A local astronomer is part of a team that announced this week that a mysterious object 170 light-years distant may have formed from the collision and merger of two developing giant planets.

The object, 2M1207B, has puzzled astronomers because its existence seems to defy physical possibility. Its temperature, luminosity, age and location do not match any theory.

"This is a strange enough object that it needs a strange explanation," said Eric Mamajek of the Harvard-Smithsonian Center for Astrophysics.

Mr. Mamajek, a Bethel Park High School and Penn State University graduate, and colleague Mike Meyer of the University of Arizona, revealed their findings Wednesday at the 211th meeting of the American Astronomical Society in Austin, Texas.

They believe 2M1207B formed when two giant protoplanets impacted then fused, creating a larger world still sizzling from the heat caused by the kinetic energy in the titanic collision.

2M1207B orbits a brown dwarf (an object with a mass below that necessary to maintain nuclear fusion in its core needed to become a star) in the southern constellation Centaurus. Because the brown dwarf is believed to be fairly young at 8 million years old, its companion also should be about that age. But 2M1207B is almost twice as hot as it should be for its age, measuring about 2,400 degrees Fahrenheit. The astronomers believe that excess heat is because of a protoplantary collision.

"Essentially the luminosity of the object is about 1/50,000th that of the sun, and we have an estimate of the temperature," Mr. Mamajek said. "You can turn that into estimating the size of the object. Once you estimate the size of the object and you have some idea of plausible planetary densities, you get a mass. The estimate of the mass you get is very small; it's probably smaller than Saturn.

"But the problem is: How do you make it hot? That's where the planetary collision mechanism comes in. This object, if it was a normal Saturn-sized object, should be much dimmer and much cooler. The only plausible mechanism we found that can explain how much heat this object is giving off is that [it collided] with a smaller body, perhaps somewhere between the mass of Earth and Neptune."

As it turns out, planetary collisions are not that uncommon. The moon is believed to have formed when the young Earth was impacted by a Mars-sized object.

"Venus is spinning backwards and Uranus is spinning on its side," Mr. Mamajek said. "Simulations suggest that the best way to produce that seems to be through the impact of smaller protoplanets.

"Young planets colliding is probably a very natural process. What we're proposing is this might be the first observational signatures of this around another star."

"We could be seeing the aftermath of a collision between a 72 Earth-mass gas giant and an eight Earth-mass planet," Mr. Meyer said of the objects, significantly more massive than our world.

Mr. Mamajek said time also supports the collision theory. If the object was older, it would have had time to radiate away its heat. Since the system is young, the chances are much better to observe it shortly after the collision while the hot aftermath is detectable.

At least one other theory, suggesting 2M1207B is obscured by a disk of dust, has been put forth by a few other astronomers to explain its oddities. Mr. Mamajek said all explanations need to be tested.

"This object is so weird, one way or another we're going to learn something very interesting about star and planet formation."