Back in the late 70’s, space artist Don Dixon did a series of paintings depicting scenes set on the moons of Jupiter & Saturn. I remember thinking how cool it would be to actually stand on one of these moons and look at the great gas giants up close. After Voyager (and other probes) sent back data on these planets in the 80’s, it seems these two planets emit high doses of radiation. This kinda makes it difficult to see these sights without suffering lots of death.
Is this a charateristic of gas giants? or do all planets emit radiation?
While Jupiter emits some radiation itself, it’s mostly harmless stuff. The dangerous radiation around Jupiter is the charged particles captured in the planet’s magnetic field.
It’s the same thing as the van Allen belts around Earth. If spacecraft flew through those all the time, it would be fatal to any inhabitants and eventually damaging to the electronics, even if hardened. The magnetic fields of Jupiter and Saturn are stronger than Earth’s, so the belts are more extensive and the radiation more dangerous.
Many planets emit some form of radiation. Many of the larger members of our Solar System, notably Jupiter and Saturn actually emit more energy than they receive from the sun. As dtilque said, Jupiter and Saturn have enormous magnetic fields–their equivalent to our Van Allen belts. But Jupiter also emits a decent amount of heat from its core–not by any sort of nuclear reaction, (I. E. we won’t be seeing a Jovian star any time soon) but from energy released as denser material continues towards the core of the planet.