Orbital Simulation: Estimating Mass from Orbit & Visual Observations

  • Context: Graduate 
  • Thread starter Thread starter DaveC426913
  • Start date Start date
  • Tags Tags
    Orbital Simulation
Click For Summary

Discussion Overview

The discussion revolves around the feasibility of a comet with a long orbital period (approximately 150 years) having a perihelion located between the orbits of Mercury and Venus. Participants explore the implications of orbital mechanics, including the relationship between orbital period, semi-major axis, and eccentricity, as well as the challenges of estimating mass from orbital characteristics without knowledge of density or albedo.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Conceptual clarification

Main Points Raised

  • Some participants suggest that the orbital period determines the semi-major axis but does not constrain eccentricity, which could allow for a perihelion between Mercury and Venus.
  • Others argue that if the orbiting mass is much smaller than the central mass, the orbit is independent of the orbiting mass, implying that mass cannot be determined from the orbit alone.
  • One participant mentions the need for a table of comets to find examples that fit the proposed perihelion and period, indicating that such orbits are plausible.
  • There is a discussion about whether astronomers can deduce mass from visual observations and orbital data without knowing density, with some suggesting that assumptions about the object's composition could narrow down possible densities.
  • Concerns are raised about the stability of orbits for comets that enter the inner solar system, noting that resonant orbits with outer planets may be necessary to avoid being thrown off course.
  • Participants highlight that many comets do not survive multiple orbits in the inner solar system, suggesting that unstable orbits may not be problematic for certain scenarios.
  • One participant expresses uncertainty about the stability requirements for the comet in a narrative context, indicating that the story's needs are still being developed.

Areas of Agreement / Disagreement

Participants express differing views on the plausibility of the proposed orbit and the implications for estimating mass. There is no consensus on the feasibility of the orbit or the methods for determining mass without density information.

Contextual Notes

Participants acknowledge that orbits have constraints and that stability is a significant factor, particularly for long-term orbits. The discussion includes assumptions about the nature of comets and their interactions within the solar system, which remain unresolved.

DaveC426913
Gold Member
2025 Award
Messages
24,482
Reaction score
8,745
(unrelated to my other post about an asteroid)

1]
I would like to check a postulation with someone who has an orbital simulator, or a good head for orbital mechanics.

Given an object such as a comet with orbital period of about 150 years, could it have a perihelion at a distance between Mercury and Venus?

If no, what does work? Change period? Change perihelion?



2] Could we tell anything about this object's mass from its orbit and/or visual observations if we do not know its density or its albedo factor?
 
Last edited:
Astronomy news on Phys.org
DaveC426913 said:
Given an object such as a comet with orbital period of about 150 years, could it have a perigee at a distance between Mercury and Venus?

I don't see why not. The period determines the semimajor axis of the orbit, but it doesn't say anything about the eccentricity (which, combined with semimajor axis, could give you the perigee).
2] Could we tell anything about this object's mass from its orbit and/or visual observations if we do not know its density or its albedo factor?

In a case where the orbiting mass is much smaller than the central one, the orbit is independent of the orbiting mass, so I would say no.
 
SpaceTiger said:
I don't see why not. The period determines the semimajor axis of the orbit, but it doesn't say anything about the eccentricity (which, combined with semimajor axis, could give you the perigee).

I guess all I have to do is find a table of comets and see if any of them have a perhelion and period similar. That'd be enough to show it's plausible.




SpaceTiger said:
In a case where the orbiting mass is much smaller than the central one, the orbit is independent of the orbiting mass, so I would say no

Yes, but do astronomers use any other techniques? If we spotted a mystery object right now, and knew its orbit and size, but not its density, could we deduce anything abojut its mass?
 
DaveC426913 said:
Yes, but do astronomers use any other techniques? If we spotted a mystery object right now, and knew its orbit and size, but not its density, could we deduce anything abojut its mass?

If it were a very small object, we would assume it was rocky...and that narrows the range of possible densities. It doesn't directly tell you about the mass, though.
 
Ach! I can't find any info online that will demo the plausibility of this orbit.

I don't know (or care about) the semi-major axis or the eccentricity, I only know (and care about) the period and the perihelion.
 
Last edited:
DaveC426913 said:
I don't know (or care about) the semi-major axis or the eccentricity, I only know (and care about) the period and the perihelion.

There are comets with periods less than 200 years (over a hundred of them) and perihelions in the inner solar system, so I don't see why you think this would be implausible.
 
I also am at a loss as to why you would seem to think this orbit might not be plausible.

Such an orbit would have a semi-major axis of about 4.2 billion Km (just inside Neptunes orbit), and an aphelion of between 8.3 & 8.35 billion Km, or just about 14% further than Pluto at its furthest.
 
Thank you. I just wasn't sure.

This is for a story for a friend (a different friend), and I wanted to check the numbers.

I know that you can't just pick numbers that are convenient. Orbits ahve some constraints.
 
But comets that pass into the inner solar system will need to have resonant orbits with the outer planets, to keep from being thrown off course, wouldn't they? It places restrictions on possible long-term stable orbits. Of course, if you ignore the planets and just look at the sun and the comet, then sure its perfectly possible.
 
  • #10
Polar orbit.
 
  • #11
DaveC426913 said:
I know that you can't just pick numbers that are convenient. Orbits ahve some constraints.

Stability constraints are more of a concern when you need your object to remain in orbit for a long time. In many cases, comets don't make it more than a few orbits into the solar system anyway, so finding one on an "unstable" orbit wouldn't be a big surprise, nor a problem. If, for some reason, you need long-term stability for your comet, that's a different story entirely and will depend in a complicated way on the many-body interactions in the solar system. Do you need it to be stable? If so, for how long?
 
  • #12
"Do you need it to be stable? If so, for how long?"

I don't know yet actually. I'll let you know when I get farther into the story! :rolleyes:

The situation at this point in the story is that they don't know how long it's been there. They only found it on its latest dive into the inner system.

In a polar orbit I presume it would be more stable.
 

Similar threads

Graduate N-Body Simulations of Chaos in the Orbits of Trappist System Planets
  • · Replies 12 ·
Replies
12
Views
3K
High School Asteroid 2024 YR4 has a 1% risk of a multi-megaton impact in 2032 (now ruled out)
  • · Replies 35 ·
2
Replies
35
Views
9K
Undergrad New Developments In The Search For Planet X
  • · Replies 2 ·
Replies
2
Views
3K
Undergrad Comet Bernardinelli-Bernstein enters inner solar system
  • · Replies 1 ·
Replies
1
Views
2K
Undergrad Why Does the Sun Have an Orbital Period Like a Year?
  • · Replies 11 ·
Replies
11
Views
4K
Undergrad I need some support, please, for a gravity assist analysis
  • · Replies 86 ·
3
Replies
86
Views
9K
Undergrad Position and Velocity in Heliocentric Ecliptic Coordinates
  • · Replies 3 ·
Replies
3
Views
5K
Graduate How is the Trappist 1 system stable?
  • · Replies 6 ·
Replies
6
Views
3K
From circular orbit to elliptical orbit
  • · Replies 3 ·
Replies
3
Views
3K
Graduate What keeps Rhea stable? Simulation shows Titan-assist escape
  • · Replies 6 ·
Replies
6
Views
3K