Nemesis (star) 89344 225505418 2008-07-14T01:24:59Z Spacepotato 271631 Undo erroneous bot edit. {{otheruses2|Nemesis}} '''Nemesis''' is a [[hypothetical astronomical objects|hypothetical]] [[red dwarf star]] or [[brown dwarf]], orbiting the [[Sun]] at a distance of about 50,000 to 100,000 [[astronomical unit|AU]], somewhat beyond the [[Oort cloud]]. The existence of this star was postulated in an attempt to explain an inferred periodicity in the rate of biological [[extinction]] in the [[history of Earth|geological record]]. ==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>{{cite journal | author = Raup, D.M. | coauthors = Sepkoski, J.J. | year = 1984 | date = [[1984-02-01]] | 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 | accessdate = 2007-04-30 | pmid = 6583680 }}</ref> They focused on the extinction intensity of fossil families of marine vertebrates, invertebrates, and protozoans, identifying 12 extinction events 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-Tertiary extinction event|Cretaceous-Tertiary]] and Late [[Eocene]]) could be shown to coincide with large impact events. Although Raup and Sepkoski could not identify the cause of their supposed periodicity, they suggested that there might be a non-terrestrial connection. The challenge to propose a mechanism was quickly addressed by several teams of astronomers. ==Development of the Nemesis hypotheses== Two teams of astronomers, Whitmire and Jackson, and Davis, Hut and Muller, independently published a similar hypothesis to explain Raup and Sepkoski's supposed extinction periodicity in the same issue of the journal ''[[Nature (journal)|Nature]]''.<ref name=Whitmire1984>{{cite journal | author = Whitmire, D.P. | coauthors = Jackson, A.A. | year = 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 | accessdate = 2007-04-30 }}</ref><ref name=Davis1984>{{cite journal | author = Davis, M. | coauthors = Hut, P., Muller, R.A. | year = 1984 | title = Extinction of species by periodic comet showers | journal = Nature | volume = 308 | issue = 5961 | pages = 715–717 | doi = 10.1038/308715a0 | accessdate = 2007-04-30 }}</ref> This hypothesis proposes that the sun may have an as yet undetected companion star in a highly elliptical orbit that periodically disturbs [[comet]]s in the [[Oort cloud]], causing a large increase in the number of comets visiting the inner solar system with a consequential increase in impact events on Earth. This became known as the Nemesis ([[Death Star]]) hypothesis. If it does exist, the exact nature of Nemesis is uncertain. [[Richard A. Muller]] suggests that the most likely object is a red dwarf with [[apparent magnitude|magnitude]] between 7 and 12,<ref>[http://muller.lbl.gov/pages/lbl-nem.htm http://muller.lbl.gov/pages/lbl-nem.htm] ''Muller.lbl.gov'' Retrieved on 05-19-07 </ref> while Daniel P. Whitmire and Albert A. Jackson argue for a brown dwarf. If a red dwarf, it would undoubtedly already exist in star catalogs, but its true nature would only be detectable by measuring its [[parallax]]; due to orbiting the Sun it would have a very low [[proper motion]] and would escape detection by proper motion surveys that have found stars like the 9th magnitude [[Barnard's star]]. The last major extinction event was about 5 million years ago, so Muller posits that Nemesis is likely 1-1.5 light years away at present, and even has ideas of what area of the sky it might be in (supported by Yarris, 1987), near Hydra, based on a hypothetical orbit derived from original [[apogee]]s of a number of atypical long-period comets that describe an orbital arc meeting the specifications of Muller's hypothesis. ==Looking for Nemesis== If Nemesis exists, it may be detected by the planned [[Pan-STARRS]] or [[Large Synoptic Survey Telescope|LSST]] astronomical surveys, or similar future projects. If Nemesis is a brown dwarf, as proposed by Dr. Dan Whitmire and Albert A. Jackson IV, then the upcoming [[WISE mission]] (scheduled for November 2009) should easily find it. ==Other hypotheses== Matese and Whitman have suggested that the supposed extinction periodicity might be caused by the solar system oscillating across the galactic plane of the [[Milky Way]]. These oscillations may lead to gravitational disturbances in the Oort cloud with the same proposed consequences as the orbit of "Nemesis". However, the period of oscillation is not well-constrained observationally, and may differ from the needed 26 million years by as much as 40%. ==Literary references== Certain parallels may be drawn between Nemesis and the red star from [[Anne McCaffrey]]'s ''[[Pern]]'' books series. Both disturb the Oort cloud and both bring destruction down upon their respective planets. [[Larry Niven]] and [[Jerry Pournelle]] also describe such a mechanism in the novel ''[[Lucifer's Hammer]]''. Niven commented in his short story collection ''[[N-Space (short story collection)|N-Space]]'' that had they named the conceptual dark companion in ''Lucifer's Hammer'', the name "Nemesis" would have been used. [[Isaac Asimov]]'s novel ''[[Nemesis (Isaac Asimov novel)|Nemesis]]'' deals with the repercussions of a future colony being established around a star named Nemesis as a way of escaping an oppressive Earth. While the star in the book is on a course that will take it through the solar system, it is not in orbit around the sun as is the theorized Nemesis. ==See also== *[[Brown dwarf]] *[[Extinction event]]s *[[Red dwarf]] *[[Stellar classification]] ==References== {{reflist}} ==External links== * Richard A. Muller, [http://muller.lbl.gov/pages/lbl-nem.htm Nemesis] ''(undated)'' * 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 * Undergraduate lecture by Richard A. Muller where he describes [http://www.youtube.com/watch?v=ERy-MTfgulc Nemesis Theory] * [http://www.planetxvideo.com Documentary on Nemesis and Planet X] * 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. * Z.K. Silagadze, ''[http://uk.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.)'' * ''(no author)'', [http://www.exitmundi.nl/Nemesis.htm Exit Mundi], ''(undated)''. ''(Nemesis an End-Of-World scenario.)'' * R. Foot, Z. K. Silagadze, ''[http://uk.arxiv.org/abs/astro-ph/0104251 Do mirror planets exist in our solar system?]'' Acta Physica Polononica '''B32''' (2001) pp. 2271-2278. * Yarris, Lynn. "Does a Companion Star to the Sun Cause Earth's Periodic Mass Extinctions?" Science Beat. Spring 1987 * [http://www.spacedaily.com/reports/Evidence_Mounts_For_Companion_Star_To_Our_Sun.html Evidence Mounts For Companion Star To Our Sun] (SpaceDaily) Apr 25, 2006 [[Category:Rеd dwarfs]] [[Category:Brown dwarfs]] [[Category:Hypothetical stars]] [[Category:Hypothetical bodies of the Solar System]] [[Category:Solar System dynamic theories]] [[ca:Hipòtesi Nèmesi]] [[de:Nemesis (Stern)]] [[es:Hipótesis Némesis]] [[fr:Némésis (étoile)]] [[ko:네메시스 (항성)]] [[it:Nemesis (stella)]] [[nl:Nemesis (ster)]] [[ja:ネメシス (恒星)]] [[pl:Nemesis (astronomia)]] [[pt:Nêmesis (astronomia)]] [[sk:Nemesis (hviezda)]] [[sr:Немеза (звезда)]] [[fi:Nemesis (tähti)]] [[sv:Nemesis (astronomi)]] [[zh:太陽伴星]]