 59Co is the only stable cobalt isotope and the only isotope to exist naturally on Earth . 22 radioisotopes have been characterized with the most stable being 60Co with a half @-@ life of 5 @.@ <unk> years , 57Co with a half @-@ life of 271 @.@ 8 days , 56Co with a half @-@ life of 77 @.@ 27 days , and <unk> with a half @-@ life of 70 @.@ 86 days . All of the remaining radioactive isotopes have half @-@ lives that are shorter than 18 hours , and the majority of these are shorter than 1 second . This element also has 4 meta states , all of which have half @-@ lives shorter than 15 minutes . 
