Nemesis (Star)

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A dwarf star typical of the class to which Nemesis, if it exists, would belong.
Date of discovery April 19, 1984 (proposed)[1]
Name of discoverer Richard A. Muller[2]
Name origin Greek goddess of retribution[3]
Orbital characteristics
Primary Sun
Perihelion 8,800 AU[4]
Aphelion 167,200 AU[4]
Semi-major axis 88,000 AU[1]
Orbital eccentricity 0.9[1]
Sidereal year 26,000,000 a[1]
Physical characteristics
Mass 2 * 10-4 to 7 * 10-2 M☉[1]
Minimum temperature 2300 K[5]
Maximum temperature 2600 K[5]
Nemesis is a hypothesized and probably factitious companion star to the sun. It is said to be trans-Neptunian and to enter the Oort Cloud every 26 million Julian years. When it so enters the cloud, according to theory, it perturbs it and sends a shower of comets into the inner solar system. A significant portion of these comets then strike the earth and cause extinction-level events. To date no astronomer has developed definitive evidence for the existence of the Nemesis star, although two comprehensive surveys of the sky that might decide the issue are currently under way, and a third survey by a polar-orbiting rocket probe is planned.

Background of the Nemesis Hypothesis

In 1984, paleontologists David Raup and Jack Sepkoski published their time-series analysis of the geologic strata that, according to uniformitarian geology, were laid down during the last 250 million years. They determined that twelve extinction-level events (ELEs) had occurred during this time, and that the time between one ELE and the next was 26 million years.[6] Previous investigators had linked two of these putative ELEs to large meteorite impacts. Raup and Sepkoski therefore concluded that such events (including the alleged extinction of the dinosaurs 65 million years ago) happened regularly and might have an extraterrestrial cause.

Proposal and naming

Two independent teams of astronomers then proposed the same type of cause: a companion star to the Sun, either a red dwarf or a brown dwarf, having a sidereal period equal to the period of Raup and Sepkoski's ELE cycle.[1][7] Subsequently, Muller published a book-length treatment of the Nemesis theory.[2][8]

Muller and others named this star Nemesis after the Greek goddess of retribution.[3]

Orbital characteristics

Nemesis, if it exists, would probably be in a highly eccentric, almost parabolic orbit around the Sun. The semimajor axis would be 88,000 AU and the eccentricity 0.9.[1] The sidereal period of 26 million years would be inferred from Raup and Sepkowski.[6]

Muller holds that Nemesis is at or near aphelion at present and would not cause another ELE until the year 15,000,000 AD.[7] Yarris[9] has suggested that Nemesis would be visible in the constellation of Hydra.

Physical characteristics

Whitmire and Jackson have suggested that Nemesis would have a mass varying from 2 * 10−4 to 7 * 10−2 times the mass of the sun. This is the range of masses of brown or black dwarf stars. Muller has argued that the star is a somewhat hotter red dwarf, of magnitude between 7 and 12.[2]


Nemesis has been a subject of heated controversy ever since the publication of the papers by Whitmire and Jackson, and Davis, Hut, and Muller.[10][11][12][13] Muller has perhaps compounded the controversy by asserting[2] that Nemesis would be visible with binocular field glasses or a small to medium-sized telescope. No astronomer, amateur or professional, has even claimed to have seen Nemesis, much less had a sighting confirmed.[11][12]

Muller has suggested that the Moon suffered a bombardment event as recently (per uniformitarian theories) as 400 to 600 million years ago, and that Nemesis might have been the cause.[14] Yet no geologist has developed evidence for periodic bombardment of the Moon, in line with the alleged 12 ELEs on the earth.

The orbit of Nemesis would be unstable, and many astronomers hold that Nemesis should long ago have escaped the Sun's gravity. Muller disputes these claims and insists that Nemesis ought to remain a part of the solar system for another billion years.[2]

Recently, Walter Cruttenden at the Binary Research Institute has decided that Sedna, a scatter disk object, actually is in orbital resonance with Nemesis.[15] Sedna's sidereal year is estimated to be 12,000 Earth years. If Sedna is in resonance with Nemesis, then it would probably have an actual period of 13,000 years and be in a 20:1 resonance with the hypothetical star.

However, even uniformitarian geologists do not necessarily accept the claimed periodicity of ELEs.[10][13]


On 2 July 2010, Mellot and Barnbach published a study suggesting that the ELEs have occurred over 500 million years, during which galactic tides and encounters with passing stars should have perturbed the orbit of the hypothetical Nemesis, but did not. Therefore, they now say, such a star cannot be blamed for ELEs occurring regularly ever 26 million years.[16]

A creationist perspective

The Nemesis hypothesis depends on uniformitarian geology, and in particular the acceptance of deep time. If, instead, one accepts the model of the Great Flood, then one has no need of a theory of a companion star (or, for that matter, a cloud of comets for the star to dive into). The alleged regular layers of extinct species could all result from laminar flow patterns during the Flood.

Search for Nemesis

As mentioned, no one has yet seen Nemesis. A recent infrared survey of the sky failed to detect it.[12] But at least two more wide-ranging surveys of the sky are planned, by the Panoramic Survey Telescope and Rapid Response System (Pan-Starrs)[17] and the Large Synoptic Survey Telescope (LSST)[2][18]


  1. 1.0 1.1 1.2 1.3 1.4 1.5 1.6 Whitmire, Daniel P., and Jackson, Albert A., IV. "Are periodic mass extinctions driven by a distant solar companion?" Nature 308:713-715, April 19, 1984. doi:10.1038/308713a0 Accessed June 10, 2008
  2. 2.0 2.1 2.2 2.3 2.4 2.5 Muller, Richard A., ed. "Nemesis." n.d. Accessed June 10, 2008.
  3. 3.0 3.1 Author unknown. "The Nemesis Theory." n.d. Accessed June 10, 2008.
  4. 4.0 4.1 Calculated
  5. 5.0 5.1 Suggested by its hypothesized spectral class of N, R, or S, consistent with its probable classification as a red or brown dwarf star. See "Harvard Spectral Classification," Study Astronomy Online at Swinburne University, accessed April 22, 2008, and Irizarry, David, "The Secrets of the Harvard Classification Revealed," The Webfooted Astronomer, Seattle Astronomical Society, February 2000, accessed April 22, 2008.
  6. 6.0 6.1 Raup, D. M., and Sepkowski, J. J. "Periodicity of extinctions in the geologic past." Proc. Nat. Acad. Sci. 81(3):801-805, February 1984. doi:10.1073/pnas.81.3.801. Accessed June 10, 2008.
  7. 7.0 7.1 Davis, Marc, Hut, Piet, and Muller, Richard A. "Extinction of species by periodic comet showers." Nature 308:715-717, April 19, 1984. doi:10.1038/308715a0 Accessed June 10, 2008
  8. Muller, Richard A. Nemesis, the Death Star: The Story of a Scientific Revolution. Wiedenfeld and Nicolson, 1988. ASIN: B000LD03W6. Cited in Muller, Nemesis (Internet site), op. cit.
  9. Yarris, Lynn. "Does a Companion Star to the Sun Cause Earth's Periodic Mass Extinctions?" Science Beat. Spring 1987.
  10. 10.0 10.1 Britt, Robert Roy. "Nemesis: Does the Sun Have a Companion?" <>, April 3, 2001. Accessed June 10, 2008.
  11. 11.0 11.1 Author unknown. "Er...Is That Really a Second Sun Up There?" n.d. Accessed June 10, 2008.
  12. 12.0 12.1 12.2 Schlyter, Paul. "Nemesis, the Companion Star," in "Hypothetical Planets." The Nine 8 Planets, Bill Arnett, ed. February 14, 2006. Accessed June 10, 2008.
  13. 13.0 13.1 Mukai, Koji, and Christian, Eric. "The Nemesis Star." Ask an Astrophysicist, Imagine the Universe!, NASA, December 1, 2005. Accessed June 10, 2008.
  14. Muller, Richard A. "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). Accessed June 10, 2008.
  15. Staff. "Evidence Mounts For Companion Star To Our Sun." SpaceDaily, April 25, 2006. Accessed June 10, 2008.
  16. Mellot A and Barnbach RK, "Nemesis reconsidered", Solar and Stellar Astrophysics, 2 July 2010. Accesssed 12 July 2010. arXiv:1007.0437v1
  17. "Pan-Starrs Home."
  18. "LSST Home."

Related Link

See also