The discovery of microfossils on carbonaceous meteorites has electrified the public with the first concrete evidence of extraterrestrial biology. But how these organisms colonized and grew on the parent body–the comet–remains a mystery. We report on several features of cyanobacteria that permit them to bioengineer comets, as well as a tantalizing look at interplanetary uses for magnetite framboids that are found in abundance on carbonaceous chondrites. We argue that these structures provide important directionality and energy harvesting features similar to magnetotactic bacteria found on Earth.