Interstellar Object gb00234 = C/2019 Q4 Borisov

Bill Gray Sep 13

Hello all,

Apologies for the cross-posting. I think this may be
of interest to some MPMLer who use Find_Orb, but aren't
on the Find_Orb mailing list. If you aren't a Find_Orb
user, you can go ahead and hit Delete now.

MPEC 2019-R106 has added in a few more observations for
this object. It brings down the uncertainties slightly,
though (unsurprisingly) not by much; we'll have to wait
for more data for that to happen.

People using the on-line Find_Orb may have been annoyed
by the fact that it'll only produce an elliptical or parabolic
orbit for this object, with increasingly ugly residuals. The
program has some "weighting" against orbits that are considered
to be extremely unlikely, such as those that would put an
object a light-year away or in a hyperbolic orbit.

If you use "interactive" Windows or Linux or Mac or *BSD
Find_Orb, this isn't an issue. You can just consider the
elliptical/parabolic orbit to be a starting point, iterate on
it, and get an hyperbolic orbit. But the on-line Find_Orb is
non-interactive. You get a default orbit, and that's it.

I've revised Find_Orb so that if the input contains the line

COM interstellar

it will drop the penalty on hyperbolic orbits. It will also
do this once the object has an interstellar (2I) designation.

Note that this should be used with care. When you don't have
enough data, almost anything can look interstellar.

For best results with this particular object, I suggest
downloading the astrometry from

https://www.projectpluto.com/temp/2i.txt

This already has the COM interstellar line, plus some headers
missing from the MPC data. Feed that file to on-line Find_Orb :

https://www.projectpluto.com/fo.htm

either by cutting/pasting the data, or clicking on "Browse"
and selecting the 2i.txt file you've downloaded. You'll get the
"right" interstellar orbit.

If you delete the COM interstellar line, it'll try for a
non-interstellar orbit, and the results will be pretty bad.

-- Bill