Orbits of Outer Planets

[WeAreBongo]

How does the sun keep the outer planets orbits in check when they're so very far away from it? Surely it's influence is much much weaker at the fringes of the solar system?

[jno]

it is, but still strong enough. If it wasn't the planets would have wandered off long ago (and maybe many have)

[Teddio]

The Sun's gravitational field strength is inversely proportional to the square of the distance. For example Jupiter is approximately 400 million miles from the Sun and Saturn is approximately 800 million miles from the Sun. The gravitation field strength at Saturn's orbital distance will be one quarter that of Jupiter's.

[New Judge]

One of the main reasons for this is that, alone among the four fundamental forces, gravity has no positive and negative effects. There is no anti-gravity (no, don�t start on about anti-matter, we�re only talking about what is known here, not what is speculated to exist). There is just gravity and all bodies are attracted to all others by virtue of their mass.

Pluto has a highly eccentric orbit and varies in its distance from the Sun between 30 and 50 times that of the earth. Light from the Sun takes five or six hours to reach it compared with just eight minutes to reach the earth.

However, the nearest significant body outside the solar system is over 4 light years away � about 6,000 times as far � and it is the Sun�s gravity which has the most profound effect on the planets. With its huge mass (about 330,000 times that of the earth) the effect of its gravity is felt over enormous distances, even allowing for the effect of distance as explained by Teddio.

[WeAreBongo]

Thanks all. Would the gravity of the gas giants effect an object like Pluto or is the sun omnipotent in matters of gravitational attraction?

[heathfield]

All of the planets in our solar systemare affected by the gravity of all the other planets to some extent. Discrepancies were noted in the predicted orbit of Uranus, and this led to the discovery of the planet Neptune.

[dundurn]

Classic example of the effects of mass and distance are tides in the Earth's seas. The Moon is almost negligible in size compared to the Sun but because it is so much nearer the Earth it has twice the effect that the Sun has in creating the tides.

[sddsddean]

Jupiter certainly affects its moons. During the Voyager probes it was discovered that one of Jupiters moons, Io, has got active volacnoes (the first non Earthly ones discovered in the solar system). It was determined that because the of Io's orbit it passes between Jupiter and other moons and the gravitational forces are constantly 'squeezing and pulling' Io to produce the active volcanic system.

[4candles]

Good answers. Also consider that the Sun comprises 99.86% of the mass of the Solar System.

[kwicky]

I can understand the attraction by gravity but when there is an eclipse by another planet passing between the sun surely the attraction would greatly diminish. For example if you tried to use a magnet to pick up an item from the table and put a barrier in between it would not work?

[beso]

Nothing gets in the way of gravity. You can't sheild it like you can with electromagnetinc fields. These fields can be shielded by guiding them into conductive materials designed to bypass the protected zone. Gravity is actually a distortion of space time itself.

[mibn2cweus]

An object in motion tends to move at a constant velocity in a straight line. Gravity tends to bring objects together. When inertia and gravity are equally matched neither side wins and an orbit is the result. How this tug-of-war comes to a draw seems at first unlikely if not bizarre. You might find yourself asking, �What tendency brings about orbital stability?� and �How are orbits initially established in the first place?� �What causal attributes preside over this unlikely marriage between two apparently opposing forces?�

Distance and velocity are inversely related to where an orbit is established. With distance comes a decrease in the attraction of gravity so that a planet can and must orbit more slowly around the gravitational centre of the system. Otherwise its momentum will throw it outward into a more distant orbit. If a planet is not orbiting fast enough it will be accelerated toward the Sun. As a planet is drawn towards the Sun and picks up momentum it will eventually gain enough speed to overtake the inward acceleration of gravity and begin to move away from the Sun (provided it does not collide with and become part of the Sun). This process of changing speed and distance brings about the elliptical orbit which is characteristic in varying degrees of all planets.

The solar system first took form as matter was drawn together by a dominant centre of gravity. As matter spiraled inward towards the centre the prevailing direction of rotation of dust and gases accelerated in the same way that a figure skaters rate of rotation speeds up as they draw their body mass inward towards the axis of rotation.

As larger bodies formed they swept their orbits clean with the gravity they accumulated with their growing mass. Bodies with highly eccentric orbits collided with other bodies with more circular orbits until only planets with orbits that did not cross the orbits of other planets remained.

[mibn2cweus]

The distance at which a given planet establishes an orbit is determined mostly by the velocity of its orbit. Mass is also a factor but the Sun is the overwhelming contributor to the systems mass.

chart for comparing planet distance from the Sun to orbital speed or period

[WeAreBongo]

Thanks for that last answer - it even answered my next question which was to begin with the words But Why Doesn't...

[Teddio]

It is highly probable that any accreting cloud of dust and gas will have an angular momentum component. Since angular momentum is always conserved, the resulting solar system will be composed of a central rotating star (or more than one star) with planets orbiting it, each planet itself revolving about its axis.
Viewed from the Sun's north pole, the Sun, planets and asteroids (with a few exceptions) revolve on their axes in an anticlockwise direction and the bodies orbit the Sun in an anticlockwise direction.

[nightmare]

New Judge
So, you are not aware of the real existence of antimatter ?
Antimatter has positive mass anyway, so is subject to (attractive) gravitational forces like "normal" matter.