  Jewitt et al. (2014) recently reported that main belt comet P/2013 R3
experienced a breakup, probably due to rotational disruption, with its
components separating on mutually hyperbolic orbits. We propose a technique for
constraining physical properties of the proto-body, especially the initial spin
period and cohesive strength, as a function of the body's estimated size and
density. The breakup conditions are developed by combining mutual orbit
dynamics of the smaller components and the failure condition of the proto-body.
Given a proto-body with a bulk density ranging from 1000 kg/m3 to 1500 kg/m3 (a
typical range of the bulk density of C-type asteroids), we obtain possible
values of the cohesive strength (40 - 210 Pa) and the initial spin state (0.48
- 1.9 hr). From this result, we conclude that although the proto-body could
have been a rubble pile, it was likely spinning beyond its gravitational
binding limit and would have needed cohesive strength to hold itself together.
Additional observations of P/2013 R3 will enable stronger constraints on this
event, and the present technique will be able to give more precise estimates of
its internal structure.
