  An accretion outburst onto a neutron star transient heats the neutron star's
crust out of thermal equilibrium with the core. After the outburst the crust
thermally relaxes toward equilibrium with the neutron star core and the surface
thermal emission powers the quiescent X-ray light curve. Crust cooling models
predict that thermal equilibrium of the crust will be established $\approx 1000
\, \mathrm{d}$ into quiescence. Recent observations of the cooling neutron star
transient MXB 1659-29, however, suggest that the crust did not reach thermal
equilibrium with the core on the predicted timescale and continued to cool
after $\approx 2500 \, \mathrm{d}$ into quiescence. Because the quiescent light
curve reveals successively deeper layers of the crust, the observed late time
cooling of MXB 1659-29 depends on the thermal transport in the inner crust. In
particular, the observed late time cooling is consistent with a low thermal
conductivity layer near the depth predicted for nuclear pasta that maintains a
temperature gradient between the neutron star's inner crust and core for
thousands of days into quiescence. As a result, the temperature near the
crust-core boundary remains above the critical temperature for neutron
superfluidity and a layer of normal neutrons forms in the inner crust. We find
that the late time cooling of MXB 1659-29 is consistent with heat release from
a normal neutron layer near the crust-core boundary with a long thermal time.
