# كيف يمكن أن تكون فترة دوران قمر / قمر كوكب ما "فوضوية" (مثل Hyperion حول زحل)؟

وفقًا لويكيبيديا (انظر المعلومات أدناه الصورة) فترة دوران هايبريون حول زحل "فوضوية".

ماذا يعني ذلك؟ الفترة (بالأيام / الساعات) تختلف كل دورة دون أي قانون يساعد في تحديدها؟

كيف يمكن أن يكون؟

وفقًا لويكيبيديا (انظر المعلومات أدناه الصورة) فترة دوران هايبريون حول زحل "فوضوية". ماذا يعني ذلك؟

تشير مقالة ويكيبيديا إلى أن دوران هايبريون فوضوي وليس مداره حول زحل. سأفترض أنك تسأل كيف يمكن أن يكون الدوران المحوري لـ Hyperion فوضويًا. (مداره ليس كذلك).

الجسم الذي لا يخضع لأي عزم دوران خارجي سيكون له زخم زاوي ثابت. هذا لا يعني أن مثل هذا الجسم سيكون له سرعة زاوية ثابتة. ضع رباطًا مطاطيًا حول كتاب وارميه في الهواء ، مما يمنحه معدل دوران لطيفًا قبل تركه يذهب.

راجع السؤال ثبات دوران المنشور المستطيل للحصول على التفاصيل.

## Orbit

The orbit of Iapetus is somewhat unusual. Although it is the Saturn's third-largest moon, it orbits much farther from Saturn than the next closest major moon, Titan. It has also the most inclined orbital plane of the regular satellites only the irregular outer satellites like Phoebe have more inclined orbits. The cause of this is unknown.

Because of this distant, inclined orbit, Iapetus is the only large moon from which the rings of Saturn would be clearly visible from the other inner moons, the rings would be edge-on and difficult to see.

## Observation and exploration

Neptune (top) and Triton (bottom) three days after Voyager 2's flyby

The orbital properties of Triton had been defined with high accuracy in the 19th century. It was found to have a retrograde orbit, at a very high angle of inclination to the plane of Neptune's orbit. The first detailed observations of Triton were not made until 1930. Little was known about the satellite until Voyager 2 arrived at the end of the 20th century. & # 913 & # 93

Before the arrival of Voyager 2, astronomers suspected that Triton might have liquid nitrogen seas and a nitrogen/methane atmosphere with a density as much as 30% that of the Earth. Like the famous overestimates of the atmospheric density of Mars, this was completely false. As with Mars, a denser atmosphere is postulated for the body's early history. ⎿]

The first attempt to measure the diameter of Triton was made by Gerard Kuiper in 1954. He obtained a value of 3,800 km. Subsequent measurement attempts arrived at values ranging from 2,500 to 6,000 km, or from slightly smaller than our Moon to nearly half the diameter of Earth. ⏀] Data from the approach of Voyager 2 to Neptune on August 25, 1989, led to a more accurate estimate of Triton's diameter (2,706 km). ⏁]

In the 1990s, various observations from Earth were made of the limb of Triton using the occultation of nearby stars, which indicated the presence of an atmosphere and an exotic surface. The observations suggest that the atmosphere is denser than the Voyager 2 measurements had indicated. ⎭]

New concepts for missions to the Neptune system to be conducted in the 2010s have been brought forward by NASA scientists on numerous occasions over the last decades. All of them identified Triton as being a prime target and a separate Triton lander comparable to the Huygens probe for Titan was frequently included in those plans. To date, however, no efforts aimed at Neptune and Triton went beyond the proposal phase and NASA's funding on missions to the outer solar system is currently focused on the Jupiter and Saturn systems. ⏂]

## Wisps and cliffs

Dione's surface contains both heavily and moderately cratered regions, with some craters as large as 62 miles (100 km). But Dione is something of a puzzle due to the location of its heavily cratered areas. Generally, the leading hemisphere of a body traveling through space plows face-on through debris, and is more heavily cratered. Dione, however, has a more heavily cratered backside than front. Scientists have speculated that a collision could have spun the moon around &mdash an impactor that created one of the 22-mile (35 km) craters could have had the force to turn the moon &mdash but the fact that it seems to have spun exactly 180 degrees is unusual.

Dione is 1.48 times as dense as water, suggesting that the moon has a dense core surrounded by ice or water. The temperature on the moon averages minus 302 degrees Fahrenheit (minus 186 degrees Celsius). The exceptionally cold temperatures cause the icy surface to behave much like rock.

When Voyager 1 surveyed the moon in 1980, it unveiled wispy features on the trailing side. NASA's Cassini-Huygens probe took close-up images more than 20 years later that revealed the wisps were ice cliffs. As dark material fell from the cliffs, they revealed brightly shining ice underneath. Created by tectonic activity, these fractured areas crisscross the moon, running tens to hundreds of kilometers in length.

Cassini also detected a wispy oxygen atmosphere on Dione. It is very thin there is just one oxygen ion for every 0.67 cubic inches (11 cubic centimeters). It is equivalent to conditions 300 miles (480 km) above Earth.

Like many moons, including Earth's, Dione is tidally locked, with the same side always facing its parent planet. The gravity of the moon keeps two smaller moons, Helene and Polydeuces, locked into the same orbital position as the three travel around Saturn. Dione also interacts with two of the larger moons of Saturn, Mimas and Enceladus, influencing their orbits. [Photo Gallery: The Rings and Moons of Saturn]

A 2016 presentation at the American Astronomical Society suggested that some of the moons of Saturn, including Dione, could have been hit by debris from a previous generation of moons. Dione's craters have also been studied for signs of change, such as a separate 2016 Icarus study of the ray system of Creusa crater. The team observed that some of the ejecta rays have been erased over time due to erosion from dark particles (which could be the same material seen on other moons such as Hyperion and Iapetus). Other contributors to the erosion likely were plasma and E-ring particles, the article noted.

## Dione, Saturn's moon

Dione was discovered in 1672 by Giovanni Domenico Cassini. Dione is composed primarily of water as ice, but, given its higher density than the other moons of Saturn (outside of Titan, whose density is increased by gravitational compression), it probably contains a quantity large enough to more dense material, such as silicate rocks. The shots taken at 500 km away by the Cassini spacecraft, used to confirm that the plumes observed are huge white cliffs of ice that crisscross Dione.
Dione is in synchronous rotation with Saturn, it made ​​a revolution in itself for a spin around Saturn in about 66 hours.