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abstract: |
    We obtained thorough photometric observations of two binary near-Earth asteroids (66391) Moshup = 1999 KW4 and (88710) 2001 SL9 from June 2000 to June 2019. We modeled the data and derived physical and dynamical properties of the binary systems. For (66391) 1999 KW4, we derived its mutual orbit’s pole, semimajor axis and eccentricity that are in agreement with radar-derived values (Ostro et al. \[2006\]. Science, 314, 1276–1280). However, we found that the data are inconsistent with a constant orbital period and we obtained unique solution with a quadratic drift of the mean anomaly of the satellite of $-0.65 \pm 0.16$ deg/$\mbox{yr}^2$ (all quoted uncertainties correspond to 3$\sigma$). This means that the semimajor axis of the mutual orbit of the components of this binary system increases in time with a mean rate of $1.2 \pm 0.3$ cm/yr.

    For (88710) 2001 SL9, we determined that the mutual orbit has a pole within ${\sim}10^{\circ}$ of $(L, B) = (302^{\circ},-73^{\circ})$ (ecliptic coordinates), and is close to circular (eccentricity $< 0.07$). The data for this system are also inconsistent with a constant orbital period and we obtained two solutions for the quadratic drift of the mean anomaly: $2.8 \pm 0.2$ and $5.2 