What if Earth had rings?

rod

Oct 22, 2019
1,405
442
1,560
The report stated "It's possible thatEarth already possessed a ring. Our planet was born about 4.5 billion years ago, and previous research suggests the moon arose a short time later. The prevailing explanation for the moon's origin is that it resulted from the collision of two protoplanets, or embryonic worlds. One of those was the newborn Earth, and the other was a Mars-size rock called Theia, named after the mother of the moon in Greek mythology. The impact would have generated a ring of debris around Earth that eventually coalesced into the moon. In essence, although the vision of a ringed Earth might seem like a fantasy, it might have once — for a moment in time — been true."

The giant impact hypothesis for the origin of the Moon calls for at least a 2 lunar mass ring around Earth, just near or outside the Roche limit for the Moon to evolve. 'Implications of Lunar Origin via Giant Impact for the Moon's Composition and the Thermal State of the Protoearth', https://ui.adsabs.harvard.edu/abs/2008LPI....39.2429C/abstract, March 2008

My observation. Using present mass of earth and moon, present lunar orbital eccentricity, the lunar period orbiting at 3.93 earth radii, the period <= 11 hours. The Moon's formation and orbit must change greatly from present parameters seen in astronomy using the giant impact model. The Moon's angular size (using same dimension for the Moon) at 3.93 earth radii is close to 8 degrees angular size in the sky. Thus observing a 2 lunar mass ring system around the early Earth - would be difficult today :)
 
  • Like
Reactions: Catastrophe
Feb 18, 2020
1,110
820
1,570
Rod

Congratulations on a really excellent summary.
One point I am missing out on.
Your ref states:
"Results of recent simulations of lunar-forming impacts that include effects of pre-impact rotation in the impactor and the target protoearth are discussed.

When I read your post I really thought I might get something on two questions which have been bothering me for some time. I bow to your superior knowledge in this field and would really appreciate any light on my darkness.

These are:

Rings seem to go both ways. Either they are the result of "body" collisions or they are a stage in the formation of "bodies". Can they do both and, if so, where is the dividing condition?

I have some problems with the Moon and the Roche limit. We are told that the newly formed Moon moved away from the Earth. Is there any infringement with the Roche limit?



Many thanks for any clarification.

Cat :)
 
  • Like
Reactions: rod

rod

Oct 22, 2019
1,405
442
1,560
Catastrophe, thanks for your post but no bowing :) I have some knowledge here based upon studies on my part for a number of years now on the subject. In my opinion, the giant impact model for the origin of the Moon is an ugly math and tidal forces problem in the equations that pops out various answers and surprises as the numbers are crunched. You asked, "Rings seem to go both ways. Either they are the result of "body" collisions or they are a stage in the formation of "bodies". Can they do both and, if so, where is the dividing condition?

My answer, I do not know here :) Different papers on the giant impact model disclose different problems I see when reviewing. Here is an example, https://ui.adsabs.harvard.edu/abs/2016arXiv161102769W/abstract, "...The main concern was that models were multi-staged and too complex. Here, we present initial impact conditions that produce an Earth-Moon system whose angular momentum and isotopic properties are correct. The model is straightforward and the results are a natural consequence of the impact." The arXiv paper is at https://arxiv.org/ftp/arxiv/papers/1611/1611.02769.pdf

So far, from what I can gather, the early Moon forms at or near Earth's Roche limit or close to 3 earth radii distance. Today the Moon orbits close to 60.3 earth radii for the mean. Another shorter report, https://skyandtelescope.org/astronomy-news/when-and-how-did-the-moon-form/

The initial angular momentum of the Earth-Moon system is difficult and the initial length of day too for the Earth, e.g. this report has a 5 hour day, https://phys.org/news/2016-10-theory-moon.html

https://ui.adsabs.harvard.edu/abs/2016Natur.539..402C/abstract, November 2016. This paper has a 2.5 hour initial length of day for the Earth. Changing different parameters here can result in some real differences in the formation of the Moon too.

Catastrophe, I still collect information on this subject from time to time. Showing the giant impact model, *warts in all* I think is still a work in progress :)
 
  • Like
Reactions: Catastrophe

ASK THE COMMUNITY

Latest posts