P.S. space.com article 16 March 2004 concerning Sedna's odd elliptical orbit. Just below here are my words, including some quotes:
Two main astronomers willing to accept and the possibility of an earth or larger-sized planet affecting Sedna's elliptical orbit and rotation:
"Brown astronomer at California Institute of Technology who led the discovery of Sedna," and
"Marsden, who heads the Minor Planet Center in Cambridge, Mass., where newfound solar system bodies are catalogued."
Just to clarify: in the following article, in this latter portion of Brown's statements, he is saying his team is [considering searching an unexplored area of the sky, for an earth -sized planet.] Below this section on Brown, see Marsden.
"Brown, astronomer at California Institute of Technology who led the discovery of Sedna, said there is one unexplored region of space left, amounting to about 20 percent of the sky, that hasn't been searched for an Earth-sized object that would be orbiting at 70 AU and presumably in the main plane of the solar system. It is the region toward the bright galactic center, which is harder to search.
Brown said his team is considering making that search now."

"Marsden, who heads the Minor Planet Center in Cambridge, Mass., where newfound solar system bodies are catalogued.
Marsden favors an object closer in, a "planetary object," he told SPACE.com , perhaps at between 400 and 1,000 AU."

"Perhaps there's more than one planet out there," Marsden said. "Who knows? But let's suppose it is something of an Earth mass, maybe even a few Earth masses. A close approach could throw this object [Sedna] from something more circular into something more eccentric."

http://www.space.com/scienceastronom...th_040316.html

from planetbarb, most of the space.com article is copied below:

copyrighted material deleted by The Bad Astronomer