Re: [find_orb] Extend close approaches to all major planets?

Bill Gray Mar 19, 2013

Hi Andrew,
>
> As new astrometry arrives for C/2013 A1 and we can update the
> orbit with Find_Orb, it would be really useful if the software
> could find close approaches of all major planets (and not just
> the earth) since there is considerable interest in the Mars
> approach on 2014 Oct. 19.
>
> Any chance this could be implemented in the next release?

It's already in there. Set the "viewpoint" to be from the
"MPC codes" (Mar), (Ven), (Ura), etc.

I recommend then setting the epoch to be close to the date/time
of the flyby. That way, you can turn on the alternative element
format (the one that shows sigmas), and do a "full step". Do that
for C/2013 A1, leave out four somewhat dodgy observations, and
you get...

Orbital elements: C/2013 A1
Perimars 2014 Oct 19.764875 +/- 0.0372 TT = 18:21:25 (JD 2456950.264875)
Epoch 2014 Oct 19.7 TT = JDT 2456950.2 Find_Orb
q151406.514 +/- 64570
M(N) 6.1 K 10.0 Peri. 58.74238 +/- 11
Node 42.85995 +/- 7
e11071.184573 +/- 4724 Incl. 73.61394 +/- 2.4
209 of 213 observations 2012 Oct. 4-2013 Mar. 15; mean residual 0".374.

...and can then run Monte Carlo clones to look for an impact,
and/or generate (Mar)-centric ephemerides for the flyby, such as

http://www.projectpluto.com/temp/a1.htm

You can also use codes (Sun) for the sun and (Lun) for the Moon.
I frequently generate (Lun)-centric ephemerides for objects coming
within 400000 km of the earth, in hopes of seeing that they might
hit the moon. (Nothing even very close yet, and the odds aren't
good; not only does the moon have 1/16 the cross-sectional area
of the earth, but it doesn't have the gravitational pull to turn
near-misses into impacts. It's amazing that it has any craters
at all...)

-- Bill