Alex Wolszczan of Penn State and Maciej Konacki of Caltech announced the discovery of the smallest planet detected outside our solar system.  The new body is located in the same planetary system where Wolszczan found the very first extrasolar planets in 1992.
The planet, approximately one-fifth the mass of Pluto, orbits the pulsar PSR B1257+12, 1500 light years from Earth.  "Despite the extreme conditions that must have existed at the time these planets were forming, nature has managed to create a planetary system that looks like a scaled-down copy of our own inner solar system," Wolszczan said.
Three terrestrial planets discovered earlier occupy orbits similar in proportion to the orbits of Mercury, Venus, and Earth.  The new fourth planet is in an orbit six times larger than the third planet's position, corresponding to our own asteroid belt.
"Surprisingly, the planetary system around this pulsar resembles our own solar system more than any extrasolar planetary system discovered around a Sun-like star," Konacki said.
"Because our observations practically rule out a possible presence of an even more distant, massive planet or planets around the pulsar, it is quite possible that the tiny fourth planet is the largest member of a cloud of interplanetary debris at the outer edge of the pulsar's planetary system, a remnant of the original protoplanetary disk that created the three inner planets," Wolszczan explained.
Since the original discovery of planets in 1992, Wolszczan and colleagues, using the 
Arecibo radio telescope in Puerto Rico, ". . . feel now, with this discovery, that the basic inventory of this planetary system has been completed."
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Tiny planet discovered in mini solar system