Other moons of Earth

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Artist's conception of Earth with two moons.

Claims of the existence of other moons of Earth—that is, of one or more natural satellites other than the Moon that orbit Earth—have existed for some time. Several candidates have been proposed, but none has been confirmed.[1] The 19th and 20th centuries have seen genuine scientific searches for more moons, but the possibility has been the subject of a greater number of non-scientific proposals and likely hoaxes.[2]

Although the Moon remains Earth's only known natural satellite, there are a number of near-Earth objects (NEOs) with orbits that are in resonance with Earth. These have been called, inaccurately but provocatively, "second", "third" or "other" moons of Earth.[3] Quasi-satellites that orbit the Sun in resonance with Earth, for instance, appear to orbit a point related to (but outside) that of Earth. An example is the asteroid 3753 Cruithne. Earth trojans, such as 2010 TK7, are asteroids whose orbits appear to lead or follow Earth along the same orbital path.

Small natural objects in orbit around the Sun can also fall temporarily into orbit around Earth. This makes them natural satellites of Earth, but only temporarily. To date, the only confirmed example has been 2006 RH120 in Earth orbit during 2006 and 2007, but further instances are already predicted.[1]


Petit's moon[edit]

The first major claim of another moon of Earth was made by French astronomer Frédéric Petit, director of the Toulouse Observatory, who in 1846 announced that he had discovered a second moon in an elliptical orbit around Earth. It was claimed to have also been reported by Lebon and Dassier at Toulouse, and by Larivière at Artenac Observatory, during the early evening of March 21, 1846.[4] Petit proposed that this second moon had an elliptical orbit, a period of 2 hours 44 minutes, with 3,570 km (2,220 mi) apogee and 11.4 km (7.1 mi) perigee.[4] This claim was soon dismissed by his peers.[5] The 11.4 km (37,000 ft) perigee is similar to the cruising altitude of most modern airliners, and within Earth's atmosphere. Petit published another paper on his 1846 observations in 1861, basing the second moon's existence on perturbations in movements of the actual Moon.[4] This second moon hypothesis was not confirmed either. Nevertheless, Petit's proposed moon became a major plot point in Jules Verne's 1870 science fiction novel Around the Moon.[6]

Waltemath's moons[edit]

In 1898 Hamburg scientist Dr. Georg Waltemath announced that he had located a system of tiny moons orbiting Earth.[7][8] He had begun his search for secondary moons based on the hypothesis that something was gravitationally affecting the Moon's orbit.[9]

Waltemath described one of the proposed moons as being 1,030,000 km (640,000 mi) from Earth, with a diameter of 700 km (430 mi), a 119-day orbital period, and a 177-day synodic period.[4] He also said it did not reflect enough sunlight to be observed without a telescope, unless viewed at certain times, and made several predictions as to when it would appear.[9] "Sometimes, it shines at night like the sun but only for an hour or so."[9][10] However, after the failure of a corroborating observation of Waltemath's moons by the scientific community, these objects were discredited. Especially problematic was a failed prediction that they would be observable in February 1898.[4] The August 1898 issue of Science mentioned that Waltemath had sent the journal "an announcement of a third moon", which he termed a wahrhafter Wetter und Magnet Mond ("real weather and magnet moon").[11] It was supposedly 746 km (464 mi) in diameter, and closer than the moon that he had described previously.[12]

Other claims[edit]

In 1918, astrologer Walter Gornold, also known as Sepharial, claimed to have confirmed the existence of Waltemath's moon. He named it Lilith. Sepharial claimed that Lilith was a 'dark' moon invisible for most of the time, but he claimed to have viewed it as it crossed the Sun.[13]

In 1926 the science journal Die Sterne published the findings of amateur German astronomer W. Spill, who claimed to have successfully viewed a second moon orbiting Earth.[10]

In the late 1960s John Bargby claimed to have observed over ten small natural satellites of Earth, but this was not confirmed.[4]

General surveys[edit]

William Henry Pickering (1858–1938) studied the possibility of a second moon and made a general search ruling out the possibility of many types of objects by 1903.[14] His 1922 article "A Meteoritic Satellite" in Popular Astronomy resulted in increased searches for small natural satellites by amateur astronomers.[4] Pickering had also proposed the Moon itself had broken off from Earth.[15]

In early 1954 the United States Army's Office of Ordnance Research commissioned Clyde Tombaugh, discoverer of Pluto, to search for near-Earth asteroids. The Army issued a public statement to explain the rationale for this survey.[16] Donald Keyhoe, who was later director of the National Investigations Committee on Aerial Phenomena (NICAP), a UFO research group, said that his Pentagon source had told him that the actual reason for the quickly initiated search was that two near-Earth objects had been picked up on new long-range radar in mid-1953. In May 1954, Keyhoe asserted that the search had been successful, and either one or two objects had been found.[17] At The Pentagon, a general who heard the news reportedly asked whether the satellites were natural or artificial. Tombaugh denied the alleged discovery in a letter to Willy Ley,[6] and the October 1955 issue of Popular Mechanics magazine reported:


At a meteor conference in Los Angeles in 1957, Tombaugh reiterated that his four-year search for natural satellites had been unsuccessful.[19] In 1959, he issued a final report stating that nothing had been found in his search.

Modern status[edit]

2010 TK7 has a helical path (green) relative to Earth and its orbit (blue dots)

It was discovered that small bodies can be temporarily captured, as shown by 2006 RH120, which was in Earth orbit in 2006–2007.[1]

In 2010, the first known Earth trojan was discovered in data from Wide-field Infrared Survey Explorer (WISE), and is currently called 2010 TK7.

In 2011, planetary scientists Erik Asphaug and Martin Jutzi proposed a model in which a second moon would have existed 4.5 billion years ago, and later impacted the Moon, as a part of the accretion process in the formation of the Moon.[20]

Quasi-satellites and trojans[edit]

The orbits of Earth and the quasi-satellite Cruithne
When observed from Earth, Cruithne appears to orbit a point beside it.

Although no other moons of Earth have been found to date, there are various types of near-Earth objects in 1:1 resonance with it, which are known as quasi-satellites. Quasi-satellites orbit the Sun from the same distance as a planet, rather than the planet itself. Their orbits are unstable, and will fall into other resonances or be kicked into other orbits over thousands of years.[3] Quasi-satellites of Earth include 2010 SO16, (164207) 2004 GU9,[21] (277810) 2006 FV35,[22] 2002 AA29[23] and 3753 Cruithne. Cruithne, discovered in 1986, orbits the Sun in an elliptical orbit but appears to have a horseshoe orbit when viewed from Earth.[3][24] Some went as far to nickname Cruithne "Earth's second moon".[24]

The key difference between a satellite and a quasi-satellite is that the orbit of a satellite of Earth fundamentally depends on the gravity of the Earth–Moon system, whereas the orbit of a quasi-satellite would negligibly change if Earth and the Moon were suddenly removed because a quasi-satellite is orbiting the Sun on an Earth-like orbit in the vicinity of Earth.[25]

Earth possesses one known trojan, a small Solar System body caught in the planet's gravitationally stable L4 Lagrangian point. This object, 2010 TK7 is roughly 300 metres across. Like quasi-satellites, it orbits the Sun in a 1:1 resonance with Earth, rather than Earth itself.

Temporary satellites[edit]

On 14 September 2006, an object estimated at 5 meters in diameter was discovered in near-polar orbit around Earth. Originally thought to be a third stage Saturn S-IVB booster from Apollo 12, it was later determined to be an asteroid and designated as 2006 RH120. The asteroid re-entered Solar orbit after 13 months and is expected to return to Earth orbit in 21 years.[26]

Computer models by astrophysicists Mikael Granvik, Jeremie Vaubaillon, and Robert Jedicke of Cornell University suggest that these "temporary satellites" should be quite common; and that "At any given time, there should be at least one natural Earth satellite of 1-meter diameter orbiting the Earth."[27] Such objects would remain in orbit for ten months on average, before returning to solar orbit once more, and so would make relatively easy targets for manned space exploration.[27] "Mini-moons" were further examined in a study published in the March issue of Icarus.[28]

The earliest known mention[25] in the scientific literature of a temporarily captured orbiter is by Clarence Chant about the Meteor procession of February 9, 1913:

"It would seem that the bodies had been traveling through space, probably in an orbit about the sun, and that on coming near the earth they were promptly captured by it and caused to move about it as a satellite."[29]

And later in 1916, William Frederick Denning surmised:

"The large meteors which passed over Northern America on February 9, 1913, presented some unique features. The length of their observed flight was about 2600 miles, and they must have been moving in paths concentric, or nearly concentric, with the earth's surface, so that they temporarily formed new terrestrial satellites.”[30]

It has been proposed that NASA search for temporary natural satellites, and use them for a sample return mission.[1][31]


  • The writer Jules Verne learned of Petit's 1861 proposal and made use of the idea in his 1865 novel, From the Earth to the Moon.[5] This fictional moon was not, however, exactly based on the Toulouse observations or Petit's proposal at a technical level, and so the orbit suggested by Verne was mathematically incorrect.[4] Petit died in 1865, and so was not alive to offer a response to Verne's fictional moon.[32]
  • Eleanor Cameron's Mushroom Planet novels for children (starting with the 1954 The Wonderful Flight to the Mushroom Planet) are set on a tiny, habitable second moon called Basidium in an invisible orbit 50,000 miles (80,000 km) from Earth. There is an even smaller moon called Lepton orbiting at only 1,000 miles (1,600 km).[33]
  • The 1956 Tom Swift, Jr. juvenile novel, Tom Swift on the Phantom Satellite, features a new moon entering Earth orbit at 50,000 miles (80,000 km) altitude.[34] A 1963 sequel, Tom Swift and the Asteroid Pirates, has the moon Nestria, also called Little Luna, which was originally an asteroid and was moved into Earth orbit at 50,000 miles (80,000 km) altitude. It was claimed for the United States and a research base was established there by Swift Enterprises.[35]
  • Samuel R. Delany's 1975 novel Dhalgren features an Earth that mysteriously acquires a second moon named George.[36]
  • In Haruki Murakami's 2011 novel 1Q84, a second moon, irregularly shaped and green in color, is visible to some characters in the story.[37]

See also[edit]


  1. ^ a b c d I. Klotz - Mystery Mini Moons: How Many Does Earth Have? (2012) - Discovery News
  2. ^ Drye, Paul (2009-01-24). "Earth's Other Moon". passingstrangeness.wordpress.com. Retrieved 2011-10-23. 
  3. ^ a b c Lloyd, Robin, More Moons Around Earth?, space.com 
  4. ^ a b c d e f g h Schlyter, Paul. nineplanets.org
  5. ^ a b Moore, Patrick. The Wandering Astronomer. CRC Press, 1999b, ISBN 0-7503-0693-9, [1]
  6. ^ a b Ley, Willy (July 1957). "For Your Information". Galaxy Science Fiction. pp. 61–71. Retrieved 11 June 2014. 
  9. ^ a b c Public Opinion: A Comprehensive Summary of the Press Throughout the World on All Important Current Topics, published by Public Opinion Co., 1898: "The Alleged Discovery of a Second Moon", p 369. Book
  10. ^ a b Bakich, Michael E. The Cambridge Planetary Handbook. Cambridge University Press, 2000, ISBN 0-521-63280-3, p. 148; see
  11. ^ "A Stray Moon". The Times (Washington, D.C.). 7 August 1898. p. 15. Retrieved 25 August 2013. It is a real weather and magnet moon, and whenever it is about to cross the earth's course it disturbs the atmosphere and surface of the earth, producing storms, rain, tempests, magnetic deviations and earthquakes... 
  12. ^ "Science" VIII (189). 12 August 1898. p. 185. Retrieved 25 August 2013. 
  13. ^ Sepharial, A. The Science of Foreknowledge: Being a Compendium of Astrological Research, Philosophy, and Practice in the East and West.; Kessinger Publishing (reprint), 1997, pp. 39–50; ISBN 1-56459-717-2 , see
  14. ^ "On a photographic search for a satellite of the Moon", Popular Astronomy, 1903
  15. ^ Pickering, W.H (1907), "The Place of Origin of the Moon — The Volcani Problems", Popular Astronomy 15: 274–287, Bibcode:1907PA.....15..274P 
  16. ^ "Armed Forces Seeks "Steppingstone to Stars"", Los Angeles Times, 1954-03-04 
  17. ^ "1 or 2 Artificial Satellites Circling Earth, Says Expert", San Francisco Examiner, 1954-05-14: 14 
  18. ^ Stimson, Thomas E., Jr (October 1955), "He Spies on Satellites", Popular Mechanics: 106 
  19. ^ Los Angeles Times, 1957-09-04 
  20. ^ doi:10.1038/nature10289
  21. ^ Brasser, R.; et al. (September 2004). "Transient co-orbital asteroids". Icarus 171 (1): 102–109. Bibcode:2004Icar..171..102B. doi:10.1016/j.icarus.2004.04.019. 
  22. ^ Dynamical evolution of Earth’s quasi-satellites: 2004 GU9 and 2006 FV35
  23. ^ Connors, Martin; Paul Chodas, Seppo Mikkola, Paul Wiegert, Christian Veillet, Kimmo Innanen (September 2002). "Earth coorbital asteroid 2002 AA29". Retrieved 16 April 2010
  24. ^ a b "More Mathematical Astronomy Morsels" (2002) ISBN 0-943396-74-3, Jean Meeus, chapter 38: Cruithne, an asteroid with a remarkable orbit
  25. ^ a b Granvik, Mikael; Jeremie Vaubaillon; Robert Jedicke (December 2011). "The population of natural Earth satellites". Icarus: 63. arXiv:1112.3781. Bibcode:2012Icar..218..262G. doi:10.1016/j.icarus.2011.12.003. 
  26. ^ Yeomans, Don (April 2010), "Is Another Moon Possible?", Astronomy 
  27. ^ a b Amy Shira Teitel (2011). "Earth's Other Moons". Universe Today. Retrieved 2012-02-04. 
  28. ^ Earth's Many Moons (University of Hawaii at Manoa)
  29. ^ Chant, Clarence A. (May–June 1913). "An Extraordinary Meteoric Display". Journal of the Royal Astronomical Society of Canada 7 (3): 144–215. Bibcode:1913JRASC...7..145C. 
  30. ^ Denning, William F. (April 1916). "The Remarkable Meteors of February 9, 1913". Nature 97 (2426): 181. Bibcode:1916Natur..97..181D. doi:10.1038/097181b0. 
  31. ^ New Asteroid-Capture Mission Idea: Go After Earth's 'Minimoons'
  32. ^ "History of the Toulouse Observatory" (in French). Archived from the original on 2009-05-28. 
  33. ^ "The Mushroom Planet Series". Retrieved 2014-05-13. 
  34. ^ "Tom Swift on the Phantom Satellite". Retrieved 2014-05-13. 
  35. ^ "Tom Swift and the Asteroid Pirates". Retrieved 2014-05-13. 
  36. ^ Pierce, John J. (1989). When World Views Collide: A Study in Imagination and Evolution. Contributions to the study of science fiction and fantasy. Greenwood Press. p. 108. ISBN 0313254575. Retrieved 2014-05-13. 
  37. ^ Judith Eve Lipton, MD (November 18, 2011). "1Q84: Living in a World With Two Moons". Psychology Today. Retrieved 2014-05-13. 

Further reading[edit]

  • Willy Ley: "Watchers of the Skies", The Viking Press NY,1963,1966,1969
  • Joseph Ashbrook: "The Many Moons of Dr Waltemath", Sky and Telescope, Vol 28, Oct 1964, p. 218, also on pp. 97–99 of "The Astronomical Scrapbook" by Joseph Ashbrook, Sky Publ. Corp. 1984, ISBN 0-933346-24-7
  • William R. Corliss: "Mysterious Universe: A handbook of astronomical anomalies", Sourcebook Project 1979, ISBN 0-915554-05-4, p 146–157 "Other moons of the Earth", pp. 500–526 "Enigmatic objects"
  • Clyde Tombaugh: Discoverer of Planet Pluto, David H. Levy, Sky Publishing Corporation, March 2006

External links[edit]