Star‐like activity from a very young ‘isolated planet’

The discovery of isolated bodies of planetary mass has challenged the paradigm that planets form only as companions to stars. To determine whether ‘isolated planets’, brown dwarfs and stars can have a common origin, we have made deep submillimetre observations of part of the ρ Oph B star formation region. Spectroscopy of the 9‐Jupiter‐mass core Oph B‐11 has revealed carbon monoxide line wings such as those of a protostar. Moreover, the estimated mass of outflowing gas lies on the force versus core‐mass relation for protostars and protobrown dwarfs. This is evidence for a common process that can form any object between planetary and stellar masses in a molecular cloud. In a submillimetre continuum map, six compact cores in ρ Oph B were found to have masses presently below the deuterium‐burning limit, extending the core mass function down to 0.01 M ⊙ with the approximate form d N /d M ∝ M −3/2 . If these lowest‐mass cores are not transient and can collapse under gravity, then isolated planets should be very common in ρ Oph in the future, as is the case in the Orion star formation region. In fact, the isolated planetary objects that may form from these cores would outnumber the massive planets that have been found as companions to stars.