Mass Measurements of Rare-Earth Nuclei Near N = 100

The recent observation of gravitational wave event GW170817 has confirmed that neutron star mergers are a site of heavy-element production from rapid neutron capture nucleosynthesis ($r$ process). As we learn more about the nature of the $r$ process, the importance of accurate nuclear data of neutron-rich isotopes far from stability will become paramount. In order to constrain calculations which model the formation of the rare-earth peak at late stages in the $r$ process, more nuclear data in the region is needed. Many of these neutron-rich isotopes are readily available at the CARIBU facility of Argonne National Laboratory where the Canadian Penning Trap mass spectrometer (CPT) is housed. A phase-imaging mass measurement technique (PI-ICR) has dramatically increased the experimental sensitivity of the CPT allowing for several new mass measurements in the rare-earth region. The experimental results as well as the astrophysical implications of these measurements will be discussed.