Talk:List of Solar System objects by greatest aphelion

Why this list has issues

Heliocentric solutions can be highly inaccurate for objects with an orbital eccentricity approaching 1 especially when the values are calculated while the objects is near perihelion and has not left the planetary region of the Solar System. Objects with aphelia more than ~1000AU from the Sun really are better listed with a barycentric value. For comets, I would use an epoch of 2050 which would get current comets out of the planetary region. Any aphelion point more than 120,000AU from the Sun can simply be considered lost to the interstellar medium. -- Kheider (talk) 15:18, 15 November 2015 (UTC)

Thanks kheider. I know its got some major issues, but I just wanted to get it started. Its very exciting to think there is another Planet X out there and I wanted to complement the article dated to current distances in 2015. Just looking at the minor planets I notice nothing yet has an aphelion between 800-900 AU? Is this were something could be or is it nothing. I understand I don't understand all the complications, and in the future I hope we can get the right barycentric value's and epoch. Thanks for making all these articles and bringing your knowledge here, it is just the most exciting time I have seen for SS discovery yet! Fotaun (talk) 16:02, 15 November 2015 (UTC)

The idea is great. But I am concerned it is creating as much confusion as it is solving given how much the values can vary. C/2012 S4 (PANSTARRS) being the obvious example. I wish the JPL SBDB would allow you to sort objects with apehlion>500AU by a barycentric solution set at epoch 2050, but I am confident JPL programmers have a higher priority. I know you have done some great lists, but often times you are also the only one maintaining them. -- Kheider (talk) 16:26, 15 November 2015 (UTC)

Keep in mind only ~30 minor planets are known with aphelion > 300AU, but 368 such comets are known. -- Kheider (talk) 20:46, 16 November 2015 (UTC)

Thanks again! I tried to make a little barycentric section and made some further updates to the TNO section. Good luck finding planet X!!! Fotaun (talk) 20:39, 24 November 2015 (UTC)

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2019 cleanup of article

I figure I should give a log of this as I plan on starting a project on cleaning this article up extensively. We're going to need to do some major changes to make this as good as it can be.

for the entire article: - list the "as of" date for the solution given in the page, so that outdated values can be easily reviewed and updated if needed. - get rid of exceptionally cluttering objects (if there's some category that has well over 100 members listed individually here, as with the TNOs-by-aphelion list, then we need to compress that for readability.) - create an explanation section detailing information on this, as well as definitions (what barycentric solutions are, why the orbit epoch is important, and the implications/meaning that the objects listed here have for relevant astronomical topics)

for the comets listing: - make a short listing for comets by greatest heliocentric aphelion at [insert current epoch here] (including error bars) - in addition to the previous, make a listing of hyperbolic comets (in order of incoming velocity, NOT eccentricity, with an explanation of why eccentricity doesn't equal their incoming velocity) - make a longer listing for comets by greatest barycentric aphelion at epoch 1800, present, and 2200 (INCLUDING ERROR BARS) - possibly in addition to the previous, make a listing for comets with incoming hyperbolic orbits (the few that there are)

for the asteroids listing: - crop the listing for asteroids by greatest heliocentric aphelion - INCLUDE ERROR BARS on the barycentric aphelion of distant asteroids.

Will currently try my hand at an explanation section. Sorry if a bad situation to ping, but could I get some input on these plans from some active editors? @Renerpho: @Kheider:? exoplanetaryscience (talk) 02:15, 5 October 2019 (UTC)

@Exoplanetaryscience: I agree that there is a lot of room for improvement, and your suggestions are good. One problem you may face is finding a source for error bars on barycentric orbits, especially away from the current standard epoch. They aren't hard to compute, it's just that the JPL database doesn't include them. Renerpho (talk) 09:17, 5 October 2019 (UTC)

Yeah, that's been a problem I've been thinking about since posting. I could calculate the barycentric orbits with find_orb, but that doesn't seem quite so "clean" of a reference to give. I thought initially JPL horizons would actually give errors with some parameter selection, but it doesn't seem that's the case. I'll have to see if there's any way to try and steal that from the minor planet center. exoplanetaryscience (talk) 17:00, 5 October 2019 (UTC)

For hyperbolic excess velocity (interstellar speed) are we going to want to use a generic JPL Horizons look up at epoch 1600 that is easier to verify via "Observer Table: 22. Speed wrt Sun" or the formula v = 42.1219 √1/r − 0.5/a, where r is the distance from the Sun (say 50000 au), and a is the barycentric major semi-axis at epoch 1600? The latter is probably better but more difficult for readers to verify. -- Kheider (talk) 18:01, 5 October 2019 (UTC)

Probably would be useful to do some testing with the difference of that from the “true” vinf for various comets. exoplanetaryscience (talk) 19:50, 5 October 2019 (UTC)

Looking at the below table I think we are going to want to use the v_inf formula otherwise the near parabolic Oort cloud results look funny due to velocity including solar escape velocity only a few hundred au from the Sun.

Object	Epoch 1600 barycentric semi-major axis	Epoch 1600 Distance (au)	Epoch 1600 Velocity wrt Sun	v = 42.1219 √1/50000 − 0.5/a
2I/Borisov	-0.85681	2858	32.20	32.17
1I/2017 U1	-1.2753	2334	26.40	26.37
C/1999 U2 (SOHO)	-3.0487	1457	17.09	17.05
C/2008 J4 (McNaught)	-59.848	444	4.34	3.85
C/2012 S1 (ISON)	-144956	312	2.39	0.20
C/2010 X1 (Elenin)	52846	310	2.39	0.13
C/1980 E1 (Bowell)	36866	292	2.47	0.10

-- Kheider (talk) 03:40, 7 October 2019 (UTC)

Right, so let's use those. I've also decided that I think I'm going to use the barycentric values from both Horizons, as well as Find_orb, which I believe does not qualify as original research, since the observations are already established, and orbit determination is a fairly mathematically sound process? I'll do some testing exoplanetaryscience (talk) 03:39, 11 October 2019 (UTC)