gas in orbit around the young star, and thus should have cores of silicates or ices. As yet it is uncertain whether gas giants possess such cores, though the Juno mission to Jupiter could resolve the issue. If it is indeed possible that a gas giant could form as a star does, then it raises the question of whether such an object should be considered an orbiting low-mass star rather than a planet. Traditionally, the defining characteristic for starhood has been an object's ability to fuse hydrogen in its core. However, stars such as brown dwarfs have always challenged that distinction. Too small to commence sustained hydrogen-1 fusion, they have been granted star status on their ability to fuse deuterium. However, due to the relative rarity of that isotope, this process lasts only a tiny fraction of the star's lifetime, and hence most brown dwarfs would have ceased fusion long before their discovery. Binary stars and other multiple-star formations are common, and many brown dwarfs orbit other stars. Therefore, since they do not produce energy through fusion, they could be described as planets. Indeed, astronomer Adam Burrows of the University of Arizona claims that "from the theoretical perspective, however different their modes of formation, extrasolar giant planets and brown dwarfs are essentially the same". Burrows also claims that such stellar remnants as white dwarfs should not be considered stars, a stance which would mean that an orbiting white dwarf, such as Sirius B, could be considered a planet. However, the current convention among astronomers is that any object massive enough to have possessed the capability to sustain atomic fusion during its lifetime and that is not a black hole should be considered a star. The confusion does not end with brown dwarfs. María Rosa Zapatero Osorio et al. have discovered many objects in young star clusters of masses below that required to sustain fusion of any sort (currently calculated to be roughly 13 Jupiter masses). These have been described as "free floating planets" because current theories of Solar System formation suggest that planets may be ejected from their star systems altogether if their orbits become unstable. However, it is also possible that these "free floating planets" could have formed in the same manner as stars. In 2003, a working group of the IAU released a position statement to establish a working definition as to what constitutes an extrasolar planet and