  Observations of C-type NEAs and lab investigations of carbonaceous chondritic
(CC) meteorites provide strong evidence for a high porosity of C-type
asteroids. Boulder microporosity values derived from in-situ measurements at
the surface of the rubble-pile NEA Ryugu of up to 55% are substantially higher
than for water-rich CC samples and could indicate distinct evolution paths for
the parent body of Ryugu and parent bodies of carbonaceous chondrites, despite
spectral similarities. In the present study, we calculate the evolution of the
temperature and porosity for early solar system's planetesimals in order to
constrain the range of parameters that result in microporosities compatible
with Ryugu's high-porosity material and likely burial depths for the boulders
observed at the surface. By varying key properties of the parent body, such as
accretion time t0 and radius R that have strong influence on temperature and
porosity and by comparing the interior porosity distribution with the measured
boulder microporosity, hydration, and partial dehydration of the material, we
constrain a field within the (R,t0)-space appropriate for bodies that are
likely to have produced such material. Our calculations indicate a parent body
size of only a few km and its early accretion within <~2-3 Myr after the
formation of Ca-Al-rich inclusions. A gradual final porosity profile of
best-fit bodies indicates production of both low- and high-density boulders
from the parent body material. By contrast, parent body properties for CI and
CM chondrites obtained by fitting carbonate formation data indicate a radius of
~20-25 km and an accretion time of ~3.75 Myr after CAIs. These results imply a
population of km-sized early accreting porous planetesimals as parent bodies of
Ryugu (and, potentially, other NEAs) and a population of larger late accreting
less porous parent bodies of water-rich carbonaceous chondrites.
