The Importance of Planetary Rings
15/10/25 The Importance of Planetary Rings Dr Phil Sutton
Many asteroids and planets have rings. The first planet that springs to mind is Saturn, as its rings can be seen by the naked eye (with the help of a telescope). However, a few more planets in our solar system also have rings, some of these include : Neptune, Uranus and Jupiter. Some of their moons have been formed with the help of rings.
What are rings?
Rings consist of a collection of particles of varying size that are moving rapidly in the same direction and are also orbiting a planet. Their sizes can be determined by measuring how light scatters from the brightness of stars that move behind the ring system. Smaller particles are more likely to forward scatter, and the bigger particles tend to backward scatter. As all the particles move in the same direction, rings quickly orientate to orbit in the same direction that the planet rotates. Although, the rings may fall off plane due to the oblateness of planets (they aren’t perfectly spherical) can cause variations in gravitation.
Most ring systems are a mono system because they are very flat yet they may extend up to 140,000km. Their flatness is caused by the many frequent collisions between the particles in the ring and the oblateness of the planet. On elliptical orbits, individual particles will collide with each other which dampens radial movement.
Embedded Moons
Some planets have moons embedded within their rings. For example, Saturn’s moon, Daphnis (8km in diameter), orbits inside the Keeler gap (42km width). Daphnis is slightly elliptical and so has inclined orbits above and below the ring plane as particles move past the moon, causing waves to form. These gaps can contain unseen moons, which can be weighed by measuring the width of the gap formed.
Orbital resonances
Two bodies are said to be in orbital resonance if their orbital periods can be expressed as a ratio of two integers [1]. Orbital resonances are another cause of gaps in rings. Primarily, this process causes the gap between Saturn’s A and b rings due to the moon Mimas which is in a 2:1 mean-motion resonance (ring particles orbit twice for every one orbit of Mimas) [2]. All of Saturn’s moons cause resonant features (for example, gaps, moons, waves).
Moon Migrations
Resonant structures that are formed in the rings by moons actually push back on the moon which causes radial migration. Spiral density waves orbit at sub-Keplerian velocities (a slower speed, like a planet around a star [3]) which increases angular momentum of the moon, causing the moon to move outwards.
Planetary rings are complex but provide a valuable insight into planet and moon formation. Rings are far from being static features, they’re shaped by continual particle collisions, gravitational effects caused by planetary oblateness, and interactions with embedded moons. Moon-ring interactions cause gaps and waves to form in the rings, as well as processes such as orbital resonance. Studying rings within our solar system allows scientists to better understand planetary evolution long-term and apply it to different galaxies.
References:
[1] “Astronomy & Astrophysics (A&A),” www.aanda.org. https://www.aanda.org/glossary/175-orbital-resonance
[2] D.G. Simpson. “The Rings of Saturn,” Nasa.gov, 2019. https://caps.gsfc.nasa.gov/simpson/kingswood/rings/
[3] A. Sanna et al., “Discovery of a sub-Keplerian disk with jet around a 20 M young star,” Astronomy and Astrophysics, vol. 623, pp. A77A77, Jan. 2019, doi: https://doi.org/10.1051/0004-6361/201833411.
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1, Blogs overall presentation: The blog does include the date title and name of speaker throughout which is well done, the grammar is also well done throoughout the blog. 3/3
2, Accuracy of reporting the seminars take home message: The message that Phil was trying to convey throughout the seminar has been conveyed well through this blog and is shown excellently through each section.
3, Accuracy of contextualisation for the research: Throughout the blog there has been well thought through research context and at the end you touch upon the social context as well. 3/3
4, Additional research and use of external sources: There is additional research present throughout the blog which shows a wider reading and draws upon other sources however there needs to be one direct quote throughout and this hasn’t been done. 2/3
5, Writing style and level for audience: The blog is written in a way that is easy to read and is very helpful for people with limited knowledge about the topic. 3/3
Overall 14/15, this is a very well writen blog and is very informative, just needs a direct quote from a source.
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The content is accurate and engaging. You have listed external sources and it is understandable for audiences without a science background. You clearly understand the topic well.