Mass is the prime attribute by which planets are distinguished from stars. No objects between the masses of the Sun and Jupiter exist in the Solar System; but there are exoplanets of this size. The lower stellar mass limit is estimated to be around 75 to 80 times that of Jupiter (M J). Some authors advocate that this be used as the upper limit for planethood, on the grounds that the internal physics of objects does not change between approximately one Saturn mass (beginning of significant self-compression) and the onset of hydrogen burning and becoming a red dwarf star. Beyond roughly 13 M J (at least for objects with solar-type isotopic abundance), an object achieves conditions suitable for nuclear fusion of deuterium : this has sometimes been advocated as a boundary, even though deuterium burning does not last very long and most brown dwarfs have long since finished burning their deuterium. This is not universally agreed upon: the exoplanets Encyclopaedia includes objects up to 60 M J, and the Exoplanet Data Explorer up to 24 M J.