tokens: in Fig. 2 correspond to ≈48 per cent of the total number of initial simulated objects, which survived during the integration time. In panels (c) and (d) of Fig. 2 , the distribution of the final osculant orbital elements, a s , e s , and i s of the ploonets with respect to the star, are shown. We observe in a peaked distribution of low-eccentric orbits with similar size than that of the planet (nearby ploonets). As expected, non-nearby ploonets are distributed in the osculating a s − e s plane following the characteristic pattern of constant Tisserand parameter. The periapsis argument is almost uniformly distributed (not shown in Fig. 2 ) and thereby no preferred orbital orientation is found. Finally, the distribution of the mean orbital motion of the surviving exomoons is plotted in panel (d) of Fig. 2 . There are three recognizable peaks close or at resonances (planet:moon) 1:2 (inner ploonets), 3:2, and 5:2 (outer ploonets). It is worthy to mention that the resonances found are transient states of the system. Moreover, almost all the orbits resulted chaotic/unstable according to the assessing of the Mean Exponential Growth factor of Nearby Orbits (MEGNO) parameter (Cincotta, Giordano Simó 2003 ), according to the implementation provided by REBOUND (Rein Tamayo 2015 ). This calculation is not shown in the plot. 3 PLOONET DETECTABILITY If according to the previous analytical and numerical models, a population of small ploonets could arise in young planetary systems hosting close-in giant planets, and we additionally assume that some of them survive to the long-term orbital evolution of the system, the next question we should address is what are the observable signatures that evidence the presence of these objects?. Besides the direct photometric or indirect stellar radial-velocity detection (that could be hard to distinguish from the observational signature of an actual small planet), we consider and evaluate here, two additional and distinctive observational signatures of ploonets: (1) the transit of rapidly evaporating planetary embryo-sized objects with an orbit closely related to an already detected close-in giant planet and (2) characteristic TTVs of the parent planet transit signal. The very existence of ploonets depends on two basic conditions: (1) planetary moons around giant close-in planets are formed before or during the migration process when abundant circumstellar gas and dust is accreted by the planet (Namouni 2010 ; Heller Pudritz 2015 ); and (2) the moons survive planetary migration (Namouni 2010 ; Spalding et al. 2016 ). Although it is hard to ensure that both conditions will be fulfilled under general circumstances, the characteristic time-scales of moon formation (10 3 –10 5 yr, Canup Ward 2006 ) and planetary migration (10 3 –10 7 yr, Armitage 2010 ) seem to favour the idea that some migrating giant planets could arrive to their final orbit, carrying along several volatile rich moons. So far, we have studied the
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