Editing Nemesis (hypothetical star)

{{short description|Hypothetical star orbiting the Sun, supposedly responsible for extinction events}}
{{other uses|Nemesis (disambiguation)}}{{distinguish|text=the hypothetical planets [[Tyche (hypothetical planet)|Tyche]] or [[Planet Nine]]}}
'''Nemesis''' is a [[hypothetical astronomical objects|hypothetical]] [[red dwarf]]<ref name=Leader/> or [[brown dwarf]],<ref name="mullen2010"/> originally postulated in 1984<ref>M. Davis, P. Hut, and R. Muller, [https://escholarship.org/content/qt9gm5c682/qt9gm5c682.pdf “Extinction of species by periodic comet showers”], ''Nature'' 308, 715 (1984).</ref> to be orbiting the [[Sun]] at a distance of about 95,000 [[astronomical unit|AU]] (1.5 [[light-year]]s),<ref name="mullen2010"/> somewhat beyond the [[Oort cloud]], to explain a perceived [[Extinction event#Patterns in frequency|cycle of mass extinctions]] in the [[history of Earth|geological record]], which seem to occur more often at intervals of 26 million years.<ref name="mullen2010"/><ref name=Raup1984/> In a 2017 paper, Sarah Sadavoy and Steven Stahler argued that the Sun was probably part of a [[binary system]] at the time of its formation, leading them to suggest "there probably was a Nemesis, a long time ago".<ref>{{Cite news|url=http://news.berkeley.edu/2017/06/13/new-evidence-that-all-stars-are-born-in-pairs/|title=New evidence that all stars are born in pairs|date=2017-06-13|work=Berkeley News|access-date=2018-06-19|language=en-US}}</ref><ref>{{Cite journal|last1=Sadavoy|first1=Sarah I.|last2=Stahler|first2=Steven W.|date=2017-05-03|title=Embedded binaries and their dense cores|journal=Monthly Notices of the Royal Astronomical Society|language=en|volume=469|issue=4|pages=3881–3900|doi=10.1093/mnras/stx1061|doi-access=free |issn=0035-8711|bibcode=2017MNRAS.469.3881S|arxiv=1705.00049|s2cid=119341787}}</ref> 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.<ref>{{Cite web|url=http://www.businessinsider.com/stars-form-in-pairs-nemesis-theory-2018-4|title=All stars in the universe may form in pairs — but we can't find the sun's missing 'Nemesis'|last=Levine|first=David|date=2018-06-19|website=Business Insider|access-date=2018-06-19}}</ref>

More recent theories suggest that other forces, like close [[List of nearest stars#Future and past|passage of other stars]], or the angular effect of the galactic gravity plane working against the outer solar orbital plane ([[Shiva Hypothesis]]), may be the cause of orbital perturbations of some outer Solar System objects.<ref name=Kenyon/> In 2010, researchers 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.<ref name="melott" /> However, in 2011, researchers analyzed the ages of known craters on Earth's surface and found strong evidence against periodic impacts, concluding that the earlier findings based on small samples were [[statistical artifact]]s.<ref>{{Cite journal |last=Bailer-Jones |first=C. A. L. |date=2011-09-11 |title=Bayesian time series analysis of terrestrial impact cratering: Time series analysis of impact cratering |journal=Monthly Notices of the Royal Astronomical Society |language=en |volume=416 |issue=2 |pages=1163–1180 |doi=10.1111/j.1365-2966.2011.19112.x|doi-access=free |arxiv=1105.4100 }}</ref><ref name="Myth2011" /> The Infrared Astronomical Satellite ([[IRAS]]) failed to discover Nemesis in the 1980s. The [[2MASS]] [[astronomical survey]], which ran from 1997 to 2001, failed to detect an additional star or brown dwarf in the Solar System.<ref name="Space2010-03"/>

Using newer and more powerful infrared telescope technology able to detect brown dwarfs as cool as 150 [[kelvin]]s out to a distance of 10 [[light-year]]s from the Sun,<ref name="browndwarf"/> the [[Wide-field Infrared Survey Explorer]] (WISE survey) has not detected Nemesis.<ref name="Morrison2012"/><ref name="Kirkpatrick2011v1"/> In 2011, [[David Morrison (astrophysicist)|David Morrison]], 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.<ref name="Morrison2012"/><ref name="Morrison"/><ref name="Morrison2010"/><ref name="NASA20140307"/>

==Claimed periodicity of mass extinctions==
In 1984, [[paleontologists]] [[David M. Raup|David Raup]] 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|time series analysis]].<ref name=Raup1984/> They focused on the extinction intensity of [[fossil]] families of marine [[vertebrates]], [[invertebrates]], and [[protozoans]], identifying 12 [[extinction event]]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 extinction event|Cretaceous–Paleogene]] and [[Eocene–Oligocene extinction event|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.<ref name=Whitmire1984/><ref name=Davis1984/>

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.<ref name="melott"/>

==Development of the Nemesis hypotheses==
Two teams of [[astronomer]]s, Daniel P. Whitmire and Albert A. Jackson IV, and [[Marc Davis (astronomer)|Marc Davis]], [[Piet Hut]], and [[Richard A. Muller]], independently published similar [[hypothesis|hypotheses]] to explain Raup and Sepkoski's extinction periodicity in the same issue of the journal ''[[Nature (journal)|Nature]]''.<ref name=Whitmire1984/><ref name=Davis1984/> This hypothesis proposes that the Sun may have an undetected [[Binary Star|companion star]] in a highly elliptical orbit that periodically disturbs [[comet]]s in the [[Oort cloud]], causing a large increase of the number of comets visiting the inner Solar System with a consequential increase of [[impact event]]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]] between 7 and 12,<ref name="Muller"/> while Daniel P. Whitmire and Albert A. Jackson argue for a [[brown dwarf]].<ref name="Whitmire1984"/> If a red dwarf, it would exist in [[star catalog]]s, but it would only be confirmed by measuring its [[parallax]]; due to orbiting the Sun it would have a low [[proper motion]] and would escape detection by older proper motion surveys that have found stars like the 9th-magnitude [[Barnard's Star]]. (The proper motion of Barnard's Star was detected in 1916.)<ref name="EEB"/> Muller expects Nemesis to be discovered by the time parallax surveys reach the 10th magnitude.<ref name="Muller2002"/>

{{As of|2012}}, more than 1800 brown dwarfs have been identified.<ref name="DwarfArchives" /> 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.<ref name="space2012" /> The majority of [[Sun|solar]]-type stars are single.<ref name="Deepak2010" /> The previous idea stated half or perhaps most stellar systems were binary, triple, or [[multiple-star system]]s associated with clusters of stars, rather than the single-star systems that tend to be seen most often.{{Citation needed|date=July 2022}}

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]] of about {{convert|1.5|ly}}<ref name="Muller"/> and suggests it is located (supported by Yarris, 1987) near [[Hydra (constellation)|Hydra]], based on a hypothetical orbit derived from original [[aphelion|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.<ref name="Muller"/> In 2002, Muller speculated that Nemesis was [[Perturbation (astronomy)|perturbed]] 400 million years ago by a [[List of nearest stars#Future and past|passing star]] from a circular orbit into an orbit with an [[Orbital eccentricity|eccentricity]] of 0.7.<ref name="Muller2002"/>

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.<ref name="melott"/><ref name="melott2">{{cite journal|title=Do periodicities in extinction—with possible astronomical connections—survive a revision of the geological timescale?|journal=The Astrophysical Journal|volume=773|pages=6|date=18 July 2013|doi=10.1088/0004-637X/773/1/6|last1=Melott|first1=Adrian L.|last2=Bambach|first2=Richard K.|issue=1|arxiv=1307.1884|bibcode=2013ApJ...773....6M|s2cid=15985292}}</ref>

==Orbit of Sedna==
[[File:Oort cloud Sedna orbit.svg|thumb|300px|Sedna orbit compared to the Solar System and Oort cloud]]

The [[trans-Neptunian object]] [[90377 Sedna|Sedna]] has an extra-long and unusual elliptical orbit around the Sun,<ref name="mullen2010"/> ranging between 76 and 937 AU. Sedna's orbit takes about 11,400 years to complete once. Its discoverer, [[Michael E. Brown|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."<ref name="discover2006"/> Brown therefore postulated that a massive unseen object may be responsible for Sedna's anomalous orbit.<ref name="mullen2010"/> This line of inquiry eventually led to the hypothesis of [[Planet Nine]].

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.<ref name="discover2006"/> In 2004, Kenyon forwarded this explanation after analysis of Sedna's orbital data and computer modeling of possible ancient non-companion star passes.<ref name=Kenyon/>

==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, Berkeley|University of California]]'s [[Leuschner Observatory]] failed to discover Nemesis by 1986.<ref>{{Cite thesis |degree=Ph.D. |title=An Astrometric Search for a Stellar Companion to the Sun |last=Perlmutter |first=Saul |author-link=Saul Perlmutter |date=1986 |publisher=University of California, Berkeley}}</ref>  The Infrared Astronomical Satellite ([[IRAS]]) failed to discover Nemesis in the 1980s. The [[2MASS]] [[astronomical survey]], which ran from 1997 to 2001, failed to detect a star, or brown dwarf, in the Solar System.<ref name="mullen2010"/> If Nemesis exists, it may be detected by [[Pan-STARRS]] or the planned [[Large Synoptic Survey Telescope|LSST]] astronomical surveys.

In particular, if Nemesis is a [[red dwarf]] or a [[brown dwarf]], the [[WISE mission]] (an infrared sky survey that covered most of the [[solar neighborhood]] in movement-verifying [[parallax]] measurements) was expected to be able to find it.<ref name="mullen2010"/> WISE can detect 150-kelvin brown dwarfs out to 10 [[light-year]]s, and the closer a brown dwarf is, the easier it is to detect.<ref name="browndwarf"/> Preliminary results of the WISE survey were released on April 14, 2011.<ref name=NASA2011-117/> On March 14, 2012, the entire catalog of the WISE mission was released.<ref name="fullrelease"/> In 2014, WISE data ruled out a [[Saturn]] or larger-sized body in the Oort cloud out to ten thousand AU.<ref>[https://www.nasa.gov/press/2014/march/nasas-wise-survey-finds-thousands-of-new-stars-but-no-planet-x/ 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<ref name="melott"/> 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]]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."<ref name="Tyche2011-060"/>

==See also==
* [[Counter-Earth]]
* [[Giant-impact hypothesis]]
* [[Lists of astronomical objects]]
* [[Nemesis (Asimov novel)]]
* [[Malmquist bias]]
* [[Planet Nine]]
* [[Planets beyond Neptune]]
* [[Shiva hypothesis]]
* [[Theia (planet)]]
* [[Tyche (hypothetical planet)]]
* [[Vulcan (hypothetical planet)]]

==References==
{{reflist
| colwidth = 30em
| refs =

<ref name=Leader>Leader-Post, [https://news.google.com/newspapers?id=yL9VAAAAIBAJ&sjid=SUANAAAAIBAJ&pg=3691,1342332&dq=nemesis+red+dwarf&hl=en "Scientists claim killer star exists"], 22 Feb 1984, Page B6, Associated Press</ref>

<ref name="Space2010-03">{{cite web
  |date=11 March 2010
  |title=Sun's Nemesis Pelted Earth with Comets, Study Suggests
  |publisher=Space.com
  |author=Leslie Mullen (Astrobiology Magazine)
  |url=http://www.space.com/8028-sun-nemesis-pelted-earth-comets-study-suggests.html
  |access-date=2010-08-22}}</ref>

<ref name="DwarfArchives">{{cite web
  |date=6 November 2012
  |title=DwarfArchives.org: Photometry, spectroscopy, and astrometry of M, L, and T dwarfs
  |publisher=caltech.edu
  |author=Chris Gelino, [[J. Davy Kirkpatrick|Davy Kirkpatrick]], Adam Burgasser
  |url=http://spider.ipac.caltech.edu/staff/davy/ARCHIVE/index.shtml
  |access-date=2012-12-28}} (M=536, L=918, T=355, Y=14)</ref>

<ref name="space2012">{{cite web
  |date=12 June 2012
  |title=Brown Dwarfs, Runts of Stellar Litter, Rarer than Thought
  |publisher=Space.com
  |author=Ian O'Neill (Discovery News)
  |url=http://www.space.com/16112-brown-dwarf-stars-sun-rare.html
  |access-date=2012-12-28}}</ref>

<ref name="Myth2011">{{cite web
  |date=August 1, 2011
  |title=Nemesis is a myth
  |publisher=Max Planck
  |url=http://www.mpg.de/4372308/nemsis_myth?filter_order=L
  |access-date=2011-10-07}}</ref>

<ref name="Kirkpatrick2011v1">{{cite journal |doi=10.1088/0067-0049/197/2/19 |display-authors=4 |authorlink=J. Davy Kirkpatrick |last1=Kirkpatrick |first1=J. Davy |last2=Cushing |first2=Michael C. |last3=Gelino |first3=Christopher R. |last4=Griffith |first4=Roger L. |last5=Skrutskie |first5=Michael F. |last6=Marsh |first6=Kenneth A. |last7=Wright |first7=Edward L. |last8=Mainzer |first8=Amy K. |last9=Eisenhardt |first9=Peter R. |last10=McLean |first10=Ian S. |last11=Thompson |first11=Maggie A. |last12=Bauer |first12=James M. |last13=Benford |first13=Dominic J. |last14=Bridge |first14=Carrie R. |last15=Lake |first15=Sean E. |last16=Petty |first16=Sara M. |last17=Stanford |first17=Spencer Adam |last18=Tsai |first18=Chao-Wei |last19=Bailey |first19=Vanessa |last20=Beichman |first20=Charles A. |last21=Bloom |first21=Joshua S. |last22=Bochanski |first22=John J. |last23=Burgasser |first23=Adam J. |last24=Capak |first24=Peter L. |last25=Cruz |first25=Kelle L. |last26=Hinz |first26=Philip M. |last27=Kartaltepe |first27=Jeyhan S. |last28=Knox |first28=Russell P. |last29=Manohar |first29=Swarnima |last30=Masters |first30=Daniel |last31=Morales-Calderon |first31=Maria |last32=Prato |first32=Lisa A. |last33=Rodigas |first33=Timothy J. |last34=Salvato |first34=Mara |last35=Schurr |first35=Steven D. |last36=Scoville |first36=Nicholas Z. |last37=Simcoe |first37=Robert A. |last38=Stapelfeldt |first38=Karl R. |last39=Stern |first39=Daniel |last40=Stock |first40=Nathan D. |last41=Vacca |first41=William D. |title=The First Hundred Brown Dwarfs Discovered by the Wide-field Infrared Survey Explorer (WISE) |date=2011 |journal=[[The Astrophysical Journal Supplement]] |volume=197 |issue=2 |pages=19 |arxiv=1108.4677v1 |bibcode=2011ApJS..197...19K |s2cid=16850733 }}</ref>

<ref name="melott">{{cite journal
 |author = Melott, A.L.
 |author2=Bambach, R.K.
 |date = 2010
 |title = Nemesis Reconsidered
 |journal = Monthly Notices of the Royal Astronomical Society Letters
 |volume = 407
 |issue=1
 |pages = L99–L102
 |arxiv=1007.0437
 |doi = 10.1111/j.1745-3933.2010.00913.x |doi-access=free
 |bibcode = 2010MNRAS.407L..99M |s2cid=7911150
 }}</ref>

<ref name="Morrison2012">{{cite web
 |date        = October 17, 2012
 |title       = The idea has been disproved by several infrared sky surveys, most recently the WISE mission
 |publisher   = NASA Ask An Astrobiologist
 |author      = David Morrison
 |author-link  = David Morrison (astrophysicist)
 |url         = http://astrobiology2.arc.nasa.gov/ask-an-astrobiologist/question/?id=21175
 |access-date  = 2012-10-18
 |url-status     = dead
 |archive-url  = https://web.archive.org/web/20121023225846/http://astrobiology2.arc.nasa.gov/ask-an-astrobiologist/question/?id=21175
 |archive-date = October 23, 2012
}}</ref>

<ref name="Morrison">{{cite web
 |date        = August 2, 2011
 |title       = Scientists today no longer think an object like Nemesis could exist
 |publisher   = NASA Ask An Astrobiologist
 |author      = David Morrison
 |author-link  = David Morrison (astrophysicist)
 |url         = http://astrobiology2.arc.nasa.gov/ask-an-astrobiologist/question/?id=16790
 |access-date  = 2011-10-22
 |url-status     = dead
 |archive-url  = https://archive.today/20121213101422/http://astrobiology2.arc.nasa.gov/ask-an-astrobiologist/question/?id=16790
 |archive-date = December 13, 2012
}}</ref>

<ref name="Morrison2010">{{cite web
 |date       = November 25, 2010
 |title      = this hypothetical Nemesis does not exist
 |publisher  = NASA Ask An Astrobiologist
 |author     = David Morrison
 |author-link = David Morrison (astrophysicist)
 |url        = http://astrobiology2.arc.nasa.gov/ask-an-astrobiologist/question/?id=13040
 |archive-url = https://archive.today/20121213141021/http://astrobiology2.arc.nasa.gov/ask-an-astrobiologist/question/?id=13040
 |url-status   = dead
 |archive-date = December 13, 2012
 |access-date = 2011-11-09
}}</ref>

<ref name=Raup1984>{{cite journal
 |author = Raup, D.M.
 |author2=Sepkoski, J.J.
 |date = 1 February 1984
 |title = Periodicity of Extinctions in the Geologic Past
 |journal = Proceedings of the National Academy of Sciences
 |volume = 81 |issue = 3 |pages = 801–805
 |doi = 10.1073/pnas.81.3.801
 |url = http://www.pnas.org/cgi/reprint/81/3/801.pdf
 |access-date = 30 April 2007
 |pmid = 6583680
 |pmc = 344925
 |bibcode = 1984PNAS...81..801R |doi-access=free
 }}</ref>

<ref name=Whitmire1984>{{cite journal
 |author = Whitmire, D.P.
 |author2=Jackson, A.A.
 |date = 1984
 |title = Are periodic mass extinctions driven by a distant solar companion?
 |journal = Nature
 |volume = 308
 |issue = 5961
 |pages = 713–715
 |doi = 10.1038/308713a0|bibcode = 1984Natur.308..713W |s2cid=4236610
 }}</ref>

<ref name=Davis1984>{{cite journal
 |author = Davis, M.
 |author2=Hut, P. |author3=Muller, R.A. 
 |date = 1984
 |title = Extinction of species by periodic comet showers
 |journal = Nature
 |volume = 308
 |issue = 5961
 |pages = 715–717
 |doi = 10.1038/308715a0|bibcode = 1984Natur.308..715D |s2cid=4267612 |url=https://digital.library.unt.edu/ark:/67531/metadc835102/ }}</ref>

<ref name="Muller">{{cite web
  |title=Nemesis
  |publisher=Lawrence Berkeley National Laboratory
  |author=Richard A. Muller |author-link=Richard A. Muller
  |url=http://muller.lbl.gov/pages/lbl-nem.htm
  |access-date=2007-05-19}}</ref>

<ref name="Muller2002">{{cite web
  |date=2002
  |title=Measurement of the lunar impact record for the past 3.5 billion years, and implications for the Nemesis theory
  |publisher=Geol. Soc. of America Special Paper 356, pp 659–665 (2002).
  |author=Richard A. Muller |author-link=Richard A. Muller
  |url=http://muller.lbl.gov/papers/Lunar_impacts_Nemesis.pdf
  |access-date=2011-11-11}}</ref>

<ref name="EEB">{{cite journal
 | first=E. E. | last=Barnard
 | author-link=Edward Emerson Barnard | date=1916
 | title=A small star with large proper motion
 | journal=Astronomical Journal | volume=29 | issue=695
 | page=181 | bibcode = 1916AJ.....29..181B
 | doi = 10.1086/104156 }}</ref>

<ref name="mullen2010">{{cite web
 |date        = 11 March 2010
 |title       = Getting WISE About Nemesis
 |publisher   = Astrobiology Magazine (Cosmic Evolution)
 |author      = Leslie Mullen
 |url         = http://www.astrobio.net/exclusive/3427/getting-wise-about-nemesis
 |access-date  = 2010-05-15
 |url-status     = usurped
 |archive-url  = https://web.archive.org/web/20100314150817/http://www.astrobio.net/exclusive/3427/getting-wise-about-nemesis
 |archive-date = 14 March 2010
}}</ref>

<ref name="discover2006">{{cite web
  |date=May 27, 2006
  |title=The Man Who Finds Planets |publisher=Discover magazine
  |author=Cal Fussman |url=https://www.discovermagazine.com/the-sciences/the-man-who-finds-planets
  |access-date=2011-10-20}}</ref>

<ref name=Kenyon>
{{cite journal
 |first=Scott J. |last=Kenyon
 |author2=Benjamin C. Bromley
 |date=2004
 |journal=Nature
 |volume=432 |issue=7017 |pages=598–602
 |title=Stellar encounters as the origin of distant Solar System objects in highly eccentric orbits
 |arxiv=astro-ph/0412030
 |doi=10.1038/nature03136
 |pmid=15577903
 |bibcode = 2004Natur.432..598K |s2cid=4427211
 }}</ref>

<ref name=NASA2011-117>{{cite web |url=http://www.nasa.gov/mission_pages/WISE/news/wise20110414.html |title=NASA – WISE Delivers Millions of Galaxies, Stars, Asteroids |publisher=Nasa.gov |access-date=2011-06-15 |archive-date=2012-03-26 |archive-url=https://web.archive.org/web/20120326204028/http://www.nasa.gov/mission_pages/WISE/news/wise20110414.html |url-status=dead }}</ref>

<ref name="fullrelease">{{cite web|url=http://www.jpl.nasa.gov/news/news.cfm?release=2012-072|title=NASA Releases New WISE Mission Catalog of Entire Infrared Sky|publisher=Nasa JPL|date=2012-03-14|access-date=2012-03-15|archive-date=2012-06-04|archive-url=https://web.archive.org/web/20120604151306/http://www.jpl.nasa.gov/news/news.cfm?release=2012-072|url-status=dead}}</ref>

<ref name="Tyche2011-060">{{cite web
  |date=February 18, 2011
  |title=Can WISE Find the Hypothetical 'Tyche'?
  |publisher=NASA/JPL     |url=https://www.jpl.nasa.gov/news/can-wise-find-the-hypothetical-tyche
  |access-date=2022-03-28}}</ref>

<ref name="browndwarf">{{cite web
  |title=Science: Brown Dwarfs
  |publisher=WISE/NASA
  |url=http://wise.ssl.berkeley.edu/science_browndwarfs.html
  |access-date=2007-12-28}}</ref>

<ref name=NASA20140307 >{{cite web|url=http://www.nasa.gov/jpl/wise/planet-x-20140307/#.UyY_qdxIhwY|title=NASA's WISE Survey Finds Thousands of New Stars, But No 'Planet X'|publisher=Nasa JPL|date=2014-03-07|access-date=2014-03-15|archive-date=2014-03-12|archive-url=https://web.archive.org/web/20140312222005/http://www.nasa.gov/jpl/wise/planet-x-20140307/#.UyY_qdxIhwY|url-status=dead}}</ref>

<ref name=Deepak2010>{{cite journal
  |last1=Raghavan |first1=Deepak
  |display-authors=etal 
  |last2=McAlister |first2=Harold A.
  |last3=Henry |first3=Todd J.
  |last4=Mason |first4=David W.
  |title=A Survey of Stellar Families: Multiplicity of Solar-Type Stars
  |journal=[[The Astrophysical Journal]]
  |date=2010
  |doi=10.1088/0067-0049/190/1/1 
  |arxiv=1007.0414|bibcode = 2010ApJS..190....1R |volume=190 |issue=1
  |pages=1–42|s2cid=368553
 }}</ref>

}}

==External links==
* [http://www.astrobio.net/exclusive/3427/getting-wise-about-nemesis "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, ''[http://www.space.com/scienceastronomy/solarsystem/nemesis_010320-1.html Nemesis: Does the Sun Have a 'Companion'?]'', Space.com, 3 April 2001.
* {{cite journal | author = Foot R., Silagadze Z. K. | year = 2001 | title = Do mirror planets exist in our solar system? | arxiv = astro-ph/0104251 | journal = Acta Physica Polonica | volume = B32 | issue = 7| pages = 2271–2278 | bibcode = 2001AcPPB..32.2271F }}
* Richard A. Muller, ''[http://muller.lbl.gov/papers/Lunar_impacts_Nemesis.pdf 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, [http://muller.lbl.gov/pages/lbl-nem.htm ''Nemesis''] (Weidenfeld & Nicolson, 1988, OP)
* Richard A. Muller, lecture where he describes [https://www.youtube.com/watch?v=ERy-MTfgulc Nemesis Theory]
* Z.K. Silagadze, ''[https://arxiv.org/abs/hep-ph/0002255 TeV scale gravity, mirror universe, and ... dinosaurs]'', [http://th-www.if.uj.edu.pl/acta/ 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. [http://www.spacedaily.com/reports/Evidence_Mounts_For_Companion_Star_To_Our_Sun.html Evidence Mounts For Companion Star To Our Sun]. Apr 25, 2006
* Lynn Yarris. "Does a Companion Star to the Sun Cause Earth's Periodic Mass Extinctions?" Science Beat. Spring 1987
* [http://www.mpg.de/4372308/nemsis_myth?filter_order=L Nemesis is a myth] (Max Planck August 1, 2011)

{{Solar System}}
{{Doomsday}}
{{Portal bar|Stars|Spaceflight|Outer space|Science}}

{{DEFAULTSORT:Nemesis (Star)}}
[[Category:Hypothetical bodies of the Solar System]]
[[Category:Hypothetical stars]]
[[Category:Theories]]
[[Category:Solar System dynamic theories]]
[[Category:M-type main-sequence stars]]
[[Category:Brown dwarfs]]
[[Category:Extinction events]]
[[Category:Hypothetical trans-Neptunian objects]]
[[Category:Oort cloud]]
[[Category:Cosmic doomsday]]
[[Category:Obsolete theories in physics]]
[[Category:Solar System]]