Earth's second moon
Encyclopedia
Claims have existed for many centuries that the Earth might possess other natural satellite
s besides the Moon
. Several candidates have been proposed, but all such claims have proven false. The Moon is Earth's only known natural satellite.
While several genuine scientific searches for "second moons" were undertaken in the 19th and 20th centuries, the field has also been the subject of several non-scientific proposals and possible hoaxes. These possible hoaxes, which were about objects of specific size and orbits, were poorly founded and all have been disproven.
Although the Moon is Earth's only known natural satellite, there are a number of near-Earth objects with orbits that are in resonance
with Earth. These can be mistaken for natural satellites and are sometimes glibly referred to as "second moons". Quasi-satellite
s, such as 3753 Cruithne
, orbit Earth in 1:1 resonance but also orbit the Sun. Earth trojans
, such as , follow the same orbital path as Earth, either trailing or following, in the vicinity of the Earth–Sun Lagrangian point
s.
There have been large generic searches for small moons, actual proposals or claimed sightings of specific objects in orbit, and finally, analysis and searches for those proposed objects. All three of these have failed to confirm a permanent natural satellite.
, director of the Toulouse Observatory
, who in 1846 announced that he had discovered a second moon in an elliptical orbit around the Earth. It was claimed to be reported by Lebon and Dassier also at Toulouse
, and Lariviere at Artenac Observatory, during the early evening of March 21, 1846. Petit proposed that this second moon had an elliptical orbit, a period of 2 hours 44 minutes, with 3570 km (2,218.3 mi) apogee
and 11.4 km (7.1 mi) perigee
. This claim was soon dismissed by his peers. The 11.4 km (37,401.6 ft) perigee is similar to the cruising altitude of most airliners.
Petit became obsessed with his 1846 observations and ended up publishing another paper 15 years later (1861), basing the second moon's existence on perturbations in movements of the existing moon. This second moon hypothesis was not confirmed either; however, the concept was taken up by science fiction writer Jules Verne
, who included a fictional moon based on Petit's second proposal for a second moon in his 1865 novel From the Earth to the Moon
. This fictional moon, however was not exactly based on the Toulouse observations or Petit's proposal at a technical level, and so the orbit suggested by Verne was mathematically incorrect. Petit died in 1865, and so was not alive to offer a response to Verne's fictional moon.
Waltemath described one of the proposed moons as being 1030000 km (640,013.9 mi) from Earth, with a diameter of 700 km (435 mi), a 119-day orbital period
, and a 177-day synodic period. 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. "Sometimes, it shines at night like the sun but only for an hour or so." 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. Waltemath proposed more moons, according to a mention in August 1898 issue of Science. The third moon was closer than the first, 746 km (463.5 mi) in diameter, and he called it "Wahrhafter Wetter-und Magnet Mond".
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.
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 the Earth.
In the late 1960s John Bargby claimed to have observed over ten small natural satellites of the Earth, but this was not confirmed.
(1858–1938) studied the possibility of a second moon and made general search ruling out the possibility of many types of objects by 1903. His 1922 article "A Meteoritic Satellite" in Popular Astronomy
resulted in increased searches for small natural satellites by amateur astronomers. Pickering had also proposed the Moon itself had broken off from Earth.
After he had discovered Pluto
, the United States Army
's Office of Ordnance Research commissioned Clyde Tombaugh
to search for near-Earth asteroids. The Army issued a public statement in March 1954 to explain the rationale for this survey. However, according to Donald Keyhoe
, later director of the National Investigations Committee on Aerial Phenomena
(NICAP), the real reason for the sudden search was because two near-Earth objects had been picked up on new long-range radar
in mid-1953, according to his Pentagon
source. Keyhoe stated in May 1954 that the search had been successful, and either one or two objects had been found. However, the story did not really break until August 23 of that year, when Aviation Week
magazine stated that two natural satellites had been found only 400 and 600 mi (643.7 and 965.6 km) out. However, Tombaugh issued public denials that anything had been found. The October 1955 issue of Popular Mechanics
magazine reported:
At a 1957 meteor conference in Los Angeles, Tombaugh reiterated that his four-year search for natural satellites had been unsuccessful. In 1959 Tombaugh issued a final report stating that nothing had been found in his search.
Although no other moons of Earth have been found to date, there are various types of near-Earth object
in 1:1 resonance with it, which are known as quasi-satellite
s. 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. Quasi-satellites of Earth include , 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. Cruithne has been nicknamed "Earth's second moon".
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 . The asteroid re-entered Solar orbit after 13 months and is expected to return to Earth orbit in 21 years.
Earth possesses one known Trojan asteroid
; a small Solar System body
caught in the planet's gravitationally stable L4 Lagrangian point
. The object, 2010 TK7
is roughly 300 metres long. Like the quasi-satellites, it orbits the Sun in a 1:1 resonance with Earth, rather than Earth itself.
learned of Petit's second proposals for a second moon theory. He became intrigued by the idea and made use of it in his 1865 novel, From the Earth to the Moon
.
The explosive popularity of Verne's book in the 19th century triggered many amateur astronomers to search for second moons around Earth although Petit did not live to see this, having died in 1865. Samuel R. Delany
's 1975 novel Dhalgren
features an Earth which mysteriously acquires a second moon. Eleanor Cameron
's Mushroom Planet novels for children (the first being The Wonderful Flight to the Mushroom Planet
) are set on a tiny, habitable second moon called Basidium in an invisible orbit 50000 miles (80,467 km) from Earth.
Natural satellite
A natural satellite or moon is a celestial body that orbits a planet or smaller body, which is called its primary. The two terms are used synonymously for non-artificial satellites of planets, of dwarf planets, and of minor planets....
s besides the Moon
Moon
The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...
. Several candidates have been proposed, but all such claims have proven false. The Moon is Earth's only known natural satellite.
While several genuine scientific searches for "second moons" were undertaken in the 19th and 20th centuries, the field has also been the subject of several non-scientific proposals and possible hoaxes. These possible hoaxes, which were about objects of specific size and orbits, were poorly founded and all have been disproven.
Although the Moon is Earth's only known natural satellite, there are a number of near-Earth objects with orbits that are in resonance
Orbital resonance
In celestial mechanics, an orbital resonance occurs when two orbiting bodies exert a regular, periodic gravitational influence on each other, usually due to their orbital periods being related by a ratio of two small integers. Orbital resonances greatly enhance the mutual gravitational influence of...
with Earth. These can be mistaken for natural satellites and are sometimes glibly referred to as "second moons". Quasi-satellite
Quasi-satellite
A quasi-satellite is an object in a 1:1 orbital resonance with its planet that stays close to the planet over many orbital periods.A quasi-satellite's orbit around the Sun takes exactly the same time as the planet's, but has a different eccentricity , as shown in the diagram on the right...
s, such as 3753 Cruithne
3753 Cruithne
3753 Cruithne is an asteroid in orbit around the Sun in approximate 1:1 orbital resonance with the Earth. It is a periodic inclusion planetoid orbiting the Sun in an apparent horseshoe orbit. It has been incorrectly called "Earth's second moon", but it is only a quasi-satellite. Cruithne never...
, orbit Earth in 1:1 resonance but also orbit the Sun. Earth trojans
Earth Trojan asteroid
Earth trojans are asteroids that orbit in the vicinity of the Earth-Sun Lagrangian points and . They are named after the Trojan asteroids that are associated with the analogous Lagrangian points of Jupiter....
, such as , follow the same orbital path as Earth, either trailing or following, in the vicinity of the Earth–Sun Lagrangian point
Lagrangian point
The Lagrangian points are the five positions in an orbital configuration where a small object affected only by gravity can theoretically be stationary relative to two larger objects...
s.
There have been large generic searches for small moons, actual proposals or claimed sightings of specific objects in orbit, and finally, analysis and searches for those proposed objects. All three of these have failed to confirm a permanent natural satellite.
Petit's moon
The first major claim of another moon of Earth was made by French astronomer Frédéric PetitFrédéric Petit (astronomer)
Frédéric Petit was a French astronomer. He was the first director of the Toulouse Observatory, located in in Toulouse, France, serving from 1838–1865. In 1846 he announced that he had discovered a second moon of Earth...
, director of the Toulouse Observatory
Toulouse Observatory
The Observatoire de Toulouse is located in Toulouse, France and was established in 1733. It was founded by l'Académie des Sciences, Inscriptions et Belles-Lettres de Toulouse . It was moved 1841 and again in 1981...
, who in 1846 announced that he had discovered a second moon in an elliptical orbit around the Earth. It was claimed to be reported by Lebon and Dassier also at Toulouse
Toulouse
Toulouse is a city in the Haute-Garonne department in southwestern FranceIt lies on the banks of the River Garonne, 590 km away from Paris and half-way between the Atlantic Ocean and the Mediterranean Sea...
, and Lariviere at Artenac Observatory, during the early evening of March 21, 1846. Petit proposed that this second moon had an elliptical orbit, a period of 2 hours 44 minutes, with 3570 km (2,218.3 mi) apogee
Apsis
An apsis , plural apsides , is the point of greatest or least distance of a body from one of the foci of its elliptical orbit. In modern celestial mechanics this focus is also the center of attraction, which is usually the center of mass of the system...
and 11.4 km (7.1 mi) perigee
Apsis
An apsis , plural apsides , is the point of greatest or least distance of a body from one of the foci of its elliptical orbit. In modern celestial mechanics this focus is also the center of attraction, which is usually the center of mass of the system...
. This claim was soon dismissed by his peers. The 11.4 km (37,401.6 ft) perigee is similar to the cruising altitude of most airliners.
Petit became obsessed with his 1846 observations and ended up publishing another paper 15 years later (1861), basing the second moon's existence on perturbations in movements of the existing moon. This second moon hypothesis was not confirmed either; however, the concept was taken up by science fiction writer Jules Verne
Jules Verne
Jules Gabriel Verne was a French author who pioneered the science fiction genre. He is best known for his novels Twenty Thousand Leagues Under the Sea , A Journey to the Center of the Earth , and Around the World in Eighty Days...
, who included a fictional moon based on Petit's second proposal for a second moon in his 1865 novel From the Earth to the Moon
From the Earth to the Moon
From the Earth to the Moon is a humorous science fantasy novel by Jules Verne and is one of the earliest entries in that genre. It tells the story of the president of a post-American Civil War gun club in Baltimore, his rival, a Philadelphia maker of armor, and a Frenchman, who build an enormous...
. This fictional moon, however was not exactly based on the Toulouse observations or Petit's proposal at a technical level, and so the orbit suggested by Verne was mathematically incorrect. Petit died in 1865, and so was not alive to offer a response to Verne's fictional moon.
Waltemath's moons
In 1898 Hamburg scientist Dr. Georg Waltemath announced that he had located a system of tiny moons orbiting the Earth. He had begun his search for secondary moons based on the hypothesis that something was gravitationally affecting the Moon's orbit.Waltemath described one of the proposed moons as being 1030000 km (640,013.9 mi) from Earth, with a diameter of 700 km (435 mi), a 119-day orbital period
Orbital period
The orbital period is the time taken for a given object to make one complete orbit about another object.When mentioned without further qualification in astronomy this refers to the sidereal period of an astronomical object, which is calculated with respect to the stars.There are several kinds of...
, and a 177-day synodic period. 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. "Sometimes, it shines at night like the sun but only for an hour or so." However, after the failure of a corroborating observation of Waltemath's moons by the scientific community
Scientific community
The scientific community consists of the total body of scientists, its relationships and interactions. It is normally divided into "sub-communities" each working on a particular field within science. Objectivity is expected to be achieved by the scientific method...
, these objects were discredited. Especially problematic was a failed prediction that they would be observable in February 1898. Waltemath proposed more moons, according to a mention in August 1898 issue of Science. The third moon was closer than the first, 746 km (463.5 mi) in diameter, and he called it "Wahrhafter Wetter-und Magnet Mond".
Other claims
In 1918, astrologerAstrologer
An astrologer practices one or more forms of astrology. Typically an astrologer draws a horoscope for the time of an event, such as a person's birth, and interprets celestial points and their placements at the time of the event to better understand someone, determine the auspiciousness of an...
Walter Gornold, also known as Sepharial
Sepharial
Dr Walter Gorn Old was a notable 19th century astrologer, better 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.
In 1926 the science journal Die Sterne
Die Sterne
Die Sterne is a two/three/four-piece indie pop band, from Hamburg, Germany. They were formed in 1992 and have released eight studio albums, the most recent in 2010.-Members:...
published the findings of amateur German astronomer W. Spill, who claimed to have successfully viewed a second moon orbiting the Earth.
In the late 1960s John Bargby claimed to have observed over ten small natural satellites of the Earth, but this was not confirmed.
General surveys
William Henry PickeringWilliam Henry Pickering
William Henry Pickering was an American astronomer, brother of Edward Charles Pickering. He was elected a Fellow of the American Academy of Arts and Sciences in 1883.-Work:...
(1858–1938) studied the possibility of a second moon and made general search ruling out the possibility of many types of objects by 1903. His 1922 article "A Meteoritic Satellite" in Popular Astronomy
Popular Astronomy (US magazine)
Popular Astronomy was a magazine for amateur astronomers published between 1893 and 1951. It was the successor to The Sidereal Messenger, which ceased publication in 1892. Each yearly volume of Popular Astronomy contained 10 issues, for a total of 59 volumes.The first editor, from 1893-1911, was...
resulted in increased searches for small natural satellites by amateur astronomers. Pickering had also proposed the Moon itself had broken off from Earth.
After he had discovered Pluto
Pluto
Pluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System and the tenth-most-massive body observed directly orbiting the Sun...
, the United States Army
United States Army
The United States Army is the main branch of the United States Armed Forces responsible for land-based military operations. It is the largest and oldest established branch of the U.S. military, and is one of seven U.S. uniformed services...
's Office of Ordnance Research commissioned Clyde Tombaugh
Clyde Tombaugh
Clyde William Tombaugh was an American astronomer. Although he is best known for discovering the dwarf planet Pluto in 1930, the first object to be discovered in what would later be identified as the Kuiper Belt, Tombaugh also discovered many asteroids; he also called for serious scientific...
to search for near-Earth asteroids. The Army issued a public statement in March 1954 to explain the rationale for this survey. However, according to Donald Keyhoe
Donald Keyhoe
Donald Edward Keyhoe was an American Marine Corps naval aviator, writer of many aviation articles and stories in a variety of leading publications, and manager of the promotional tours of aviation pioneers, especially of Charles Lindbergh.In the 1950s he became well-known as an UFO researcher,...
, later director of the National Investigations Committee on Aerial Phenomena
National Investigations Committee On Aerial Phenomena
The National Investigations Committee On Aerial Phenomena was a civilian unidentified flying object research group active in the United States from the 1950s to the 1980s.-Overview:...
(NICAP), the real reason for the sudden search was because two near-Earth objects had been picked up on new long-range radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
in mid-1953, according to his Pentagon
The Pentagon
The Pentagon is the headquarters of the United States Department of Defense, located in Arlington County, Virginia. As a symbol of the U.S. military, "the Pentagon" is often used metonymically to refer to the Department of Defense rather than the building itself.Designed by the American architect...
source. Keyhoe stated in May 1954 that the search had been successful, and either one or two objects had been found. However, the story did not really break until August 23 of that year, when Aviation Week
Aviation Week & Space Technology
Aviation Week & Space Technology, often abbreviated Aviation Week or AW&ST, is a weekly magazine owned and published by McGraw-Hill...
magazine stated that two natural satellites had been found only 400 and 600 mi (643.7 and 965.6 km) out. However, Tombaugh issued public denials that anything had been found. The October 1955 issue of Popular Mechanics
Popular Mechanics
Popular Mechanics is an American magazine first published January 11, 1902 by H. H. Windsor, and has been owned since 1958 by the Hearst Corporation...
magazine reported:
At a 1957 meteor conference in Los Angeles, Tombaugh reiterated that his four-year search for natural satellites had been unsuccessful. In 1959 Tombaugh issued a final report stating that nothing had been found in his search.
Quasi-satellites and Trojans
Near-Earth object
A near-Earth object is a Solar System object whose orbit brings it into close proximity with the Earth. All NEOs have a perihelion distance less than 1.3 AU. They include a few thousand near-Earth asteroids , near-Earth comets, a number of solar-orbiting spacecraft, and meteoroids large enough to...
in 1:1 resonance with it, which are known as quasi-satellite
Quasi-satellite
A quasi-satellite is an object in a 1:1 orbital resonance with its planet that stays close to the planet over many orbital periods.A quasi-satellite's orbit around the Sun takes exactly the same time as the planet's, but has a different eccentricity , as shown in the diagram on the right...
s. 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. Quasi-satellites of Earth include , and 3753 Cruithne
3753 Cruithne
3753 Cruithne is an asteroid in orbit around the Sun in approximate 1:1 orbital resonance with the Earth. It is a periodic inclusion planetoid orbiting the Sun in an apparent horseshoe orbit. It has been incorrectly called "Earth's second moon", but it is only a quasi-satellite. Cruithne never...
.
Cruithne, discovered in 1986, orbits the Sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...
in an elliptical orbit but appears to have a horseshoe orbit
Horseshoe orbit
A horseshoe orbit is a type of co-orbital motion of a small orbiting body relative to a larger orbiting body . The orbital period of the smaller body is very nearly the same as for the larger body, and its path appears to have a horseshoe shape in a rotating reference frame as viewed from the...
when viewed from Earth. Cruithne has been nicknamed "Earth's second moon".
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
S-IVB
The S-IVB was built by the Douglas Aircraft Company and served as the third stage on the Saturn V and second stage on the Saturn IB. It had one J-2 engine...
booster from Apollo 12
Apollo 12
Apollo 12 was the sixth manned flight in the American Apollo program and the second to land on the Moon . It was launched on November 14, 1969 from the Kennedy Space Center, Florida, four months after Apollo 11. Mission commander Charles "Pete" Conrad and Lunar Module Pilot Alan L...
, it was later determined to be an asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
and designated as . The asteroid re-entered Solar orbit after 13 months and is expected to return to Earth orbit in 21 years.
Earth possesses one known Trojan asteroid
Trojan asteroid
The Jupiter Trojans, commonly called Trojans or Trojan asteroids, are a large group of objects that share the orbit of the planet Jupiter around the Sun. Relative to Jupiter, each Trojan librates around one of the planet's two Lagrangian points of stability, and , that respectively lie 60° ahead...
; a small Solar System body
Small Solar System body
A small Solar System body is an object in the Solar System that is neither a planet nor a dwarf planet, nor a satellite of a planet or dwarf planet:...
caught in the planet's gravitationally stable L4 Lagrangian point
Lagrangian point
The Lagrangian points are the five positions in an orbital configuration where a small object affected only by gravity can theoretically be stationary relative to two larger objects...
. The object, 2010 TK7
2010 TK7
2010 TK7 is the first Earth trojan asteroid to be discovered; it precedes Earth in its orbit around the Sun. Trojan objects are most easily conceived as orbiting at a Lagrangian point, a dynamically stable location 60 degrees ahead of or behind a massive orbiting body, in a type of 1:1 orbital...
is roughly 300 metres long. Like the quasi-satellites, it orbits the Sun in a 1:1 resonance with Earth, rather than Earth itself.
Literature
Petit's second moon was not accepted, but he continued to search explanations resulting another proposal 15 years later. The writer Jules VerneJules Verne
Jules Gabriel Verne was a French author who pioneered the science fiction genre. He is best known for his novels Twenty Thousand Leagues Under the Sea , A Journey to the Center of the Earth , and Around the World in Eighty Days...
learned of Petit's second proposals for a second moon theory. He became intrigued by the idea and made use of it in his 1865 novel, From the Earth to the Moon
From the Earth to the Moon
From the Earth to the Moon is a humorous science fantasy novel by Jules Verne and is one of the earliest entries in that genre. It tells the story of the president of a post-American Civil War gun club in Baltimore, his rival, a Philadelphia maker of armor, and a Frenchman, who build an enormous...
.
The explosive popularity of Verne's book in the 19th century triggered many amateur astronomers to search for second moons around Earth although Petit did not live to see this, having died in 1865. Samuel R. Delany
Samuel R. Delany
Samuel Ray Delany, Jr., also known as "Chip" is an American author, professor and literary critic. His work includes a number of novels, many in the science fiction genre, as well as memoir, criticism, and essays on sexuality and society.His science fiction novels include Babel-17, The Einstein...
's 1975 novel Dhalgren
Dhalgren
Dhalgren is a science fiction novel by Samuel R. Delany. The story begins with a cryptic passage:to wound the autumnal city.So howled out for the world to give him a name.The in-dark answered with wind....
features an Earth which mysteriously acquires a second moon. Eleanor Cameron
Eleanor Cameron
Eleanor Frances Butler Cameron was a Canadian children's author. Her first book was The Unheard Music, published in 1950.-Life:...
's Mushroom Planet novels for children (the first being The Wonderful Flight to the Mushroom Planet
The Wonderful Flight to the Mushroom Planet
The Wonderful Flight to the Mushroom Planet is a science fiction/fantasy children's novel written by Eleanor Cameron in 1954. It is set in a beach community in California, as well as on a tiny, habitable moon, "Basidium," in an invisible orbit 50,000 miles from Earth...
) are set on a tiny, habitable second moon called Basidium in an invisible orbit 50000 miles (80,467 km) from Earth.
See also
- List of hypothetical Solar System objects
- Lilith (hypothetical moon), second moon in astrology
- Counter-EarthCounter-EarthThe Counter-Earth is a hypothetical body of the Solar system first hypothesized by the presocratic philosopher Philolaus to support his non-geocentric cosmology, in which all objects in the universe revolve around a Central Fire...
Further reading
- Willy Ley: "Watchers of the Skies", The Viking Press NY,1963,1966,1969
- Carl Sagan, Ann Druyan: "Comet", Michael Joseph Ltd, 1985, ISBN 0-7181-2631-9
- Tom van Flandern: "Dark Matter, Missing Planets & New Comets. Paradoxes resolved, origins illuminated", North Atlantic Books 1993, ISBN 1-55643-155-4
- Joseph Ashbrook: "The Many Moons of Dr Waltemath", Sky and Telescope, Vol 28, Oct 1964, p 218, also on page 97-99 of "The Astronomical Scrapbook" by Joseph Ashbrook, Sky Publ. Corp. 1984, ISBN 0-933346-24-7
- Delphine Jay: "The Lilith Ephemeris", American Federation of Astrologers 1983, ISBN 0-86690-255-4
- 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", p 500-526 "Enigmatic objects"
- Clyde Tombaugh: Discoverer of Planet Pluto, David H. Levy, Sky Publishing Corporation, March 2006
- Richard Baum & William Sheehan: "In Search of Planet Vulcan" Plenum Press, New York, 1997 ISBN 0-306-45567-6 , QB605.2.B38