# Planets/Saturn Lecture

Saturn is the name of one of the planets in orbit around the Sun. It is a part of the Solar System.
The image on the right shows how the position of Saturn's rings appears throughout an orbit of Saturn around the Sun.

## Solar System

Picture dictionary :
Solar System
The sun
Mercury
Venus
Earth
Moon
Mars
Jupiter
[[Saturn|Saturn]]
Uranus
Neptune
comet
asteroid belt
orbit :
The picture dictionary display on the right shows Saturn's approximate position in the Sol (or Sun) or the Solar System.

## Planets

As expected Saturn revolves around the Sun more slowly than the planets closer to the Sun.

## Theoretical planetary Saturn

Perhaps the simplest theory for the formation of Saturn would be as a part of the solar nebula from which the Sun may have originated. If this theory is correct the orbital pole of Saturn should align with the geographic pole of the Sun to a high degree.
An orbital pole is either end of an imaginary line running through the center of an orbit perpendicular to the orbital plane, projected onto the celestial sphere. It is similar in concept to a celestial pole but based on the planet's orbit instead of the planet's rotation.
The north orbital pole of a celestial body is defined by the right-hand rule: If you curve the fingers of your right hand along the direction of orbital motion, with your thumb extended parallel to the orbital axis, the direction your thumb points is defined to be north.
At right is a snapshot of the planetary orbital poles. The field of view is about 30°. The yellow dot in the centre is the Sun's North pole. Off to the side, the orange dot is Jupiter's orbital pole. Clustered around it are the other planets: Mercury in pale blue (closer to the Sun than to Jupiter), Venus in green, the Earth in blue, Mars in red, Saturn in violet, Uranus in grey partly underneath Earth and Neptune in lavender. Dwarf planet Pluto is the dotless cross off in Cepheus.
Calculations using the determined orbital parameters of Saturn suggest that its current orbit has been stable for at least 2,000 years.
However, historical observations suggest that Saturn's orbital position may have changed to what it is now.
The current orbit may be the farthest away from the Sun or the closest to the equatorial plane of the Sun's equator.
If Saturn's orbit has been much farther away from the Sun's equatorial plane than today at least one of the hemispheres of the Earth where hominin observers have existed for at least 40,000 years may have recorded in some way either the orbital migration or a much earlier placement.
"Planets are believed to have formed through the accumulation of a large number of small bodies$^{1,2,3,4}$. In the case of the gas-giant planets Jupiter and Saturn, they accreted a significant amount of gas directly from the protosolar nebula after accumulating solid cores of about 5–15 Earth masses$^{5,6}$. Such models, however, have been unable to produce the smaller ice giants$^{7,8}$ Uranus and Neptune at their present locations, because in that region of the Solar System the small planetary bodies will have been more widely spaced, and less tightly bound gravitationally to the Sun."
"When applied to the current Jupiter–Saturn zone, a recent theory predicts that, in addition to the solid cores of Jupiter and Saturn, two or three other solid bodies of comparable mass are likely to have formed$^9$. [Model calculations] demonstrate that such cores will have been gravitationally scattered outwards as Jupiter, and perhaps Saturn, accreted nebular gas. The orbits of these cores then evolve into orbits that resemble those of Uranus and Neptune, as a result of gravitational interactions with the small bodies in the outer disk of the protosolar nebula."
In the gaseous protoplanetary disk, the "mutual interactions between Jupiter and Saturn prevented [...] migration from driving these planets much closer to the Sun."
"After a phase of inward runaway migration, Saturn was captured into the 2:3 mean motion resonance with Jupiter. At that point, the planets reversed their migration, moving outward in parallel, while preserving their resonant relationship."
"In fact, after Jupiter and Saturn lock in their mutual 2:3 resonance, their outward migration is rather fast. Jupiter increases its orbital radius by ∼40% in 1000 orbits. If this really occurred in the Solar System, Jupiter would have been at some time in the middle of the asteroid belt. The properties of the asteroid belt (in particular the quite tight zoning of the taxonomic types) exclude this possibility."
The "migration reversal [...] does not depend on the history of the previous migration."
Arguments "favor [...] a close formation of Saturn [...] The direction of migration of Jupiter determines the subsequent evolution of both planets, once they are locked in resonance. The planets have to move in parallel to preserve the resonant configuration."
"In most cases, the planets migrate outward, which is not a viable evolution in our Solar System, because it would imply that Jupiter was in the asteroid belt in the past. However, there is a range of values of viscosity and disk’s scale height such that, once in resonance, the planets have a quasi-stationary evolution during which their semi-major axes remain practically constant. We argue that Jupiter and Saturn actually followed this kind of evolution."

## Planetary astronomy

"The Saturn system experienced equinox, when the sun lies directly over a planet's equator and seasons change, in August 2009. (A full Saturn “year” is almost 30 Earth years.)"
In the first image down on the right Saturn is about an Earth day and a half after equinox.

## Saturn systems

The first image down on the right shows a stellarium simulation of Saturn and its major moons as they appeared on March 19, 2008.
In the second image down on the right, Saturn is apparent magnitude 0.8 in this image taken at 2010-03-04 11:45 UT. Saturn is overexposed to bring out fainter objects, including some members of the Saturn system.
Objects visible in this photo:
* Two bright background stars to the upper left of Saturn,
* Iapetus: 2 o'clock position (directly above NGC 4179 at 4 o'clock), labeled I,
* Titan: bright-outer moon (magnitude 8) at 3 o'clock, labeled T,
* Dione: 3 o'clock inner moon, labeled D,
* NGC 4179: 4 o'clock,
* Hyperion: faint-outer moon (magnitude 14) at 9 o'clock, labeled H,
* Rhea: inner moon at 9 o'clock, labeled R.
The second system among the Saturn systems is the rings, characterized with radar in the third image down on the right.
On the left is a telescope image of a Saturn system.
"Six of its largest satellites can be seen here, though, in a sharp Saturnian family portrait taken on March 9. Larger than Earth's Moon and even slightly larger than Mercury, Titan has a diameter of 5,150 kilometers and starts the line-up at the lower left. Continuing to the right across the frame are Mimas, Tethys, [Saturn], Enceladus, Dione, and Rhea at far right."

## Prehistory

The prehistory period dates from around 7 x 10$^6$ b2k to about 7,000 b2k.
Saturn has been known since prehistoric times.

## Paleolithic

The paleolithic period dates from around 2.6 x 10$^6$ b2k to the end of the Pleistocene around 12,000 b2k.

## Mesolithic

The mesolithic period dates from around 13,000 to 8,500 b2k.
"All that we have considered up to now indicates that Saturn [Arka] once exploded in a nova-like burst of light. The date of this event I would be hard-put to specify, even approximately, but possibly it took place about ten thousand years ago. The solar system and reaches beyond it were illuminated by the exploded star, and in a matter of a week the Earth was enveloped in waters of Saturnian origin."

## Ancient history

The ancient history period dates from around 8,000 to 3,000 b2k.
Apparently 5102 b2k (before the year 2000.0), -3102 or 3102 BC, is the historical year assigned to a Hindu table of planets that does include the classical planet Saturn. "Babylonian astronomy, too, had a four-planet system. In ancient prayers the planets Saturn, Jupiter, Mars, and Mercury are invoked; ... and one speaks of "the four-planet system of the ancient astronomers of Babylonia.""
Babylonian astronomers systematically observed and recorded the movements of Saturn.
Ancient Chinese and Japanese culture designated the planet Saturn as the earth star.

## Early history

The early history period dates from around 3,000 to 2,000 b2k.

## Classical history

The classical history period dates from around 2,000 to 1,000 b2k.

## Recent history

The recent history period dates from around 1,000 b2k to present.
On the right is the frontispiece "of Riccioli's 1651 New Almagest. [In it mythological] figures observe the heavens with a telescope and weigh the heliocentric theory of Copernicus in a balance against his modified version of Tycho Brahe's geo-heliocentric system, in which the Sun, Moon, Jupiter and Saturn orbit the Earth while Mercury, Venus, and Mars orbit the Sun. The old Ptolemaic geocentric theory lies discarded on the ground, made obsolete by the telescope's discoveries. These are illustrated at top and include phases of Venus and Mercury and a surface feature on Mars (left), moons of Jupiter, rings of Saturn, and features on the moon (right). The balance tips in favor of Riccioli's "Tychonic" system."
The figure on the left contains Huygens Systema Saturnium. The top diagram shows how Saturn's appearance to us changes due the changing positions of the Earth (E) and Saturn as they orbit the Sun (G). The bottom portion contains Huygens observation of Saturn presenting its rings to us at their greatest inclination. Both parts date from 1659, 341 b2k.
The second page down on the right is dated to 1661, 339 b2k, and describes the theory of Ptolemy.
The second page on the left is a chart of the Solar System up to the orbit of the planet Saturn. The tracks of three comets are indicated, which appeared in the years 1662, 1680 and 1682, respectively. The page is dated to 1727, 273 b2k.

## Hypotheses

* Sufficient evidence may exist to demonstrate that the apparently stable orbit of Saturn today was arrived at within hominin collective and recorded history.