Planet X

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This article is about the astronomical hypothesis. For the "Planet X" 2003 \ 2012 doomsday scare, see ZetaTalk. For other uses, see Planet X (disambiguation).

In astronomy, Planet X is a large hypothetical planet beyond Neptune. It was postulated to explain apparent discrepancies in the orbits of the gas giants, especially those of Uranus and Neptune. Those discrepancies were resolved by measurements made in the 1980s.[1]

The "X" in the name represents an unknown and is pronounced as the letter, as opposed to the Roman numeral for ten. At the time of its conception there were eight known planets in the solar system; it was accordingly counted as a "ninth planet" in its initial decades, and then as a "tenth planet" from 1930 until the theory's demise in the early 1990s, and it is now generally accepted in the astronomical community that Planet X, as originally envisioned, doesn't exist.

Although Pluto was discovered as a result of the search for Planet X, it is not considered Planet X. Neither is Eris, even though it was at one point considered for reclassification as a planet under a proposal outlined by the International Astronomical Union (see 2006 definition of planet). In popular culture, "Planet X" has become a stand-in term for an undiscovered planet in the solar system. The term has also been appropriated by pseudoscientific theorists such as Nancy Lieder and Marshall Masters.

Contents

[edit] Origin of the discrepancy

See also: Discovery of Neptune

At the beginning of the 20th century, many astronomers speculated about the existence of a planet beyond Neptune. Neptune had been discovered via calculations of the mathematicians John Couch Adams and Urbain Le Verrier to explain discrepancies between the calculated and observed orbits of Uranus, Saturn, and Jupiter.

After the discovery of Neptune, however, there still were some slight discrepancies in those orbits, and also in the orbit of Neptune itself. These were taken to indicate the existence of yet another planet orbiting beyond Neptune.

In 1905, Percival Lowell, a wealthy Bostonian who had founded the Lowell Observatory in Flagstaff, Arizona in 1894, started an extensive project in search of a possible ninth planet, which he termed "Planet X".[2] Lowell's hope in tracking down Planet X was to establish his scientific credibility, which had been dented by his widely derided belief that channel-like features visible on the surface of Mars were in fact canals constructed by an intelligent civilization.[3] He performed two searches for it without success, the first ending in 1909, and after revising his prediction for where it should be found, the second from 1913 to 1915, after which Lowell published his mathematical hypothesis of the parameters for Planet X. Ironically, at his observatory that year, two faint images of Pluto were recorded, but were not recognized at the time.[4]

[edit] Discovery of Pluto

Main article: Pluto

Lowell and his observatory conducted his search from 1905 until his death in 1916, but to no avail. Lowell's disappointment at not locating Planet X, according to one friend, "virtually killed him".[5]

Constance Lowell, Percival Lowell's widow, subsequently embroiled the observatory in a decade-long legal battle to secure the observatory's million-dollar portion of Lowell's legacy for herself, which meant that its search for Planet X could not resume until 1929.[6] In that year, the observatory's director, Vesto Melvin Slipher, summarily handed the job of locating Planet X to Clyde Tombaugh, a 22-year-old Kansas farm boy who had only just arrived at the Lowell Observatory after Slipher had been impressed by a sample of his astronomical drawings.[6]

Discovery photographs of Pluto
Discovery photographs of Pluto

Tombaugh's task was systematically to image the night sky in pairs of photographs taken two weeks apart, then examine each pair and determine whether any objects had shifted position. Using a machine called a blink comparator, he rapidly shifted back and forth between views of each of the plates, to create the illusion of movement of any objects that had changed position or appearance between photographs. On February 18, 1930, after nearly a year of searching, Tombaugh discovered a possible moving object on photographic plates taken on January 23 and January 29 of that year. A lesser-quality photograph taken on January 20 helped confirm the movement. Upon confirmation, Tombaugh walked into Slipher's office and declared, "Doctor Slipher, I have found your Planet X."[7] After the observatory obtained further confirmatory photographs, news of the discovery was telegraphed to the Harvard College Observatory on March 13, 1930. The new object would later be found on photographs dating back to March 19, 1915.[8]

Once found, Pluto's faintness and lack of a resolvable disc cast doubt on the idea that it could be Lowell's Planet X. Throughout the mid-20th century, estimates of Pluto's mass were often revised downward. In 1978, the discovery of Pluto's moon Charon allowed the measurement of Pluto's mass for the first time. Its mass, roughly 0.2 percent that of the Earth, was far too small to account for the discrepancies in Uranus.

[edit] Further searches for Planet(s) X

See also: Hypothetical trans-Neptunian planets

After discovering Pluto, Tombaugh continued to search the ecliptic for other distant planets. He found asteroids, variable stars, and even a comet, but no more planets.

In the 1980s and 1990s, astronomer Robert Sutton Harrington of the US Naval Observatory, who had first calculated that Pluto was too small to have perturbed the orbits of Uranus and Neptune, led a search to determine the real cause of the planets' apparently irregular orbits.[9] He calculated that any Planet X would be at roughly three times the distance from the sun of Neptune's orbit, highly elliptical, and far below the ecliptic (the planet's orbit would be at roughly a 90-degree angle from the orbital plane of the other known planets).[10] This hypothesis was met with a mixed reception. Noted Planet X skeptic Brian Marsden of Harvard University's Minor Planet Center has pointed out that these discrepancies are a hundred times smaller than those noticed by Adams and Le Verrier, and could easily be due to observational error.[9]

In 1972, Joseph Brady of the Lawrence Livermore National Laboratory studied irregularities in the motion of Halley's Comet. Brady claimed that they could have been caused by a Jupiter-sized planet beyond Neptune that orbited the Sun backward. However, both Marsden and Planet X proponent P. Kenneth Seidelmann attacked the hypothesis, showing that Halley's Comet jetted randomly and irregularly, causing changes to its own orbital trajectory, and that such a massive object as Brady's Planet X would have severely affected the orbits of the outer planets.[9]

While its mission did not involve a search for "Planet X", the IRAS space observatory made headlines briefly in 1983 due to an "unknown object" that was at first described as "possibly as large as the giant planet Jupiter and possibly so close to Earth that it would be part of this solar system."[11][12] However, further analysis revealed that of several unidentified objects, nine were distant galaxies and the tenth was "intergalactic cirrus".[13] None were found to be Solar System bodies.[13]

[edit] Kuiper belt

After Pluto and Charon (discovered in 1978), no more trans-Neptunian objects were found until the discovery of (15760) 1992 QB1 in 1992. Since that time, hundreds of trans-Neptunian objects have been discovered. The objects are now recognized as mostly belonging to the Kuiper belt: a swarm of icy bodies orbiting in the ecliptic plane beyond Neptune, which are left over from the formation of the Solar System.

In 2005, astronomer Mike Brown and his team announced the discovery of 2003 UB313 (later named Eris),[14] a trans-Neptunian object larger than Pluto. Soon after the announcement, NASA's Jet Propulsion Laboratory put out a press release describing the object as the "tenth planet";[15] however, its status was not decided until the following year, when the IAU created a separate category for it and similar objects, "dwarf planet".[16] Pluto itself is now recognized as being a member of the Kuiper belt, and the second largest dwarf planet after Eris. Pluto lost its status as a planet in 2006 because it failed to meet the new IAU definition of a planet, which would require it to have cleared the neighbourhood around its orbit. Regardless of whether or not Eris is a planet, it is not and never was Planet X, as it is far too small to have affected the orbits of the outer planets in any way.[17]

[edit] Planet X disproved

Harrington died in 1993, having never found Planet X.[9] That same year, Myles Standish used data from Voyager 2's 1989 flyby of Neptune, which had revised the planet's total mass downward by 0.5 percent (an amount comparable to the mass of Mars),[18] to recalculate its gravitational effect on Uranus.[19] When the newly determined mass was used in the Jet Propulsion Laboratory Developmental Ephemeris (JPL DE), the supposed discrepancies in its orbit vanished.[1]

Also, to date there are no discrepancies in the trajectories of any space probes (Pioneer 10, Pioneer 11, Voyager 1 and Voyager 2) that can be attributed to the gravitational pull of a large undiscovered object in the outer solar system.[20]

Today the overwhelming consensus among astronomers is that Planet X, as Lowell defined it, does not exist. Lowell had made a prediction of Planet X's position in 1915 that was fairly close to Pluto's actual position at that time; however, Ernest W. Brown concluded almost immediately that this was a coincidence, a view still held today.[21]

[edit] Planet X revived

See also: The "Kuiper cliff"

The search for Planet X may not be over yet. The Kuiper Belt terminates suddenly at a distance of 55 AU from the Sun, and there is some speculation this sudden dropoff may be caused by the presence of an object with a mass between that of Mars and Earth located beyond 55 AU. Patryk Lykawka, astronomer at Kobe University, Japan, claims that we will discern this object's existence or lack thereof by 2013.[22] Lykawka's computer simulations suggest that a body roughly the size of Earth, ejected outward by Neptune early in the Solar System's formation and currently set in elongated orbit between 80 and 170 AU from the Sun, could explain not only the Kuiper cliff but also the peculiar "detached" TNOs such as 90377 Sedna. While some astronomers have cautiously supported Lykawka's claims, others have dismissed them as contrived.[22]

An alternative theory, proposed in 1999 by John Murray of the Open University and John Matese, Patrick Whitman and Daniel Whitmire of the University of Louisiana at Lafayette, has long period comets originating from specific regions of the sky, rather than coming from random directions as proposed by Oort. This would result from comets being disturbed by an unseen object at least as large as Jupiter, and possibly a brown dwarf.[23]

[edit] See also

[edit] External links

[edit] References

  1. ^ a b The Neptune File: A Story of Astronomical Rivalry and the Pioneers of Planet Hunting, by Tom Standage, pg. 188
  2. ^ J. Rao (11 March 2005). Finding Pluto: Tough Task, Even 75 Years Later. SPACE.com. Retrieved on 2006-09-08.
  3. ^ Croswell p. 48
  4. ^ Planets Beyond: Discovering the Outer Solar System, by Mark Littman, 1990, pg. 70
  5. ^ Ken Croswell (1997). Planet Quest: The Epic Discovery of Alien Solar Systems. The Free Press, 49. 
  6. ^ a b Croswell, p. 50
  7. ^ Croswell p. 52
  8. ^ W. G. Hoyt (1976). "W. H. Pickering's Planetary Predictions and the Discovery of Pluto". Isis 67 (4): 551–564.. doi:10.1086/351668. 
  9. ^ a b c d Croswell pp. 56-71
  10. ^ P. K. Seidelmann and R. S. Harrington (1987). Planet X — The current status. U. S. Naval Observatory. Retrieved on 2007-11-04.
  11. ^ Thomas O'Toole. "Mystery Heavenly Body Discovered", Washington Post, 30 December 1983, p. A1. Retrieved on 2008-01-28. 
  12. ^ Thomas O'Toole. "Mystery Heavenly Body Discovered", Washington Post, 30 December 1983, p. A1. Retrieved on 2008-01-28. 
  13. ^ a b Thomas J. Chester. No Tenth Planet Yet From IRAS. Thomas J. Chester (CalTech). Retrieved on 2008-01-28.
  14. ^ Central Bureau for Astronomical Telegrams, International Astronomical Union (2006). Circular No. 8747. Retrieved on 2007-02-23.
  15. ^ NASA-Funded Scientists Discover Tenth Planet. Jet Propulsion Laboratory (2005). Retrieved on 2007-02-22.
  16. ^ Planet Definition. IAU (2006). Retrieved on 2006-08-14.
  17. ^ David Jewitt (2006). David Jewitt:Planet X. University of Hawaii. Retrieved on 2008-05-21.
  18. ^ Croswell, pg. 66
  19. ^ Ken Croswell (1993). Hopes Fade in hunt for Planet X. Retrieved on 2007-11-04.
  20. ^ Littmann, pg. 204
  21. ^ History I: The Lowell Observatory in 20th century Astronomy. The Astronomical Society of the Pacific (1994-06-28). Retrieved on 2006-03-05.
  22. ^ a b Govert Schilling (2008). The mystery of Planet X. New Scientist. Retrieved on 2008-02-08.
  23. ^ SETH BORENSTEIN (1999). A 10th planet may be out there or new object could be the sun's long-lost twin, astronomers say. Huston Chronicle. Retrieved on 2007-04-01.
  • P. K. Seidelmann, R. S. Harrington (1987). "Planet X - The current status". Journa Celestial Mechanics and Dynamical Astronomy 43 (1-4): 55-68. doi:10.1007/BF01234554. 
  • D. P. Whitmire, J. J. Matese (1985). "Periodic comet showers and planet X". Nature 313: 36 - 38. doi:10.1038/313036a0. 
  • G. D. Quinlan (1985). "Planet X: a myth exposed". Nature 363: 18 - 19. doi:10.1038/363018b0. 
  • xfacts.com