Possible criteria or parameters for planetary collision?

Click For Summary

Discussion Overview

The discussion revolves around the criteria or parameters that influence planetary collisions and the subsequent behavior of moons in their orbits, particularly focusing on the dynamics of tidal acceleration and deceleration following such events. The scope includes theoretical modeling, orbital mechanics, and the formation processes of moons.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants inquire about the factors that determine whether moons spiral outward or inward after a collision, suggesting a need for specific criteria related to moon formation.
  • One participant distinguishes between the immediate effects of a collision event and the long-term orbital changes of moons, emphasizing the different timescales involved.
  • Another participant proposes that the orbital period of a moon relative to the planet's rotation period influences whether the moon will experience tidal acceleration or deceleration.
  • It is suggested that the size of the tides on both the planet and the moon also plays a role in determining the magnitude of these orbital changes.
  • Participants discuss the concept of "sign" in relation to the direction of orbital change, with one suggesting that outward orbits could be considered "positive" and inward orbits "negative," though this is noted to be arbitrary.

Areas of Agreement / Disagreement

Participants express varying views on the definitions and implications of tidal forces and orbital dynamics, indicating that multiple competing perspectives remain without a clear consensus on the criteria for planetary collision and moon behavior.

Contextual Notes

Limitations include the dependence on specific definitions of terms like "positive" and "negative" in the context of orbital dynamics, as well as the unresolved nature of the parameters influencing moon behavior post-collision.

Who May Find This Useful

This discussion may be of interest to those studying celestial mechanics, planetary formation, and the dynamics of moons in relation to their parent planets.

Positron137
Messages
41
Reaction score
0
Possible "criteria" or parameters for planetary collision?

Suppose a computer model were created to simulate two proto-type planets on a collision course (for example, the Earth-Moon collision in the Hartman theory of the Moon formation). We know that the Moon is spiraling outwards (tidal acceleration). The first question I have, is why do certain moons of planets spiral outwards or inwards (into a main planet)? Second question: is the tendency of these moons to spiral outward or inward dependent on a "criteria: of some sort of the formation of the moon (so if a moon, or moons were created by a proto-planet collision, or by gravitational attraction past the Roche radius)? WOuld there have to be several parameters regarding the collision to determine the behavior of the moon's orbit? And if there are parameters, what would they be? Thanks!
 
Last edited:
Astronomy news on Phys.org
I think you are mixing two different things here.

- the collision event and moon formation. That happens in (relatively) short timescales.
- orbital changes long afterwards. The moon spirals out for billions of years now.

The orbital radius of a moon increases if the orbital period is longer than a day of the planet, and if the planet shows significant tides due to this moon.
 
Ah ok. I understand. So I guess the proper thing to ask is, after the collision though, what determines whether the moon will tidally accelerate (orbit outward) or decelerate (spiral inward) after billions of years?
 
If there are no other objects influencing this:
The periods of one moon orbit compared to the rotation period of the planet determines the sign (neglecting the rotation of the moon here), the size of tides on the planet (and moon) determines the magnitude.
 
Ok. What do mean by "sign" exactly?
 
Outwards (like our moon: one orbit takes longer than a day) or inwards (like Phobos at Mars).
 
Ah ok. So is it "positive" if it orbits outwards, and "negative" if it orbits inwards?
 
That depends on your arbitrary definition of "positive" and "negative".
 
I see. Alright.
 

Similar threads

Undergrad Planetary Formation: Could Collisions Explain Our Solar System?
  • · Replies 52 ·
2
Replies
52
Views
7K
Undergrad Question of accuracy of galactic collision simulations
  • · Replies 11 ·
Replies
11
Views
2K
Undergrad How Big of an Object Orbiting Closer to the Sun Than Earth Could Be Overlooked?
  • · Replies 17 ·
Replies
17
Views
4K
Undergrad New Developments In The Search For Planet X
  • · Replies 2 ·
Replies
2
Views
3K
Graduate Why Are Saturn's Rings and Planetary Orbits Aligned Despite Cosmic Disturbances?
  • · Replies 5 ·
Replies
5
Views
2K
Graduate What keeps Rhea stable? Simulation shows Titan-assist escape
  • · Replies 6 ·
Replies
6
Views
3K
Questions about a habitable second moon
  • · Replies 37 ·
2
Replies
37
Views
8K
Graduate Would a larger Martian moon create a stronger magnetic field
  • · Replies 3 ·
Replies
3
Views
2K
Is my fictional Solar System stable and realistic?
  • · Replies 21 ·
Replies
21
Views
6K
High School Miscellaneous Trivia: Planets and Moons
  • · Replies 7 ·
Replies
7
Views
3K