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A comment from @planetmaker to this question gives this link to the Minor Planet Centre (MPC) to find a list with Near-Earth comets.
Here's the list with orbits for current comets on that site, but I don't know what all those numbers mean, I don't see an explanation where they stand for.

How can I select the comets from this list that could come into close approach with Venus?

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  • $\begingroup$ P/2005 T4(SWAN), P/2007 T2(Kowalski), C/2009 E1(Itagaki). $\endgroup$
    – Cornelis
    Jul 26, 2021 at 14:42
  • $\begingroup$ C/2009 O2(Catalina), P/2009 WX51(Catalina), C/2010 L5(WISE). $\endgroup$
    – Cornelis
    Jul 26, 2021 at 16:43
  • $\begingroup$ P/2012 A3(SOHO), P/2013 CU129(PANSTARRS). $\endgroup$
    – Cornelis
    Jul 28, 2021 at 16:44
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    $\begingroup$ Horizons knows 3,814 comets. Here are 40 with QR (perihelion): 0.7 < QR < 0.75. ssd.jpl.nasa.gov/api/… $\endgroup$
    – PM 2Ring
    Aug 9 at 3:01
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    $\begingroup$ When you have a record number or SPKID, you can get orbit elements, eg ssd.jpl.nasa.gov/api/… or generate an ephemeris. I guess you want comets for the water content. But you might need to be very patient. Eg, that comet SWAN (C/2015 P3) has a period of 3874.7 years. $\endgroup$
    – PM 2Ring
    Aug 9 at 3:11

2 Answers 2

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Sometimes space exploration requires a little detective work.

As seen from the last part of the entry copied below, the first comet listed is the Hale-Bopp comet, which is actually a long-period comet that came close to Earth in the 1990s and now is back on its way out to what would probably be considered the Oort Cloud.

CJ95O010 1997 03 29.6531 0.89080 0.994971 130.4149 282.7818 89.2644 20220808 -2.0 4.0 C/1995 O1 (Hale-Bopp) MPC106342

By matching some of the numbers with the entries given in the Wikipedia information box, we can identify some key elements that can be used to identify a comet that remains near both Earth and Venus. Below us what I am able to find for the numbers in the Hale-Bopp entry:

CJ95O010 -- Code for comet designation, compare with the C/1995 O10 entry

1997 03 29.6531 -- Date of perihelion, the third number incorporating the hour of the day (in this case shortly before 16:00), presumably UTC time.

0.890801 -- perihelion distance in astronomical units; Earth is 0.983 and Venus is 0.718.

0.994971 -- orbital eccentricity (e), from which you may derive the aphelion from multiplying the perihelion by (1+e)/(1-e). Here that would be

$0.890801×1.994971/0.005029 = 353 AU$

(Compared with 1.017 for Earth and 0.728 for Venus)

Wikipedia gives a slighty longer aphelion, 371 AU, because it uses a slightly different perihelion distance. Such a situation is common with long period comets and should be less of a problem with the short period comets you are interested in (which have a much lower eccentricity number).

Skipping the rest of the numbers which probably are related to a specific observation, I go to the end:

C/1995 O1 (Hale-Bopp) MPC106342 -- Additional comet designations including the discoverer.

I would use the perihelion and eccentricity numbers, from which you can get the aphelion as above, to match orbital distances with Earth and Venus for the remaining comets in the list and thus identify comets that are generally nearest to Earth and Venus. The designation data are then used to identify comets that give good numbers.

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  • $\begingroup$ Thanks for the explanation, as you can see in my comments below my question I already found some comets that have both perihelia less than that of Venus and low eccentricities. Half way the list I gave up . Just to few comets to lessen the thirst of Venus ! $\endgroup$
    – Cornelis
    Aug 9 at 10:04
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If you are strictly speaking of data pipelines (winnowing the MPC list), then it is YOUR responsibility to ingest the entries with some algorithm, i. e., learn how to calculate MOID from q (in 2D, for no specific date), q, i, and ascending node (in 3D like most comets imply, still no specific date), or q, i, and arguments of perigees (absolute position, including some putative date). The MPC is badly underfunded and by some measures understaffed, has old computers, and is not here to entertain you. Or volunteer with the MPC: if they feel nice they may feel like teaching you, in exchange for your time and effort.

If you are speaking of academic numbers (impact rate and probabilities), this question will likely never be answered, at least to any conclusive result. Poorly-observed and (currently) unobservable comets (including “comets”) are present, with varying water contents. A surprising number of comets are now being found, with bigger telescopes: they have low activity, and were invisible in prior telescopes. You can easily postulate bigger and bigger telescopes continuing to more and more phenomena, including ones we are currently speculating on, or completely unaware of now. We can continue ad infinitum to hydrous dust particles, which will never truly be imaged, but measured via population, or scatterings or other inferences.

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