Hi Grant,

On 03/03/2013 12:54 PM, grantcblair wrote:
> I realize this may not be the 100% appopriate forum for this,
> but since find_orb is available on the ProjectPluto website...

There's a separate Find_Orb group at

http://groups.yahoo.com/group/find_orb/

Still, just to answer the questions you raised...

> I tinker with find_orb from time to time have recently been
> following the orbit refinements of C/2013 A1 as new observations
> become available. C/2013 A1, of course, is the well-known "Mars
> Buzzer" which is expected to make a close pass to Mars in October 2014.
>
> My questions:
>
> 1. when solving for C/2013 A1's orbit, there is a "Ma" value displayed
> - it this the expected distance in AU between the comet and the center
> of Mars? It appears to be about the right order of magnitude.

Yes. Find_Orb will show MOIDs for any planet if it's small enough
(within one AU for the Earth and gas giants, .1 AU for the other
inner planets).

> 2. is there somewhere I can edit in Mars' orbital elements instead
> of Earth's to be able to spit the comet-planet MOID out in more detail?

Easiest way to do that is to set Find_Orb's epoch to 2014 Oct 19.8
(the time of closest approach). Do that, and you'll get Mars-centric
elements (because, at closest approach, the gravity of Mars is dominant;
it makes sense to switch from heliocentric to Mars-centric elements.)

I recommend use of the "in development" version at

http://www.projectpluto.com/pluto/devel/find_orb.htm

This includes some improvements and bug fixes. Specifically, you'll
get better numerical stability when projecting the orbit ahead to 19.8
October 2014.

> Grant (who obviously has way too much time on his hands).

Guess that applies to me, too, then. I've run this object through
Find_Orb, set the epoch as described above, and then applied run
Monte Carlo variants ("virtual asteroids" that match the observations)
to get impact probabilities.

-- Bill