Building rocky worlds containing appreciable amounts atmophile elements such as carbon, hydrogen, and nitrogen is required to establish an enduring atmosphere via outgassing of the planetary interior. Yet, the timing and the mechanism of volatile accretion on rocky bodies remains debated. In particular, the presence of atmophile elements during planetesimal formations may be crucial. Accretion and differentiation on small bodies involves high-temperature magmatic events, wherein, molten metal alloy is segregated in the core, while atmophile elements are outgassed from the magma ocean. Low gravity prevailing on small bodies inescapably implies that, in principle, the totality of these outgassed volatiles is lost to space. This renders impossible the capture of volatile elements or requires that these planetesimals were much more massive than usually assumed, generating sufficient gravitational attraction. Here, experiments are conducted using internally heated pressure vessel and piston cylinder at 20-1000 MPa and T in the range 1250-1450°C. A basaltic glass mixed with 10-20 wt% of nitride, graphite ± sulfide was used as starting materials and produced reduced conditions enabling the formation of Fe-rich molten alloys, silicate melt and gas. These experiments lasted minutes to hours and show that volatile-bearing gas bubbles are preferentially attached to metal droplets. 3-D X-ray tomographic images show that small gas bubbles attached to large metal droplets can sink, whereas small metal droplets attached to large bubbles can float. Up-scaling modelling shows that such attachments should prevail between bubble-droplet compounds up to 1 mm in size for Earth's gravity, whereas on small bodies, characterized by lesser gravity, cm-size bubble-droplet compounds must remain attached. This new mechanism allows volatile elements to be entrapped in small bodies. Metal-silicate separation must also be perturbated by the flotation properties of bubble-droplet compounds, which can drastically affect Earth's mantle endowment in siderophile elements. This mecanism links ultra-volatile and ultra-siderophile elements.