Search for the Tenth Planet – December 1981 – Astronomy
Astronomers are readying telescopes to probe the outer reaches of our solar system for an elusive planet much larger than Earth. Its existence would explain a 160-year-old mystery. … The pull exerted by its gravity would account for a wobble in Uranus’ orbit that was first detected in 1821 by a French astronomer, Alexis Bouvard. Beyond Pluto, in the cold, dark regions of space, may lie an undiscovered tenth planet two to five times the size of Earth. Astronomers at the U.S. Naval Observatory (USNO) are using a powerful computer to identify the best target zones, and a telescopic search will follow soon after. … Van Flandern thinks the tenth planet may have between two and five Earth masses and lie 50 to 100 astronomical units from the Sun. (An astronomical unit is the mean distance between Earth and the Sun.) His team also presumes that, like Pluto’s, the plane of the undiscovered body’s orbit is tilted with respect to that of most other planets, and that its path around the Sun is highly elliptical.
Search for The 10th Planet – 1982-06-19 – New York Times
A pair of American spacecraft may help scientists detect what could be a 10th planet or a giant object billions of miles away, the national Aeronautics and Space Administration said Thursday. Scientists at the space agency’s Ames Research Center said the two spacecraft, Pioneer 10 and 11, which are already farther into space than any other man-made object, might add to knowledge of a mysterious object believed to be beyond the solar system’s outermost known planets. The space agency said that persistent irregularities in the orbits of Uranus and Neptune “suggest some kind of mystery object is really there” with its distance depending on what it is. If the mystery object is a new planet, it may lie five billion miles beyond the outer orbital ring of known planets, the space agency said. If it is a dark star type of objet, it may be 50 billion miles beyond the known planets; if it is a black hole, 100 billion miles. A black hole is a hypothetical body in space, believed to be a collapsed star so condensed that neither light nor matter can escape from its gravitational field.
Does the Sun Have a Dark Companion? – 1982-06-28 – Newsweek
When scientists noticed that Uranus wasn’t following its predicted orbit for example, they didn’t question their theories. Instead they blamed the anomalies on an as yet unseen planet and, sure enough, Neptune was discovered in 1846. Now astronomers are using the same strategy to explain quirks in the orbits of Uranus and Neptune. According to John Anderson of the Jet Propulsion Laboratory in Pasadena, Calif., this odd behavior suggests that the sun has an unseen companion, a dark star gravitationally bound to it but billions of miles away. … Other scientists suggest that the most likely cause of the orbital snags is a tenth planet 4 to 7 billion miles beyond Neptune. A companion star would tug the outer planets, not just Uranus and Neptune, says Thomas Van Flandern of the U.S Naval Observatory. And where he admits a tenth planet is possible, but argues that it would have to be so big – a least the size of Uranus – that it should have been discovered by now. To resolve the question, NASA is staying tuned to Pioneer 10 and 11, the planetary probes that are flying through the dim reaches of the solar system on opposite sides of the sun.
Searching for a 10th Planet – October 1982 – Astronomy
The hunt for new worlds hasn’t ended. Both Uranus and Neptune follow irregular paths that observers can explain only by assuming the presence of an unknown body whose gravity tugs at the two planets. Astronomers originally though Pluto might be the body perturbing its neighbors, but the combined mass of Pluto and its moon, Charon, is too small for such a role. … While astronomers believe that something is out there, they aren’t sure what it is. Three possibilities stand out: First, the object could be a planet – but any world large and close enough to affect the orbits of Uranus and Neptune should already have been spotted. Searchers might have missed the planet, though, if it’s unusually dark or has an odd orbit. (…)
NASA has been recording velocities for a year now and will continue for as long as necessary. This past spring, it appeared that budget cuts might force the end of the Pioneer project. The space agency now believes that it will have the money to continue mission operations. Next year, the JPL group will begin analyzing the data. By the time the Pioneer experiment shows results, an Earth-orbiting infrared telescope may have discovered the body. … Together, IRAS and the Pioneers will allow astronomers to mount a comprehensive search for new solar system members. The two deep space probes should detect bodies near enough to disturb their trajectories and the orbits or Uranus and Neptune. IRAS should detect any large body in or near the solar system. Within the next year or two, astronomers may discover not one new world, but several.
Clues Get Warm in the Search for Planet X! – 1983-01-30 – New York Times
By, John Noble Wilford
Something out there beyond the farthest reaches of the known solar system seems to be tugging at Uranus and Neptune. Some gravitational force keeps perturbing the two giant planets, causing irregularities in their orbits. The force suggests a presence far away and unseen, a large object that may be the long-sought Planet X.
Evidence assembled in recent years has led several groups of astronomers to renew the search for the 10th planet. They are devoting more time to visual observations with the 200-inch telescope at Mount Palomar in California. They are tracking two Pioneer spacecraft, now approaching the orbit of distant Pluto, to see if variations in their trajectories provide clues to the source of the mysterious force. And they are hoping that a satellite-borne telescope launched last week will detect heat “signatures” from the planet, or whatever it is out there.
The Infrared Astronomical Satellite was boosted into a 560-mile-high polar orbit Tuesday night from Vandenberg Air Force Base, CA. It represents an $80-million venture by the United States, Britain and the Netherlands. In the next six or seven months, the telescope is expected to conduct a wide-ranging survey of nearly all the sky, detecting sources not of ordinary light, but of infrared radiation, which is invisible to the human eye and largely absorbed by the atmosphere. Scientists thus hope that the new telescope will chart thousands or infrared-emitting objects that have gone undetected – stars, interstellar clouds, asteroids and, with any luck, the object that pulls at Uranus and Neptune.
The last time a serious search of the skies was made, it led to the discovery in 1930 of Pluto, the ninth planet. But the story begins more than a century before that, after the discovery of Uranus in 1781 by the English astronomer and musician William Herschel. Until then, the planetary system seemed to end with Saturn.
As astronomers observed Uranus, noting irregularities in its orbital path, many speculated that they were witnessing the gravitational pull of an unknown planet. So began the first planetary search based on astronomers’ predictions, which ended in the 1840’s with the discovery of Neptune almost simultaneously by English, French and German astronomers.
But Neptune was not massive enough to account entirely for the orbital behavior of Uranus. Indeed, Neptune itself seemed to be affected by a still more remote planet. In the late 19th century, two American astronomers, William H. Pickering and Percival Lowell, predicted the size and approximate location of the trans-Neptunian body, which Lowell called Planet X.
Years later, Pluto was detected by Clyde W. Tombaugh working at Lowell Observatory in Arizona. Several astronomers, however, suspected it might not be the Planet X of prediction. Subsequent observations proved them right. Pluto was too small to change the orbits of Uranus and Neptune; the combined mass of Pluto and its recently discovered satellite, Charon, is only one-fifth that of Earth’s moon.
Recent calculations by the United States Naval Observatory have confirmed the orbital perturbation exhibited by Uranus and Neptune, which Dr. Thomas C. Van Flandern, an astronomer at the observatory, says could be explained by “a single undiscovered planet.” He and a colleague, Dr. Robert Harrington, calculate that the 10th planet should be two to five times more massive than Earth and have a highly elliptical orbit that takes it some 5 billion miles beyond that of Pluto – hardly next-door but still within the gravitational influence of the Sun.
Some astronomers have reacted cautiously to the 10th-planet predictions. They remember the long, futile quest for the planet Vulcan inside the orbit of Mercury; Vulcan, it turned out, did not exist. They wonder why such a large object as a 10th planet escaped the exhaustive survey by Mr. Tombaugh, who is sure it is not in the two-thirds of the sky he examined. But according to Dr. Ray T. Reynolds of the Ames Research Center in Mountain View, CA, other astronomers “are so sure of the 10th planet, they think there’s nothing left but to name it.”
At a scientific meeting last summer, 10th-planet partisans tended to prevail. Alternative explanations for the outer-planet perturbations were offered. The something out there, some scientists said, might be an unseen black hole or neutron star passing through the Sun’s vicinity. Defenders of the 10th planet parried the suggestions. Material falling into the gravitational field of a black hole, the remains of a very massive star after its complete gravitational collapse, should give off detectable x-rays, they noted; no X-rays have been detected. A neutron star, a less massive star that has collapsed to a highly dense state, should affect the courses of comets, they said, yet no such changes have been observed.
More credence was given to the hypothesis that a “brown dwarf” star accounts for the mysterious force. This is the informal name astronomers give to celestial bodies that were not massive enough for their thermonuclear furnaces to ignite; perhaps like the huge planet Jupiter, they just missed being self-illuminating stars.
Most stars are paired, so it is not unreasonable to suggest that the Sun has a dim companion. Moreover, a brown dwarf in the neighborhood might not reflect enough light to be seen far away, said Dr. John Anderson of the Jet Propulsion Laboratory in Pasadena, CA. Its gravitational forces, however, should produce energy detectable by the Infrared Astronomical Satellite.
Whatever the mysterious force, be it a brown dwarf or a large planet, Dr. Anderson said he was “quite optimistic” that the infrared telescope might find it and that the Pioneer spacecraft could supply an estimate of the object’s mass. Of course, no one can be sure that even this discovery would define the outermost boundary of the solar system.
Planet X – Is It Really Out There? – 1984-09-10 – US News World Report
Shrouded from the sun’s light, mysteriously tugging at the orbits of Uranus and Neptune, is an unseen force that astronomers suspect may be PLanet X — a 10th resident of the Earth’s celestial neighborhood.
Last year, the infrared astronomical satellite (IRAS), circling in a polar orbit 560 miles from the Earth, detected heat from an object about 50 billion miles away that is now the subject of intense speculation.
“All I can say is that we don’t know what it is yet,” says Gerry Neugenbaur, director of the Palomar Observatory for the California Instititute of Technology. Scientists are hopeful that the one-way journeys of the Pioneer 10 and 11 space probes may help to locate the nameless body.
Some astronomers say the heat-emitting object is an unseen collapsed star or possibly a “brown dwarf” — a protostar that never got hot enough to become a star. However, a growing number of astronomers insist that the object is a dar, gaseous mass that is slowly evolving into a planet.
For decades, astromers have noted that the orbits of two huge, distant planets — Neptune and Uranus —deviate slightly from what they should be according to the laws of physics. Gravitational pull from Planet X would explain that deviation.
Morever, says Neugebaur, “if we can show that our own solar system is still creating planets, we’ll know that it’s happening around other stars, too.”
NASA Press Release – 1982
Unexplained deviations in the orbits of Uranus and Neptune point to a large outer solar system body of 4 to 8 Earth masses, on a highly tilted orbit, beyond 7 billion miles from the sun.