Some astronomers think that the two gas-giants do not sport solid surfaces secreted beneath their immense and heavy gaseous atmospheres, although others suggest that the jumbo-size duo do, indeed, harbor relatively small cores of rocky-icy stuff. The two other large inhabitants of the outer limits of our Sun's family are Uranus and Neptune, which are both classified as ice-giants, because they harbor large icy cores secreted deep down beneath their heavy, dense gaseous atmospheres which, though very massive, are not nearly as heavy as the gaseous envelopes possessed by Jupiter and Saturn.
Jupiter, along with its beautiful ringed sister planet, Saturn, are the gas-giant duo of our Sun's family of eight major planets. The other two giant planets--that dwell in our Solar System's outer limits--are Uranus and Neptune. Uranus and Neptune are classified as ice giants, because they carry within them larger cores than Jupiter and Saturn, as well as thinner gaseous envelopes. Jupiter and Saturn may (or may not) contain small, hidden cores, that are heavily veiled by extremely massive, dense gaseous envelopes.
Cassini's successful mission of exploration to the Saturn system is over, but planetary scientists are left with a cornucopia filled with important new information that Cassini/Huygens sent back to Earth before its mission ended. A collaborative NASA/European Space Agency/Italian Space Agency mission, the robotic spacecraft was made up of two components. The first was the European Space Agency's (ESA's) Huygens Probe, that had been named in honor of the Dutch mathematician and astronomer Christiaan Huygens (1629-1695), who discovered Titan. The Huygens Probe also closely observed Saturn's lovely system of gossamer rings. The second component, the NASA-designed Cassini Orbiter, was named after the Italian-French astronomer Giovanni Dominico Cassini (1625-1712), who discovered four of Saturn's other intriguing, numerous, and icy moons.