Free-floating planetary mass objects -worlds that roam interstellar space untethered to a parent star-challenge conventional notions of planetary formation and migration, but also of star and brown dwarf formation. We focus on the multiplicity among free-floating planets. By virtue of their low binding energy (compared to other objects formed in these environments), these low-mass substellar binaries represent a most sensitive probe of the mechanisms at play during the star formation process. We use the Hubble Space Telescope and its Wide Field Camera 3 and the Very Large Telescope and its ERIS adaptive optics facility to search for visual companions among a sample of 77 objects members of the Upper Scorpius and Taurus young nearby associations with estimated masses in the range between approximately 6-66Mjup We report the discovery of one companion candidate around a Taurus member with a separation of 111.9+/-0.4mas, or ~18au assuming a distance of 160pc, with an estimated primary mass in the range between 3-6Mjup and a secondary mass between 2.6-5.2M_Jup_, depending on the assumed age. This corresponds to an overall binary fraction of 1.8^+2.6^-1.3% among low-mass brown dwarfs and free-floating planetary mass objects over the separation range >7au. Despite the limitations of small-number statistics and variations in spatial resolution and sensitivity, our results, combined with previous high-spatial-resolution surveys, suggest a notable difference in the multiplicity properties of objects below ~30-50Mjup between Upper Sco and Taurus. In Taurus, a binary fraction of 5.6^+3.2^-2.3% is found for objects with masses below 30Mjup, and of 7.8^+3.0^-2.4% for objects with masses below 50Mjup, whereas no binary were found among 80 objects over the matching luminosity range in Upper Sco, corresponding to an upper limit of >=1.2%. This difference may point to intrinsically distinct formation conditions, with warmer parental molecular clouds originally present in Upper Sco potentially inhibiting fragmentation into the lowest-mass brown dwarfs and free-floating planets compared to cooler environments such as Taurus.

Cone search capability for table J/A+A/708/A218/tablea1 (HST targets)

Cone search capability for table J/A+A/708/A218/tablea2 (VLT targets)

Cone search capability for table J/A+A/708/A218/tablec1 (List of Taurus late type members observed at high spatial resolution)

Cone search capability for table J/A+A/708/A218/tablec2 (List of Usco late type members observed at high spatial resolution)