Celestia Forums

I thought it would be entertaining to define the orbit of Shoemaker-Levy 9 and watch it go crashing through Jupiter. (Of course, Celestia would show it coming out the other side afterward, but what the heck...)

Unfortunately, when I put in what I thought were the right orbital elements, I found that Celestia didn't draw the orbits as being at all near one another on that fateful day in 1994.

So far I've only found the orbital elements from 1993 in IAU circular 5800 by Brian Marsden. They wouldn't be as precise as elements measured closer to the collision date, of course. Unfortunately, as best I can tell, the differences between the apparent orbits of 1993e and Jupiter are much too large to be due to small corrections. After all, the 1993 elements are the ones that first indicated that a collision would happen.

I'd greatly appreciate it if someone with experience in converting between comet and asteroid orbital conventions would take a look at the .SSC file I came up with and see if I've done something really stupid. It's at http://www.lns.cornell.edu/~seb/celestia/shoemaker-levy-9.ssc I've tried to include comments showing most of the calculations.

Thanks.

I don't seen anything obviously wrong, but I'll look at it in closer detail later. One possibility is that the gravitational influence of Jupiter throws off any attempt to model the orbit with an ellipse. Or perhaps the elements you have are Jupiter centered rather than Sun centered? Seems unlikely though, since the semimajor axis is 5au.

--Chris

Chris,

Please don't spend any more time on it than you already have.

I found some more recent ephemerides for dates closer to the collision. It's clear that gravitional effects were not directly included in the IAU ciircular, so it really was only accurate for dates near its epoch. Later Keplerian ephemerides show the comet fragments getting closer and closer, but their orbits still don't actually intersect Jupiter.

Unfortunately, the last few have eccentricities greater than 1.
How soon can Celestia handle hyperbolic orbits???

I've generated an updated SSC file containing four sets of elements, each closer to the collision date. It's on the Web at http://www.lns.cornell.edu/~seb/celestia/sl9_2.ssc
and includes comments on the data sources and conversion method.

selden wrote:Unfortunately, the last few have eccentricities greater than 1.
How soon can Celestia handle hyperbolic orbits???

It should be able to handle hyperbolic orbits right now, though I haven't done a lot of testing of that code.

--Chris

OK, I'll try it again. When I included one by accident, the coment was put way off in the outer solar system instead of close to jupiter. I may have messed up some of the other elements, though.

OK, I give up... What parameters with what names does Celestia need when defining a hyperbolic orbit?

Thanks.

Since Celestia does not compute the gravity forces, the only way, right now, to simulate this comet in Celestia is to use the .xyz files possibility.

There might be one thing to add in the xyz feature: it is to have a validity date. Like start date and end date. So we could not see the comet after it collapsed in Jupiter.
This feature could be implemented for the other orbits. That way we could only see the apollo spacescraft on appropriate dates.
Is this someting chris would like to implement?
---Eric

This already happens. Download the Voyager xyz file and you'll see it doesn't appear until it's actually launched. Nice to see this in ssc files, maybe...