200-Year Mystery : Planet X, Are You Out There? Most Think So
Two spacecraft gliding through the outer reaches of the solar system have been unable to resolve a mystery that has bedeviled scientists for two centuries, but some scientists believe that failure supports evidence that the sun has a 10th planet.
If they are right, Planet X, as it has been called for decades, orbits the sun far beyond Pluto.
No one has ever seen Planet X, even though thousands of telescopes have been turned toward the heavens in the last four centuries. And if it exists, it has eluded the search of many who believe the peculiar orbits of two other planets justify the search.
Some are convinced that the existence of Planet X best explains why Neptune and Uranus are not in the orbits that historical records indicate they should be.
John D. Anderson, a senior scientist at the Jet Propulsion Laboratory in the hills above Pasadena, and fellow JPL scientist E. Myles Standish Jr. thought they had a chance to resolve the controversy through an imaginative experiment with Pioneers 10 and 11, two aging spacecraft that the National Aeronautics and Space Administration launched in 1972 and 1973 to explore the most distant regions of the solar system.
They had hoped that the tiny spacecraft would pinpoint a weak gravitational force that some scientists believe changed the courses of Neptune and Uranus during the 18th and 19th centuries. The Pioneer spacecraft, which are stabilized only on one axis by spinning, are far more sensitive to gravitational influences than most other spacecraft that rely on tiny thrusters to maintain their orientation, Anderson said.
Should Have Affected the Spacecraft
If whatever pulled Neptune and Uranus off their courses was a distant star, as some have postulated, then its faint gravity should have affected the sensitive spacecraft as well.
“We looked at it for four years,” Anderson said, “and we didn’t see anything.”
That has led both scientists to conclude that whatever disturbed Neptune and Uranus is no longer in the area. And that, the two suggest, means it most likely passed near the planets in the 1700s or 1800s but is now too far away to influence their orbits.
The best candidate, they believe, is Planet X, which would be in an orbit even more eccentric than that of Pluto, the only planet known to travel far above and below the flat disk in which the other eight planets orbit the sun. Planet X would move in an orbit so large that it would circle the sun only once every 700 to 1,000 years.
If the theory seems farfetched, it is worth noting that both Neptune and Pluto were discovered because disturbances in the orbits of other planets betrayed their hiding places.
The mystery of Planet X has its roots in ancient astronomy, when the earliest astronomers charted the apparent movement of objects across the sky. In those days it was obvious that some objects, when viewed for a long period, moved quite differently than others, even appearing to wander back and forth as they made their way across the sky.
The Greeks called the objects planetai, which means “wandering stars.” In English, they are called planets, and they appear to wander because they are viewed from different positions as the planets and the Earth revolve around the sun.
The pioneering astronomers charted the skies with such precision that men like Galileo, Kepler and Newton were able to determine the basic laws of physics that govern the universe. Some of the earliest observations are still vital to scientists who are trying to study a universe in which subtle changes are acted out over hundreds--and sometimes millions--of years.
Those records are so complete and reliable that scientists today, who are just beginning to understand such spectacular exhibitions as exploding stars, have been able to match the debris they see through their sophisticated telescopes with primitive observations of the explosions hundreds of years ago.
Early astronomers found that they could plot the course of the “wandering stars” as they moved across the heavens, even if they did not understand why the stars wandered. Others found they could predict the course of comets, the most famous being Edmond Halley, whose comet bears his name.
But in the 18th and 19th centuries, the outer planets, especially Uranus, were found to be veering from their orbits, leading some scientists to conclude that some other object--probably another planet--was tugging on them. Planets, just like all other objects in the universe, attract each other gravitationally in proportion to their mass and distance. When they are close enough together, their orbits are altered slightly by the mutual attraction.
Neptune Discovered
On Sept. 23, 1846, scientists in England who were looking where they thought a planet might be found, discovered Neptune.
That did not resolve the problem, however.
The newly discovered planet, like Uranus, moved across the sky in such a way as to indicate the existence of yet another planet.
On Feb. 18, 1930, a young astronomer named Clyde W. Tombaugh, using a new telescope at the Lowell Observatory in Arizona, thought he had found what some had already labeled Planet X. Tombaugh had indeed found a new planet, Pluto, but the discovery was largely accidental because Pluto’s highly eccentric orbit just happened to carry it though the area Tombaugh was searching.
At first it appeared that the search for Planet X had ended. But over the years scientists learned that Pluto was far too small to have accounted for the peculiar orbits of the far larger planets of Neptune and Uranus.
But about that time a strange thing happened, Anderson said during an interview at JPL.
Neptune and Uranus started behaving themselves.
No Unexplained Variations
Since about 1910, Anderson said, scientists have not observed any unexplained variations in the orbits of the outer planets, although they had expected the deviations to continue. The problem does not go away, however, just because everything seems to be fine now, he added.
“It’s when you try to fit 200 years on a single orbit that you run into trouble,” he said. “Over a 200-year period, you get certain trends. The orbit begins to drift off.”
Thus the planets are simply not following the orbits they should today if astronomical data from the last century is taken into account, he added.
Anderson said that he has studied the older data extensively, and he is convinced the problem does not lie in the quality of the material. “We can’t find any flaws,” he said. “There are no systematic biases.”
The data include the same material that led to the discovery of Neptune.
Continuing Puzzle
Many other scientists have puzzled over the orbiting peculiarities of Neptune and Uranus, especially at the U.S. Naval Observatory in Washington, where experts try to keep track of celestial objects because of their importance to navigation. Scientists there have searched for years for Planet X.
Given the advanced state of astronomy today, it might seem preposterous that a 10th planet could have escaped detection. But Anderson said there are good reasons why no one has been able to find it.
For one thing, no one knows where to look. And if there is a 10th planet, its orbit would be so large and it would be so far away that it would look like just another dim star. And its movement would be so slow that it would not be detected except through a “blink comparison” in which images taken at different times are viewed in rapid succession so that a change in the position of any star would reveal it as a wanderer.
That kind of systematic search could take many years, since no one knows where to begin.
