For millenia massive floating cities were placed within the atmosphere of Jupiter at just the right altitude to allow for 1 G of pull. Each city was surrounded by large domes to create an atmosphere. Thanks to the recent advanced research in antigrav technology more cities are being built and older cities are being refitted with the safer technology.
Because of the precarious nature of dirigible cities, 20 billion people live on Jupiter. The largest and oldest city, Zeus, only has around 90,000 people living on it. There have been discussions throughout the interplanetary community to terraform the planet by building a massive artificial surface around the same level as the artificial cities and creating a warm atmosphere as well as super-continents and immense oceans.