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Influence of planets on planets

  1. Oct 15, 2003 #1
    What are the influences of planets on other planets ?

    As far as I'm concerned I know about the gravitational influence

    For example the coming close of Mars near Earth
  2. jcsd
  3. Oct 15, 2003 #2


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    Planet to planet influences are almost exclusively gravitational. The closer the planets are to each other, the stronger the gravitational influence. But no planet is close enough to Earth to be of concern...even Mars. Mars is not closer to Earth this month due to the Earth's gravity. The orbits of Earth and Mars around the sun are not perfect circles...they are slightly elliptical. Also, the Earth goes around the sun faster than Mars. So, periodically (like once a year plus a bit more) the sun-Earth-Mars line up (Mars is said to be "in opposition"). Because of the non-circular orbits, the distance of Mars from Earth during opposition varies from time to time. This time, it is closer than it has been in about 50,000 to 60,000 years. Still nothing to worry about. The gravitational influence of the Earth's Moon far outweighs the gravitational influence by Mars on Earth.

    Not much else is exchanged between planets other than reflected light from the sun and occasional meteorites.

    Certainly, the planets have had a lot of cultural influence on human civilization.

    Also, Jupiter may protect the inner solar system from some cometary impacts.
  4. Oct 17, 2003 #3
    One of the reasons given for the variation in the calculations for the next time Mars should be as close to the Earth (approx 230 years) and the Possible last time it was so close (5000 to 60,000) was the effect not of our planet's gravitation, but the effect of Jupiter's gravitation on Mars.
  5. Oct 17, 2003 #4


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    No, I don't think it had anything to do with an influence from Jupiter. Phobos said it right, it was the particular conditions of Earth's and Mars' orbits.

    To add a little more, for this "close" event to happen at opposition, Earth would have to be at "Aphelion" (farthest from the sun in orbit) and Mars would have to be at "Perihelion" (closest to the sun), or very near these positions. But, it would seem that this would happen more often than it did since 50,000 to 60,000 years ago. It does. However, there is one more "orbital condition" to consider that I haven't seen mentioned here on PF.

    The Earth's orbit is inclined from the ecliptic at 0.00 degrees. (This is how the ecliptic was determined, in relation to Earth only). Mars is inclined at 1.31 degrees. So, not only do we need the Aphelion-Perihelion thing going on, but Mars would have to be at the particular point in orbit where its inclination is 0, or very near to it. It is all three conditions that have to be met to make such a close opposition happen.

    Last edited: Oct 17, 2003
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