It has been suggested that CO2 clathrate hydrate forms in the Martian polar regions in winter. A large deposit of hydrate would affect the polar energy budget because of its low thermal conductivity and its sizeable latent heat of dissociation, and it could also be important to the total CO2 budget. In this paper we present the far-infrared spectrum of CO2 hydrate at 150 K. The spectrum exhibits a broad absorption centered near 17 cm-1 (0.59 mm) that is probably due to a rattling transition. Our radiative transfer model predicts that the absorption gives rise to a distinctive emission spectrum for densely packed particles having average diameters greater than 100 &mgr;m. ¿ American Geophysical Union 1994