corresponding to an individual apparent magnitude of 22.6. The satellite has an estimated diameter of and a semi-major axis of , orbiting its primary in . It is estimated to only have a mass of about . System dynamics The orbital dynamics of the Lempo system are highly complex and could not be modelled with solely Keplerian dynamics. Many crucial parameters such as initial spin states and shapes of the individual components are unknown and thus could not adequately model the dynamics of the Lempo system as a three-body problem without leading to significantly chaotic behavior. In a 2018 dynamical study, Alexandre Correia found that simulated models using realistically assumed spin states and shapes failed to explain the presently eccentric mutual orbit of the inner Lempo–Hiisi binary, even with the inclusion of eccentricity-damping tidal forces. Correia concluded that the present orbits, spin states and shapes of all components of the Lempo system needed to be remeasured to a greater precision before a more sophisticated model could be developed. Origin There exist two main hypotheses on how this triple system formed. The first one is a giant collision and subsequent reaccretion in the disc. The second one is gravitational capture of a third object by a preexisting binary. The similar sizes of Lempo and Hiisi favor the latter hypothesis. Physical characteristics The combined observations by the infrared Spitzer Space Telescope, Herschel Space Telescope and the Hubble Space Telescope (HST) make it possible to estimate the sizes of the system's components and consequently provide the range of possible values for the objects' bulk density. The single-body diameter (effective system size) of Lempo is currently estimated at . The very low estimated density of 0.3–0.8 g/cm3 obtained in 2006 (when the system was thought to be a binary) would require an unusually high porosity of 50–75%, assuming an equal mixture of rock and ice. The direct measurement of visible fluxes of all three components of the system in 2009 by the HST has resulted in an improved average density of confirming the earlier conclusion that the object is probably a rubble pile. The density was revised up to in 2012 when new information from the Herschel became available. For a bulk density in the range 1–2 g/cm3 the porosity is in the range 36–68%, again confirming that the object is a rubble pile. Lempo has a very red spectral slope in visible light