  We report the discovery of a second planet orbiting the K giant star 7 CMa
based on 166 high-precision radial velocities obtained with Lick, HARPS, UCLES
and SONG. The periodogram analysis reveals two periodic signals of
approximately 745 and 980 d, associated to planetary companions. A
double-Keplerian orbital fit of the data reveals two Jupiter-like planets with
minimum masses $m_b\sin i \sim 1.9 \,\mathrm{M_{J}}$ and $m_c\sin i \sim 0.9
\,\mathrm{M_{J}}$, orbiting at semi-major axes of $a_b \sim 1.75\,\mathrm{au}$
and $a_c \sim 2.15\,\mathrm{au}$, respectively. Given the small orbital
separation and the large minimum masses of the planets close encounters may
occur within the time baseline of the observations, thus, a more accurate
N-body dynamical modeling of the available data is performed. The dynamical
best-fit solution leads to collision of the planets and we explore the
long-term stable configuration of the system in a Bayesian framework,
confirming that 13% of the posterior samples are stable for at least 10 Myr.
The result from the stability analysis indicates that the two-planets are
trapped in a low-eccentricity 4:3 mean-motion resonance. This is only the third
discovered system to be inside a 4:3 resonance, making it very valuable for
planet formation and orbital evolution models.
