Dr. Patryk Sofia Lykawka and Prof. MUKAI Tadashi of Kobe University have conducted a theoretical work on the origin and dynamical evolution of Trans-Neptunian objects (TNOs). The results strongly suggest the presence of a yet unknown massive planet in the Solar System. With the upcoming future sky surveys, we can expect the planet to be found within 5-10 years.
The first TNO was discovered in 1992 orbiting in a region known as the Edgeworth-Kuiper belt, located beyond Neptune's orbit. Today, more than 1,000 TNOs have been found. Surprisingly, several TNOs possess unusually large eccentricities and/or high orbital inclinations, which are larger than that expected from standard theory of planetary system formation. The Edgeworth-Kuiper belt has also revealed other intriguing features. Based on numerical simulations of the orbital evolution of TNOs during the last 4.5 billion years, Dr. Lykawka and Prof. MUKAI have shown that a hypothetical planet in a distant orbit beyond Neptune, so-called Planet X, could explain the origin of the complex orbital structure of TNOs, including those objects in peculiar orbits.
Planet X should have a perihelion distance of at least 80 AU (1 AU is approximately the mean distance between the Earth and the Sun), a semimajor axis of 100-175 AU, and an orbital inclination of 20-40°. The planet would take 1,000-2,300 years to complete an orbit around the Sun. Furthermore, the mass of Planet X is estimated at 0.3-0.7 times the Earth's mass. If Planet X is near perihelion approach at a distance of about 80 AU, it could appear as bright as Pluto, with an apparent 14.8-17.3 magnitude. Worth noting, under these circumstances the planet would be detectable by future dedicated surveys. The planet's diameter would be 10,000-16,000 km, which is comparable to the size of the Earth. In summary, having the physical and orbital characteristics described above, Planet X would very probably fulfill the conditions of the IAU planet definition, and thus it would be considered a new planet in the solar system.
(The results of this research will appear in the Astronomical Journal, April issue, 2008.)
Please, visit the Center for Planetary Science website for more details: http://www.org.kobe-u.ac.jp/cps/index.html