ИСТИНА

We consider a common class of relatively large silicate-icy bodies (R≥100 km) from Kuiper belt objects (KBOs) originated in situ at 30-50 AU to planetesimals existed in the formation zones of the outer giant planets in the early Solar system. For an elevated capability of the bodies to accumulation of radiogenic and other heat energies, they could undergo a considerable thermal modification from a pristine state. The decay of a short-lived 26Al in the bodies’ matter and/or thermal consequences of their mutual collisions could be the main source of heating sufficient for water ice melting and for the formation of an internal water ocean. Particularly, the ocean in large KBOs would form within 2 Myr (about 3.5 Myr after CAI formation) and exist up to ~10 Myr at 4-7°C before complete freezing. The later process could preserve separated layers enriched with different types of organics and a mostly silicate (and/or phyllosilicate) core (~0.5-0.6R) of the KBOs (Busarev V. V. et al., 2003, EM&P 92, 345-357; Busarev V. V. et al., 2005, LPSC 36th, abs. #1074). Crushing or partial removing external icy covers of the KBOs under subsequent high-velocity collisions could expose materials from their different depth levels. That is probably confirmed by observed diversity of KBOs’ colours and phyllosilicate absorption features in the visible-range reflectance spectra of some of them (e. g., Luu J. and Jewitt D., 1996, AJ 112, 2310-2318; Fornasier S. et al., 2004, A&A 421, 353-363). Because of a higher planetesimal surface density and accretion rate in Jupiter formation zone, planetesimals in this zone could have sizes and masses considerably bigger than those in the formation zones of the outer planets and KBOs. They could also be distinguished from KBOs by a greater content of silicates (up to 1.3 times in average) and, hence, of 26Al. For these reasons the radiogenic heat could keep H2O in interiors of large Jupiter zone bodies in a liquid state for a longer time (up to ~100 Myr) comparable to the “heavy bombardment” period.