Earth-Size Planet to Be Found in Outer Solar System?

Julian Ryall
for National Geographic News
March 17, 2008

A planet roughly the size of Earth could be tracing a vast, elliptical orbit at the outer edge of our solar system—and astronomers in Japan think they know where to find it.

The presence of this unnamed body has been suggested before, noted Tadashi Mukai, a professor at Kobe University's department of earth and planetary sciences.

"We have been able to identify more than 1,100 objects beyond Neptune since 1992, and a huge number of objects are showing large orbital eccentricities and elliptical orbits," Mukai said.

This suggests that a body with sizeable mass must be influencing the movement of these objects by exerting a gravitational pull.

But the extreme distance and unusual orbit of the elusive "Planet X" have made it difficult to spot even with the most advanced telescopes.

In a paper appearing in an upcoming issue of the Astronomical Journal, Mukai and colleagues propose that other researchers have simply been looking in the wrong place.

"We have reached our conclusions from simulations that explain the orbital elements," Mukai said.

"We are now looking in places that we have not looked before, and I think we will be able to see the planet within the next five or ten years."

Big, But Light

The eight known planets in our solar system are on very similar elliptical orbits and are all almost within the ecliptic plane, the geometric plane that roughly describes Earth's orbit around the sun.

"Most surveys [looking for Planet X] are concentrated toward the ecliptic plane, since that is where most solar system objects concentrate," said Mark Sykes, director of the Planetary Science Institute in Tucson, Arizona.

The new models, however, suggest that Planet X is circling the sun on a 20 to 40 degree angle relative to the ecliptic plane.

Continued on Next Page >>


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