a "living worlds hypothesis" in which our understanding of what constitutes habitability cannot be separated from life already extant on a planet. Planets that are geologically and meteorologically alive are much more likely to be biologically alive as well and "a planet and its life will co-evolve." This is the basis of Earth system science.


title: Planetary habitability

text: In 2020 a computer simulation of the evolution of planetary climates over 3 billion years suggested that feedbacks are a necessary but not a sufficient condition for preventing planets from ever becoming too hot or cold for life, and that chance also plays a crucial role.<ref name="10.1038/s43247-020-00057-8"> Available under CC BY 4.0.</ref> Related considerations include yet unknown factors influencing the thermal habitability of planets such as "feedback mechanism (or mechanisms) that prevents the climate ever wandering to fatal temperatures".


title: Call of Cthulhu (video game)

text: Call of Cthulhu is a role-playing survival horror video game developed by Cyanide and published by Focus Home Interactive for Microsoft Windows, PlayStation 4, Xbox One and Nintendo Switch. The game features a semi-open world environment and incorporates themes of Lovecraftian and psychological horror into a story which includes elements of investigation and stealth. It is inspired by H. P. Lovecraft's short story "The Call of Cthulhu", while also being an adaptation of the 1981 role-playing game of the same title.


title: Call of Cthulhu (video game)

text: In 1924 Boston, private investigator and war veteran Edward Pierce suffers from increasingly bizarre nightmares and self-medicates with sleeping pills and alcohol. He is soon contacted to look into the case of the Hawkins family, who mysteriously died in a fire. As the only clue is a strange picture painted by the wife, Sarah, shortly before her death, Edward has to set out to Darkwater Island off the coast to find out more about the matter.


title: Call of Cthulhu (video game)

text: Upon arriving in Darkwater, Pierce is steeped in the strange local culture. Darkwater was home to a booming whaling industry until a sudden scarcity in 1847. That year, the island's last ship, the Scylla, returned with a legendary "Miraculous Catch", that saved the island. The islanders are superstitious and suspicious of outsiders like Pierce. The detective meets Captain Fitzroy, who provides him with a few details of the Hawkins family; Officer Bradley, who handled the case; and Cat Baker, a successful bootlegger and feared gang leader. He also sees a beached killer whale, killed by ghastly wounds, being dragged back into the sea by the police, much to the locals' chagrin.


title: Call of Cthulhu (video game)

text: While exploring the Hawkins' mansion with Bradley, Pierce learns more about the Hawkins family. Sarah was a famous painter known for her macabre style, but also rumoured to have been mentally unstable. Pierce determines that the fire may not have been an accident, and furthermore, someone may have survived. Shortly after, he is accosted by a robed man who is stealing something from the attic. Pierce and Bradley give chase and soon discover a hidden door that leads to secret caves and tunnels beneath the island. There, they discover the thief and other cultists performing a ritual. Bradley recognizes the leader as Charles Hawkins, thought dead in the fire. Hawkins is horrifically mutated now and kills Bradley with a tentacled arm. Pierce barely escapes, but passes out when he is trapped in the collapsing cave.


title: Call of Cthulhu (video game)

text: He awakens in the basement of the Riverside Institute, a suspiciously large mental hospital, under the care of Dr. Fuller. He is drugged and suffers more nightmares and hallucinations, including visits from an otherworldly voice that seems to be directing certain events. Eventually, he escapes with the help of Dr. Marie Colden. Along the way he discovers evidence of strange experiments by Fuller. He also encounters Francis Sanders, who had been given a painting by Sarah. Francis is another patient/prisoner of Fuller, and after speaking to Pierce about "The Shambler", he is brutally killed by an unseen force. Once back at the Hawkins mansion, Pierce, Colden and a suddenly alive Bradley (who has a broken recollection of his supposed death) decide to visit the widowed Mrs. Sanders and learn more about Francis and The Shambler. At the Sanders house, he also finds Cat once more, there to help the widow sell her late husband's art collection.


title: Call of Cthulhu (video game)

text: The Shambler was a painting by Sarah that she gave to Francis after much resistance. Pierce examines the painting, which comes to life and pits him against the physical manifestation of the creature. He manages to banish it by slashing the painting with a ritualistic dagger from the Sanders art gallery.


title: Call of Cthulhu (video game)

text: His investigation then leads him to a bookstore owned by Algernon Drake, a friend of Sarah Hawkins, where he discovers the Necronomicon in a safe. Upon reading the book, he has an out of body experience that places him into the mind of Marie Colden, seeing events at the Institute through her eyes. After discovering numerous patients exhibiting signs of mutation, Colden confronts Fuller about his experiments and is knocked out. Upon returning to his body, Pierce is confronted by Drake, and the two form a shaky alliance.


title: Call of Cthulhu (video game)

text: Pierce rushes to the institute to save Colden, but after suffering more hallucinations and taunting by the voice in his head, finds her dead at Fuller's hands. Exploring further, he discovers Sarah Hawkins, imprisoned but alive. The two run, but are stopped by the monstrous Charles Hawkins, who claims he was trying to protect Sarah from the cult due to her gifts as an "Oracle". Pierce and Sarah defeat and kill Charles, before escaping back to the mansion, leaving the Institute in flames. In their fight with Charles, a strange liquid, responsible for a gas that causes hallucinations and mutations in the living and is circulated throughout the Institute basement, is set alight by the institute's furnace.


title: Call of Cthulhu (video game)

text: There, Pierce finds an amulet Charles had hidden, which Drake says can protect Sarah from the cult's influence. Exiting the house, Pierce is arrested by Darkwater police after being identified as the perpetrator of the Riverside Institute fire. While at the jail, he is visited by a ghostly figure, who identifies itself as "Leviathan". It speaks to Pierce about destiny and offers him a gift in the form of knowledge. Pierce once again leaves his body and experiences events through Sarah's eyes as she and Drake perform a ritual to banish the Shambler for good (Drake can die here, depending on the player's actions). Back in his cell, Pierce is again visited by Leviathan, and shown visions of his companions: Bradley doubts himself and their fight against the cult; Cat is shown shooting and killing Pierce; and Sarah is shown painting a portrait of him, calling him the "Truth Seeker". His consciousness is then sent to Cat at her gang's warehouse examining a dead policeman left there, where she discovers he was killed by a Cult after happening upon their meeting. The gang is then attacked by the local fishermen, seemingly bewitched by Leviathan's influence.


title: Call of Cthulhu (video game)

text: Pierce is released from his cell by Bradley, who is also succumbing to the madness. Pierce takes his gun and fights his way to the whaling station, where Sarah was seen heading. There, he discovers the secret of the island's dark history. The "Miraculous Catch" of 1847 was Leviathan. The crew of the Scylla captured the enormous creature and were driven mad by its influence. Some of them, namely Fitzroy, Fuller and Charles Hawkins, ate its flesh, gaining immortality. The Leviathan seems to have wanted to be caught, in order to direct through its influence the events that followed, including Pierce's arrival to the island and his actions in the whaling station. While trapped in a hallucination, Pierce causes an explosion that destroys the whaling station, freeing Leviathan. The Cult, led by Fitzroy, tell Pierce that he is not there of his own accord. Pierce rebels, attempting to flee, but falls into the water, encountering Leviathan one last time before it swims back to the depths of the sea.


title: Call of Cthulhu (video game)

text: Pierce washes up near a coastal cave and makes his way through the tunnels toward Alabaster Point, a place of cyclopean architecture. Along the way, he encounters visions of Marie Colden, Dr. Fuller and Charles Hawkins. He finally arrives at the Cult's meeting place, where a strange storm is brewing over the ocean, and a great tentacle can be seen beyond the veil. Drake (if he survived) is seen captured and held hostage by the cult. Sarah, a fully willing cultist now, explains his destiny to Pierce and he is given the choice to give in to the madness and help perform the Cult's ritual or not. Depending on choices made throughout the game: dialogue, exploration and events that affect Pierce's sanity, there are four possible endings:


title: Call of Cthulhu (video game)

text: On 16 January 2014, publisher Focus Home Interactive announced via Twitter that video game developer Frogwares was working on developing the game. They also announced that the game would be released on Microsoft Windows and "next-gen consoles". Later that month, a Frogwares spokesperson said that the game was still in "early development". They noted that the game would have a focus on investigations in a horror setting and that they would be using the experience from developing their "Adventures of Sherlock Holmes" series. They also revealed that they were working with multiple writers who had written scenarios for the 1981 role-playing game "Call of Cthulhu".


title: Call of Cthulhu (video game)

text: After two years of inactivity on the title, prompting concerns that the game might have been canceled, Focus Home announced the game again in February 2016, in development for release in 2017 by studio Cyanide. They revealed that the game would be a semi-open world investigative role-playing game with elements of stealth and psychological horror. The game will be built on the Unreal Engine 4 game engine. It will be more closely based on the "Call of Cthulhu" "pen and paper" role-playing video game than on H. P. Lovecraft's original short story of the same name. Frogwares went on to make their own Cthulhu-esque game called "The Sinking City", which came out in 2019.


title: Call of Cthulhu (video game)

text: Focus Home Interactive released the first trailer for the game just before E3 2016, on 10 June 2016. A "Depths of Madness" trailer was released on 19 January 2017. The game was at first scheduled for release on Microsoft Windows, PlayStation 4 and Xbox One in the fourth quarter of 2017. In September 2017, however, the game was delayed to 2018. The game was released worldwide on 30 October 2018.


title: Call of Cthulhu (video game)

text: "Call of Cthulhu" received "mixed or average" reviews, according to review aggregator Metacritic. The general consensus is that while both the graphics and atmosphere is great, the game progression is not well implemented with unclear story elements and poor RPG mechanics.


title: Call of Cthulhu (video game)

text: GameSpot's David Wildgoose was critical of "Call of Cthulhu" saying that the RPG element felt "undernourished". He added that "the differences between having leveled up your Strength stat instead of your Investigation stat feel ambiguous at best and trivial at worst." Neil Bolt of BloodyDisgusting writes that both stealth and combat gameplay is not well explained in the game. While it captures the essence of Lovecraft's work well, he criticised the character models for their unpolished look and the fact most of them look so similar. PC Gamer's Samuel Horti calls it "a mediocre detective game with predictable stealth and a surreal story that runs out of steam near the end."


title: Call of Cthulhu (video game)

text: However, Dm Schmeyer of IGN praised the game with a rating of 8.6/10. He said the dialogue options is one of the best features in "Call of Cthulhu," unlike other games that are more "stunted and unimaginative". He concluded that despite its poor level and encounter design, the "engaging mystery and an intriguing utilization of RPG mechanics make it one of the more enjoyable Lovecraftian games in years."


title: Pontypool (film)

text: Pontypool (stylized as POИTYPOOL) a 2008 Canadian horror film directed by Bruce McDonald and written by Tony Burgess, based on his novel "Pontypool Changes Everything". A spin-off, "Dreamland", was released in 2019. , a direct sequel, "Pontypool Changes", has been repeatedly teased (2009 for 2010 release, 2012 for 2013 release, and 2018 for 2019 release) as supposedly being in active development over the past 13 years.


title: Pontypool (film)

text: In the small town of Pontypool, Ontario, radio announcer Grant Mazzy is accosted by a nonsensical woman who repeats the word "blood" several times before staggering away.


title: Pontypool (film)

text: At the radio station, Grant's shock jock style and on-air persona entertain his technical assistant, Laurel-Ann, while irritating his station manager, Sydney. Helicopter reporter Ken Loney calls in with a report about a riot at the office of Dr. Jon Mendez that has resulted in numerous deaths. After Ken is unexpectedly cut off, the group tries to confirm his report, but their witnesses are disconnected before being put on the airwaves. After they are contacted by the BBC for breaking the story, Ken calls back and says he has taken refuge in a grain silo. He describes the rioters as trying to eat one another or even themselves. When one of the rioters attacks the silo, Ken's call is interrupted by an audio transmission in French.


title: Pontypool (film)

text: Laurel-Ann translates the transmission, which is an instruction to remain indoors, not to use terms of endearment, rhetorical discourse, or the English language and not to translate the message. Pontypool is declared to be under quarantine. Ken calls back again and gets his phone close enough to his attacker so that his murmurs of "Help me" in a baby-like voice are audible. A horde of people attack the radio station, and Grant, Sydney, and Laurel-Ann lock themselves inside. Meanwhile, Laurel-Ann begins repeating the word "missing" and imitates the sound of a tea kettle.


title: Pontypool (film)

text: Dr. Mendez arrives at the radio station through a window and hides with Grant and Sydney in the soundproof booth. Ken calls in and, while on the air, succumbs to the virus. Laurel-Ann begins to slam her head against the sound booth's window and chews off her lower lip. Mendez hypothesizes that a virus has infected certain words in the English language; only certain words infect certain people who then find another infected person to kill themselves with. Sydney receives a call from her children, only to hear them becoming infected. Outside the booth, Laurel-Ann vomits a large amount of blood and falls down, dead. Mendez suspects this has happened since she failed to find a victim.


title: Pontypool (film)

text: The horde then breaks into the radio station, attacking the sound booth. Sydney draws the mob outside with a looped recording of Grant's voice saying 'Sydney Briar is alive". When he fears that he is about to succumb to the virus, Dr. Mendez begins to speak in Armenian upon realizing that the virus is exclusive to the English language, which prevents the virus from taking over. When the recording fails, the mob returns but Mendez lures them away, saving Sydney and Grant, who now lock themselves in the equipment room.


title: Pontypool (film)

text: While Grant tries to figure out how to reverse the symptom, Sydney begins to succumb to the word "kill". Grant convinces her that the word "kill" now means "kiss" and her symptoms subside. Hoping to stop the virus, the pair go on the air, spouting a series of self-contradicting and confusing phrases to help their infected listeners, ignoring warnings from the authorities who are trying to get them off the air. While an amplified voice from outside counts down from ten, Sydney joins Grant in the booth and they kiss. An explosion can be heard when the film cuts to black.


title: Pontypool (film)

text: Over the black, news reports of further outbreaks of the virus suggest that the quarantine failed, spread by the news itself and eventually reaching England, the source of its targeted language. In a post-credits scene, Sydney and Grant (now known as "Lisa" and "Johnny Deadeyes") survive the virus and continue speaking English by maintaining a system of improvisational roleplay as the screen shifts from black and white to color.


title: Pontypool (film)

text: Whilst the radio play version of the story changes a few features, such as the more visual elements being restyled for audio or removed all together; it also features an alternative ending. In this ending when Grant convinces Sydney that "kill" now means "kiss" she asks Grant to "kiss" her (in the film version she says "kill" leading to them kissing).


title: Pontypool (film)

text: Soon after when broadcasting his own obituaries of Laurel-Ann and Mendez (who Grant assumes will meet his demise eventually), he confirms the death of Sydney, implying that he "kissed" her at her request.


title: Pontypool (film)

text: Grant, now completely alone, realises that he has become infected through the word "paper". Resigned to his fate, he allows himself to be taken by the word, repeating it over and over again, before finally uttering one different word: "trap".


title: Pontypool (film)

text: "Pontypool" is based on Tony Burgess' novel "Pontypool Changes Everything". Burgess adapted the material for the screen himself. According to McDonald, the writer hashed out a script in 48 hours. Orson Welles' infamous radio broadcast of "The War of the Worlds" inspired the approach that they decided to take. It was simultaneously produced as a motion picture and a radio play.


title: Pontypool (film)

text: At "Rue Morgue"s 2008 Festival of Fear expo, director Bruce McDonald stressed the victims of the virus detailed in the film were not zombies and called them "conversationalists". He described the stages of the disease:There are three stages to this virus. The first stage is you might begin to repeat a word. Something gets stuck. And usually it's words that are terms of endearment like sweetheart or honey. The second stage is your language becomes scrambled and you can't express yourself properly. The third stage you become so distraught at your condition that the only way out of the situation you feel, as an infected person, is to try and chew your way through the mouth of another person.


title: Pontypool (film)

text: According to McDonald, the final scene of Grant and Sydney, now presented in a kicker, was originally placed before the credits. However, audiences in early screenings found the original ending to be too confusing, so the scene was moved behind the credits instead.


title: Pontypool (film)

text: "Rue Morgue" and "ChiZine Publications" held a special screening of "Pontypool" on 3 December 2009 at the Toronto Underground Cinema and following the screening, it featured a Q&A with Stephen McHattie, Lisa Houle, and Tony Burgess.


title: Pontypool (film)

text: The film was released theatrically in Canada on March 6, 2009. The film was released on DVD and Blu-ray on 25 January 2010.


title: Pontypool (film)

text: "Pontypool" received generally positive reviews from critics, currently holding an 84% rating on Rotten Tomatoes based on 86 reviews; the consensus states: "Witty and restrained but still taut and funny, this "Pontypool" is a different breed of low-budget zombie film." On Metacritic, which uses an average of critics' reviews, the film has a rating of 54/100, indicating "mixed or average reviews".


title: Pontypool (film)

text: , a direct sequel, "Pontypool Changes", has been repeatedly teased (2009 for 2010 release, 2012 for 2013 release, and 2018 for 2019 release) as supposedly being in active development over the previous 13 years.


title: Pontypool (film)

text: In May 2009, "Pontypool Changes" was confirmed to be in development, with McDonald returning as director for production in 2010. In July 2012, a teaser poster for the film was released at the Fantasia Film Festival, with an intended release date of 2013. In April 2018, McDonald and Burgess revealed that their film "Dreamland", which ultimately saw release in 2019, would be a spin-off of "Pontypool" serving as "a sequel to the [film's] post-credit non-sequitur scene, with McHattie and Houle" reprising their roles. Burgess additionally confirmed that "Pontypool Changes", also known as "Typo Chan", would follow the English language virus passing into the written word, would feature McHattie and Houle reprising their roles, and would go into production by 2019.


title: Shenandoah Valley

text: The Shenandoah Valley () is a geographic valley and cultural region of western Virginia and the Eastern Panhandle of West Virginia. The valley is bounded to the east by the Blue Ridge Mountains, to the west by the eastern front of the Ridge-and-Valley Appalachians (excluding Massanutten Mountain), to the north by the Potomac River and to the south by the James River. The cultural region covers a larger area that includes all of the valley plus the Virginia highlands to the west, and the Roanoke Valley to the south. It is physiographically located within the Ridge and Valley province and is a portion of the Great Appalachian Valley.


title: Shenandoah Valley

text: Named for the river that stretches much of its length, the Shenandoah Valley encompasses eight counties in Virginia and two counties in West Virginia.


title: Shenandoah Valley

text: The antebellum composition included four additional counties that are now in West Virginia as well as four additional Virginia counties.


title: Shenandoah Valley

text: Between the Roanoke Valley in the south and Harpers Ferry in the north, where the Shenandoah River joins the Potomac, the Valley cultural region contains 10 independent cities:


title: Shenandoah Valley

text: The central section of the Shenandoah Valley is split in half by the Massanutten Mountain range, with the smaller associated Page Valley lying to its east and the Fort Valley within the mountain range.


title: Shenandoah Valley

text: The Shenandoah Valley contains a number of geologically and historically significant limestone caves:


title: Shenandoah Valley

text: The word "Shenandoah" is of unknown Native American origin. It has been described as being derived from the Anglicization of Native American terms, resulting in words such as Gerando, Gerundo, Genantua, Shendo and Sherando. The meaning of these words is of some question. "Schin-han-dowi", the "River Through the Spruces"; "On-an-da-goa", the "River of High Mountains" or "Silver-Water"; and an Iroquois word for "Big Meadow", have all been proposed by Native American etymologists. The most popular, romanticized belief is that the name comes from a Native American expression for "Beautiful Daughter of the Stars".


title: Shenandoah Valley

text: Another legend relates that the name is derived from the name of the Iroquoian chief "Sherando" (Sherando was also the name of his people), who fought against the Algonquian Chief "Opechancanough", ruler of the Powhatan Confederacy (1618–1644). Opechancanough liked the interior country so much that he sent his son "Sheewa-a-nee" from the Tidewater with a large party to colonize the valley. Sheewa-a-nee drove Sherando back to his former territory near the Great Lakes. According to this account, descendants of Sheewanee's party became the Shawnee. According to tradition, another branch of Iroquoians, the "Senedo", lived in present-day Shenandoah County. They were exterminated by "Southern Indians" (Catawba or Cherokee) before the arrival of white settlers.


title: Shenandoah Valley

text: Another story dates to the American Revolutionary War. Throughout the war, Chief Skenandoa of the Oneida, an Iroquois nation based in New York, persuaded many of the tribe to side with the colonials against the British. Four Iroquois nations became British allies, and caused many fatalities and damage in the frontier settlements west of Albany. Skenandoa led 250 warriors against the British and Iroquois allies. According to Oneida oral tradition, during the harsh winter of 1777–1778 at Valley Forge, where the colonials suffered, Chief Skenando provided aid to the soldiers. The Oneida delivered bushels of dry corn to the troops to help them survive. Polly Cooper, an Oneida woman, stayed some time with the troops to teach them how to cook the corn properly and care for the sick. General Washington gave her a shawl in thanks, which is displayed at "Shako:wi," the museum of the Oneida Nation near Syracuse, New York. Many Oneida believe that after the war, George Washington named the Shenandoah River and valley after his ally.


title: Shenandoah Valley

text: Despite the valley's potential for productive farmland, colonial settlement from the east was long delayed by the barrier of the Blue Ridge Mountains. These were crossed by explorers John Lederer at Manassas Gap in 1671, Batts and Fallam the same year, and Cadwallader Jones in 1682. The Swiss Franz Ludwig Michel and Christoph von Graffenried explored and mapped the Valley in 1706 and 1712, respectively. Von Graffenried reported that the Indians of "Senantona" (Shenandoah) had been alarmed by news of the recent Tuscarora War in North Carolina.


title: Shenandoah Valley

text: Governor Alexander Spotswood's legendary Knights of the Golden Horseshoe Expedition of 1716 crossed the Blue Ridge at Swift Run Gap and reached the river at Elkton, Virginia. Settlers did not immediately follow, but someone who heard the reports and later became the first permanent settler in the Valley was Adam Miller (Mueller), who in 1727 staked out claims on the south fork of the Shenandoah River, near the line that now divides Rockingham County from Page County.


title: Shenandoah Valley

text: The Great Wagon Road (later called the Valley Pike or Valley Turnpike) began as the Great Warriors Trail or Indian Road, a Native road through common hunting grounds shared by several tribes settled around the periphery, which included Iroquoian, Siouan and Algonquian-language family tribes. Known native settlements within the Valley were few, but included the Shawnee occupying the region around Winchester, and Tuscarora around what is now Martinsburg, West Virginia. In the late 1720s and 1730s, Quakers and Mennonites began to move in from Pennsylvania. They were tolerated by the natives, while "Long Knives" (English settlers from coastal Virginia colony) were less welcomed. During these same decades, the valley route continued to be used by war parties of Seneca (Iroquois) and Lenape "en route" from New York, Pennsylvania and New Jersey to attack the distant Catawba in the Carolinas, with whom they were at war. The Catawba in turn pursued the war parties northward, often overtaking them by the time they reached the Potomac. Several fierce battles were fought among the warring nations in the Valley region, as attested by the earliest European-American settlers.


title: Shenandoah Valley

text: Later colonists called this route the Great Wagon Road; it became the major thoroughfare for immigrants' moving by wagons from Pennsylvania and northern Virginia into the backcountry of the South. The Valley Turnpike Company improved the road by paving it with macadam prior to the Civil War and set up toll gates to collect fees to pay for the improvements. After the advent of motor vehicles, the road was refined and paved appropriately for their use. In the 20th century, the road was acquired by the Commonwealth of Virginia, which incorporated it into the state highway system as U.S. Route 11. For much of its length, the newer Interstate 81, constructed in the 1960s, parallels the old Valley Pike.


title: Shenandoah Valley

text: Along with the first German settlers, known as "Shenandoah Deitsch", many Scotch-Irish immigrants came south in the 1730s from Pennsylvania into the valley, via the Potomac River. The Scotch-Irish comprised the largest group of non-English immigrants from the British Isles before the Revolutionary War, and most migrated into the backcountry of the South. This was in contrast to the chiefly English immigrants who had settled the Virginia Tidewater and Carolina Piedmont regions.


title: Shenandoah Valley

text: Along with the Ulster Scots many Irishmen arrived in the Shenandoah valley, usually after their indentured service was up. These Irishmen usually had converted to Protestantism or kept their faith secret. In the 18th-century Thirteen Colonies and the independent United States, while interethnic marriage among Catholics remained a dominant pattern, Catholic-Protestant intermarriage became more common (notably in the Shenandoah Valley where intermarriage among Ulster Protestants and the significant minority of Irish Catholics in particular was not uncommon or stigmatized), and while fewer Catholic parents required that their children be disinherited in their wills if they renounced Catholicism, it remained more common among Catholic parents to do so if their children renounced their parents' faith than it was in the rest of the U.S. population.


title: Shenandoah Valley

text: Governor Spotswood had arranged the Treaty of Albany with the Iroquois (Six Nations) in 1721, whereby they had agreed not to come east of the Blue Ridge in their raiding parties on tribes farther to the South. In 1736, the Iroquois began to object, claiming that they still legally owned the land to the west of the Blue Ridge; this led to a skirmish with Valley settlers in 1743. The Iroquois were on the verge of declaring war on the Virginia Colony as a result, when Governor Gooch paid them the sum of 100 pounds sterling for any settled land in the Valley that was claimed by them. The following year at the Treaty of Lancaster, the Iroquois sold all their remaining claim to the Valley for 200 pounds in gold.


title: Shenandoah Valley

text: The few Shawnees who still resided in the Valley abruptly headed westward in 1754, having been approached the year before by emissaries from their kindred beyond the Alleghenies.


title: Shenandoah Valley

text: The Shenandoah Valley was known as the breadbasket of the Confederacy during the Civil War and was seen as a backdoor for Confederate raids on Maryland, Washington, and Pennsylvania. Because of its strategic importance it was the scene of three major campaigns. The first was the Valley Campaign of 1862, in which Confederate General Stonewall Jackson defended the valley against three numerically superior Union armies. The final two were the Valley Campaigns of 1864. First, in the summer of 1864, Confederate General Jubal Early cleared the valley of its Union occupiers and then proceeded to raid Maryland, Pennsylvania, and D.C. Then during the autumn, Union General Philip Sheridan was sent to drive Early from the valley and once-and-for-all deny its use to the Confederates by putting it to the torch using scorched-earth tactics. The valley, especially in the lower northern section, was also the scene of bitter partisan fighting as the region's inhabitants were deeply divided over loyalties, and Confederate partisan John Mosby and his Rangers frequently operated in the area.


title: Shenandoah Valley

text: A series of newspaper mergers, ending in 1914, established the Daily News-Record of Harrisonburg as the daily newspaper of the Shenandoah Valley.


title: Shenandoah Valley

text: In the late 20th century, the valley's vineyards began to reach maturity. They constituted the new industry of the Shenandoah Valley American Viticultural Area.


title: Shenandoah Valley

text: Transportation in the Shenandoah Valley consists mainly of road and rail and contains several metropolitan area transit authorities. The main north-south road transportation is Interstate 81, which parallels the old Valley Turnpike (U.S. Route 11) and the ancient Great Path of the Native Americans through its course in the valley. In the lower (northern) valley, on the eastern side, U.S. Route 340 also runs north-south, starting from Waynesboro in the south, running through the Page Valley to Front Royal, and on to Harpers Ferry, West Virginia, where it exits the valley into Maryland. Major east-west roads cross the valley as well, providing access to the Piedmont and the Allegheny Mountains. Starting from the north, these routes include U.S. Route 50, U.S. Route 522, Interstate 66, U.S. Route 33, U.S. Route 250, Interstate 64, and U.S. Route 60.


title: Shenandoah Valley

text: CSX Transportation operates several rail lines through the valley, including the old Baltimore and Ohio Railroad, the old Manassas Gap Railroad and the old Virginia Central Railroad. There are also more modern lines that run the length of the valley parallel to the Valley Pike and U.S. 340. The rail lines are primarily used for freight transportation, though Maryland Area Rail Commuter (MARC) trains utilize the old B&O line from stations in Martinsburg, Duffields, and Harper's Ferry to Washington Union Station and vice versa.


title: Shenandoah Valley

text: Several localities in the valley operate public transportation systems, including Front Royal Area Transit (FRAT), which provides weekday transit for the town of Front Royal; Page County Transit, providing weekday transit for the town of Luray and weekday service between Luray and Front Royal; and Winchester Transit, which provides weekday transit for the city of Winchester. In addition, Shenandoah Valley Commuter Bus Service offers weekday commuter bus service from the northern Shenandoah Valley, including Shenandoah County and Warren County, to Northern Virginia (Arlington County and Fairfax County) and Washington. Origination points in Shenandoah County include Woodstock. Origination points in Warren County include Front Royal and Linden.


title: Shenandoah Valley

text: The Shenandoah Valley serves as the setting for the 1965 film "Shenandoah" and its 1974 musical adaptation. Both stories follow the Anderson family during the Civil War. An associated song by James Stewart titled "The Legend of Shenandoah" was a very minor hit in 1965, reaching #133 on the "Billboard" Bubbling Under the Hot 100 chart. One of the most famous cultural references to the area does not mention the valley itself: West Virginia's state song, "Take Me Home, Country Roads" by John Denver, simply contains the words "Shenandoah River" in the first verse.


title: Human furniture

text: Human furniture is furniture in which a person's body is used as a tray, foot stool, chair, table, cabinet or other item. In some cases a sculpture of a human body is used instead. Examples of human furniture have appeared in modern art. Forniphilia is the practice of creating human furniture in fetish photography and bondage pornography.


title: Human furniture

text: A model used as human furniture may be nude or semi-nude to add to the erotic or aesthetic appeal. A classic example of the depiction of human furniture as art is the set of three sculptures "Hatstand", "Table" and "Chair" made in 1969 by British pop artist Allen Jones which show semi-naked white women in the roles of furniture. Allen Jones' artwork was the subject of a feminist protest when it was auctioned at Sotheby's in 2012.


title: Human furniture

text: Norwegian artist Bjarne Melgaard created a sculpture called "Chair" which has the same shape as the Allen Jones' chair but depicts a black woman. In 2014 art collector Dasha Zhukova, the partner of Russian billionaire Roman Abramovich, caused controversy by appearing in a photograph sitting on Melgaard's chair. Zhukova apologized for the photograph saying that she "utterly abhor[s] racism, and would like to apologise to anyone who has been offended by this image".


title: Human furniture

text: The Japanese fetish artist Namio Harukawa depicted voluptuous women, who dominated and used men as human furniture.


title: Human furniture

text: The term "forniphilia" was coined by bondage artist Jeff Gord who specialized in the subgenre and maintained the website "House of Gord" on the subject. Forniphilia as a form of bondage usually involves the subject being tightly bound and expected to stay immobile for a prolonged period. Gord said that the maximum period he used depended on the bondage techniques involved but it did not generally exceed two hours. Gord also warned that the dangers inherent in fornophilia meant that it should only be carried out by experts. Gord used gags in some of his creations. A forniphilic gag is a type of gag that has the primary purpose of sexual objectification or erotic humiliation. Proper safety requires frequent checks of the submissive's well-being.


title: Human furniture

text: The 1971 film "A Clockwork Orange" includes a scene of a gang sitting in the Korova Milk Bar, which is furnished with tables shaped like naked women.


title: Human furniture

text: In Episode 7 of the 2021 Netflix Original Korean Drama, "Squid Game", the anonymous VIPs invited to watch the show's blood sport are surrounded by human furniture, which are seen wearing elaborate body paint.


title: Selegiline

text: Selegiline, also known as -deprenyl and sold under the brand names Eldepryl and Emsam among others, is a medication which is used in the treatment of Parkinson's disease and major depressive disorder. It is provided in the form of a capsule or tablet taken by mouth for Parkinson's disease and as a patch applied to skin for depression.


title: Selegiline

text: Selegiline acts as a monoamine oxidase inhibitor, and increases levels of monoamine neurotransmitters in the brain. At typical clinical doses used for Parkinson's disease, selegiline is a selective and irreversible inhibitor of monoamine oxidase B (MAO-B), increasing levels of dopamine in the brain. In larger doses (more than 20 mg/day), it loses its specificity for MAO-B and also inhibits MAO-A, which increases serotonin and norepinephrine levels in the brain.


title: Selegiline

text: In its pill form, selegiline is used to treat symptoms of Parkinson's disease. It is most often used as an adjunct to drugs such as levodopa (-DOPA), although it has been used off-label as a monotherapy. The rationale for adding selegiline to levodopa is to decrease the required dose of levodopa and thus reduce the motor complications of levodopa therapy. Selegiline delays the point when levodopa treatment becomes necessary from about 11 months to about 18 months after diagnosis. There is some evidence that selegiline acts as a neuroprotectant and reduces the rate of disease progression, though this is disputed.


title: Selegiline

text: Selegiline has also been used off-label as a palliative treatment for dementia in Alzheimer's disease.


title: Selegiline

text: Selegiline is also delivered via a transdermal patch used as a treatment for major depressive disorder.


title: Selegiline

text: Administration of transdermal selegiline bypasses hepatic first pass metabolism. This avoids inhibition of gastrointestinal and hepatic MAO-A activity, which would result in an increase of food-borne tyramine in the blood and possible related adverse effects, while allowing for a sufficient amount of selegiline to reach the brain for an antidepressant effect.


title: Selegiline

text: A quantitative review published in 2015 found that for the pooled results of the pivotal trials, the number needed to treat (a sign of effect size, so a low number is better) for the patch for symptom reduction was 11, and for remission, was 9. The number needed to harm (inverse of the NNT, a high number here is better) ranged from 387 for sexual side effects to 7 for application site reaction. With regard to the likelihood to be helped or harmed (LHH), the analysis showed that the selegiline patch was 3.6 times as likely to lead to a remission vs. a discontinuation due to side effects; the LHH for remission vs. incidence of insomnia was 2.1; the LHH for remission vs. discontinuation due to insomnia was 32.7. The LHH for remission vs. insomnia and sexual dysfunction were both very low.


title: Selegiline

text: For all human uses and all forms, selegiline is pregnancy category C: studies in pregnant lab animals have shown adverse effects on the fetus but there are no adequate studies in humans.


title: Selegiline

text: Side effects of the tablet form in conjunction with levodopa include, in decreasing order of frequency, nausea, hallucinations, confusion, depression, loss of balance, insomnia, increased involuntary movements, agitation, slow or irregular heart rate, delusions, hypertension, new or increased angina pectoris, and syncope. Most of the side effects are due to a high dopamine signaling, and can be alleviated by reducing the dose of levodopa.


title: Selegiline

text: The main side effects of the patch form for depression include application-site reactions, insomnia, diarrhea, and sore throat. The selegiline patch carries a black box warning about a possible increased risk of suicide, especially for young people, as do all antidepressants since 2007.


title: Selegiline

text: Both the oral and patch forms come with strong warnings against combining selegiline with drugs that could produce serotonin syndrome, such as SSRIs and the cough medicine dextromethorphan. Selegiline in combination with the opioid analgesic pethidine is not recommended, as it can lead to severe adverse effects. Several other synthetic opioids such as tramadol and methadone, as well as various triptans, are contraindicated due to potential for serotonin syndrome.


title: Selegiline

text: Birth control pills containing ethinylestradiol and a progestin increase the bioavailability of selegiline by 10- to 20-fold. High levels can lead to loss of MAO-B selectivity, and selegiline may begin inhibiting MAO-A as well. This increases susceptibility to side effects of non-selective MAOIs, such as tyramine-induced hypertensive crisis and serotonin toxicity when combined with serotonergic medications.


title: Selegiline

text: Both forms of the drug carry warnings about food restrictions to avoid hypertensive crisis that are associated with MAO inhibitors. The patch form was created in part to overcome food restrictions; clinical trials showed that it was successful. Additionally, in post-marketing surveillance from April 2006 to October 2010, only 13 self-reports of possible hypertensive events or hypertension were made out of 29,141 exposures to the drug, and none were accompanied by objective clinical data. The lowest dose of the patch method of delivery, 6 mg/24 hours, does not require any dietary restrictions. Higher doses of the patch and oral formulations, whether in combination with the older non-selective MAOIs or in combination with the reversible MAO-A inhibitor moclobemide, require a low-tyramine diet.


title: Selegiline

text: Selegiline is a selective inhibitor of MAO-B, irreversibly inhibiting it by binding to it covalently. It is generally believed to exert its effects by blocking the breakdown of dopamine, thus increasing its activity; however, recent evidence suggests that MAO-A is solely or almost entirely responsible for the metabolism of dopamine. Its possible neuroprotective properties may be due to protecting nearby neurons from the free oxygen radicals that are released by MAO-B activity. At higher doses, selegiline loses its selectivity for MAO-B and inhibits MAO-A as well.


title: Selegiline

text: Selegiline also inhibits CYP2A6 and can increase the effects of nicotine as a result. Selegiline also appears to activate σ receptors, having a relatively high affinity for these receptors of approximately 400 nM.


title: Selegiline

text: Selegiline has an oral bioavailability of about 10%, which increases when ingested together with a fatty meal, as the molecule is fat soluble. Selegiline and its metabolites bind extensively to plasma proteins (at a rate of 94%). They cross the blood–brain barrier and enter the brain, where they most concentrated at the thalamus, basal ganglia, midbrain, and cingulate gyrus.


title: Selegiline

text: Selegiline is mostly metabolized in the intestines and liver; it and its metabolites are excreted in the urine.


title: Selegiline

text: Buccal administration of selegiline results in 5-fold higher bioavailability, more reproducible blood concentration, and produces fewer amphetamine metabolites than the oral tablet form.


title: Selegiline

text: Selegiline is metabolized by cytochrome P450 to -desmethylselegiline and levomethamphetamine. Desmethylselegiline has some activity against MAO-B, but much less than that of selegiline. It is thought to be further metabolized by CYP2C19. Levomethamphetamine (the less potent of the two enantiomers of methamphetamine) is converted to levoamphetamine (the less potent of the two enantiomers of amphetamine, with regards to psychological effects).


title: Selegiline

text: Due to the presence of these metabolites, people taking selegiline may test positive for "amphetamine" or "methamphetamine" on drug screening tests. While the amphetamine metabolites may contribute to selegiline's ability to inhibit reuptake of the neurotransmitters dopamine and norepinephrine, they have also been associated with orthostatic hypotension and hallucinations. The amphetamine metabolites are hydroxylated and, in phase II, conjugated by glucuronyltransferase.


title: Selegiline

text: A newer anti-Parkinson MAO-B inhibitor, rasagiline, metabolizes into 1("R")-aminoindan, which has no amphetamine-like characteristics.


title: Selegiline

text: Following application of the patch to humans, an average of 25% to 30% of the selegiline content is delivered systemically over 24 hours. Transdermal dosing results in significantly higher exposure to selegiline and lower exposure to all metabolites when compared to oral dosing; this is due to the extensive first-pass metabolism of the pill form and low first-pass metabolism of the patch form. The site of application is not a significant factor in how the drug is distributed. In humans, selegiline does not accumulate in the skin, nor is it metabolized there.


title: Selegiline

text: Selegiline belongs to the phenethylamine and amphetamine chemical families. It is also known as -deprenyl, as well as ("R")-(–)-"N",α-dimethyl-"N"-(2-propynyl)phenethylamine or ("R")-(–)-"N"-methyl-"N"-2-propynylamphetamine. The compound is a derivative of levomethamphetamine (-methamphetamine) with a propargyl group attached to the nitrogen atom. This detail is borrowed from pargyline, an older MAO-B inhibitor of the phenylalkylamine group. Selegiline is the levorotatory enantiomer of the racemic mixture deprenyl.


title: Selegiline

text: Following the discovery that the tuberculosis drug iproniazid elevated the mood of people taking it, and the subsequent discovery that the effect was likely due to inhibition of MAO, many people and companies started trying to discover MAO inhibitors to use as antidepressants. Selegiline was discovered by Zoltan Ecseri at the Hungarian drug company, Chinoin (part of Sanofi since 1993), which they called E-250. Chinoin received a patent on the drug in 1962 and the compound was first published in the scientific literature in English in 1965. Work on the biology and effects of E-250 in animals and humans was conducted by a group led by József Knoll at Semmelweis University which was also in Budapest.


title: Selegiline

text: Deprenyl is a racemic compound a mixture of two isomers called enantiomers. Further work determined that the levorotatory enantiomer was a more potent MAO-inhibitor, which was published in 1967, and subsequent work was done with the single enantiomer -deprenyl.


title: Selegiline

text: In 1971, Knoll showed that selegiline selectively inhibits the B-isoform of monoamine oxidase (MAO-B) and proposed that it is unlikely to cause the infamous "cheese effect" (hypertensive crisis resulting from consuming foods containing tyramine) that occurs with non-selective MAO inhibitors. A few years later, two Parkinson's disease researchers based in Vienna, Peter Riederer and Walther Birkmayer, realized that selegiline could be useful in Parkinson's disease. One of their colleagues, Prof. Moussa B.H. Youdim, visited Knoll in Budapest and took selegiline from him to Vienna. In 1975, Birkmayer's group published the first paper on the effect of selegiline in Parkinson's disease.


title: Selegiline

text: In 1987 Somerset Pharmaceuticals in New Jersey, which had acquired the US rights to develop selegiline, filed a new drug application (NDA) with the FDA to market the drug for Parkinson's disease in the US. While the NDA was under review, Somerset was acquired in a joint venture by two generic drug companies, Mylan and Bolan Pharmaceuticals. Selegiline was approved for Parkinson's disease by the FDA in 1989.


title: Selegiline

text: In the 1990s, J. Alexander Bodkin at McLean Hospital, an affiliate of Harvard Medical School, began a collaboration with Somerset to develop delivery of selegiline via a transdermal patch in order to avoid the well known dietary restrictions of MAO inhibitors. Somerset obtained FDA approval to market the patch in 2006.


title: Selegiline

text: In "E for Ecstasy" (a book examining the uses of the street drug ecstasy in the UK) the writer, activist and ecstasy advocate Nicholas Saunders highlighted test results showing that certain consignments of the drug also contained selegiline. Consignments of ecstasy known as "Strawberry" contained what Saunders described as a "potentially dangerous combination of ketamine, ephedrine and selegiline," as did a consignment of "Sitting Duck" Ecstasy tablets.


title: Selegiline

text: In Gregg Hurwitz's novel "Out of the Dark", selegiline ("Emsam") and tyramine-containing food were used to assassinate the president of the United States.


title: Selegiline

text: In veterinary medicine, selegiline is sold under the brand name Anipryl (manufactured by Zoetis). It is used in dogs to treat canine cognitive dysfunction and, at higher doses, pituitary-dependent hyperadrenocorticism (PDH). Canine cognitive dysfunction is a form of dementia that mimics Alzheimer's disease in humans. Geriatric dogs treated with selegiline show improvements in sleeping pattern, reduced incontinence, and increased activity level; most show improvements by one month. Though it is labeled for dog use only, selegiline has been used off-label for geriatric cats with cognitive dysfunction.


title: Selegiline

text: Selegiline's efficacy in treating pituitary-dependent hyperadrenocorticism has been disputed. Theoretically, it works by increasing dopamine levels, which downregulates the release of ACTH, eventually leading to reduced levels of cortisol. Some claim that selegiline is only effective at treating PDH caused by lesions in the anterior pituitary (which comprise most canine cases). The greatest sign of improvement is lessening of abdominal distention.


title: Selegiline

text: Side effects in dogs are uncommon, but they include vomiting, diarrhea, diminished hearing, salivation, decreased weight and behavioral changes such as hyperactivity, listlessness, disorientation, and repetitive motions.


title: Selegiline

text: Selegiline has been limitedly studied in the treatment of attention deficit hyperactivity disorder (ADHD) in both children/adolescents and adults. In a small randomized trial of selegiline for treatment of ADHD in children, there were improvements in attention, hyperactivity, and learning/memory performance but not in impulsivity. In another small randomized controlled trial of selegiline for the treatment of adult ADHD, a high dose of the medication for 6 weeks was not significantly more effective than placebo in improving symptoms.


title: Gunbuster

text: Gunbuster, known in Japan as , is a Japanese OVA anime series produced by Bandai, Victor, and Gainax and released from 1988 to 1989. It was the directorial debut of Hideaki Anno, best known as the creator and director of "Neon Genesis Evangelion". The title is a combination of the titles of classic tennis manga and anime "Aim for the Ace!" and hit action drama film "Top Gun", whose plot inspired "Gunbuster"s. To celebrate Gainax's 20th anniversary in 2004, a sequel to "Gunbuster", "Diebuster" (or "Gunbuster 2"), was released as an OVA. The sequel features new characters and mecha, but retains the format and many of the concepts of the original series.