Neptune's Rings

Image of Neptune's Rings taken from Voyager 2 in 1989.

Three rings are easily seen in this image: Adams (outermost), Le Verrier (middle) and Galle (inner ring). To the left of the image, in the Adams Ring, Galatea is visible. Between Adams and Le Verrier, two faint rings can be made out: Arago and Lassell.

Image Credit:

NASA/JPL/Voyager

 

Neptune has five main rings: Galle, Le Verrier, Lassell, Arago, and Adams, named after five important astronomers in Neptune's history. Much like the rings of Uranus, the rings of Neptune are made up of dust particles, and kept in place by shepherd moons, which include Galatea (Adams Ring) and Despina (Le Verrier Ring). It is believed that Neptune has other moons which help keep the rings narrow and stable (so to speak), but they have yet to be discovered.

The Adams Ring is unique in that it contains arcs, which are caused by gravity from Galatea. The arcs were discovered when Neptune occulted a star and where the rings should have been, the star shone through the rings. Close ups by Voyager confirmed that the Adams Ring contained arcs.

Much like the rings around Jupiter, Saturn, and Uranus, the material in the rings of Neptune are not permanent. They are continuously replenished by collisions with the moons of Neptune and are kept in orbit by shepherd satellites. The rings themselves are mostly dust with some ice particles and are covered in organic material (carbon compounds) that make them dark.

Image Credit:

Sky and Telescope

F Ring and Shepherd Satellites

The F-Ring, Prometheus (inner moon), and Pandora (outer moon). The A-Ring fills up the bottom half of the image with the Keepler Gap easily visible

Image Credit:

NASA/JPL/Voyager

 

Saturn's F-Ring is the outermost of the discrete rings discovered in 1979 by Pioneer 11. Compared to the other rings, it is very active with features changing in the structure of the ring on a timescale of hours. The F-Ring is 3,000 km from the A-Ring and is separated from the A-Ring by the Roche Division. Compared to the other discrete rings, the F-Ring is very narrow, only a few hundred kilometers thick. So how exactly does the F-Ring maintain its shape?

The ring is between the orbits of two satellites, Prometheus and Pandora. Prometheus orbits just inside the inner edge of the F-Ring and Pandor just outside the outer edge. These two satellites are able to use their gravitational influence on the ring to keep it stationary and in place. If these moons were not there, the F-Ring would have dissipated long ago.

Prometheus also creates kinks and knots in the ring from its orbit which show up in the ring when Prometheus is at apoapis (farthest distance from Saturn). Because Prometheus does have an elliptical orbit, at each successive apoapis, the knots and kinks are 3.2° ahead of the previous section.

Prometheus creating knots and streamers in the inner F-Ring

Image Credit:

Cassini/ISS/JPL/EPA/NASA

Saturn

Image Credit:

NASA/Voyager 2

 

Saturn is the second largest planet in the Solar System, about 95 times the mass of the Earth. However, compared to Jupiter, Saturn is tiny. It is only 30% the mass of Jupiter. Its radius at the equator is 9.44 times that of Earth and its polar radius is only 8.5 times Earth's. Despite this, if you could stand on Saturn, you would feel the same gravity as you do on Earth. Its day is just a little longer than Jupiter's at 10.57 Earth hours. Its average distance from the Sun is 9.5 AU which gives it an orbital period of 29.46 Earth years. It has an inclination of 26.5° with respect to its orbit and its orbit is only tilted at 2.5° to the ecliptic (the orbit of the Earth). With respect to the Sun's equator, it is tilted at 5.51°.

 

The thing Saturn is most known for is seen in the above image from Voyager 2. Its ring system is the most extensive of all the Jovian planets and Saturn has been known to have rings since the 1600s. The rings are a fascinating aspect of the most beautiful planet (in my opinion) in our Solar System, so that I can't talk about all rings in only one post. Stay tuned to learn a lot about Saturn's rings.

 

Saturn also has many moons, almost three times as many as Jupiter with 150 known, though only 51 have formal names. The largest satellite in the Solar System, Titan, belongs to Saturn and could be considered a mini-world in its own right. It also has moons that keep some of Saturn's rings in line, called shepherd satellites. It has a moon that doesn't look like a moon and moons that share an orbit.

 

Saturn's composition is similar to Jupiter, containing the same gases, but in different concentrations. This difference in concentrations, the thickness of its atmosphere, and the size of its heavy element core give rise to a strange phenomenon when looking at Saturn's density.