7 Orbital properties of binary minor planets 3.3. Dependence on mass/size 3.4. Binary trans-Neptunian objects vs. binary asteroids 3.5. Multiple systems eccentricity and inclinations ( | cos i | ) distributions to be uncorrelated is ∼ 0 . 04 (with the correlation coefficient found to be 0 . 7 ). We conclude that although understanding the shape of the inclinations distribution requires more data, it is clear that high inclinations serve as the rule and not the exception, and point to an excitation mecha- nism, possibly a highly collisional environment at the epoch of BMPs formation and/or evolution, with fur- ther KCTF evolution playing a role and producing cor- relations between the BMPs orbital properties (separa- tions/eccentricities/inclinations). The masses and sizes of BMP components, mostly the smaller secondaries, are not accurately known. Never- theless, some interesting trends with masses/sizes may already be observed in our binary TNOs sample. Binary TNOs with the largest primaries ( > 500 km ; see table 1 and fig. 3), are observed to have satellites at small sepa- rations and low eccentricities, possibly indicating a colli- sional formation mechanism (Canup 2005; Brown 2008; Ragozzine & Brown 2009). We also note that these bi- naries seem to cluster at relatively high inclinations (not shown, but see table 1), although this may not be sta- tistically significant given our currently small sample, it may suggest KCTF (highly efficient at high inclinations) was involved in catalyzing mergers/collisions or tidal evo- lution of pre-formed binaries (see Perets & Naoz 2009). We do not see any trends in the current sample of binary asteroids, but note that no massive ( > 500 km ) binary asteroids are known. Nevertheless, it is worth pointing out that most of the binary asteroids share similarities with the massive binary TNOs, i.e. small separations and low eccentricities, as discussed above, suggesting a similar, possibly collisional, origin. We find that both the observed populations of binary asteroids and binary TNOs present similar orbital prop- erties (e.g. high inclinations). This suggest that some ba- sic features in their formation and evolution were similar (e.g. dense collisional environment). Although binary TNOs show typically much higher eccentricities, most of these binaries have much wider orbits than those of binary asteroids (both due to observational selection ef- fects, as well as the much smaller Hill radii in which bi- nary asteroids can exist; see figure 3). The differences in eccentricities may therefore only reflect the tendency of closer binaries to be more circularized (since tidal friction effects become stronger ). The last few years have seen the discovery and char- acterization of the first asteroids and TNOs with mul- tiple satellites, which deserve special mention. Such systems with well-known published orbits include Pluto (Tholen et al. 2008), Haumea (Ragozzine & Brown 2009), 1999 TC36 (Benecchi et al. 2009b) and Sylvia (Marchis et al. 2006), while the asteroids Eugenia, Balam, Kleopatra, Minerva, 2001 SN263, and 1994 CC have only recently been announced as triple systems. Though the detection biases described in Section 2 are Fig. 3.— Eccentricity as a function of the binary separations normalized to the primary’s radius. We consider both TNOs (open circles) and asteroids (squares). The large circles correspond to the largest size primary TNOs ( > 500 km ). The solid line shows the critical separation-eccentricity beyond which typical binaries are expected to be strongly affected by tides and be circularized (where we choose Pulcova and OJ4 as representative for the asteroid and TNO binaries respectively). The dotted lines show the the critical separation-eccentricity beyond which typical binaries become un- stable due to the perturbation by the Sun (the Hill radius); lines are shown for both asteroids (left line) and TNOs (right), as the Hill radius is strongly dependent on the distance from the Sun.. present for these systems, the majority of these systems were first known as binaries with additional companions found during subsequent study. It is therefore difficult to estimate the frequency of multiple systems in the various populations. Nevertheless, the existence of several such objects indicates that these are not rare. Detailed obser- vations of these systems can yield mass determinations for each of the bodies independently, which is not possi- ble for binaries (Tholen et al. 2008; Ragozzine & Brown 2009). Multiple systems provide unique additional leverage in determining the formation and evolution of binaries. For example, the coplanar nature of the satellite sys- tem of Pluto likely requires a dense collisional formation (Stephens & Noll 2006), although the detailed forma- tion and evolution of this system is still not understood (Ward & Canup 2006; Lithwick & Wu 2008). Even for systems with unknown orbits, the small sizes and com- pact configurations suggest that all of these systems are collisionally formed, except for 1999 TC36; though mul- tiple episodes of YORP-induced fission may be relevant for the smaller bodies (Walsh et al. 2008). The hierar- chical and nearly-equal mass nature of the 1999 TC36 triple system cannot be explained by a single collision and is likely the result of sequential formation by capture (e.g. Goldreich et al. 2002; Lee et al. 2007). Balam has a very unusual satellite system, including an outer satel- lite with a putative eccentricity of ∼ 0.9 (Marchis et al. 2008b), and possibly an unbound satellite that separated from Balam less than a million years ago (Vokrouhlický 2009). These systems also present examples of unique orbital evolution. As pointed out by (Ragozzine & Brown 2009), the combination of rapid orbital expansion (compared to the weak expansion around giant planets, which are ineffective at dissipating tidal energy) and gravitation- 0 0.5 1 1.5 2 2.5 3 3.5 4 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 log (a/r$_{p}$) e Main Belt TNOs