  The Clarissa family is a small collisional family composed of primitive
C-type asteroids. It is located in a dynamically stable zone of the inner
asteroid belt. In this work we determine the formation age of the Clarissa
family by modeling planetary perturbations as well as thermal drift of family
members due to the Yarkovsky effect. Simulations were carried out using the
Swift-rmvs4 integrator modified to account for the Yarkovsky and
Yarkovsky-O'Keefe-Radzievskii-Paddack (YORP) effects. We ran multiple
simulations starting with different ejection velocity fields of fragments,
varying proportion of initially retrograde spins, and also tested different
Yarkovsky/YORP models. Our goal was to match the observed orbital structure of
the Clarissa family which is notably asymmetrical in the proper semimajor axis.
The best fits were obtained with the initial ejection velocities < ~20 m/s of
diameter D=2 km fragments, 4:1 preference for spin-up by YORP, and assuming
that 80% of small family members initially had retrograde rotation. The age of
the Clarissa family was found to be 56+/-6 Myr for the assumed asteroid density
1.5 g/cm3. Small variation of density to smaller or larger value would lead to
slightly younger or older age estimates. This is the first case where the
Yarkovsky effect chronology has been successfully applied to an asteroid family
younger than 100 Myr.
