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Asteroid families with ages younger than $1$ Myr offer an interestingpossibility of studying the outcomes of asteroid disruptions that are littlemodified by subsequent evolutionary processes. We analyze a very young asteroidfamily associated with (18777) Hobson in the central part of the main belt. Weaim at (i) understanding its peculiar size distribution, and (ii) setting anupper limit on the characteristic dispersal velocity at subkilometer sizescorresponding to the smallest visible Hobson members. We identified the Hobsonfamily using an up-to-date asteroid catalog. A significant increase in thenumber of its known members allowed us to study their size distribution andcompare it with computer simulations of catastrophic disruptions. Backwardorbital integrations of the heliocentric orbits allowed us to confirm thepreviously suggested age of Hobson and helped to estimate limits of theejection speed. The Hobson family has an unusual size distribution: two nearlyequal-size bodies, followed by a population of smaller asteroids, whosedistribution takes a characteristic power law. There are two possibilities toexplain these data. Either a canonical impact onto a single parent body,requiring fine-tuned impact conditions that have not been studied so far, or anunconventional model for the parent object of the Hobson family, namely abinary with $\simeq 7-9$ km primary and a $\simeq 2.5$ km secondary. In thelatter case, the primary was disrupted, leaving behind the largest remnant(18777) Hobson and a suite of subkilometer asteroids. The second largestasteroid, (57738) 2001 UZ160, is the nearly intact satellite of the parentbinary. The excellent convergence of nominal orbits of Hobson members sets anupper limit of $\simeq (10-20)$ m s$^{-1}$ for the initial dispersal velocityof the known members, which is consistent with both formation models.

The young Hobson family: Possible binary parent body and low-velocity dispersal