Saturn’s orbit would cause havoc for inner planets if different

Posted: November 24, 2014 by tallbloke in Astrophysics, solar system dynamics

saturn2From New Scientist:

Earth’s comfortable temperatures may be thanks to Saturn’s good behaviour. If the ringed giant’s orbit had been slightly different, Earth’s orbit could have been wildly elongated, like that of a long-period comet.

Our solar system is a tidy sort of place: planetary orbits here tend to be circular and lie in the same plane, unlike the highly eccentric orbits of many exoplanets. Elke Pilat-Lohinger of the University of Vienna, Austria, was interested in the idea that the combined influence of Jupiter and Saturn – the solar system’s heavyweights – could have shaped other planets’ orbits. She used computer models to study how changing the orbits of these two giant planets might affect the Earth.

Earth’s orbit is so nearly circular that its distance from the sun only varies between 147 and 152 million kilometres, or around 2 per cent about the average. Moving Saturn’s orbit just 10 percent closer in would disrupt that by creating a resonance – essentially a periodic tug – that would stretch out the Earth’s orbit by tens of millions of kilometres. That would result in the Earth spending part of each year outside the habitable zone, the ring around the sun where temperatures are right for liquid water.

Tilting Saturn’s orbit would also stretch out Earth’s orbit. According to a simple model that did not include other inner planets, the greater the tilt, the more the elongation increased. Adding Venus and Mars to the model stabilised the orbits of all three planets, but the elongation nonetheless rose as Saturn’s orbit got more tilted. Pilat-Lohinger says a 20-degree tilt would bring the innermost part of Earth’s orbit closer to the sun than Venus.

Away from such simulations, the circularity of every planet’s orbit does fluctuate over time. If the orbit is already highly elongated, such fluctuations would allow a planet to escape the sun’s gravity. A 20-degree tilt of Saturn’s orbit could eventually boot Mars out, while Earth would require a 30-degree tilt.

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  1. steverichards1984 says:

    Who’d have thought it, planets affect earths temperature!!

    Next, they will be telling us about planetary cycles affecting earth’s climate – what a minute – they already have…….

  2. Brian H says:

    Well, then, whatever you do, don’t mess with Saturn’s orbit!

  3. tchannon says:

    That makes sense so it does not come as a surprise.

    I seem to recall the term forbidden zones in an orbital context. A quick search doesn’t find anything obvious.

  4. Off topic I know, but after four days writing this in response to Steve Goddard I’d appreciate some feedback from any of the regulars here familiar with the science of greenhouse warming: A scientist’s guide to greenhouse warming

  5. doug Proctor says:

    We go from the absolute specialness of the pre- galileo world to the common speck of dust of the 1975 world to the sort-of specialness of 2013 habitable zone to the absolute specialness of 2014 where Everything has to be aligned for us to be here.

    Next year I’m expecting that God thr Clockmaker has been sighted on the Jovian new moon, Japetus.

    Full circle.

  6. steverichards1984 says:

    Just to amplify: the study ‘found’ that major changes to the orbits of the larger planets in the solar system would have catastrophic effects on earth.

    A potential implication of this is: smaller changes to the orbits of the larger planets could have small but noticeable effects to us on earth. Maybe climate change?

  7. tallbloke says:

    Stevie: Yes. My second PRP paper shows a link between the motion of the gas giant planets and the changes in the speed Earth rotates at. Changes will affect ocean bottom pressures and internal tides which produce cold upwelling (nutrients) and a raft of other linked meteorology outlined in Judy Curry and Marcia Wyatt’s paper on the ‘stadium wave’.

    Click to access prp-1-199-2013.pdf