Question: Callisto is the Solar System's third largest moon after Titan, which is a moon of which planet named for the Roman god of agriculture?

Context paragraphs:
Moons of Saturn: The moons of Saturn are numerous and diverse, ranging from tiny moonlets less than 1 kilometer across to the enormous Titan, which is larger than the planet Mercury.  Saturn has 62 moons with confirmed orbits, 53 of which have names and only 13 of which have diameters larger than 50 kilometers, as well as dense rings with complex orbital motions of their own.  Seven Saturnian moons are large enough to be ellipsoidal in shape, though only two of those, Titan and Rhea, are currently in hydrostatic equilibrium.  Particularly notable among Saturn's moons are Titan, the second-largest moon (after Jupiter's Ganymede) in the Solar System, with a nitrogen-rich Earth-like atmosphere and a landscape featuring dry river networks and hydrocarbon lakes found nowhere else in the solar system; and Enceladus since its chemical composition is similar to that of comets.  In particular, Enceladus emits jets of gas and dust which could indicate presence of liquid water under its south pole region and could potentially harbor a global ocean under its surface.

Atmosphere of Titan: The atmosphere of Titan is the layer of gases surrounding Titan, the largest moon of Saturn.  It is the only thick atmosphere of a natural satellite in the Solar System.

Nice model: The Nice ( ) model is a scenario for the dynamical evolution of the Solar System.  It is named for the location of the Observatoire de la Côte d'Azur, where it was initially developed, in Nice, France.  It proposes the migration of the giant planets from an initial compact configuration into their present positions, long after the dissipation of the initial protoplanetary gas disk.  In this way, it differs from earlier models of the Solar System's formation.  This planetary migration is used in dynamical simulations of the Solar System to explain historical events including the Late Heavy Bombardment of the inner Solar System, the formation of the Oort cloud, and the existence of populations of small Solar System bodies including the Kuiper belt, the Neptune and Jupiter trojans, and the numerous resonant trans-Neptunian objects dominated by Neptune.  Its success at reproducing many of the observed features of the Solar System means that it is widely accepted as the current most realistic model of the Solar System's early evolution, although it is not universally favoured among planetary scientists.  Later research revealed a number of differences between the original Nice model's predictions and observations of the current Solar System, for example the orbits of the terrestrial planets and the asteroids, leading to its modification.

Galilean moons: The Galilean moons are the four largest moons of Jupiter—Io, Europa, Ganymede, and Callisto.  They were first seen by Galileo Galilei in January 1610, and recognized by him as satellites of Jupiter in March 1610.  They are the first objects found to orbit another planet.  Their names derive from the lovers of Zeus.  They are among the largest objects in the Solar System with the exception of the Sun and the eight planets, with a radius larger than any of the dwarf planets. Ganymede is the largest moon in the Solar System, and is even bigger than the planet Mercury.  The three inner moons—Io, Europa, and Ganymede—are in a 4:2:1 orbital resonance with each other.  Because of their much smaller size, and therefore weaker self-gravitation, all of Jupiter's remaining moons have irregular forms rather than a spherical shape.

Neptune: Neptune is the eighth and farthest known planet from the Sun in the Solar System.  In the Solar System, it is the fourth-largest planet by diameter, the third-most-massive planet, and the densest giant planet.  Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 times the mass of Earth and slightly larger than Neptune.  Neptune orbits the Sun once every 164.8 years at an average distance of 30.1 AU .  It is named after the Roman god of the sea and has the astronomical symbol ♆, a stylised version of the god Neptune's trident.

Mars: Located at a varying distance no closer than 33 million miles from the earth, Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System after Mercury.  In English Mars carries a name of the Roman god of war, and is often referred to as the "Red Planet" because the reddish iron oxide prevalent on its surface gives it a reddish appearance that is distinctive among the astronomical bodies visible to the naked eye.  Mars is a terrestrial planet with a thin atmosphere, having surface features reminiscent both of the impact craters of the Moon and the valleys, deserts, and polar ice caps of Earth.

Saturn: Saturn is the sixth planet from the Sun and the second-largest in the Solar System, after Jupiter.  It is a gas giant with an average radius about nine times that of Earth.  Although it has only one-eighth the average density of Earth, with its larger volume Saturn is just over 95 times more massive.  Saturn is named after the Roman god of agriculture; its astronomical symbol (♄) represents the god's sickle.

Ganymede (moon): Ganymede (Jupiter III) is the largest and most massive moon of Jupiter and in the Solar System.  The ninth largest object in the Solar System, it is the largest without a substantial atmosphere.  It has a diameter of 5,268 km and is 8% larger than the planet Mercury, although only 45% as massive.  Possessing a metallic core, it has the lowest moment of inertia factor of any solid body in the Solar System and is the only moon known to have a magnetic field.  It is the third of the Galilean moons, the first group of objects discovered orbiting another planet, and the seventh satellite outward from Jupiter, Ganymede orbits Jupiter in roughly seven days and is in a 1:2:4 orbital resonance with the moons Europa and Io, respectively.

Titan in fiction: Titan is the largest moon of Saturn.  It has a substantial atmosphere and is the most Earth-like satellite in the Solar System, making it a popular science fiction setting.  Science fiction set on Titan can be roughly divided into the pre- and post-Pioneer eras, with a division set by the flyby of Saturn by the Pioneer 11 space probe on April 5, 1973, which showed that Titan's surface was too cold to sustain (Earthlike) life.  Somewhat later, the arrival of Cassini–Huygens mission in 2004 with the Huygens probe's landing in 2005 showed the presence of hydrocarbon lakes on Titan, leading to further changes in its depiction in science fiction.

Callisto (moon): Callisto (Jupiter IV) is the second-largest moon of Jupiter, after Ganymede.  It is the third-largest moon in the Solar System after Ganymede and Saturn's largest moon Titan, and the largest object in the Solar System not to be properly differentiated.  Callisto was discovered in 1610 by Galileo Galilei.  At in diameter, Callisto has about 99% the diameter of the planet Mercury but only about a third of its mass.  It is the fourth Galilean moon of Jupiter by distance, with an orbital radius of about .  It is not in an orbital resonance like the three other Galilean satellites—Io, Europa, and Ganymede—and is thus not appreciably tidally heated.  Callisto's rotation is tidally locked to its orbit around Jupiter, so that the same hemisphere always faces inward; Jupiter appears to stand nearly still in Callisto's sky.  It is less affected by Jupiter's magnetosphere than the other inner satellites because of its more remote orbit, located just outside Jupiter's main radiation belt.

Supporting paragraphs: Callisto (moon) Saturn
Answer: Saturn