Nemesis is a

hypothetical A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous obse ...

red dwarf or

brown dwarf Brown dwarfs (also called failed stars) are substellar objects that are not massive enough to sustain nuclear fusion of ordinary hydrogen ( 1H) into helium in their cores, unlike a main-sequence star. Instead, they have a mass between the most m ...

, originally postulated in 1984 to be orbiting the

Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...

at a distance of about 95,000 AU (1.5

light-year A light-year, alternatively spelled light year, is a large unit of length used to express astronomical distances and is equivalent to about 9.46 trillion kilometers (), or 5.88 trillion miles ().One trillion here is taken to be 1012 ...

s), somewhat beyond the

Oort cloud The Oort cloud (), sometimes called the Öpik–Oort cloud, first described in 1950 by the Dutch astronomer Jan Oort, is a theoretical concept of a cloud of predominantly icy planetesimals proposed to surround the Sun at distances ranging fro ...

, to explain a perceived cycle of mass extinctions in the geological record, which seem to occur more often at intervals of 26 million years. In a 2017 paper, Sarah Sadavoy and Steven Stahler argued that the Sun was likely part of a

binary system A binary system is a system of two astronomical bodies which are close enough that their gravitational attraction causes them to orbit each other around a barycenter ''(also see animated examples)''. More restrictive definitions require that t ...

at the time of its formation, leading them to suggest "there probably was a Nemesis, a long time ago". Such a star would have separated from this binary system over four billion years ago, meaning it could not be responsible for the more recent perceived cycle of mass extinctions. More recent theories suggest that other forces, like close passage of other stars, or the angular effect of the galactic gravity plane working against the outer solar orbital plane (

Shiva Hypothesis The Shiva hypothesis, also known as coherent catastrophism, is the idea that global natural catastrophes on Earth, such as extinction events, happen at regular intervals because of the periodic motion of the Sun in relation to the Milky Way galaxy. ...

), may be the cause of orbital perturbations of some outer Solar System objects. In 2010, A. L. Melott and R. K. Bambach found evidence in the fossil record confirming the extinction event periodicity originally identified in 1984, but at a higher confidence level and over a time period nearly twice as long. However, in 2011, Coryn Bailer-Jones analyzed craters on the surface of the Earth and reached the conclusion that the earlier findings were statistical artifacts, and found that the crater record shows no evidence for Nemesis. The Infrared Astronomical Satellite (

IRAS The Infrared Astronomical Satellite (Dutch: ''Infrarood Astronomische Satelliet'') (IRAS) was the first space telescope to perform a survey of the entire night sky at infrared wavelengths. Launched on 25 January 1983, its mission lasted ten mon ...

) failed to discover Nemesis in the 1980s. The

2MASS The Two Micron All-Sky Survey, or 2MASS, was an astronomical survey of the whole sky in infrared light. It took place between 1997 and 2001, in two different locations: at the U.S. Fred Lawrence Whipple Observatory on Mount Hopkins, Arizona, and ...

astronomical survey An astronomical survey is a general map or image of a region of the sky (or of the whole sky) that lacks a specific observational target. Alternatively, an astronomical survey may comprise a set of images, spectra, or other observations of obj ...

, which ran from 1997 to 2001, failed to detect an additional star or brown dwarf in the Solar System. Using newer and more powerful infrared telescope technology which is able to detect brown dwarfs as cool as 150

kelvin The kelvin, symbol K, is the primary unit of temperature in the International System of Units (SI), used alongside its prefixed forms and the degree Celsius. It is named after the Belfast-born and University of Glasgow-based engineer and phys ...

s out to a distance of 10

s from the Sun, the

Wide-field Infrared Survey Explorer Wide-field Infrared Survey Explorer (WISE, observatory code C51, Explorer 92 and SMEX-6) is a NASA infrared astronomy space telescope in the Explorers Program. It was launched in December 2009, and placed in hibernation mode in February 2011 ...

(WISE survey) has not detected Nemesis. In 2011,

David Morrison Lieutenant General David Lindsay Morrison (born 24 May 1956) is a retired senior officer of the Australian Army. He served as Chief of Army from June 2011 until his retirement in May 2015. He was named Australian of the Year for 2016. Early ...

, a senior scientist at NASA known for his work in risk assessment of near Earth objects, has written that there is no confidence in the existence of an object like Nemesis, since it should have been detected in infrared sky surveys.

Claimed periodicity of mass extinctions

In 1984, paleontologists

David Raup David M. Raup (April 24, 1933 – July 9, 2015) was a University of Chicago paleontologist. Raup studied the fossil record and the diversity of life on Earth. Raup contributed to the knowledge of extinction events along with his colleague Jack Se ...

and Jack Sepkoski published a paper claiming that they had identified a statistical periodicity in extinction rates over the last 250 million years using various forms of

time series analysis In mathematics, a time series is a series of data points indexed (or listed or graphed) in time order. Most commonly, a time series is a sequence taken at successive equally spaced points in time. Thus it is a sequence of discrete-time data. Ex ...

. They focused on the extinction intensity of

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

families of marine

vertebrates Vertebrates () comprise all animal taxa within the subphylum Vertebrata () ( chordates with backbones), including all mammals, birds, reptiles, amphibians, and fish. Vertebrates represent the overwhelming majority of the phylum Chordata, ...

invertebrates Invertebrates are a paraphyletic group of animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This is a grouping including all animals apart from the chordate ...

, and

protozoans Protozoa (singular: protozoan or protozoon; alternative plural: protozoans) are a group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic tissues and debris. Histor ...

, identifying 12

extinction event An extinction event (also known as a mass extinction or biotic crisis) is a widespread and rapid decrease in the biodiversity on Earth. Such an event is identified by a sharp change in the diversity and abundance of multicellular organisms. It ...

s over the time period in question. The average time interval between extinction events was determined as 26 million years. At the time, two of the identified extinction events ( Cretaceous–Paleogene and Eocene–Oligocene) could be shown to coincide with large impact events. Although Raup and Sepkoski could not identify the cause of their supposed periodicity, they suggested a possible non-terrestrial connection. The challenge to propose a mechanism was quickly addressed by several teams of astronomers. In 2010, Melott & Bambach re-examined the fossil data, including the now-improved dating, and using a second independent database in addition to that Raup & Sepkoski had used. They found evidence for a signal showing an excess extinction rate with a 27-million-year periodicity, now going back 500 million years, and at a much higher statistical significance than in the older work.

Development of the Nemesis hypotheses

Two teams of

astronomer An astronomer is a scientist in the field of astronomy who focuses their studies on a specific question or field outside the scope of Earth. They observe astronomical objects such as stars, planets, moons, comets and galaxies – in either ...

s, Daniel P. Whitmire and Albert A. Jackson IV, and Marc Davis,

Piet Hut Piet Hut (born September 26, 1952) is a Dutch-American astrophysicist, who divides his time between research in computer simulations of dense stellar systems and broadly interdisciplinary collaborations, ranging from other fields in natural scien ...

, and Richard A. Muller, independently published similar

hypotheses A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous obse ...

to explain Raup and Sepkoski's extinction periodicity in the same issue of the journal ''

Nature Nature, in the broadest sense, is the physical world or universe. "Nature" can refer to the phenomena of the physical world, and also to life in general. The study of nature is a large, if not the only, part of science. Although humans are p ...

''. This hypothesis proposes that the Sun may have an undetected

companion star A binary star is a system of two stars that are gravitationally bound to and in orbit around each other. Binary stars in the night sky that are seen as a single object to the naked eye are often resolved using a telescope as separate stars, in w ...

in a highly elliptical orbit that periodically disturbs

comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ...

s in the

, causing a large increase of the number of comets visiting the inner Solar System with a consequential increase of

impact event An impact event is a collision between astronomical objects causing measurable effects. Impact events have physical consequences and have been found to regularly occur in planetary systems, though the most frequent involve asteroids, comets or ...

s on Earth. This became known as the "Nemesis" or "Death Star" hypothesis. If it does exist, the exact nature of Nemesis is uncertain. Muller suggests that the most likely object is a red dwarf with an

apparent magnitude Apparent magnitude () is a measure of the brightness of a star or other astronomical object observed from Earth. An object's apparent magnitude depends on its intrinsic luminosity, its distance from Earth, and any extinction of the object's ...

between 7 and 12, while Daniel P. Whitmire and Albert A. Jackson argue for a

. If a red dwarf, it would exist in

star catalog A star catalogue is an astronomical catalogue that lists stars. In astronomy, many stars are referred to simply by catalogue numbers. There are a great many different star catalogues which have been produced for different purposes over the years ...

s, but it would only be confirmed by measuring its

parallax Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or semi-angle of inclination between those two lines. Due to foreshortening, nearby objects ...

; due to orbiting the Sun it would have a low

proper motion Proper motion is the astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more dista ...

and would escape detection by older proper motion surveys that have found stars like the 9th-magnitude

Barnard's Star Barnard's Star is a red dwarf about six light-years from Earth in the constellation of Ophiuchus. It is the fourth-nearest-known individual star to the Sun after the three components of the Alpha Centauri system, and the closest star in the ...

. (The proper motion of Barnard's Star was detected in 1916.) Muller expects Nemesis to be discovered by the time parallax surveys reach the 10th magnitude. , more than 1800 brown dwarfs have been identified. There are actually fewer brown dwarfs in our cosmic neighborhood than previously thought. Rather than one star for every brown dwarf, there may be as many as six stars for every brown dwarf. The majority of solar-type stars are single. The previous idea stated half or perhaps most stellar systems were binary, triple, or

multiple-star system A star system or stellar system is a small number of stars that orbit each other, bound by gravitational attraction. A large group of stars bound by gravitation is generally called a ''star cluster'' or ''galaxy'', although, broadly speaking ...

s associated with clusters of stars, rather than the single-star systems that tend to be seen most often. Muller, referring to the date of a recent extinction at 11 million years before the present day, posits that Nemesis has a

semi-major axis In geometry, the major axis of an ellipse is its longest diameter: a line segment that runs through the center and both foci, with ends at the two most widely separated points of the perimeter. The semi-major axis (major semiaxis) is the long ...

of about and suggests it is located (supported by Yarris, 1987) near Hydra, based on a hypothetical orbit derived from original aphelia of a number of atypical long-period comets that describe an orbital arc meeting the specifications of Muller's hypothesis. Richard Muller's most recent paper relevant to the Nemesis theory was published in 2002. In 2002, Muller speculated that Nemesis was perturbed 400 million years ago by a passing star from a circular orbit into an orbit with an

eccentricity Eccentricity or eccentric may refer to: * Eccentricity (behavior), odd behavior on the part of a person, as opposed to being "normal" Mathematics, science and technology Mathematics * Off-center, in geometry * Eccentricity (graph theory) of a ...

of 0.7. In 2010, and again in 2013, Melott & Bambach found evidence for a signal showing an excess extinction rate with a 27-million-year periodicity. However, because Nemesis is so distant from the Sun, it is expected to be subject to perturbations by passing stars, and therefore its orbital period should shift by 15–30%. The existence of a sharp 27-million year peak in extinction events is therefore inconsistent with Nemesis.

Orbit of Sedna

The trans-Neptunian object Sedna has an extra-long and unusual elliptical orbit around the Sun, ranging between 76 and 937 AU. Sedna's orbit takes about 11,400 years to complete once. Its discoverer, Michael Brown of Caltech, noted in a ''Discover'' magazine article that Sedna's location seemed to defy reasoning: "Sedna shouldn't be there", Brown said. "There's no way to put Sedna where it is. It never comes close enough to be affected by the Sun, but it never goes far enough away from the Sun to be affected by other stars." Brown therefore postulated that a massive unseen object may be responsible for Sedna's anomalous orbit. This line of inquiry eventually led to the hypothesis of

Planet Nine Planet Nine is a hypothetical planet in the outer region of the Solar System. Its gravitational effects could explain the peculiar clustering of orbits for a group of extreme trans-Neptunian objects (ETNOs), bodies beyond Neptune that orbi ...

. Brown has stated that it is more likely that one or more non-companion stars, passing near the Sun billions of years ago, could have pulled Sedna out into its current orbit. In 2004, Kenyon forwarded this explanation after analysis of Sedna's orbital data and computer modeling of possible ancient non-companion star passes.

Past, current, and pending searches for Nemesis

Searches for Nemesis in the infrared are important because cooler stars comparatively shine brighter in infrared light. The University of California's Leuschner Observatory failed to discover Nemesis by 1986. The Infrared Astronomical Satellite (

) failed to discover Nemesis in the 1980s. The

, which ran from 1997 to 2001, failed to detect a star, or brown dwarf, in the Solar System. If Nemesis exists, it may be detected by

Pan-STARRS The Panoramic Survey Telescope and Rapid Response System (Pan-STARRS1; obs. code: F51 and Pan-STARRS2 obs. code: F52) located at Haleakala Observatory, Hawaii, US, consists of astronomical cameras, telescopes and a computing facility that is ...

or the planned LSST astronomical surveys. In particular, if Nemesis is a red dwarf or a

, the WISE mission (an infrared sky survey that covered most of the

solar neighborhood The Local Interstellar Cloud (LIC), also known as the Local Fluff, is an interstellar cloud roughly across, through which the Solar System is moving. This feature overlaps a region around the Sun referred to as the solar neighborhood. It is un ...

in movement-verifying

measurements) was expected to be able to find it. WISE can detect 150-kelvin brown dwarfs out to 10

s, and the closer a brown dwarf is, the easier it is to detect. Preliminary results of the WISE survey were released on April 14, 2011. On March 14, 2012, the entire catalog of the WISE mission was released. In 2014 WISE data ruled out a

Saturn Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter. It is a gas giant with an average radius of about nine and a half times that of Earth. It has only one-eighth the average density of Earth; h ...

or larger-sized body in the Oort cloud out to ten thousand AU.NASA's WISE Survey Finds Thousands of New Stars, But No 'Planet X'
/ref> Calculations in the 1980s suggested that a Nemesis object would have an irregular orbit due to perturbations from the galaxy and passing stars. The Melott and Bambach work shows an extremely regular signal, inconsistent with the expected irregularities in such an orbit. Thus, while supporting the extinction periodicity, it appears to be inconsistent with the Nemesis hypothesis, though of course not inconsistent with other kinds of

substellar object A substellar object, sometimes called a substar, is an astronomical object the mass of which is smaller than the smallest mass at which hydrogen fusion can be sustained (approximately 0.08 solar masses). This definition includes brown dwarfs and f ...

s. According to a 2011 NASA news release, "recent scientific analysis no longer supports the idea that extinctions on Earth happen at regular, repeating intervals, and thus, the Nemesis hypothesis is no longer needed."

References

External links

"Astrobiology Magazine", "Cosmic Evolution" Section, "Getting WISE about Nemesis"
03/11/10, Author: Leslie Mullen, Article about Nemesis and Tyche theory, and how the WISE Sky Survey Mission may prove or disprove the theories. * Robert Roy Britt,

', Space.com, 3 April 2001. * * Richard A. Muller,
Measurement of the lunar impact record for the past 3.5 billion years, and implications for the Nemesis theory
', Geological Society of America Special Paper 356, pp 659–665 (2002). I * Richard A. Muller

(Weidenfeld & Nicolson, 1988, OP) * Richard A. Muller, lecture where he describe
Nemesis Theory
* Z.K. Silagadze,
TeV scale gravity, mirror universe, and ... dinosaurs
'
Acta Physica Polonica
B32 (2001) 99–128. ''(Provides a very entertaining and readable review of the Nemesis extinction hypothesis, including dozens of references to scientific articles on the topic.)'' * SpaceDaily

Apr 25, 2006 * Lynn Yarris. "Does a Companion Star to the Sun Cause Earth's Periodic Mass Extinctions?" Science Beat. Spring 1987
Nemesis is a myth
(Max Planck August 1, 2011) {{DEFAULTSORT:Nemesis (Star) Hypothetical bodies of the Solar System Hypothetical stars Theories Solar System dynamic theories M-type main-sequence stars Brown dwarfs Extinction events Hypothetical trans-Neptunian objects Oort cloud Cosmic doomsday Obsolete theories in physics