Question

I understand that both Saturn and Jupiter have extreamly active atmospheres and give out lethal doses of radiation, so are they hot or cold?

Jupiter and Saturn are both hot and cold; cold in their upper atmospheres and very hot in their interiors (just as is true for Earth). The lethal doses of radiation originate outside the planet, in the charged atomic particles moving in the magnetospheres of Jupiter and Saturn. You are running into an ambiguity of terminology here. The word "radiation" has several different meanings. To astronomers, it means electromagnetic radiation, such as light and radio waves that are emitted by hot objects (stars and planets). To a life scientist, radiation means ionizing radiation which is generally bad for you, and I think this is what you are referring to when you mention lethal doses of radiation at Jupiter and Saturn. And to an evolutionary biologist radiation is speciation, the emergence of many new species. As you can see, all three meanings of the word are used by astrobiologists, and this situation can easily become confusing. David Morrison
NAI Senior Scientist
March 20, 2007