The Missing Planet

Is there a yet-undiscovered planet in our solar system slowly circling the Sun that has remained elusive to astronomers on Earth? Evidence for its existence was first detected in 1821 by a French astronomer, Alexis Bouvard. He noticed that the observed position of Uranus, discovered only 40 years earlier, did not agree with its calculated orbit. The planet was being perturbed, or pulled slightly off course, by the gravitational attraction of an outer planet. Working independently, an Englishman, John Couch Adams, and U.J.J. Leverrier of France used the discrepancy to calculate the theoretical position of an eighth planet, Neptune, which was finally spotted in 1846 by John Galle of the Berlin Observatory. But the mass of the new planet did not fully account for the distortion of Uranus' orbit, and so a search was begun for a ninth planet. Pluto was discovered by Clyde Tombaugh, working with photographic methods, on February 18, 1930.

However, tiny Pluto is 100 to 1,000 times too small to fully account for Uranus' wobble, according to Thomas Van Flandern of the U.S. Naval Observatory. A brief flurry of excitement followed Charles Kowal's 1977 discovery of the planet Chiron, orbiting between Saturn and Uranus, until it was determined that it was too minute to be planet 10. Van Flandern noted at the time that the search for the planet "Vulcan," once proposed to account for Mercury's strange orbit, ended when Einsteinian physics revealed that the distortion of space caused by the Sun's huge mass created the irregularity. Another unexpected change in physical law is possible, he said, but "our best bet is for a tenth planet out there."


How to find it? First make a few educated guesses about position and mass. Some astronomers think the tenth planet may be 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.) Like Pluto, the plane of the undiscovered body's orbit is likely to be tilted with respect to that of most other planets and its path around the Sun probably highly elliptical. Could it support life? Probably not as we would know it, Jim.