What Is a Planet?

Abstract

Cool objects found in young star clusters in Orion and Perseus, such as those reported by M. R. Zapatero Osorio and colleagues in their research article (6 Oct., p. 103), have been described variously as "planetary mass objects," "isolated giant planets," "free-floating planets," and "superplanets" (1). The word "planet" has been invoked because the masses of these objects are apparently only about 5 to 10 times that of Jupiter. However, even if those masses are confirmed, we maintain that such bodies are better thought of as low-mass brown dwarfs, as they are not in orbit around stars.

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