Habitability is the conformance of a residence or abode to the implied warranty of habitability. A residence that complies is said to be habitable. It is an implied warranty or contract, meaning it does not have to be an express contract, covenant, or provision of a contract. There was no implied warranty of habitability for tenants at common law and the legal doctrine has since developed in many jurisdictions through housing laws and regulations.[1][2] Habitability is synonymous with tenantability.[3]

In order to be habitable, such housing usually:

New York law

Some states, such as New York, have given additional statutory protections in addition to those created by caselaw.[14] These statutes include:

  1. Lobby attendant service by a concierge or landlord [15]
  2. Elevator mirrors [16]
  3. Smoke detectors[17]
  4. Window guards[18]
  5. Intercoms and self-locking doors[19]
  6. Protection from lead paint [20]


Violation of the warranty of habitability results in constructive eviction, whereby the landlord or lessor has, in effect, evicted the tenant or lessee.[21] The tenant may remedy the problem,[22][23] or complain to local government authorities for remedies.[24]

See also


  1. ^ "Landlord-Tenant Law". Wex. Cornell Law School. Retrieved 16 December 2017.
  2. ^ "Duties of the Landlord". LawShelf. National Paralegal College. Retrieved 16 December 2017.
  3. ^ "Is tenantability broader than habitability?"
  4. ^ In New York, see N.Y. Multiple Dwelling Law § 79.
  5. ^ Mold in condominium: Negligent maintenance: Breach of warranty of habitability: Settlement: Verdict | Law Reporter | Find Articles at BNET.com
  6. ^ "Archived copy". Archived from the original on 2007-09-28. Retrieved 2007-05-02.CS1 maint: Archived copy as title (link)
  7. ^ Pennsylvania
  8. ^ generally, United States
  9. ^ California
  10. ^ District of Columbia
  11. ^ Vermont (form).
  13. ^ Massachusetts
  14. ^ See N.Y. Attorney General's Website Archived 2007-03-12 at the Wayback Machine, q.v., and in External sources.
  15. ^ N.Y. Multiple Dwelling Law §50-c
  16. ^ N.Y. Multiple Dwelling Law §51-b; NYC Admin. Code §27-2042
  17. ^ N.Y. Multiple Residence Law §15; Buffalo Code Ch. 395; NYC Admin. Code §27-2045, §27-2046
  18. ^ NYC Health Code §131.15
  19. ^ N.Y. Multiple Dwelling Law §50-a
  20. ^ NYC Health Code §173.14;
  21. ^ Josephson, Richard C. (1971). "The Implied Warranty of Habitability in Landlord-Tenant Relations". William & Mary Law Review. 12 (3): 580. Retrieved 16 December 2017.
  22. ^ See N.Y. Real Property Law §235-b.
  23. ^ Warranty of Habitability (rev 7/96)
  24. ^ N.Y. Multiple Dwelling Law (MDL) §78 and §80; Multiple Residence Law (MRL) §174. (Note: The MDL applies to cities with a population of 325,000 or more and the MRL applies to cities with less than 325,000 and to all towns and villages; from N.Y. Attorney General's Website Archived 2007-03-12 at the Wayback Machine.
  25. ^ (Note to editors: merge with this article?)

External links


Astrobiology, formerly known as exobiology, is an interdisciplinary scientific field concerned with the origins, early evolution, distribution, and future of life in the universe. Astrobiology considers the question of whether extraterrestrial life exists, and how humans can detect it if it does.Astrobiology makes use of molecular biology, biophysics, biochemistry, chemistry, astronomy, physical cosmology, exoplanetology and geology to investigate the possibility of life on other worlds and help recognize biospheres that might be different from that on Earth. The origin and early evolution of life is an inseparable part of the discipline of astrobiology. Astrobiology concerns itself with interpretation of existing scientific data, and although speculation is entertained to give context, astrobiology concerns itself primarily with hypotheses that fit firmly into existing scientific theories.

This interdisciplinary field encompasses research on the origin of planetary systems, origins of organic compounds in space, rock-water-carbon interactions, abiogenesis on Earth, planetary habitability, research on biosignatures for life detection, and studies on the potential for life to adapt to challenges on Earth and in outer space.Biochemistry may have begun shortly after the Big Bang, 13.8 billion years ago, during a habitable epoch when the Universe was only 10–17 million years old. According to the panspermia hypothesis, microscopic life—distributed by meteoroids, asteroids and other small Solar System bodies—may exist throughout the universe. According to research published in August 2015, very large galaxies may be more favorable to the creation and development of habitable planets than such smaller galaxies as the Milky Way. Nonetheless, Earth is the only place in the universe humans know to harbor life. Estimates of habitable zones around other stars, sometimes referred to as "Goldilocks zones," along with the discovery of hundreds of extrasolar planets and new insights into extreme habitats here on Earth, suggest that there may be many more habitable places in the universe than considered possible until very recently.Current studies on the planet Mars by the Curiosity and Opportunity rovers are searching for evidence of ancient life as well as plains related to ancient rivers or lakes that may have been habitable. The search for evidence of habitability, taphonomy (related to fossils), and organic molecules on the planet Mars is now a primary NASA and ESA objective.

Even if extraterrestrial life is never discovered, the interdisciplinary nature of astrobiology, and the cosmic and evolutionary perspectives engendered by it, may still result in a range of benefits here on Earth.

Circumstellar habitable zone

In astronomy and astrobiology, the circumstellar habitable zone (CHZ), or simply the habitable zone, is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure. The bounds of the CHZ are based on Earth's position in the Solar System and the amount of radiant energy it receives from the Sun. Due to the importance of liquid water to Earth's biosphere, the nature of the CHZ and the objects within it may be instrumental in determining the scope and distribution of Earth-like extraterrestrial life and intelligence.

The habitable zone is also called the Goldilocks zone, a metaphor of the children's fairy tale of "Goldilocks and the Three Bears", in which a little girl chooses from sets of three items, ignoring the ones that are too extreme (large or small, hot or cold, etc.), and settling on the one in the middle, which is "just right".

Since the concept was first presented in 1953, many stars have been confirmed to possess a CHZ planet, including some systems that consist of multiple CHZ planets. Most such planets, being super-Earths or gas giants, are more massive than Earth, because such planets are easier to detect. On November 4, 2013, astronomers reported, based on Kepler data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarfs in the Milky Way. 11 billion of these may be orbiting Sun-like stars. Proxima Centauri b, located about 4.2 light-years (1.3 parsecs) from Earth in the constellation of Centaurus, is the nearest known exoplanet, and is orbiting in the habitable zone of its star. The CHZ is also of particular interest to the emerging field of habitability of natural satellites, because planetary-mass moons in the CHZ might outnumber planets.In subsequent decades, the CHZ concept began to be challenged as a primary criterion for life, so the concept is still evolving. Since the discovery of evidence for extraterrestrial liquid water, substantial quantities of it are now thought to occur outside the circumstellar habitable zone. The concept of deep biospheres, like Earth's, that exist independently of stellar energy, are now generally accepted in astrobiology given the large amount of liquid water known to exist within in lithospheres and asthenospheres of the Solar System. Sustained by other energy sources, such as tidal heating or radioactive decay or pressurized by non-atmospheric means, liquid water may be found even on rogue planets, or their moons. Liquid water can also exist at a wider range of temperatures and pressures as a solution, for example with sodium chlorides in seawater on Earth, chlorides and sulphates on equatorial Mars, or ammoniates, due to its different colligative properties. In addition, other circumstellar zones, where non-water solvents favorable to hypothetical life based on alternative biochemistries could exist in liquid form at the surface, have been proposed.

Enceladus Life Signatures and Habitability

Enceladus Life Signatures and Habitability (ELSAH) is an astrobiology concept mission proposed in 2017 to NASA's New Frontiers program to send a spacecraft to Enceladus to search for biosignatures and assess its habitability. The Principal Investigator is Christopher P. McKay, an astrobiologist at NASA Ames Research Center, and the managing NASA center is Goddard Space Flight Center. No details of the mission have been made public, but observers speculate that it would be a plume-sampling orbiter mission.The two finalists, announced on 20 December 2017, are Dragonfly to Titan, and CAESAR (Comet Astrobiology Exploration Sample Return) which is a sample-return mission from comet 67P/Churyumov–Gerasimenko.Although ELSAH was not selected for launch in this instance, it received technology development funds to prepare it for future mission competitions. The funds are meant to develop techniques that limit spacecraft contamination and thereby enable life detection measurements on cost-capped missions.

Explorer of Enceladus and Titan

Explorer of Enceladus and Titan (E2T) is a space mission concept that would investigate the evolution and habitability of the Saturnian satellites Enceladus and Titan and is proposed by the European Space Agency in collaboration with NASA.The proposed mission would address key scientific questions regarding extraterrestrial habitability, abiotic/prebiotic chemistry and emergence of life, which are among the highest priorities of ESA's Cosmic Vision program.

Galactic habitable zone

In astrobiology and planetary astrophysics, the galactic habitable zone is the region of a galaxy in which life might most likely develop. More specifically, the concept of a galactic habitable zone incorporates various factors, such as metallicity and the rate of major catastrophes such as supernovae, to calculate which regions of the galaxy are more likely to form terrestrial planets, initially develop simple life, and provide a suitable environment for this life to evolve and advance. According to research published in August 2015, very large galaxies may favor the birth and development of habitable planets more than smaller galaxies such as the Milky Way. In the case of the Milky Way, its galactic habitable zone is commonly believed to be an annulus with an outer radius of about 10 kiloparsecs and an inner radius close to the Galactic Center (with both radii lacking hard boundaries).Galactic habitable-zone theory has been criticized due to an inability to quantify accurately the factors making a region of a galaxy favorable for the emergence of life. In addition, computer simulations suggest that stars may change their orbits around the galactic center significantly, therefore challenging at least part of the view that some galactic areas are necessarily more life-supporting than others.

Habitability of K-type main-sequence star systems

K-type main-sequence stars may be candidates for supporting extraterrestrial life. These stars are known as "Goldilocks stars" as they emit enough radiation in the non-UV ray spectrum to provide a temperature that allows liquid water to exist on the surface of a planet; they also remain stable in the main phase longer than the Sun, allowing more time for life to form on a planet around a K-type main-sequence star. The planet's habitable zone, ranging from 0.1–0.4 to 0.3–1.3 astronomical units (AU), depending on the size of the star, is often far enough from the star so as not to be tidally locked to the star, and to have a sufficiently low solar flare activity not to be lethal to life. In comparison, red dwarf stars have too much solar activity and quickly tidally lock the planets in their habitable zones, making them less suitable for life. The odds of intelligent life arising may be better on planets around K-type main-sequence stars than around Sun-like stars, given the extra time available for it to evolve. Few planets thus far have been found around K-type main-sequence stars, but those that have are potential candidates for extraterrestrial life.

Habitability of binary star systems

Planets in binary star systems may be candidates for supporting extraterrestrial life. Habitability of binary star systems is determined by a large number of factors from a variety of sources. Typical estimates often suggest that 50% or more of all star systems are binary systems. This may be partly due to 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.The separation between stars in a binary may range from less than one astronomical unit (au, the "average" Earth-to-Sun distance) to several hundred au. 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). In reality, some orbital ranges are impossible for dynamical reasons (the planet would be expelled from its orbit relatively quickly, being either ejected from the system altogether or transferred to a more inner or outer orbital range), whilst other orbits present serious challenges for eventual biospheres because of likely extreme variations in surface temperature during different parts of the orbit. If the separation is significantly close to the planet's distance, a stable orbit may be impossible.

Planets that orbit just one star in a binary pair are said to have "S-type" orbits, whereas those that orbit around both stars have "P-type" or "circumbinary" orbits. It is estimated that 50–60% of binary stars are capable of supporting habitable terrestrial planets within stable orbital ranges.

Habitability of natural satellites

The habitability of natural satellites is a measure of the potential of natural satellites to have environments hospitable to life. Habitable environments do not necessarily harbor life. Planetary habitability is an emerging study which is considered important to astrobiology for several reasons, foremost being that natural satellites are predicted to greatly outnumber planets and that it is hypothesized that habitability factors are likely to be similar to those of planets. There are, however, key environmental differences which have a bearing on moons as potential sites for extraterrestrial life.

The strongest candidates for natural satellite habitability are currently icy satellites such as those of Jupiter and Saturn—Europa and Enceladus respectively, although if life exists in either place, it would probably be confined to subsurface habitats. Historically, life on Earth was thought to be strictly a surface phenomenon, but recent studies have shown that up to half of Earth's biomass could live below the surface. Europa and Enceladus exist outside the circumstellar habitable zone which has historically defined the limits of life within the Solar System as the zone in which water can exist as liquid at the surface. In the Solar System's habitable zone, there are only three natural satellites—the Moon, and Mars's moons Phobos and Deimos (although some estimates show Mars and its moons to be slightly outside the habitable zone) —none of which sustain an atmosphere or water in liquid form. Tidal forces are likely to play as significant a role providing heat as stellar radiation in the potential habitability of natural satellites.Exomoons are not yet confirmed to exist. Detecting them is extremely difficult, because current methods are limited to transit timing. It is possible that some of their attributes could be determined by similar methods as those of transiting planets. Despite this, some scientists estimate that there are as many habitable exomoons as habitable exoplanets. Given the general planet-to-satellite(s) mass ratio of 10,000, large Saturn or Jupiter sized gas planets in the habitable zone are thought to be the best candidates to harbour Earth-like moons.

Habitability of red dwarf systems

The habitability of red dwarf systems is determined by a large number of factors from a variety of sources. Although the low stellar flux, high probability of tidal locking, small circumstellar habitable zones, and high stellar variation experienced by planets of red dwarf stars are impediments to their planetary habitability, the ubiquity and longevity of red dwarfs are positive factors. Determining how the interactions between these factors affect habitability may help to reveal the frequency of extraterrestrial life and intelligence.

Intense tidal heating caused by the proximity of planets to their host red dwarfs is a major impediment to life developing in these systems. Other tidal effects, such as the extreme temperature differences created by one side of habitable-zone planets permanently facing the star and the other perpetually turned away and lack of planetary axial tilts, reduce the probability of life around red dwarfs. Non-tidal factors, such as extreme stellar variation, spectral energy distributions shifted to the infrared relative to the Sun, and small circumstellar habitable zones due to low light output, further reduce the prospects for life in red-dwarf systems.There are, however, several effects that increase the likelihood of life on red dwarf planets. Intense cloud formation on the star-facing side of a tidally locked planet may reduce overall thermal flux and drastically reduce equilibrium temperature differences between the two sides of the planet. In addition, the sheer number of red dwarfs, which account for about 85% of at least 100 billion stars in the Milky Way, statistically increases the probability that there might exist habitable planets orbiting some of them. As of 2013, there are expected to be tens of billions of super-Earth planets in the habitable zones of red dwarf stars in the Milky Way.

High island

In geology (and sometimes in archaeology), a high island or volcanic island is an island of volcanic origin. The term can be used to distinguish such islands from low islands, which are formed from sedimentation or the uplifting of coral reefs (which have often formed on sunken volcanos).

Implied warranty

In common law jurisdictions, an implied warranty is a contract law term for certain assurances that are presumed to be made in the sale of products or real property, due to the circumstances of the sale. These assurances are characterized as warranties irrespective of whether the seller has expressly promised them orally or in writing. They include an implied warranty of fitness for a particular purpose, an implied warranty of merchantability for products, implied warranty of workmanlike quality for services, and an implied warranty of habitability for a home.

The warranty of merchantability is implied, unless expressly disclaimed by name, or the sale is identified with the phrase "as is" or "with all faults". To be "merchantable", the goods must reasonably conform to an ordinary buyer's expectations, i.e., they are what they say they are. For example, a fruit that looks and smells good but has hidden defects would violate the implied warranty of merchantability if its quality does not meet the standards for such fruit "as passes ordinarily in the trade". In Massachusetts consumer protection law, it is illegal to disclaim this warranty on household goods sold to consumers.

The warranty of fitness for a particular purpose is implied when a buyer relies upon the seller to select the goods to fit a specific request. For example, this warranty is violated when a buyer asks a mechanic to provide snow tires and receives tires that are unsafe to use in snow. This implied warranty can also be expressly disclaimed by name, thereby shifting the risk of unfitness back to the buyer.

Another implied warranty is the warranty of title, which implies that the seller of goods has the right to sell them (e.g., they are not stolen, or patent infringements, or already sold to someone else). Theoretically, this saves a buyer from having to "pay twice" for a product, if it is confiscated by the rightful owner, but only if the seller can be found and makes restitution.


Kepler-62f (also known by its Kepler Object of Interest designation KOI-701.04) is a super-Earth exoplanet orbiting within the habitable zone of the star Kepler-62, the outermost of five such planets discovered around the star by NASA's Kepler spacecraft. It is located about 990 light-years (304 parsecs) from Earth in the constellation of Lyra.Kepler-62f orbits its star at a distance of 0.718 AU (107,400,000 km; 66,700,000 mi) from its host star with an orbital period of roughly 267.3 days, has a mass at least 2.8 times that of Earth, and has a radius of around 1.41 times that of Earth. It is one of the more promising candidates for potential habitability, as its parent star is a relatively quiet star, and has less mass than the Sun – thus it can live up to a span of about 30 billion years or so. Due to its mass, Kepler-62f is likely a terrestrial or ocean-covered planet. However, key components of the exoplanet still need to be assessed to determine habitability; such as its atmosphere if one exists, since it lies within the outer part of its host star's habitable zone.The discovery of the exoplanet (along with Kepler-62e) was announced in April 2013 by NASA as part of the Kepler spacecraft data release. The exoplanet was found by using the transit method, in which the dimming effect that a planet causes as it crosses in front of its star is measured. According to scientists, it is a potential candidate to search for extraterrestrial life, and was chosen as one of the targets to study by the Search for Extraterrestrial Intelligence (SETI) program.

Life on Mars

The possibility of life on Mars is a subject of significant interest to astrobiology due to its proximity and similarities to Earth. To date, no proof has been found of past or present life on Mars. Cumulative evidence shows that during the ancient Noachian time period, the surface environment of Mars had liquid water and may have been habitable for microorganisms. The existence of habitable conditions does not necessarily indicate the presence of life.Scientific searches for evidence of life began in the 19th century, and they continue today via telescopic investigations and deployed probes. While early work focused on phenomenology and bordered on fantasy, the modern scientific inquiry has emphasized the search for water, chemical biosignatures in the soil and rocks at the planet's surface, and biomarker gases in the atmosphere.Mars is of particular interest for the study of the origins of life because of its similarity to the early Earth. This is especially so since Mars has a cold climate and lacks plate tectonics or continental drift, so it has remained almost unchanged since the end of the Hesperian period. At least two-thirds of Mars's surface is more than 3.5 billion years old, and Mars may thus hold the best record of the prebiotic conditions leading to abiogenesis, even if life does not or has never existed there.Following the confirmation of the past existence of surface liquid water, the Curiosity and Opportunity rovers started searching for evidence of past life, including a past biosphere based on autotrophic, chemotrophic, or chemolithoautotrophic microorganisms, as well as ancient water, including fluvio-lacustrine environments (plains related to ancient rivers or lakes) that may have been habitable. The search for evidence of habitability, taphonomy (related to fossils), and organic compounds on Mars is now a primary NASA and ESA objective.

The findings of organic compounds inside sedimentary rocks and of boron on Mars are of interest as they are precursors for prebiotic chemistry. Such findings, along with previous discoveries that liquid water was clearly present on ancient Mars, further supports the possible early habitability of Gale Crater on Mars. Currently, the surface of Mars is bathed with radiation, and when reacting with the perchlorates on the surface, it may be more toxic to microorganisms than thought earlier. Therefore, the consensus is that if life exists —or existed— on Mars, it could be found or is best preserved in the subsurface, away from present-day harsh surface processes.

In June 2018, NASA announced the detection of seasonal variation of methane levels on Mars. Methane could be produced by microorganisms or by geological means. The European ExoMars Trace Gas Orbiter started mapping the atmospheric methane in April 2018, and the 2020 ExoMars rover will drill and analyze subsurface samples, while the NASA Mars 2020 rover will cache dozens of drill samples for their potential transport to Earth laboratories in the late 2020s or 2030s.

Life on Venus

The speculation of life currently existing on Venus decreased significantly since the early 1960s, when spacecraft began studying Venus and it became clear that the conditions on Venus are extreme compared to those on Earth.

Venus's location closer to the Sun than Earth and the extreme greenhouse effect raising temperatures on the surface to nearly 735 K (462 °C), and the atmospheric pressure 90 times that of Earth, make water-based life as we know it unlikely on the surface of the planet. However, a few scientists have speculated that thermoacidophilic extremophile microorganisms might exist in the lower-temperature, acidic upper layers of the Venusian atmosphere.

List of potentially habitable exoplanets

This is a list of potentially habitable exoplanets and possible exoplanets. The list is based on estimates of habitability by the Habitable Exoplanets Catalog (HEC), and data from the NASA Exoplanet Archive. The HEC is maintained by the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo.Surface planetary habitability is thought to require orbiting at the right distance from the host star for liquid surface water to be present, in addition of various geophysical and geodynamical aspects, atmospheric density, radiation type and intensity, and the host star's plasma environment.

Mars rover

A Mars rover is a motor vehicle that travels across the surface of the planet Mars upon arrival. Rovers have several advantages over stationary landers: they examine more territory, they can be directed to interesting features, they can place themselves in sunny positions to weather winter months, and they can advance the knowledge of how to perform very remote robotic vehicle control.

There have been four successful robotically operated Mars rovers. The Jet Propulsion Laboratory managed the Sojourner rover, the Opportunity rover, Spirit rover, and, now the Curiosity rover. On January 24, 2016, NASA reported that current studies on Mars by the Curiosity and Opportunity (the latter now defunct) would be searching for evidence of ancient life, including a biosphere based on autotrophic, chemotrophic or chemolithoautotrophic microorganisms, as well as ancient water, including fluvio-lacustrine environments (plains related to ancient rivers or lakes) that may have been habitable. The search for evidence of habitability, taphonomy (related to fossils), and organic carbon on Mars is now a primary NASA objective. On June 2018, the Opportunity rover went out of contact after going into hibernation mode in a dust storm. NASA declared the Opportunity complete on February 13, 2019 after numerous failures to wake up the rover from the repeated signals.Mars 2, Mars 3 were physically tethered probes; Sojourner was dependent on the Mars Pathfinder base station for communication with Earth; MER-A & B and Curiosity were on their own. As of February 2019, Curiosity is still active, while Spirit, Opportunity, and Sojourner completed their missions before losing contact.

Oceanus (Titan orbiter)

Oceanus is a NASA/JPL orbiter mission concept proposed in 2017 for the New Frontiers mission #4, but it was not selected for development. If selected at some future opportunity, Oceanus would travel to Saturn's moon Titan to assess its habitability. Studying Titan would help understand the early Earth and exoplanets which orbit other stars. The mission is named after Oceanus, the Greek god of oceans.

Planetary habitability

Planetary habitability is the measure of a planet's or a natural satellite's potential to develop and maintain environments hospitable to life. Life may be generated directly on a planet or satellite endogenously or be transferred to it from another body, a hypothetical process known as panspermia. Environments do not need to contain life to be considered habitable nor are accepted habitable zones the only areas in which life might arise.As the existence of life beyond Earth is unknown, planetary habitability is largely an extrapolation of conditions on Earth and the characteristics of the Sun and Solar System which appear favorable to life's flourishing. Of particular interest are those factors that have sustained complex, multicellular organisms on Earth and not just simpler, unicellular creatures. Research and theory in this regard is a component of a number of natural sciences, such as astronomy, planetary science and the emerging discipline of astrobiology.

An absolute requirement for life is an energy source, and the notion of planetary habitability implies that many other geophysical, geochemical, and astrophysical criteria must be met before an astronomical body can support life. In its astrobiology roadmap, NASA has defined the principal habitability criteria as "extended regions of liquid water, conditions favorable for the assembly of complex organic molecules, and energy sources to sustain metabolism". In August 2018, researchers reported that water worlds could support life.Habitability indicators and biosignatures must be interpreted within a planetary and environmental context. In determining the habitability potential of a body, studies focus on its bulk composition, orbital properties, atmosphere, and potential chemical interactions. Stellar characteristics of importance include mass and luminosity, stable variability, and high metallicity. Rocky, wet terrestrial-type planets and moons with the potential for Earth-like chemistry are a primary focus of astrobiological research, although more speculative habitability theories occasionally examine alternative biochemistries and other types of astronomical bodies.

The idea that planets beyond Earth might host life is an ancient one, though historically it was framed by philosophy as much as physical science. The late 20th century saw two breakthroughs in the field. The observation and robotic spacecraft exploration of other planets and moons within the Solar System has provided critical information on defining habitability criteria and allowed for substantial geophysical comparisons between the Earth and other bodies. The discovery of extrasolar planets, beginning in the early 1990s and accelerating thereafter, has provided further information for the study of possible extraterrestrial life. These findings confirm that the Sun is not unique among stars in hosting planets and expands the habitability research horizon beyond the Solar System.


THEO (Testing the Habitability of Enceladus's Ocean) is a feasibility study for a New Frontiers class orbiter mission to Enceladus that would directly sample its south pole water plumes in order to study its internal habitability and to search for biosignatures. Specifically, it would take advantage of the direct sampling opportunities of a subsurface ocean.

The study concept was produced by the 2015 Jet Propulsion Laboratory Planetary Science Summer School under the guidance of TeamX. The study has not yet been formally proposed for funding.

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