A hypothetical planet is a planet whose existence is not known, but
has been inferred from observational scientific evidence. Over the years a
number of hypothetical planets have been proposed, and many have been disproven.
However, even today there is scientific speculation about the possibility of
planets yet unknown that may exist beyond the range of our current knowledge.
Within our solar system
"Our solar system is by no means fully
mapped and charted. Much of its territory is still unknown"
Our solar system is by no means fully mapped and charted. Much of its
territory is still unknown, and many astronomers have hypothesized from indirect
observation that other substantial objects could still exist undetected in its
In the 19th century, the astronomer
Urbain Le Verrier, credited with the discovery of Neptune, attempted to
locate a hypothetical planet within the orbit of
Mercury that he believed was causing perturbations in its orbit. This
planet, which he named
Vulcan after the Roman god of the forge due to its closeness to the Sun, was
never observed, and
general relativity theory subsequently resolved the issue of Mercury's
However, a gravitationally stable region does exist between Mercury and the
Sun, and some astronomers, notably
contend that a field of small minor planets, the
Vulcanoids, should exist within it. However repeated observations of the
region have yet to yield any results, and the Vulcanoids, if they exist, must be
rather small and few in number.
Some conclude that the existence of the Vulcanoids is impossible, as any minor
planet within the orbit of Mercury would eventually be destabilised by the
Yarkovsky effect; motion by the force of its own heat.
In the early 20th century, astronomer
Percival Lowell's observation of apparent irregularities in the orbits of
him to conclude that a distant planet, which he called
must lie beyond them. The Lowell Observatory's long search for this planet
ultimately led to the discovery of
Pluto's mass was found to be too small to disturb the other planets' orbits
significantly, and subsequent measurements by the
spacecraft showed that earlier calculations of Neptune's mass had been in error,
leading to the irregularities observed.
few scientists accept Lowell's theory; however, a number of recent observations
have reopened the debate on the existence of a "Planet X", even if it would bear
little resemblance to that envisioned by Lowell.
- The Kuiper Belt has a very sharply defined edge. At around 49 AU, a sharp
dropoff occurs in the number of objects observed. This dropoff is known as the
"Kuiper Cliff", and as yet its cause is unknown. Some speculate that something
must exist beyond the belt large enough to sweep up the remaining debris,
perhaps as large as Earth or Mars. This view is still controversial, however.
Richard A. Muller has hypothesised that the Sun may be part of a
star system, with a distant companion named
Nemesis. Nemesis was proposed to explain some timing regularities of the
great extinctions of life on Earth. The hypothesis says that Nemesis creates
periodical perturbations in the
of comets surrounding the solar system, causing a "comet shower". Some of them
hit Earth, causing destruction of life. This hypothesis is no longer taken
seriously by most scientists, mostly because
surveys failed to spot any such object, which should have been very conspicuous
at those wavelengths.
John Murray of the
Open University and
John Matese of the
University of Louisiana at Lafayette believe that the motions of long-term
comets in the sky suggest the existence of a large, distant planet, or, more
likely, a small substellar companion such as a
dwarf, in the deep solar system. This hypothetical substellar object is not
Nemesis, since its existence is inferred from a different set of data; however
there is the possibility that both sets of data could be true for the same
Trojan to the Earth that, once its size grew to roughly that of
unstable in its orbit and collided with the Earth, transforming its crust and
upper mantle into a magma ocean, and ejecting massive amounts of light material
into orbit, which eventually coalesced into the
Moon. This theory
is known as the
giant impact hypothesis.
Planets between Mars and Jupiter
A planet situated between the orbits of
destruction supposedly led to the formation of asteroids and meteorites. One of
the first who believed that asteroids are the result of an exploded planet was
Wilhelm Olbers (1758–1840). The name "Phaeton" for this planet was chosen by
the Russian scientist, E. L. Krinov. Nowadays this hypothesis is disregarded by
is a hypothetical planet thought by
John Chambers and
Jack Lissauer to have once existed between
Mars and the
asteroid belt, based on computer simulations. The computer modeling findings
of Chambers and Lissauer were presented during the 33rd
Lunar and Planetary Science Conference, held March 11 thru 15, 2002, and
sponsored by NASA and the
Lunar and Planetary Institute.
Hypothetical extrasolar planets
PSR 1829-10's planet, proposed by
University of Manchester on
1991, was retracted
in 1992. A
combination of an inaccurate position for the pulsar and a timing model
Earth's orbit about the
Sun with a circle
yielded processed data resembling that which would have been expected from a
pulsar planet with an orbital period of half a year.
PSR 1257+12 D, the proposed fourth planet in the first extra solar
planetary system, was retracted due to further detection refinements. (It
has subsequently been replaced by a proposal for a comet)
- A microlensing event in 1996 of the gravitationally lensed
R. E. Schild in the A lobe of the double imaged quasar, has lead to a
controversial, and unconfirmable speculation that a 3 Earth mass planet is
possibly in the unknown lensing galaxy, between Earth and the quasar.