Low-eccentricity orbits and the Plane of the Elliptic

In summary, the planets in our solar system all have orbits that are close to circular, and they have achieved this by bringing their eccentricity down to near 0. All of the planets have done this without any course corrections. It is likely that this is a property of the system as a whole, and is not something that can be shown by Kerbal Space Program.
  • #1
GofG
22
0
So I've been playing some Kerbal Space Program, and it's taught me a couple things. Primarily, that circularizing an orbit (bringing its eccentricity down to near 0) is a matter of extremely precise engineering, and that matching planes with another satellite's orbit is also extremely nontrivial.

How is it that an inordinate amount of the stuff orbiting Sol all shares the same plane of the elliptic? All of the planets, all the asteroids, most of the transneptunian junk... I scoured Wikipedia for an explanation, but couldn't find one. Is it normal for star systems to have a single plane of the elliptic for most of their satellites? What caused this?

Secondly and more importantly, why do the orbits of all the planets and junk have such low eccentricity? In KSP, I can spend hours with a high-ISP engine and kilotons of rocket fuel trying to get my eccentricity below 0.10, and yet all of the planets in our system seem to have accomplished this feat without even any course corrections! How did this happen? I would expect Earth's orbit to be circular á la the anthropic principle, but why do the other planets have this property as well?

I suspect the answer is simple and I'll feel foolish when I hear it, but I'm still quite eager to hear it.
 
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  • #2
Is it normal for star systems to have a single plane of the elliptic for most of their satellites?
According to computer models and the hundreds of planetary systems studied so far, yes.

What caused this?
During formation of a stellar system, the cloud of dust and gas becomes a disk (a disk is the only "stable" configuration without permanent collisions). And in the very long run, other orbits have problems with stability. That's nothing Kerbal Space program can show.

Long-term stability is also important for the eccentricity. In a planetary system as dense as ours, any highly eccentric orbit would be very unstable due to the influences of other planets.
 
  • #3
GofG said:
In KSP, I can spend hours with a high-ISP engine and kilotons of rocket fuel trying to get my eccentricity below 0.10, and yet all of the planets in our system seem to have accomplished this feat without even any course corrections!
To reinforce what mfb has said: you have spent hours trying to achieve a result. The planets spent a few million, or even a few scores of millions of years to achieve that low eccentricity.

A high eccentricity planet will eventually collide with another planet, plunge into the sun, or through gravitational interaction be ejected from the system. Highly eccentric orbits are rarely going to be stable over billions of years.

Note that the Trans-Neptunian objects have higher eccentricities and stray further from the ecliptic, while that is even more the case for Oort cloud comets - there is just so much more space out there (and the objects are that much smaller) that they can 'get away with' being eccentric.
 

1. What is a low-eccentricity orbit?

A low-eccentricity orbit is a type of elliptical orbit where the distance between the orbiting body and its focus (usually a larger celestial body) remains relatively constant throughout the orbit. This means that the orbit is nearly circular in shape, with a low eccentricity value close to 0.

2. What is the plane of the elliptic?

The plane of the elliptic refers to the flat surface in which the elliptical orbit lies. In other words, it is the two-dimensional space in which the orbiting body moves around its focus. The plane of the elliptic is often used as a reference point for measuring the inclination of an orbit.

3. How does eccentricity affect an orbit?

Eccentricity is a measure of how much an orbit deviates from a perfect circle. In low-eccentricity orbits, the eccentricity value is close to 0, meaning that the orbit is nearly circular. Higher eccentricity values indicate more elliptical orbits, with the orbiting body moving closer and further away from its focus at different points in the orbit.

4. What are some examples of low-eccentricity orbits?

Some examples of low-eccentricity orbits include the orbit of Earth around the Sun, the Moon around Earth, and the International Space Station around Earth. These orbits are nearly circular, with eccentricity values close to 0.

5. Why are low-eccentricity orbits important in space exploration?

Low-eccentricity orbits are important in space exploration because they provide stable and predictable paths for spacecraft and satellites to follow. This allows for more accurate and efficient navigation, as well as easier maintenance and communication with orbiting objects.

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