  We present ALMA 1.3 mm observations of the HD~53143 debris disk - the first
infrared or millimeter image produced of this ~1 Gyr-old solar-analogue.
Previous HST STIS coronagraphic imaging did not detect flux along the minor
axis of the disk which could suggest a face-on geometry with two 'clumps' of
dust. These ALMA observations reveal a disk with a strikingly different
structure. In order to fit models to the millimeter visibilities and constrain
the uncertainties on the disk parameters, we adopt an MCMC approach. This is
the most eccentric debris disk observed to date with a forced eccentricity of
$0.21\pm0.02$, nearly twice that of the Fomalhaut debris disk, and also
displays apocenter glow. Although this eccentric model fits the outer debris
disk well, there are significant interior residuals remaining that may suggest
a possible edge-on inner disk, which remains unresolved in these observations.
Combined with the observed structure difference between HST and ALMA, these
results suggest a potential previous scattering event or dynamical instability
in this system. We also note that the stellar flux changes considerably over
the course of our observations, suggesting flaring at millimeter wavelengths.
Using simultaneous TESS observations, we determine the stellar rotation period
to be $9.6\pm0.1$ days.
