Nemesis is a hypothetical red dwarf star or brown dwarf, orbiting the Sun at a distance of about 50,000 to 100,000 AU, somewhat beyond the Oort cloud. This star was originally postulated to exist as part of a hypothesis to explain a perceived cycle of mass extinctions in the geological record, which seem to occur once every 26 million years or so.
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Claimed periodicity of mass extinctions
In 1984, paleontologists 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 analysis.[1] 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 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 similar hypotheses to explain Raup and Sepkoski's extinction periodicity in the same issue of the journal Nature.[2][3] This hypothesis proposes that the sun may have an as yet undetected companion star in a highly elliptical orbit that periodically disturbs comets 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 (or, more colorfully, 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 magnitude between 7 and 12,[4] 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 to 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 apogees 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 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 WISE mission 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%.
See also
- Brown dwarf
- Extinction events
- Red dwarf
- Stellar classification
- Shiva Hypothesis
- Nemesis, a book on the hypothetical star by Isaac Asimov
References
- ^ Raup, D.M.; Sepkoski, J.J. (1 February 1984). "Periodicity of Extinctions in the Geologic Past". Proceedings of the National Academy of Sciences 81 (3): 801–805. doi:. PMID 6583680. http://www.pnas.org/cgi/reprint/81/3/801.pdf. Retrieved 30 April 2007.
- ^ Whitmire, D.P.; Jackson, A.A. (1984). "Are periodic mass extinctions driven by a distant solar companion?". Nature 308 (5961): 713–715. doi:.
- ^ Davis, M.; Hut, P., Muller, R.A. (1984). "Extinction of species by periodic comet showers". Nature 308 (5961): 715–717. doi:.
- ^ http://muller.lbl.gov/pages/lbl-nem.htm Muller.lbl.gov Retrieved on 05-19-07
External links
- Richard A. Muller, Nemesis (Weidenfeld and Nichoson, 1988, OP)
- 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
- Undergraduate lecture by Richard A. Muller where he describes Nemesis Theory
- Robert Roy Britt, Nemesis: Does the Sun Have a 'Companion'?, Space.com, 3 April 2001.
- 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.)
- (no author), Exit Mundi, (undated). (Nemesis an End-Of-World scenario.)
- R. Foot, Z. K. Silagadze, 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
- Evidence Mounts For Companion Star To Our Sun (SpaceDaily) Apr 25, 2006
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