  We demonstrate the long-term ($<$ 1 minute) trapping of Stark-decelerated OH
radicals in their $X~^{2}\Pi _{3/2}~(\nu = 0,~J = 3/2,~M_{J} = 3/2,~f)$ state
in a permanent magnetic trap. The trap environment was cryogenically cooled to
a temperature of 17 K in order to efficiently suppress
black-body-radiation-induced pumping of the molecules out of trappable quantum
states and collisions with residual background gas molecules which usually
limit the trap lifetimes. The cold molecules were kept confined on timescales
approaching minutes, an improvement of up to two orders of magnitude compared
to room-temperature experiments, at translational temperatures on the order of
25 mK. The present results pave the way for spectroscopic studies of trapped
molecules with long interaction times enabling high precision, for
investigations of cold collisions and reactions with very small reaction rates,
for new avenues for the production of ultracold molecules via sympathetic
cooling and for the realisation of new forms of hybrid matter with co-trapped
atoms or ions.
