McCaughrean agrees. The improved measurement of these objects and their masses shows that science proceeds from an ongoing dialogue with data, he said, not from finished facts dropped down from ivory towers on stone tablets.

In recent years, astronomers have relied on a mass distinction proposed by the University of Arizona's Adam Burrows -- a planet is an object with a mass 1.3 percent or less than the Sun. But some astronomers, like McCaughrean, question that definition. Burrows used that figure because objects below that limit never burn deuterium -- a hydrogen isotope that briefly fuels brown dwarfs -- in their cores.

But deuterium burns so briefly in the life of a brown dwarf, McCaughrean says, that its activity shouldn't be used to distinguish free-floating objects that likely formed in the same way as stars.

The issue has become so complex that the International Astronomical Union (IAU) has convened a working group to set a standard definition for planets. Meanwhile, the public waits for an answer to the question of worlds and possibly life beyond Earth and our solar system.

Aizenman said he'll defer to the IAU's consensus, expected to come sometime in the next two years. But for him, a planet has to be orbiting a star. And its size is a criterion that he largely throws out the window.

"If you've got one object that's a star and another that's clearly orbiting it and not shining by its own internal nuclear fuel, I'd be tempted to call it a planet. Some would call it a brown dwarf. But I'd call it a planet."

The other concern is whether the object burns hydrogen, the mark of a star. Brown dwarfs burn deuterium for a relatively short time and do not emit much light.

"Of course once an object begins to shine by its own light, then you have a binary system of two stars orbiting one another," he said.