Talk:2I/Borisov

Size?
Using H=12.5, and albedo between 5%-20%, a full phase diameter estimate comes out as 8 to 20 km, small, but much larger than Oumuamua. Tom Ruen (talk) 01:07, 11 September 2019 (UTC)


 * But the object has been confirmed to be a comet so you can not use the asteroid scale. There is good chance the nucleus is less than 5km in diameter. -- Kheider (talk) 01:12, 11 September 2019 (UTC)
 * The albedo can only be assumed to be 5-20% for asteroids, it doesn't work for comets. There is no direct link between absolute magnitude and size for comets. This object doesn't appear to be extremely active right now, but I don't think 20 km is an option. Karen Meech estimated it to be between 2 and 16 km in diameter. I'd be surprised if the higher limit holds, but the lower limit sounds perfectly realistic. Note that it corresponds to an albedo of 450%, which is perfectly fine for comets (we mostly see light reflected from the coma, not the nucleus). This object is much larger than anyone would expect to see for an interstellar interloper. Renerpho (talk) 00:11, 13 September 2019 (UTC)

JPL orbit
JPL small body database browser has e=3.52161 +/- 0.19684, a=-0.817754 +/- 0.045762, I calculate v infinity as 32.9 km/s using the latter. Agmartin (talk) 22:41, 11 September 2019 (UTC)
 * I can confirm your calculation. JPL's value is different from that given by the MPC mostly because JPL uses a different weighting scheme. Bill Gray, using the same model as JPL, got an eccentricity of about 3.5, too, and about 3.1 without weightings. The difference between these is hard to see with so little data, we have to wait a few weeks to pin it down. v_inf is certainly around 30-35 km/s. — Preceding unsigned comment added by Renerpho (talk • contribs) 00:21, 13 September 2019 (UTC)

JPL's HORIZONS Web-Interface gave these elements on 22 October 2019, using 651 observations over 51 days.

a = −0.8522734226967555 AU

e = 3.353491649120846

i = 44.05785522652224°

Ω = 308.1419761457706°

ω = 209.1427356972629°

T = 2458826.0758495377 JD

There are four events of geometrical significance upcoming: (1) ecliptic crossing, (2) perihelion, (3) closest approach to Mars, and (4) closest approach to Earth. Calculations below are mine, based upon JPL's published elements shown above. If original research continues to be prohibited (regardless of its quality), then simply delete this contribution, and it will not reappear by any doing of mine.

ECLIPTIC CROSSING

Descending node at 10h 8m 1s on 26 October 2019 UTC (JD 2458782.922228)

Borisov mean anomaly: −54.0571181°

Borisov eccentric anomaly: −22.1742336°

Borisov true anomaly: −29.1427358°

HEC x = −1.37267094 AU

HEC y = +1.74799326 AU

HEC z = 0

HEC Vx = −12216.1913 m/s

HEC Vy = −30522.4355 m/s

HEC Vz = −27537.9848 m/s

HEC distance: 2.22254492 AU

HEC longitude: 128.141976°

HEC latitude: 0°

speed relative to the sun: 42885.8369 m/s = 0.000143051754 c

obliquity of the ecliptic: 23.4367145°

Geocentric distance: 2.52356355 AU = 20.9878381 light minutes

Geocentric right ascension: 10h 13m 1.00s

Geocentric declination: +11° 02′ 23.2″

That's about 1.5° SE of Regulus.

Angle Sun-Earth-Borisov: 61.2034864°

Angle Earth-Sun-Borisov: 95.7171398°

PERIHELION

time: 13h 49m 13s on 8 Dec 2019 UTC (JD 2458826.075850)

Borisov mean anomaly: 0°

Borisov eccentric anomaly: 0°

Borisov true anomaly: 0°

HEC x = −1.63408309 AU

HEC y = +0.944293541 AU

HEC z = −0.679256624 AU

HEC Vx = −8463.50553 m/s

HEC Vy = −33816.5464 m/s

HEC Vz = −26650.7156 m/s

HEC distance: 2.00581838 AU

HEC longitude: 149.977515°

HEC latitude: −19.794228°

speed relative to the sun: 43879.9542 m/s = 0.000146367772 c

obliquity of the ecliptic: 23.4366991°

Geocentric distance: 1.99346613 AU = 16.57915225 light minutes

Geocentric right ascension: 11h 28m 24.28s

Geocentric declination: −18° 20′ 58.0″

That's about a degree ~SE from γ Crateris and about a degree east of λ Crateris.

Angle Sun-Earth-Borisov: 76.4386454°

Angle Earth-Sun-Borisov: 75.0459011°

CLOSEST APPROACH TO MARS

time: 4h 17m 40s on 9 December 2019 UTC (JD 2458826.678945)

Borisov mean anomaly: 0.755470974°

Borisov eccentric anomaly: 0.320997673°

Borisov true anomaly: 0.436577391°

HEC x = −1.63702014 AU

HEC y = +0.932508505 AU

HEC z = −0.688534883 AU

HEC Vx = −8400.8821 m/s

HEC Vy = −33852.4767 m/s

HEC Vz = −26624.5300 m/s

HEC distance: 2.00586324 AU

HEC longitude: 150.332527°

HEC latitude: −20.0756848°

speed relative to the sun: 43879.7288 m/s = 0.000146367020 c

Distance from Mars: 1.72621629 AU = 14.3565031 light minutes

Angle Sun-Mars-Borisov: 73.7430109°

Angle Mars-Sun-Borisov: 55.7078353°

CLOSEST APPROACH TO EARTH

time: 3h 51m 39s on 28 December 2019 UTC (JD 2458845.66087)

Borisov mean anomaly: 24.5335093°

Borisov eccentric anomaly: 10.3441027°

Borisov true anomaly: 13.9611652°

HEC x = −1.71825045 AU

HEC y = +0.556105460 AU

HEC z = −0.975302747 AU

HEC Vx = −6424.98835 m/s

HEC Vy = −34731.9036 m/s

HEC Vz = −25646.3778 m/s

HEC distance: 2.05252365 AU

HEC longitude: 162.066016°

HEC latitude: −28.3705806°

speed relative to the sun: 43649.9977 m/s = 0.000145600720 c

obliquity of the ecliptic: 23.4366921°

Geocentric distance: 1.93616544 AU = 16.1025969 light minutes

Geocentric right ascension: 11h 59m 55.39s

Geocentric declination: −33° 17′ 24.0″

That's about 1.5° east of β Hydrae.

Angle Sun-Earth-Borisov: 82.4110836°

Angle Earth-Sun-Borisov: 69.2357937°

It is possible to calculate an observer's ephemeris, also.

EPHEMERIS for December 2019

All positions for 9pm Eastern Standard Time

(date) (right ascension) (declination) (geoc. distance)

1 Dec 11h 17m 28.36s  −13° 23' 23.3"  2.03899613

6 Dec 11h 25m 54.52s  −17° 12' 08.2"  2.00274664

11 Dec 11h 34m 13.59s  −21° 03' 14.3"  1.97444977

Full moon on 12 Dec.

16 Dec 11h 42m 24.47s  −24° 54' 36.4"  1.95407529

21 Dec 11h 50m 25.76s  −28° 44' 04.9"  1.94146290

26 Dec 11h 58m 15.77s  −32° 29' 32.2"  1.93632864

31 Dec 12h 05m 52.42s  −36° 08' 58.2"  1.93827961

Borisov's expected brightest apparent magnitude: +15.3 (in mid-December 2019)

Borisov's hyperbolic excess speed: 32262.9190 m/s

HEC : heliocentric ecliptic coordinates

Right ascension and declination are measured in geocentric celestial coordinates.

Borisov entered the solar system from a direction that is closely marked by the Stock 2 open star cluster near the border between Cassiopia and Perseus. It is about two-and-a-half degrees north by northwest of the Double Cluster in Perseus.

Note: I was unaware of the rules regarding changes to own comments until after I posted this revised comment. I did not keep a record of the original comment. 50.110.127.237 (talk) 08:14, 4 October 2019 (UTC)

To 50.110.127.237 a.k.a. 50.110.118.26: — UnladenSwallow (talk) 04:29, 12 October 2019 (UTC)
 * 1) If you want to make changes to your own comment after a short while, you have to follow certain rules: . I have reverted your comment to the revision as of 08:25, 4 October 2019 (UTC). You can repeat your edits, but this time you have to clearly mark the changes with   (deletion) and   (insertion) tags, add a new timestamp  after the original one, and provide an explanation of the changes in a new comment immediately below your original.
 * 2) I have wrapped your comment in a collapse box to make the page easier to navigate.

Distance detected?
Roughly how far away was this object when it was first detected? And, why didn't PanStarrs find it? --213.233.88.147 (talk) 13:23, 12 September 2019 (UTC)


 * 2019 Q4 was $3.75 au$ from Earth on 30 August 2019. It was not detected by Pan-STARRS because the Solar elongation has been less than 45 degrees since early May 2019. -- Kheider (talk) 14:06, 12 September 2019 (UTC)


 * Is it worth mentioning the comet will cross the solar system plain somewhere between Mars and Jupiter? I think it gives an idea (in addition of the au) to the closest it will get to the Sun. Cheers, Rowan Forest (talk) 13:17, 13 September 2019 (UTC)

2I/Borisov
Until the MPC makes an official announcement we should not title it as 2I/Borisov. JPL has no link to 2I. -- Kheider (talk) 14:58, 13 September 2019 (UTC)
 * Yes - *entirely* agree - there is no official designation of "C/2019 Q4 (Borisov)" as "2I/Borisov" at the moment afaik - however - the comet seems to be "also known as '2I/Borisov'" (unofficially) by some    - there may be more  - hope this helps - in any case - Enjoy! :) Drbogdan (talk) 15:32, 13 September 2019 (UTC)


 * Wikipedia should not encourage the use of that name until it is official, and as an interstellar object it might get a more exotic name. -- Kheider (talk)
 * Thanks for your reply - yes - agreed - no problem whatsoever - Thanks again - and - Enjoy! :) Drbogdan (talk) 16:02, 13 September 2019 (UTC)

"Reachability" section
I rendered that section invisible as it looks not right to me. The object was just discovered, so it is unlikely a spacecraft was to be launched last year to intercept it.

In a related matter, there is Europe's Comet Interceptor to intercept an appropriate long period comet, and in case it doesn't find one, it could go after an interstellar object. But one needs references relating both, otherwise it is synthesis. Rowan Forest (talk) 22:26, 13 September 2019 (UTC)

A separate article on Gennadiy Borisov
An interview with Borisov with lots of interesting details: https://www.fontanka.ru/2019/09/13/052/. Machine translation is surprisingly readable, except for a few mistakes (him → it, sit → land, lovers/fans → amateurs, removed → captured). He has already discovered 7 comets since 2013 (for which he received three Edgar Wilson Awards), so this one is his 8th. In 2016 he was the only amateur astronomer in the world who managed to discover a comet. His previous discoveries were also made using his own custom-built telescopes: "small Genon" (2 discoveries) and "large Genon" (5 discoveries). He works as an engineer at the Crimean Observatory of the Sternberg Astronomical Institute of the Moscow State University. There he helps with the telescopes, but does not make observations himself. He also works for Astronomicheskiy Nauchnyy Tsentr, where he creates experimental telescopes in cooperation with Roscosmos. His discoveries are his own hobby. He thinks that soon amateurs will no longer be able to discover new comets: "In 2016, only I discovered a comet. In 2013, there were seven of us. Every year less and less. There are more and more huge telescopes. Amateurs will soon have nothing left."

I think that as this is his 8th comet (for which he will surely receive another Edgar Wilson Award, becoming a four-time winner) and the first interstellar comet ever discovered, Borisov deserves a separate article, even though he's an amateur astronomer. What do you think? If you agree, I'll create an article on him. — UnladenSwallow (talk) 14:18, 16 September 2019 (UTC)
 * Support - Yes - agree that an article about Gennadiy Borisov seems indicated - afaik, Borisov seems sufficiently notable according to WP:PERSON guidelines - hope this helps - in any case - Enjoy! :) Drbogdan (talk) 15:00, 16 September 2019 (UTC)
 * Support - he is notable by the discoveries he has done, amateur or not. Rowan Forest (talk) 17:42, 16 September 2019 (UTC)
 * I started the article on Gennadiy Borisov as a result of the discussion here. Editors may wish to know that it has been nominated for deletion. If interested, the discussion can be found at Articles for deletion/Gennadiy Borisov Hallucegenia (talk) 21:10, 18 September 2019 (UTC)


 * Support - as per the above. There should be enough material about him by now. Much of the material is in Russian, but Google and Youtube should help to translate. Material on his earlier discoveries can be found here and here. Renerpho (talk) 11:18, 19 September 2019 (UTC)
 * Support – Strange that he doesn't have a page on Russian wikipedia. Should be at Геннадий Борисов. — JFG talk 12:07, 19 September 2019 (UTC)

Is it good to mention here that the discussion about deletion has resulted in a "keep" decision? (As of 24 September 2019.)

By the way, a Russian article exists: Борисов, Геннадий Владимирович Geke (talk) 12:54, 28 September 2019 (UTC)

Inbound velocity when 3au from the Sun
Generated with JPL Horizons Observer Location: @sun and Table Settings: 22 Speed wrt Sun (VmagSn)

I wanted to put this table somewhere and did not want to risk cluttering up the main article for casual readers. -- Kheider (talk) 01:23, 17 September 2019 (UTC)

From a recent article on arXiv: "The orbit of C/2019 Q4 implies an excess heliocentric velocity of ∼ 31 km s−1. The heliocentric incoming velocity at infinity of the meteor in right-handed Galactic coordinates is v∞(U, V,W) ≈ (21, −23, 1) km s−1, which is ∼ 35 km s−1 away from the velocity of the Local Standard of Rest (LSR)" Agmartin (talk) 15:25, 17 September 2019 (UTC)


 * $$v_\infty$$ will be less than velocities that are closer to the Sun as the Sun will "pull the object inwards". At perihelion (2au) the comet will be doing 43.8 km/s wrt the Sun. — Preceding unsigned comment added by Kheider (talk • contribs) 15:36, 17 September 2019 (UTC)
 * During 2019, the velocity wrt Earth varies from 24.8 km/s in mid-February to 65.6 km/s in early September. — Preceding unsigned comment added by Kheider (talk • contribs) 18:48, 23 September 2019 (UTC)

Developing story
This comet is being closely watched, and the article might be subject to frequent updates. Is there a standard tag for fast-moving stories, and should this be headed with one? JDAWiseman (talk) 10:54, 19 September 2019 (UTC)
 * There is a current event notice, but that should only be used for really fast-moving developments receiving widespread and hourly coverage. Perhaps as the object approaches and becomes more visible that will be the case, but not now. — JFG talk 12:10, 19 September 2019 (UTC)

Requested move 25 September 2019

 * The following is a closed discussion of a requested move. Please do not modify it. Subsequent comments should be made in a new section on the talk page. Editors desiring to contest the closing decision should consider a move review after discussing it on the closer's talk page. No further edits should be made to this discussion. 

The result of the move request was: Speedy Close. Even though this discussion could go on longer, opposition is nearly unanimous due to the special status of this comet and the fact that barely any sources call it "Comet Borisov." &#124; abequinnfourteen 21:13, 28 September 2019 (UTC)

2I/Borisov → Comet Borisov – Opening up a move discussion on this topic, because I'm genuinely curious whether or not a natural disambiguation based on precedents set by article titles such as Comet Hale–Bopp, Comet Hyakutake, Comet ISON, Comet Shoemaker–Levy 9, ect., would be accepted in this particular situation. – PhilipTerryGraham (talk &middot;&#32;articles &middot;&#32;reviews) 12:55, 25 September 2019 (UTC)
 * Opposed Support, as done to other famous comets, such as Comet Kohutek, Comet Bennett, Comet Machholz, Comet Lulin, Comet Morehouse, etc. Rowan Forest (talk) 15:30, 25 September 2019 (UTC) PD: Changed my vote because he has other comets named after him. Rowan Forest (talk) 21:53, 26 September 2019 (UTC)
 * As a side note: There are four comets found by and named after Kohoutek, two by Bennett and nine by Machholz. I agree with you that the article shouldn't be renamed, but the fact that there are several comets that bear Borisov's name doesn't preclude a rename. What sets the comets above apart is that they have become the common names for a person's most significant find, usually because the comet reached naked eye brightness. Renerpho (talk) 01:33, 27 September 2019 (UTC)


 * Oppose at this time Support — 1I/ʻOumuamua's article is titled simply ʻOumuamua, so I don't see why we can't use Comet Borisov or even Borisov (comet) as the title. Here are a few examples of "Comet Borisov" name used in the media:
 * We Could Chase Down Interstellar Comet Borisov by 2045 (space.com, September 20, 2019)
 * Comet Borisov: Interstellar visitor might just be the most important comet in our system (express.co.uk, September 18, 2019)
 * Our best look at likely interstellar comet Borisov so far (cnet.com, September 13, 2019)
 * — UnladenSwallow (talk) 15:45, 25 September 2019 (UTC) Update: For the article to be renamed, "Comet Borisov" has to be widely used in the media and academic literature. A few examples are not enough. — UnladenSwallow (talk) 17:45, 27 September 2019 (UTC)
 * This might be a good case for common name recognition – the naming conventions for articles on astronomical objects preferences common names first, after all. – PhilipTerryGraham (talk &middot;&#32;articles &middot;&#32;reviews) 17:18, 25 September 2019 (UTC)


 * Oppose at this time - To quote from the IAU press release: here, "In this case, the IAU has decided to follow the tradition of naming cometary objects after their discoverers, so the object has been named 2I/Borisov." So the official name for the object is "2I/Borisov". It seems premature to name the main article something else, unless and until we have a much longer history of other Reliable Sources using another term. Hallucegenia (talk) 16:43, 25 September 2019 (UTC)
 * Strong Oppose, Unlike all above comets listed, 2I/Borisov is an object of interstellar origin, a class of object with exactly 1 existing precursor, 1I/ʻOumuamua. The listing of it as simply a "comet" Borisov would introduce unnecessary confusion in the title, not to mention the fact that the official title of it is 2I/Borisov and unlike any of the above comets, it's not going to be a great comet, or have any sort of exceptional qualities other than the fact that it's an interstellar comet, which is addressed quite succinctly already by the 2I designation. exoplanetaryscience (talk) 16:59, 25 September 2019 (UTC)
 * Two things to note though – 1) it is a comet, so it isn't necessarily confusing to call it as such, and 2) I'm not sure most readers would recognise what the designation "2I" even means, and it would be best to find a better disambiguator if "comet" doesn't suffice. – PhilipTerryGraham (talk &middot;&#32;articles &middot;&#32;reviews) 17:24, 25 September 2019 (UTC)
 * I'll give you that, those are both fair points. I suppose more what I was going for for the first thing was that calling a "comet" would be understating what its most notable feature is, when there is already an existing designation giving its most notable feature. Perhaps the 2I designation isn't the most obvious to a reader, and this is easily Borisov's most famous comet discovery, I still think there would need to be a lot of popular referring to it as "comet Borisov" rather than "2I/Borisov" for me to be convinced it's more appropriate of a title per WP:COMMONNAME
 * unlike any of the above comets, it's not going to […] have any sort of exceptional qualities other than the fact that it's an interstellar comet seems self-contradictory. The fact that it came from another star system makes it exceptional – perhaps, the most exceptional of all the comets listed above (of course, many comets are suspected of having extrasolar origin, but it's one thing to suspect, and another thing to know for a fact). — UnladenSwallow (talk) 19:09, 25 September 2019 (UTC)
 * Sorry about the ambiguity, what I'd meant is that its primary notable quality is the fact that it's an interstellar comet, and aside from that there isn't much to speak of, at least anything exceptionally article-worthy. exoplanetaryscience (talk) 20:12, 25 September 2019 (UTC)
 * But how is it different in this regard from other comets listed above? Comet Kohoutek's primary notable quality is the fact that it was overhyped as the "comet of the century". Comet Bennett and Comet Machholz do not seem to have any primary notable qualities. Comet Lulin's primary notable quality is that a team of Italian astronomers saw part of its tail get torn away. And so on and so forth. Do you mean to say that a comet should be large/bright/visible to the naked eye to be named "Comet (Discoverer's name)"? — UnladenSwallow (talk) 21:56, 25 September 2019 (UTC)

What's wrong with "Comet 2I/Borisov"? — Preceding unsigned comment added by 82.69.104.66 (talk) 18:05, 28 September 2019 (UTC)
 * Oppose at this time Pages that come up when I google Comet Borisov and 'in the last 24' use 2I/Borisov. Give it a couple of more days to see if it stays that way or if they start using Comet Borisov once it get more mainstream coverage. Agmartin (talk) 21:21, 25 September 2019 (UTC)
 * Oppose for a simple reason: this is the eighth comet that Gennadiy Borisov has discovered (list here), and is unlikely to be the last. We don't yet know which (if any) should be the "Comet Borisov".  I agree with a redirect because this is definitely the most famous (and currently newsworthy) so far, but a permanent name requires additional WP:Disambiguation. 38.39.199.2 (talk) 22:46, 25 September 2019 (UTC)
 * Strong oppose as 38.39.199.2 above: what should we do with seven other "his" comets: C/2013 N4 (Borisov), C/2013 V2 (Borisov), C/2014 Q3 (Borisov), C/2014 R1 (Borisov), C/2015 D4 (Borisov), C/2016 R3 (Borisov), C/2017 E1 (Borisov) discovered since 2013? Julo (talk) 23:48, 25 September 2019 (UTC)
 * Oppose at this time Gennady Borisov has been known for his comet discoveries before he found 2I/Borisov. At least one of his finds (C/2014 Q3) has received considerable attention. 2I/Borisov may be his most significant find to date, but naming the article "Comet Borisov" would be premature. If that name becomes the WP:COMMONNAME in the literature then we can reconsider. We don't have a WP:CRYSTALBALL. Renerpho (talk) 00:46, 26 September 2019 (UTC)
 * Oppose for reasons above (and for my personal preference to prefer IAU names).  ― Дрейгорич / Dreigorich  Talk  06:16, 26 September 2019 (UTC)
 * Oppose: it is not a "random" comet, and before 2I was discovered, there were already 7 Solar-System comets named Borisov (see fr:Comète Borissov for the list). The IAU designation has the advantage to have no ambiguity. SenseiAC (talk) 16:10, 26 September 2019 (UTC)
 * Oppose: For now, Comet Borisov does not represent the most common name. --Harlock81 (talk) 21:46, 26 September 2019 (UTC)
 * Oppose, as per 38.39.199.2. Nigos (talk • Contribs) 00:25, 27 September 2019 (UTC)
 * Oppose, per above. &#32; Headbomb {t · c · p · b} 01:47, 27 September 2019 (UTC)
 * Neutral, the naming conventions for articles on astronomical objects recommend using common names over official names and it does appear that "Comet Borisov" is being widely used, although it isn't clear yet that it is the true common name. I imagine, however, that if we change the title of this article to "Comet Borisov" it will quickly become the common name given Wikipedia's prominence as a reference for science topics. Kaldari (talk) 04:27, 28 September 2019 (UTC)


 * The above discussion is preserved as an archive of a requested move. Please do not modify it. Subsequent comments should be made in a new section on this talk page or in a move review. No further edits should be made to this section.

In case:
Right now there is an image from the Gemini Observatory in Hawaii of the comet. However, this would be a non-free image presently, and there is a potential that NASA or other bodies will release a free image over the next 3-4 months as it nears. In case that does not happen by... say April 2020? then this would be a permissible use of a non-free image since we will likely never see this comet again in our current editors' lifetimes (eg no chance at a free image :) --M asem (t) 16:18, 25 September 2019 (UTC)
 * We will have NASA images by mid-October as the comet gets a greater solar elongation. -- Kheider (talk) 16:57, 25 September 2019 (UTC)
 * You can put a link to it in the "External links" section. — UnladenSwallow (talk) 19:20, 25 September 2019 (UTC)
 * Good point. Could also be a external media template but I don't think there's a lot of side room with images there now. --M asem (t) 19:40, 25 September 2019 (UTC)
 * Well, the image of the comet is the first thing most people want to see, so I think is certainly warranted here and should take precedence over other images if necessary. — UnladenSwallow (talk) 20:14, 25 September 2019 (UTC)
 * I have a friend who took an image of the comet - if they gave permission for wikipedia to use it would that be enough to provide? or would it need to be released under CC? 134.114.223.244 (talk) 20:27, 25 September 2019 (UTC)
 * It seems that in this particular case a permission would be enough (see Non-free content for details), but it would be better if he released it under CC. — UnladenSwallow (talk) 21:13, 25 September 2019 (UTC)
 * Well, we'd really can only accept a free image here - which either means public domain, or CC-BY or CC-BY-SA. Given that we can expect NASA to release an image too - which will be public domain due to NASA being a US Government agency, any non-free will not be helpful here. --M asem (t) 21:50, 25 September 2019 (UTC)
 * Actually, we can accept a non-free image here (with author's permission, of course), because there is no easy way to produce a free image of the comet (read the rules in Non-free content). However, as soon as a free image becomes available, the non-free image must be immediately replaced. I agree with you that it's better to wait for the NASA image, which is likely to be of higher quality than the image taken by 134.114.223.244's friend. — UnladenSwallow (talk) 22:47, 25 September 2019 (UTC)
 * Just FYI, the template only drops a link in a floating box in the body, doesn't show the image. (This template also supports external video links too). --M asem  (t) 21:50, 25 September 2019 (UTC)
 * Thanks, I know this. What I mean to say is that if the box says "Image of 2I/Borisov", everyone will click on it. And it should be placed near the top of the article, because most people would prefer to see the image first (in this case, a link to the image), orbits second. — UnladenSwallow (talk) 22:36, 25 September 2019 (UTC)
 * Hi all, I got an image from a friend to use. Unfortunately I wasn't quite sure what path to take to say that a friend released the image under creative commons when the image was previously private, but I think this should be compatible with the rules. exoplanetaryscience (talk) 06:25, 30 September 2019 (UTC)
 * Hubble observations are scheduled for October 12th (as per the currrent weekly HST schedule). Those observations will be in the public domain. With some luck, there will soon be a high resolution image suitable for Wikipedia. Renerpho (talk) 23:06, 8 October 2019 (UTC)
 * I have uploaded a processed version of the Hubble data from the first four orbits. Renerpho (talk) 23:03, 12 October 2019 (UTC)
 * The next observations with Hubble are scheduled for around November 9th. Renerpho (talk) 20:48, 15 October 2019 (UTC)

Page view log for this article
The page views shown in the log for this article are strangely low prior to two days ago. Does anyone know why that might be? ↠Pine (✉)  06:49, 26 September 2019 (UTC)
 * ↠Pine (✉)  You are comparing the talk page views to the article views is my guess, was there a prize 121.99.108.78 (talk) 07:17, 26 September 2019 (UTC)
 * No, I am looking at the page views for the article. --↠Pine (✉)  07:26, 26 September 2019 (UTC)
 * You need to check 2I/Borisov, C/2019 Q4 (Borisov) and gb00234 as the article has moved twice. -- Kheider (talk) 07:30, 26 September 2019 (UTC)
 * Kheider thanks, I was looking at those earlier but I couldn't figure out what happened. I think that this article was previously at |C/2019 Q4 (Borisov), and while the content was moved here and replaced on the old page with a redirect, that was an error and instead the entire original page should have been moved here to keep the view log intact and so that page watchers could keep the current page on their watchlists. Then a new redirect page could be created under the old page name. ↠Pine (✉)  07:33, 26 September 2019 (UTC)
 * The revision history is intact, so the article has been moved properly. I guess the Move action doesn't carry over the page views. — UnladenSwallow (talk) 10:24, 26 September 2019 (UTC)
 * I believe the pageviews list the number of hits to the first wikipedia page that receives the hit so if someone searched for an old name it gets counted there and not to where it redirects. If you plot all three of the names you will see that pageviews are still being tabulated for C/2019 Q4 (Borisov) and gb000234. Some were being counted for 2I/Borisov even before the name change and are also being counted for Comet Borisov which only exists as a redirect. Agmartin (talk) 17:20, 26 September 2019 (UTC)

Apparently is a known issue. See Phabricator task. ↠Pine (✉)  00:21, 3 October 2019 (UTC)

Lost in the weeds.
The sections on previous names and trajectory get deep into the weeds discussing early estimates of its orbit. I suggest they be trimmed. Agmartin (talk) 20:25, 27 September 2019 (UTC)
 * I have trimmed the NEOCP section. -- Kheider (talk) 21:02, 27 September 2019 (UTC)
 * I think it's still too long. The previous estimates shouldn't take up more than 2-3 sentences, IMO. Renerpho (talk) 23:34, 27 September 2019 (UTC)
 * The NEOCP mention is only 2 sentences and the C/2019 Q4 (Borisov) talk is also 2 sentences. Not sure making them any shorter is beneficial. Another option is to create a section called "early orbit solutions" and put it below "trajectory" as I do think the topic is worth some coverage. -- Kheider (talk) 23:43, 27 September 2019 (UTC)
 * I agree with Kheider. At first glance nobody said, "hey, look at that interstellar comet." The realization that this comet was interstellar was a step-wise scientific process that Wikipedia can explain in layman terms -if possible- within the Discovery section. Cheers, Rowan Forest (talk) 00:46, 28 September 2019 (UTC)
 * I have moved the steps into a discovery section. Agmartin (talk) 21:23, 28 September 2019 (UTC)
 * Thank you. Now lets remember we are writing for the general public not for trained astronomers. There is ample space to soften the language without dumbing it down. Cheers. Rowan Forest (talk) 00:11, 29 September 2019 (UTC) Rowan Forest (talk) 00:11, 29 September 2019 (UTC)
 * I have tried to move the eccentricity stuff to that later section so that the naming section requires no "deep" understanding. I'm writing here as one aware of what these terms mean but I can see that an average reader is not going to appreciate what a 3.4 eccentricity implies or means. --M asem (t) 00:49, 28 September 2019 (UTC)
 * I find the trajectory section hard to read. I know what the text wants to tell me and I still have problems to follow. Quote: "For hyperbolic trajectories with a given excess velocity, the higher the perihelion, the larger the eccentricity as the Sun's gravity is less able to bend the trajectory, roughly 34 degrees for 2I/Borisov." It took me three attempts to understand the syntax of that sentence. I know I asked earlier to reduce the number of sentences, but longer sentences wasn't what I had in mind. Renerpho (talk) 06:43, 29 September 2019 (UTC)
 * I have added a request to that sentence. My understanding is that "34 degrees" refers to the angle between the inward and outward directions of the comet's trajectory. I guess it's an interesting piece of information that could be added to the caption under the trajectory diagram in the gallery. But the rest of this sentence has to go. It reads like a textbook. — UnladenSwallow (talk) 09:13, 29 September 2019 (UTC)

discovery date
In the section OBSERVATION, there is a quote from Borisov starting "I observed it on August 29, but it was August 30 GMT". This is strange because Crimea is located east of Greenwich. It seems the actual quote was in Russian, so perhaps a translation error? Or just a mistake? Anyone know? 110.145.170.78 (talk) 01:48, 28 September 2019 (UTC)
 * The first observation was made at 2019-08-30.04398 (01:03 UTC), which is 04:03 UTC in Crimea. Borisov was either mistaken or mistranslated. What is stated in the quote is definitely not correct. Renerpho (talk) 06:18, 29 September 2019 (UTC)
 * I quote your edit : "What he said is indeed incorrect, but that's what he said in the interview. I don't know why he said it. Could it be that he actually observed the comet on August 29 UTC / August 30 Crimean Time, but got the dates mixed up and incorrectly reported his time of observation as August 30 UTC?" - No, the time of observation is in the data sent to the Minor Planet Center, see the Date (UT) in the first line of the "Observations" section. This time is correct to within a second, otherwise it wouldn't fit the data collected by others. Unless he observed it earlier, saw it on his screen, and decided it would be better not to report it (which would be idiotic), his statement (or the translation of it) is in error. Renerpho (talk) 09:16, 29 September 2019 (UTC)
 * The translation is correct. "Я наблюдал ее 29 августа, но по Гринвичу это было 30 августа." = "I observed it on August 29, but it was August 30 Greenwich time". You can check it with Google Translate. Obviously, what he said can not be true, but there must be a reason he mentioned two dates. Perhaps he did observe it earlier, on August 29 GMT, close to midnight (so it was already August 30 Crimean Time), but didn't immediately report it for some reason. So when he got around to actually sending the data, it was already August 30 GMT. What might sound idiotic for a professional, could be normal for an amateur. In his interview he says that he always observes the sky "live", at night. He does use a scanning program, but he likes actually sitting there watching it working. He's not sleeping during nights. — UnladenSwallow (talk) 09:33, 29 September 2019 (UTC)
 * Maybe he just meant that he started observing on the evening of the 29th, but that it was August 30th by the time the comet became observable. Notice that 2I/Borisov is (and was) only observable shortly before local sunrise. If he actually observed it on the 29th then that was 24 hours earlier. He'd have had no way to predict the position of the object 24 hours ahead, and he did not report observations from the 29th, so I am pretty sure he did not see it on that date. Or maybe he simply is excited about his discovery and made a mistake when he recounted the events of that night. "What might sound idiotic for a professional, could be normal for an amateur." How does being paid for it change how normal it sounds? Renerpho (talk) 09:42, 29 September 2019 (UTC) To clarify things: We are also following along live when we record data at my observatory. We watch the data coming in, as it is displayed live on the screen. This does not affect the time of observation (there was no way for him to see it without imaging it in that way). And the amateur/professional distinction - the only difference is being paid, really. Borisov is an experienced observer, he would find it (i.e., observing a possible Near-Earth asteroid, but not reporting it, but to wait 24 hours) as idiotic as anyone who does this regularly. Renerpho (talk) 09:47, 29 September 2019 (UTC)
 * No, he said "наблюдал ее", lit. "observed her" (the comet is a feminine noun in Russian). I'm not an astronomer, so my apologies if I'm saying something stupid, but "2019-08-30.0" is midnight at Greenwich, right? So it could be that the true first observation happened, say, at "2019-08-29.99" GMT, which was already August 30 Crimean Time, almost 3 AM, shortly before local sunrise. So he actually saw it on August 29 GMT, August 30 Crimean Time. But because of some delay or mistake he reported his first observation to MPC on August 30 GMT. And in the interview he wanted to mention this discrepancy, but misspoke and said "August 30 GMT, August 29 Crimean Time". I think it's best to write him an email and ask him what really happened. Because if my interpretation is right, then the discovery date needs to be changed. — UnladenSwallow (talk) 10:15, 29 September 2019 (UTC)
 * From MPEC R106 Observations: CK19Q040* C2019 08 30.04398 08 26 37.82 +33 39 52.7         17.8 RqER106L51 https://minorplanetcenter.net/mpec/K19/K19RA6.html
 * I assume times in the MPECs are UT so that is 30 August 03:03:20 GMT for the discovery observation. Agmartin (talk) 15:36, 29 September 2019 (UTC)
 * My assumption is that the sentence has not been completely reported, and what he said (or meant to say) was "I first observed it on August 29, but it was August 30 (GMT) before I had made reportable measurements." or something like that. I doubt very much if an astronomer as careful and diligent as Borisov would make a mistake in dates. And anyway, he wouldn't report it immediately on first observation. He would need to watch it for a while to be sure it was moving, and then get at least two observations, so that he could report direction and rate of apparent movement. Guidance from the MPC here (section 17) states "It is most efficient to make two or three observations (over a period of an hour or so) per object per night.... You should not make only one observation of each object per night." Hallucegenia (talk) 15:55, 29 September 2019 (UTC)
 * He had three observations on the 30th, so motion would be apparent, and four on the 31st. I only quoted the first which was the one relevant to the discussion. Agmartin (talk) 16:28, 29 September 2019 (UTC)
 * I didn't mean to imply that you said something stupid (apologies if it sounded like that). I checked again the position of the comet in the sky at his location. It was at an altitude of 8° above the horizon at midnight, and rising. That is usually too low for observations (except under very good conditions), so I don't think Borisov could have observed it before midnight. It may be best to ask him directly. If any of you can email him, that would be great. A possibility is that Borisov started observing it just before midnight, but needed to wait for it to reach sufficient altitude to get good data on it. Kudos to him if he was able to see it at an altitude of less than 8°. The first measurement was from data collected at 2019-08-30.04398, yes. That is 01:03:20 UT (same in GMT). Crimea is GMT+3, so it's 04:03:20 local time. At that time, the comet was at an altitude of 17° - an altitude at which observations were possible. Renerpho (talk) 21:49, 29 September 2019 (UTC)
 * It is worth mentioning that the times reported are mid times: If you start observing at midnight, and need to collect two hours of data to get a single measurement, then you would report the observation time as 1 o'clock. There is no way to tell from that number when he started (the start time). But the second observation (2019-08-30.05691) was made at 01:22 UT, so the first data point can not have an end time after 01:22, and cannot have had a start time before 00:44 UT, on August 30th. Renerpho (talk) 22:00, 29 September 2019 (UTC)
 * I didn't mean to imply that you said something stupid. Oh, no worries, I didn't take it like that at all! I just feel out of my depth discussing this issue with real astronomers, when the best instrument I have ever used to watch the stars was a pair of binoculars. A possibility is that Borisov started observing it just before midnight, but needed to wait for it to reach sufficient altitude to get good data on it. That is exactly what I am proposing. Kudos to him if he was able to see it at an altitude of less than 8°. Borisov said in the Russkaya Planeta interview that the only way for amateur astronomers to beat large-scale projects is to observe at very low altitudes before dawn. I should stop procrastinating and translate and add that bit to the Gennadiy Borisov article. Maybe it is even worth mentioning in this article, because a reader might wonder: how could it be that a man who built his own telescope beat large scientific organizations? But the second observation (2019-08-30.05691) was made at 01:22 UT, so the first data point can not have an end time after 01:22, and cannot have had a start time before 00:44 UT This is where my theory gets weak. The full list of observations that night is:

CK19Q040* C2019 08 30.04398 08 26 37.82 +33 39 52.7         17.8 RqER106L51 CK19Q040 C2019 08 30.05691 08 26 39.35 +33 39 39.9          17.8 RqER106L51 CK19Q040 C2019 08 30.06759 08 26 40.50 +33 39 30.3          17.7 RqER106L51
 * He has multiple telescopes, so the second observation could have been made on an auxiliary telescope (GENON Max). But then it would mean that the first observation (on the 0.65 m telescope) was taken from, say, 29.99000 to 30.09796 (midpoint 30.04398), 2.6 hours, which is too long, right? He uses some custom software written by his friend, so maybe it's not too long? Another explanation could be that he had another observation at 29.9xxxx, but did not report it for some reason, which would be strange. So I really don't have a solid answer to this. — UnladenSwallow (talk) 02:29, 30 September 2019 (UTC)
 * He has multiple telescopes, so the second observation could have been made on an auxiliary telescope. No, the MPEC lists the instruments he used, and it only lists one telescope (the 0.65-m). If he had used several instruments, that would be mentioned.

L51 MARGO, Nauchnij. Observer G. Borisov. 0.65-m f/1.5 astrograph + CCD.
 * 2.6 hours, which is too long, right? It's unusually long, but not impossible. He uses some custom software written by his friend, so maybe it's not too long? The software is not an issue, it's just that he would have wasted 2.6 hours that he could have spent observing something else. the only way for amateur astronomers to beat large-scale projects is to observe at very low altitudes before dawn Yes! (To look at low altitude in twilight, or near the full Moon, or far from the ecliptic within the galactic plane - basically all the places missed by the big boys.) But there aren't many sites on Earth where it is physically possible to observe something faint at less than 8° elevation. Another explanation could be that he had another observation at 29.9xxxx, but did not report it for some reason, which would be strange. That's absolutely possible. The reason would be that the extremely low altitude meant the data wasn't good enough. This happens! I guess he's the only one who can clarify what he meant. Renerpho (talk) 04:55, 30 September 2019 (UTC)
 * So it was 30 August UTC, and 30 August in Crimea. But now it occurs to me it was 29 August in the U.S. Minor Planet Center is in the U.S. Lots of websites and media in the U.S. Maybe the 29th date was already out there and in the interview Borisov just wanted to clarify that? 110.145.170.78 (talk) 03:50, 9 October 2019 (UTC)

Wrong comet in table
I just removed comet C/2010 X1 (Elenin) from the table in the article. This comet is not hyperbolic. I believe whoever created that table was referring to C/1980 E1 (Bowell), which has an eccentricity of 1.057, the value given in that table, following an encounter with Jupiter. However, that comet was not hyperbolic on its inbound trajectory, so no excess velocity could be calculated (and it doesn't make a good example). I don't know if that table has been copied to anywhere else. If so, the error should be corrected there as well. I also replaced the limit of what velocity could be explained by perturbations. Previously, it was given as 3 km/s (likely based on the velocity of C/2010 X1, which was moving at 2.96 km/s at one point), but that example is flawed. I replaced it with "a few km/s". There is no hard limit on this, really. Renerpho (talk) 06:15, 29 September 2019 (UTC)
 * Allowing for observational errors, the limit would be roughly the escape velocity from the Sun at a given distance. For 200 au that would be 2.98 km/s. -- Kheider (talk) 18:50, 29 September 2019 (UTC)
 * This paper https://pdfs.semanticscholar.org/536c/61bda480e158db5dc66d903b1f2b4c73d808.pdf lists a number of hyperbolic comets. The one describes as the most hyperbolic has a 1/a of 1071*10^-6 au^-1 (that's the units they use) doing the math that comes out to a v_inf of 0.95 km/s. They also note that if non-gravitational forces are included that it's original orbit was bound. Agmartin (talk) 21:39, 29 September 2019 (UTC)
 * On their table that includes non-gravitational effects the most hyperbolic is C/1996 E1 1/a of 97(+-60)*10^-6 au^-1 unwhich gives me v_inf of 0.29 km/s. Agmartin (talk) 21:47, 29 September 2019 (UTC)
 * I checked 1980 E1, its outgoing semimajor axis in 2500 was -62.5 au. Using that I calculate its outgoing excess velocity to be 3.77 km/s. Agmartin (talk) 01:06, 30 September 2019 (UTC)
 * Yes, but its outgoing orbit was the result of an encounter with Jupiter. That's why only inbound solutions are meaningful. I don't think it would be helpful to give the number 3.77 km/s in the table, it would give a false impression unless you explained very carefully what caused it. Renerpho (talk) 09:06, 30 September 2019 (UTC)
 * The ~3 km/s example was removed from the table but the text still includes "much higher than what could be explained by perturbations, which could produce velocities when approaching an infinite distance from the Sun of less than a few km/s." which isn't specific as to what the perturber was and when the perturbation occurred so I decided to be thorough. Earlier in that section 300+ hyperbolic comets are mentioned, I suspect that refers to hyperbolic heliocentric orbits, if so I think that should be changed. Agmartin (talk) 11:16, 30 September 2019 (UTC)
 * I wish the "JPL Small-Body Database Search Engine" web-interface gave the option of listing barycentric eccentricities/semi-major axis at an epoch of ±200 years so that the results would be before/after all planetary perturbations. -- Kheider (talk) 15:03, 30 September 2019 (UTC)
 * List of the comets with barycentric incoming hyperbolic orbits as of early November 2018 (not including those that were flagged as two body model): Talk:List of hyperbolic comets Agmartin (talk) 17:14, 30 September 2019 (UTC)
 * thank you for the list. I have looked at that list a few times over the last few years as it saves some footwork. I have noticed some of the wiki-comets such as C/2013 A1 (Siding Spring) and C/2007 N3 (Lulin) now generate "barycentric epoch 1600" closed orbits. -- Kheider (talk) 18:57, 30 September 2019 (UTC)
 * Comet ISON (2012 S1) had an epoch 1600 barycentric semi-major axis of −144956 and would have an inbound v_infinite of 0.2 km/s, but I wonder if the one-size-fits-all orbit solution includes some non-gravs for the perihelion disintegration. -- Kheider (talk) 07:59, 30 September 2019 (UTC)
 * The last astrometry of comet ISON was taken on 2013-11-22, six days before perihelion. By that point it had not yet disintegrated. But I get a barycentric eccentricity of $1$ for epoch 1600. If there ever was a parabolic comet then it's ISON. Renerpho (talk) 08:17, 30 September 2019 (UTC)
 * But I notice Alan's solution is dated 2013-Dec-03, five days after the 2013-Nov-28 perihelion. -- Kheider (talk) 08:27, 30 September 2019 (UTC)
 * That may be, but the last observation used dates 2013-11-22, and with that, I get non-gravitational parameters with Find_Orb similar to those found by JPL. The JPL solution does not appear to do anything fancy. The only thing changed by the 2013-Dec-03 solution seems to be the epoch (which is now set to December 4th). Renerpho (talk) 09:02, 30 September 2019 (UTC)
 * At interstellar interloper, I swapped out C/2010 X1 (Elenin) with "barycentric e<1 (bound)" for C/2012 S1 (ISON) with "barycentric e>1 (weakly hyperbolic)" and v_infinite ≈0.2 km/s. I think it is illustrative to list a weakly hyperbolic Oort Cloud object for comparison. -- Kheider (talk) 18:26, 30 September 2019 (UTC)

To anyone interested in a big pile of data, last year I collected the barycentric data for all objects with heliocentric semimajor axes greater than 100 au. I've uploaded the file) to onedrive: (link deleted) It's the data only data only, no calculations. I recommend using the two body not true data (2B N True sheet) for comets as the JPL Horizons data for those flagged as two body model = true included a warning not to use for times far from time of observation. Agmartin (talk) 20:17, 30 September 2019 (UTC)
 * That is a nice dataset, thank you! Renerpho (talk) 00:26, 1 October 2019 (UTC)

@Renerpho @Kheider and anyone else that downloaded the above data. Yesterday I noticed some of the data in that big comet file was heliocentric instead of barycentric. Here is the new file with the correct data: https://1drv.ms/x/s!AqydZ5n8k5pCfjHE5gps2Jfoyzg?e=EPsuW8 Agmartin (talk) 22:34, 2 October 2019 (UTC)
 * To send a notification to another user (like I just did to you), type  and sign your comment. Simply typing the @ character will not produce a notification. — UnladenSwallow (talk) 07:46, 3 October 2019 (UTC)

"The higher hyperbolic excess velocity of 2I/Borisov of 32 km/s makes it even harder to reach for a spacecraft than 1I/'Oumuamua (26 km/s)"
This sentence in the beginning of the exploration section has a few problems- well, one major problem. The hyperbolic excess velocity isn't the only thing that affects the difficulty of reaching it- the trajectory that velocity is in is also important. 'Oumuamua was orbiting retrograde at an inclination of 60 degrees from the ecliptic, and Borisov only has an inclination of 44 degrees prograde, arguably making it comparatively much easier to reach due to the earth's own orbital velocity of ~30 km/s in that direction. We should have some sort of clarifying sentence mentioning this without making it overly confusing- although I'm not confident enough to write something like that myself, considering I haven't been as involved with this article as I'd like to be. exoplanetaryscience (talk) 20:22, 29 September 2019 (UTC)
 * Yes, an inclination change is very "expensive" in terms of delta-v. I agree this sentence should be reworded. Renerpho (talk) 21:53, 29 September 2019 (UTC)
 * Perhaps, like this: "Even though 2I/Borisov has a higher excess velocity of 32 km/s versus 1I/'Oumuamua's 26 km/s, reaching 2I/Borisov is easier as a mission to do that would require a minimum delta-v budget of ___ km/s (to reach it in ____ at a relative speed of ___ km/s), while a mission to reach 1I/'Oumuamua would require a minimum delta-v budget of ___ km/s (to reach it in ____ at a relative speed of ___ km/s). This is because 1I/'Oumuamua was orbiting retrograde at an inclination of 60° from the ecliptic, and 2I/Borisov only has an inclination of 44° prograde, making it much easier to reach due to the Earth's own orbital velocity of 30 km/s in that direction."


 * Someone will have to dig through the papers to find the Δv numbers, but it will result in an easy-to-understand and informative sentence, which would also lead the reader to explore additional information on how the energy to reach various {time, location, speed} points is calculated. — UnladenSwallow (talk) 03:05, 30 September 2019 (UTC)
 * It's not that easy. There is no one number for the delta_v that's required. The delta_v also depends on the launch date and flight time. Studies for both 'Oumuamua and Borisov included delta_v numbers for some exemplary scenarios, but the minimum required delta_v for both comets lies in the past, and so each would be hypothetical scenarios. The study for comet Borisov gives an example for a launch date in 2030 and arrival in 2045 (total delta_v for that is 21.35+11.19=32.54 km/s), but there are other possible launch dates. The minimum possible delta_v to 2I/Borisov, for a launch date in July 2018, would have been 5.53+11.19=16.72 km/s. This study gives a delta_v of 18.33+11.19=29.52 km/s for a mission to 'Oumuamua with launch in 2021, but the minimum delta_v, which would have been in the past, is not calculated in that study. This sentence will get complicated if you tried to include all that information. Renerpho (talk) 08:50, 30 September 2019 (UTC)
 * It's all quite irrelevant anyway. The suggested trajectory requires an Oberth Manoeuvre at a distance of just 3 solar radii from the sun. That's half the distance ultimately planned for the Parker Solar probe. I suggest we delete the whole section as a distraction. Hallucegenia (talk) 15:25, 30 September 2019 (UTC)
 * I agree with Hallucegenia. The concept of launching a probe was just a thought experiment, which is being overblown in scope and importance, especially by naming that section "Exploration". There are exactly ZERO proposals for its exploration. Splitting hairs on the physics of it gives the impression that there are proposals to do it, and going into the rocketry simply distracts the focus from the object of this article. Rowan Forest (talk) 15:55, 30 September 2019 (UTC)
 * I think the authors of the papers might disagree with that, but Hallucegenia and you have a point. I know one of the authors of the 'Oumuamua paper, and I can tell they are taking it seriously. But in the end, it's a concept study, not more, showing either the possibility, or the impossibility, of exploration. Nobody is seriously expecting that those missions are actually built. The point of the studies is to show that such missions aren't easy. Maybe the section should be called Possibility of exploration? Renerpho (talk) 00:34, 1 October 2019 (UTC)
 * Let me explain what I meant. We know the trajectories of the Earth $$\mathbf{r}_\oplus(t)$$ and Borisov $$\mathbf{r}_B(t)$$. For every two $$(t_1, \mathbf{r}_1, \mathbf{v}_1)$$ and $$(t_2, \mathbf{r}_2, \mathbf{v}_2)$$, there is a minimum delta-v budget $$\Delta v_{min}(t_1, \mathbf{r}_1, \mathbf{v}_1; t_2, \mathbf{r}_2, \mathbf{v}_2)$$ across all possible trajectories from 1 to 2, including gravity assists etc. (if there is no such trajectory, then $$\Delta v_{min} = \infty$$). Putting one into another, we define $$\Delta v^{\oplus,B}_{min}(t_1, t_2) =$$$\Delta v_{min}(t_1, \mathbf{r}_\oplus(t_1), \dot\mathbf{r}_\oplus(t_1); t_2, \mathbf{r}_B(t_2), \dot\mathbf{r}_B(t_2))$. Then we find

$$ \begin{align} (t_{start}, t_{end}) & = \underset{T_1 \le t_1 < t_2 \le T_2}{\operatorname{argmin}} \Delta v^{\oplus,B}_{min}(t_1, t_2) \\ \Delta v^{\oplus,B}_{abs. min} & = \underset{T_1 \le t_1 < t_2 \le T_2}{\min} \Delta v^{\oplus,B}_{min}(t_1, t_2) \,\,, \\ \end{align} $$
 * where $$[T_1, T_2]$$ is some interval (say, from now to 100 years from now). So we can find the absolute minimum delta-v budget (with specific departure and arrival times) required to get to an object no later than, say, 100 years from now. That's what I meant by "a minimum delta-v budget".
 * I agree that delta-v budgets are beyond the scope of this article, but perhaps it makes sense to mention them in the Interstellar object article. After all, one of the reasons we are so excited about interstellar interlopers is the possibility to obtain samples from another star system. — UnladenSwallow (talk) 12:03, 1 October 2019 (UTC)
 * The calculation isn't the issue, the problem I had was that I find no source for a minimum delta-v for 'Oumuamua. It is not included in the Project Lyra study, presumably because it was considered irrelevant (the launch date for it was in the past). We do know the minimum delta-v for Borisov, see above. Minimum delta-v's are of theoretical interest only, because they almost always require an early launch, usually before a discovery is feasible, so they aren't relevant to the "excitement about retrieving a sample". Regarding what article to include it in - yes, maybe the "interstellar object" article would be better. But remember that Wikipedia is not a textbook. Leave the formulas out of the article if you can just reference them. Renerpho (talk) 12:29, 1 October 2019 (UTC)
 * Minimum delta-v's are of theoretical interest only, because they almost always require an early launch, usually before a discovery is feasible. Well, that's why I've written the formulas, to clarify that I refer to minimum delta-v over a specified time interval ($$[T_1, T_2]$$ in the above), and not over all time (which might give a launch date in the past). I'm not proposing to include these formulas into the article at all, this was just to clarify that I was talking about minimum delta-vs in the future, not general minimum delta-vs. We do know the minimum delta-v for Borisov, see above. Thanks for the references! — UnladenSwallow (talk) 13:06, 1 October 2019 (UTC)

I agree in that the "Exploration" section fits better within the Interstellar object article. As a side note, check out this planned spacecraft by ESA & JAXA: Comet Interceptor, that will be parked at Sun-Earth L2, and has the potential of intercepting an interstellar object in short notice. Rowan Forest (talk) 15:46, 1 October 2019 (UTC)

Do we need mph?
has added mph conversions to some of the values. Is it useful to have miles per hour in a space article? Perhaps, it would be better to use miles per second instead? — UnladenSwallow (talk) 14:02, 2 October 2019 (UTC)
 * No, I know that common media may make that comparison to help give average readers the idea of what that speed is, but it doesn't make sense for this level. The au/yr conversion is more proper however for space. --M asem (t) 14:07, 2 October 2019 (UTC)
 * Along those lines, I had to look up MOID. I would suggest which fraction of a light year and how many millions of kilometres (miles for those in the cheap seats). Its perihelion is between the orbits of Mars and Jupiter, after all. Same issues apply to its perigee. kencf0618 (talk) 14:20, 2 October 2019 (UTC)
 * I'm not so on the MOID but the term, as a uncommon abbreviation (compared to something like "NASA") needs to be spelled out on first use in the prose. --M asem (t) 14:35, 2 October 2019 (UTC)
 * I also think mph is useless in this article as people do not really see 2000+ mph in their daily usage. The conversation would be more practical if the comet starts fragmenting and the fragments come off the nucleus at 2 m/s (4 mph). -- Kheider (talk) 14:59, 2 October 2019 (UTC)
 * If we started with m/s, the better conversion unit would be ft/s, but that would be unnecessary. Basically, I'm seeing the conversion to miles per (something) here as a "common man" point of relevance; the typical person at home reading the newspaper doesn't have a good grasp of what "km/s" is relative to, but even a 10,000 mph gives them some sense that that's super fast. But that's for the media. We're an encyclopedia, so we're starting from a more technically grounded POV, and to that end, we can fairly assume the reader at least has awareness of how to convert km/s to any other speed unit that they want. And since most space calculations are based on SI or the other astornomical units like au, we don't need the English units here at all. So presenting velocities as "km/s" with conversion to "au/yr" seems like the best approach, as it covers two scales. --M asem (t) 15:15, 2 October 2019 (UTC)
 * Okay, I'm going to remove it then. — UnladenSwallow (talk) 19:29, 2 October 2019 (UTC)

For purposes of comparison, the 'Oumuanua article has MOID 0.0959 AU & 37.3 LD; 2I/Borisov's AU converts to 424.6 LD. kencf0618 (talk) 10:27, 3 October 2019 (UTC)
 * As far as I understand, LD as a unit of distance is mostly used with PHOs. With Borisov's Earth MOID of 424.6 LD, it's not a PHO by any conceivable standard, so there's no need for its Earth MOID to be expressed in LD. I'm not an astronomer, though, so let's hear what the real astronomers who frequent this page will say. — UnladenSwallow (talk) 11:36, 3 October 2019 (UTC)
 * I concur. kencf0618 (talk) 11:44, 3 October 2019 (UTC)
 * Yes, there is no point expressing it in LD. Renerpho (talk) 15:31, 3 October 2019 (UTC)
 * It's expressed here, which is fine by me. kencf0618 (talk) 15:13, 4 October 2019 (UTC)

FWIW - perhaps a bit belatedly - but in defense of using the "mph" units - it may be helpful to note that non-technical wordings seem to be encouraged on Wikipedia, esp in terms of being more accessible and useful to the average reader - at least afaik atm - after all => "Readability of Wikipedia Articles" (BEST? => Score of 60/"9th grade/14yo" level) - Comments Welcome of course - in any case - Enjoy! :) Drbogdan (talk) 15:40, 4 October 2019 (UTC)
 * Our project-wide advice is here Make technical articles understandable. Reading this, maybe at one instance of presenting "km/s" that we can add like "(or approximately XX,000 miles per hour)" to help give the sense of scope of the speed. But it should not be part of the convert templates or the like for each instance of km/s. Linking units helps this too. --M asem  (t) 15:46, 4 October 2019 (UTC)

The order of (sub)sections
I think we should put before  – that's the order used in infoboxes and in most articles I've seen. — UnladenSwallow (talk) 13:15, 3 October 2019 (UTC)
 * I agree Hallucegenia (talk) 12:26, 5 October 2019 (UTC)
 * I went ahead and moved it. -- Kheider (talk) 16:47, 5 October 2019 (UTC)

Initial Characterization
On arXiv Initial Characterization of Interstellar Comet 2I/2019 Q4 (Borisov) mentions colors, estimate of mass loss rate, argues that radius may as small as a few hundred meters. Agmartin (talk) 12:07, 8 October 2019 (UTC)
 * While still in arXive, the info is vastly reliable and there is nothing fringe or controversial in there. I would include that info in this article. Regarding the lack of red color (tholins) on its surface, that is surprising for an icy body. Rowan Forest (talk) 12:22, 8 October 2019 (UTC)
 * Neither the small size nor the lack of ultrared material is surprising. Quote from the paper: The lack of ultrared matter (likely to consist of complex irradiated organics, c.f. Cruikshank et al. 1998, Dalle Ore et al. 2015) mirrors its absence in the solar system at distances <10 AU. As in the active comets of the solar system, we surmise that the particles ejected into the coma and tail of Q4 are derived from beneath a pre-existing ultrared mantle of cosmic-ray irradiated material. The ultrared matter is either thermodynamically unstable in the inner solar system as a result of the elevated temperatures or perhaps ejected or buried by fallback debris (Jewitt 2002). The object likely was ultrared before it entered the Solar System, but that material either does not survive even a short time in the vicinity of the Sun, or is already burried due to the activity of the comet. Regarding the size: That is very reminiscent of other comets, where the first estimates were 1-2 orders of magnitude too large. See C/2013 A1 (Siding Spring) (first estimate: 50 km; final estimate: 400-700 metres). Renerpho (talk) 16:29, 8 October 2019 (UTC)
 * Reading that bit it appears that they are measuring the spectra of the dust and gas released rather than the surface. Agmartin (talk) 19:46, 8 October 2019 (UTC)
 * That's correct; the surface is unobservable. That's the problem with active comets, and it's why we know so little about its bulk properties (size etc). The composition of the coma dust/gas is clearly related to the composition of the comet. It is not necessarily related to its surface composition. Renerpho (talk) 19:53, 8 October 2019 (UTC)
 * They make comparisons to other comets, and correctly say that the composition of 2I/Borisov's coma is similar to that of other Solar System comets. They (probably correctly) conclude that the composition of its nucleus is similar to the nuclei of Oort cloud comets. The problem is, we have never seen the nucleus of an Oort cloud comet. We don't know what their surfaces are like. Renerpho (talk) 19:57, 8 October 2019 (UTC)
 * Very interesting comments, thank you. It is looking increasingly likely that all Oort cloud comets were interstellar objects, albeit slower-moving than 'Oumuamua or Borisov, hence captured by our star. If this is true, then we can estimate the number of slow-moving interstellar objects in the galactic disc from the number of Oort cloud comets. — UnladenSwallow (talk) 21:34, 8 October 2019 (UTC)
 * There was something by Levison that speculated that many members the Oort cloud were 'interstellar comets captured during encounters between stars. But the similarity in compositions could just mean comets originating around different stars have similar compositions. Agmartin (talk) 21:52, 8 October 2019 (UTC)
 * I think that's the wrong way around. Many interstellar comets are analogues to Oort cloud objects (both in terms of their formation, and in terms of the environment they "live" in). It doesn't mean that Oort cloud objects don't originate at the Sun. There is no way how even a tiny fraction of Oort cloud objects could be captured. What can happen is that an Oort cloud object is perturbed into a short-period orbit; or that an interstellar object is captured by a planet and now looks like a former Oort cloud comet. But both of these require an encounter to a planet. This does not work for dynamically new comets on their initial approach. Renerpho (talk) 22:25, 8 October 2019 (UTC)
 * This is what I was remembering Capture of the Sun's Oort Cloud from Stars in Its Birth Cluster. The Oort cloud is thought to have formed when the giant planets are clearing their neighborhood and later when they are migrating outward like in the Nice model. IIRC roughly 5% of planeetesimals are supposed to end in the Oort cloud with the rest being ejected. Those that were ejected when the sun was in its birth cluster would form a free floating population in the cluster. Levison etal used simulations to show the capture of some of this free floating population via three body interactions as the sun was leaving the cluster, similar to how the irregular satellites are proposed to have been captured by the giant planets. If that is what happened all of the stars in the cluster should have comets with similar compositions, or at least the same variety of compositions. The article is paywalled so I'm not sure if they are talking about the inner or outer Oort cloud, however. Agmartin (talk) 00:14, 9 October 2019 (UTC)
 * Interesting article, thanks! I had a look at it. They consider semi-major axes between 10,000 and 50,000 au -- that is the outer Oort cloud. So, yes - captures that happened during the formation of the Sun are an exception (I didn't consider this when I ruled out captures). Captures of random interstellar objects after the dispersal of the birth cluster are almost impossible, though. Renerpho (talk) 00:28, 9 October 2019 (UTC)
 * I suspect the 90% are from other stars is out of date. The Nice model has changed since 2010 with the planets migrating slower. In Origin and Evolution of Long-period Comets the predicted number of comets from the Nice model is about half that observed. Agmartin (talk) 04:34, 9 October 2019 (UTC)
 * David Jewitt (who is the lead author of many of the studies regarding 2I/Borisov) has expressed doubt about the Nice Model and related models in general. This paper is an interesting read. Renerpho (talk) 09:13, 9 October 2019 (UTC)
 * It's details certainly have changed, which does leave it open to criticism that it is not falsifiable. If you ignore the details there are two parts of it that you can't get rid of though: planets migrating, which is needed to explain why so many objects are in resonance; and encounters between planets, which is needed to explain the planets' inclinations. The 2:1 resonance crossing was originally an explanation for Jupiter's eccentricity. The resulting instability, bombardment, trojans, and irregular satellites came as a bonus, which made it look predictive. Nowadays observations are being used to try to constrain a bunch of the model's parameters instead. Agmartin (talk) 18:57, 9 October 2019 (UTC)

More articles
Two more articles discussing observations of 2I/Borisov: Velocity of Dust Ejected from Interstellar Comet 2I/Borisov and Clues to Understanding the Microphysics of Dust in the Interstellar Comet C/2019 Q4 (Borisov) Agmartin (talk) 23:42, 13 October 2019 (UTC)
 * Interesting physics. I am more eager to expand this article on the composition. Cheers, Rowan Forest (talk) 00:41, 14 October 2019 (UTC)
 * I currently have a short paper under review, about the difficulty of predicting stellar occultations by interstellar comet 2I/Borisov. I hope it will be ready soon. I'll post a link to it here when it is online. Renerpho (talk) 06:02, 14 October 2019 (UTC)
 * That would be interesting, thanks. Rowan Forest (talk) 19:00, 14 October 2019 (UTC)

There is also the peer reviewed version of Interstellar comet C/2019 Q4 (Borisov) published today in Nature Astronomy (link goes to open access copy) under a different title. (which just happens to be the title of Jewitt's recent article on arxiv to make things more confusing) This is the source of a number of news articles. I see some numbers in the abstract that have been changed but haven't had time to read it in detail yet. Agmartin (talk) 17:16, 14 October 2019 (UTC)

Another one: Are 2I/Borisov and Oort Cloud Comets Alike? Agmartin (talk) 05:16, 21 October 2019 (UTC)
 * How come they have not done more spectroscopy? Do they need occultations to perform them? Rowan Forest (talk) 13:21, 21 October 2019 (UTC)
 * Could be there are no new molecules to report yet. Or they may need it to get to a higher elongation, one of the articles mentioned they used a particular telescope because it could aim closer to the horizon. Agmartin (talk) 17:21, 21 October 2019 (UTC)
 * Or they are taking more time to double check things. There were observations at the William Herschel Telescope on October 2 and October 13 that didn't detect C2 and put upper limits for it below those reported at MMT by Kareta et al. (mentioned on twitter, I'd wait until this appears on arXiv before adding it to the article.) Agmartin (talk) 18:42, 21 October 2019 (UTC)

Couple more: Note on the HST Image of Comet 2I/Borisov Taken on 2019 October 12 Detection of a Water Tracer in Interstellar Comet 2I/Borisov Agmartin (talk) 01:27, 29 October 2019 (UTC)

Two more: Sublimation of Water Ice from a Population of Large, Long-Lasting Grains Near the Nucleus of 2I/Borisov? and Pre-discovery Activity of New Interstellar Comet 2I/Borisov Beyond 5 AU Agmartin (talk) 02:22, 15 November 2019 (UTC)

Related images
FWIW - added PD color image of comet 2I/Borisov and related references - hope this helps in some way - in any case - Enjoy! :) Drbogdan (talk) 17:55, 14 October 2019 (UTC)
 * The colour does not look natural (and being a 2-colour image, it can't be). The comet certainly isn't yellow. I don't know if this is actually helpful. Renerpho (talk) 18:02, 14 October 2019 (UTC)
 * Brief followup - restored original image - seems earlier color image may not be pd after all - also - rm (remmed code) dup image/caption - Enjoy! :) Drbogdan (talk) 19:22, 15 October 2019 (UTC)

Seems another image - File:Comet-2IBorisov-HubbleST-20191016-compass.png - seemingly PD at the moment afaik - is now available from the Hubble Space Telescope website - and has been added as the lead image to the main article - iac - Enjoy! :) Drbogdan (talk) 23:22, 16 October 2019 (UTC)
 * Added newly released video to the main article => File:Video-NASA-InterstellarComet-2IBorisov-HubbleST-20191016.webm  - iac - Enjoy! :) Drbogdan (talk) 13:45, 17 October 2019 (UTC)

Possible additions
I don't have much time to work on the article at the moment, but here are some things that I would add. Some of this is work I have been involved in myself, and I don't want to add this material myself due to possible conflict of interest. Maybe someone likes to give it a go:
 * Comet 2I/Borisov is reddish in colour - redder than the Sun, and redder than 1I/'Oumuamua, but similar to some Solar System comets. (Opitom et al., p.2, "the dust coma", and table 2).
 * The Hubble image has been colourized blue. To avoid confusion, I believe it should be mentioned that the data is actually grayscale, and the colouration is pseudo-colour.


 * No carbon chain molecules (C2, C3) have been detected, according to the Opitom paper. Their upper bounds are much stronger than the claimed abbundance of C2 by Kareta et al., and they find that the earlier finding is likely in error (p.4, "conclusions"). This contradicts what is currently written in the article.
 * It may be worth mentioning here that CN and C2 are usually the first species detected in a comet, followed by either C3 or OH. That no C2 has been found indicates that 2I/Borisov is carbon-chain depleted, similar to some Jupiter-family comets. 67P/Churyumov-Gerasimenko is an example of a carbon-chain depleted comet (Opitom p.4, "conclusions"). Carbon-chain depleted comets make up about 30% of known Solar System comets, the majority of them are Jupiter-family comets (Opitom p.4, "discussion").


 * My own paper The Difficulty of Predicting Stellar Occultations by Interstellar Comet 2I/Borisov has been published today. It may contain material that is relevant to the article, maybe for the "2019-2020" section. Renerpho (talk) 14:47, 22 October 2019 (UTC)

Precovery
2I/Borisov spotted in old images from March: "Mining the ZTF’s archive, the researchers were able to identify images from as far back as March in which the object had appeared, unnoticed. “Effectively, we have about 7 months of observations of this comet,” Bolin says. The data revealed that, when the comet was still farther from the Sun than Jupiter, its surface was already releasing gas and dust, which would eventually form the bright tail." from Alien comets may be common, object from beyond Solar System suggests Agmartin (talk) 21:58, 30 October 2019 (UTC)
 * Also mentioned here, I'm not sure where this should go in the article. Mentions a second paper that will discuss the ZTF observations which are not yet listed by the MPC. Agmartin (talk) 19:57, 31 October 2019 (UTC)
 * The observations have now been published by the MPC, here. First precovery dating back to December 2018. JPL has not yet included it in their orbit calculation, but this should happen within the next couple of hours. Renerpho (talk) 21:58, 3 November 2019 (UTC)

Crossing the ecliptic - when?
There is an inconsistency in the article. The lead says "The comet will pass through the ecliptic of the Solar System in December 2019", while the image File:Sky_plot_13.png included in the "Trajectory" section shows it crossing the ecliptic by 1 November, before crossing the celestial equator. Which is right? Chris Thompson (talk) 13:42, 14 November 2019 (UTC)
 * I checked the JPL ephemeris. it crossing ecliptic on Oct 26 near Regulus, Celestial equator on Nov 13, and galactic plane on Feb 20 near Crux. December it reaches perhelion as well as being closest to earth. Tom Ruen (talk) 16:50, 14 November 2019 (UTC)

Magnitude?
How bright did it get? J S Ayer (talk) 22:50, 3 January 2020 (UTC)
 * Looking at the MPC's database for 2I/Borisov, about 16th magnitude. Agmartin (talk) 21:50, 5 January 2020 (UTC)
 * Something about apparent magnitude should be added to the main article. At the moment the only mention is in the external links. Chris Thompson (talk) 15:58, 6 January 2020 (UTC)

2I/Borisov fragmenting
2I/Borisov appears to have fragmented see image here: https://twitter.com/aussiastronomer/status/1245806606484291584 Agmartin (talk) 04:16, 3 April 2020 (UTC)
 * Science Alert #1 and #2 that could be used. --M asem (t) 04:28, 3 April 2020 (UTC)
 * ✅ Following was added to the main article => In April 2020, more evidence of possible fragmentation of the comet was reported.    - should be ok - comment if otherwise of course - iac - Enjoy! :) Drbogdan (talk) 13:26, 3 April 2020 (UTC)

Review article
The Interstellar Interlopers a review article discussing Oumuamua and 2I/Borisov. Agmartin (talk) 16:51, 25 September 2022 (UTC)