Terrans working in the inner Jupiter system when performing space walks of EVAs on the inner moons must wear special space suits.
Particular areas in the Jovian system are worse than others, owing to the radiation belts and magnetosphere of the planet and its intersection with particular moon orbits. The radiation belts start almost at the top pf the atmosphere of the planet and doesn't get significantly weaker for the first two Galilean moons.
The radiation belts are composed of high energy protons that can penetrate suits and body tissues and will ionise atoms and break molecular bonds. This can damage DNA and build up radicals of H and OH from broken water molecules. Exposure for a few hours is high enough to cause acute radiation syndrome and without suitable treatment leads to death within a few days to weeks.
Io is the worst of the main moons and given the intense scientific and resource exploration of this moon, many dangers exist for explorers and workers on this moon other than the volatile geology.
Europa, while further out still is not a safe place, with lethal exposure measured in hours without suitable Jovian space suit protection. Given the scientific interest in Europa and its under ice seas, habitats are normally buried under sufficient ice to shield researchers based there.
Ganymede is considered to be a good staging area for the inner the Galilean moons, largely because Ganymede has its own magnetic field and affords increased protection to those operating on its surface. Most operators still tend to use Jovian space suits however, especially near the poles where aurorae occur, which are considered dangerous without an atmospheric shield like Earth has.
Callisto is located just outside the radiation belts, but within the magnetosphere of Jupiter, shielding it from from cosmic radiation. Someone on an surface EVA receives less radiation than in deep space or even than the surface of Earth's moon. It is the preferred location for human surface bases within the Jovian system and a lot of activity occurs both on the surface and in orbit.
A Jovian spacesuit is a specially designed heavy space suit with rigid parts designs to include extra shielding, including a modest electromagnetic field to aid in slowing down and deflecting some of the damaging proton based radiation.
Generally these suits raise the time to lethal exposure by about 10 times, allowing for short human operations, and radiation exposure damage that can typically be cured with 22nd century medicine if suitable gaps are observed between exposures.
The suits initially retailed for around 20 million Eurocredits, but have dropped in recent years thanks to improvements in manufacturing, safety features and bulk ordering by various space agencies and commercial interests. Today these suits retail for around 3 times the normal heavy space suit cost.