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I recently made an n-body simulation and thought it would be interesting to try and model it on the interior of our solar system (Sun to Mars), but I cannot find initial conditions for such an undertaking. My biggest problem seems to be that I'm not working with a spherical coordinate system and instead have opted to using the 3D Cartesian system. Does anyone know of any data that gives initial positions and velocities of the Solar System's planets and their moons in 3D Cartesian coordinates, so I can plug this into a system of differential equations as initial conditions?

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marked as duplicate by Sjoerd C. de Vries, whuber, m_goldberg, Michael E2, Artes May 21 '13 at 6:17

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FWIW, AstronomicalData[] has a nice bounty of information, including orbit paths and eccentricities. See e.g. this question. On the other hand, there's a certain appeal in using numerical integration instead of merely taking coordinates from an ephemeris... –  J. M. May 20 '13 at 19:25
    
Just in case you are interested in accuracy, it might be worth noting that the system of ODEs described in your previous question at mathematica.stackexchange.com/questions/25039/… is not what is usually meant by an "n-body simulation," because it does not account for interactions among the bodies: it's just a collection of independent central field solutions. It might be a fine approximation for times close to the initial time but will be observably incorrect. –  whuber May 20 '13 at 19:36
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@J.M.: Yeah, there's something very satisfying about using a system of ODEs to calculate each planet's path, so I'd love to have initial conditions to work with and see how the system evolves :) –  user7388 May 20 '13 at 20:08
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You were asking for positions and velocities. These can be found using AstronomicalData as demonstrated in that question. –  Sjoerd C. de Vries May 20 '13 at 21:44
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Since your question got closed... if you're interested in seeing how JPL does it, you might want to see this. –  J. M. May 21 '13 at 7:44