Uranus and Neptune
The next two gas giant planets in our Solar system are Uranus and Neptune. They are smaller than Jupiter and Saturn, but still much larger than any of the terrestrial planets. In many ways, they are similar to the other gas giant planets, but there are also striking differences.
This image of the planet Uranus is a composite of photographs taken by the Hubble Space telescope in 2011 during a period of heightened solar activity. The overall blue color of Uranus is due to the presence of methane. Although Uranus is mostly made of hydrogen like the other gas giant planets in our solar system, it has slightly more methane than Jupiter and Saturn. The bright white spot is an aurora, resulting from the high energy particles in the solar wind. The magnetic field is inclined 59 degrees from its rotational axis, so auroral spots appear far from the north and south poles.
This infrared image of Uranus from the Keck telescope is tilted to show how the rotational axis of this gas giant planet is nearly aligned with the plane of the solar system. False color has been used to differentiate various features of the planet. Here, the white spots are high clouds, while medium level cloud bands and lower level clouds are shown in green and blue. The faint rings of Uranus show in red.
Neptune is a deeper blue than Uranus, with a somewhat higher methane content. Storms are more evident on Neptune, a seen here in the Great Dark Spot, similar to the Great Red Spot on Jupiter. The storm on Neptune was seen to disappear in 1994, only to reappear in 2016.
This graphic compares the sizes, rotation axes and magnetic fields of the Jovian planets. The rotation axis of Uranus lies close to the plane of the solar system, while the offset of Neptune's rotation axis is more like that of Earth.
Perhaps the most striking feature shown in this graphic is the orientation of the magnetic fields of Uranus and Neptune. Their magnetic fields are not centered on the middles of the planets and are widely offset from the rotation axes. The reason for this anomaly is not well understood. At the temperatures and pressures present in Uranus and Neptune, we do not believe that layers of metallic hydrogen are present, as found in Jupiter.
As shown in this scale diagram of the solar system, the orbits of the Jovian planets are widely spaced. Uranus and Neptune are much farther away from the sun than are Jupiter and Saturn. Jupiter is about 5 AU from the Sun, and Saturn is about twice as far from the sun, at 9.5 AU. Uranus and Neptune are 19 and 30 AU from the Sun, respectively. At this great distance from the Sun, space in this region is extremely cold.
Neptune and its largest moon, Triton, are shown here in crescent phase. This photograph was taken by Voyager 2 in 1989. This sight is impossible to see from Earth, even with powerful telescopes, because the crescent phase of Neptune is not visible from Earth, since Earth is closer to the Sun than Neptune.
The obvious resurfacing on the surface of Triton is revealed in this photograph taken by Voyager 2. Tidal flexing in the gravitational field of Neptune creates internal heat on this moon, resulting in ice volcanoes and a thin atmosphere. Titan exhibits a retrograde orbit around Neptune, and is the only large moon in the solar system to orbit in the opposite sense of the other bodies. This means that Triton probably did not form near Neptune, but came from somewhere else in the solar Nebula and was captured by Neptune's gravitational field.