Talk:C/2013 A1 (Siding Spring)

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A news item involving C/2013 A1 (Siding Spring) was featured on Wikipedia's Main Page in the In the news section on 19 October 2014.

A back-of-the-envelope calculation suggests there's currently about a 1:73k chance of the comet hitting Mars.
—WWoods (talk) 18:40, 28 February 2013 (UTC)

The best estimate I have seen suggests roughly a 1 in 7075 chance. -- Kheider (talk) 00:00, 1 March 2013 (UTC)

Do we really want to use mAU in the table? I am concerned that the average reader will just be further confused by it. -- Kheider (talk) 11:49, 1 March 2013 (UTC)

Point. But I don't like AU in this context; it's the wrong scale unit, so you have to count the zeros to see the difference between 0.007 and 0.0007. What about converting to Mm?

—WWoods (talk) 19:30, 1 March 2013 (UTC)

For now I have gone back to using standard AUs to better match the JPL Database source and to hopefully prevent confusion for casual readers. Hopefully adding in the spaces "&nbsp ;" will help align the columns better. -- Kheider (talk) 20:43, 1 March 2013 (UTC)

With an observation arc of 74 days, the nominal comet makes a backside pass of Mars (21:00), increasing orbital energy. With an arc of 148 days, the nominal comet makes a front-side pass of Mars (19:28), decreasing orbital energy. Looking at Aldo Vitagliano's magenta impactor, impact scenarios seem to occur around 20:00 to 20:30. -- Kheider (talk) 18:00, 3 March 2013 (UTC)

Inbound the comet had an orbital period of millions of years (Barycentric Epoch 1950 = 11 million years). -- Kheider (talk) 13:44, 17 January 2014 (UTC)

I believe the first line in that section should read: "The comet will pass extremely close to Mars on or around 19 October 2014". Not the current, "The comet will pass extremely close to Mars on 19 October 2014." Does anyone agree with me? – AJL^talk 07:23, 6 March 2013 (UTC)

The closest approach will occur at 2014-Oct-19 19:28 (± 01 hr 03 min). Even the 44 day observation arc had a closet approach of 2014-Oct-19 10:26 (± 10 hr 05min). The orbit is well determined. What is not determined is whether it will impact Mars since Mars is inside the 310,000km uncertainty region. -- Kheider (talk) 10:49, 6 March 2013 (UTC)

Fair enough. I hadn't read the reference attached to that statement before posting. Thanks for the pleasant reply. :) – AJL^talk 01:18, 14 March 2013 (UTC)

Is all of the discussion about the impact results needed, since now an impact is essentially ruled out? Bubba73 ^{You talkin' to me?} 02:54, 16 April 2013 (UTC)

I see only two sentences discussing impact results ("The resulting upper limit energy of impact could reach 20 billion megatons.", "The diameter of an impact crater would be roughly ten times the diameter of the comet's nucleus.") plus the table, which seem reasonable to keep IMO, since much of the notability of the comet came from the potential impact. --Roentgenium111 (talk) 12:55, 16 April 2013 (UTC)

There is no need for the first table to be sortable. It is already in order by the only thing that matters - the length of the observation arc. There is no need for the reader to sort it on any of the other columns. Bubba73 ^{You talkin' to me?} 14:59, 16 April 2013 (UTC)

Someone might want to sort it by nominal passage time. -- Kheider (talk) 17:42, 16 April 2013 (UTC)

Table titled "Comet impact at 56 km/s into sedimentary rock" - please, use Megatons, Gigatons (preferably with scientific number notation or teratons/petatons) of TNT for Kinetic energy. 100 million Mega Tons (cause I guess that's what "100 million Mt" is suppose to mean) is very confusing making recalculations and comparisons more difficult than needed. SkywalkerPL (talk) 10:30, 18 November 2013 (UTC)

Mt stands for Megatons. I believe using a single unit makes it easier for the layperson as I find scientific notation often loses the layperson. For better or worse most asteroid impacts are estimated using Mt. -- Kheider (talk) 17:43, 18 November 2013 (UTC)

Since we're talking about 10s of thousands of miles can we get specific about distances with respect to what? I mean the coma of the comet might be tens of thousands of miles wide while the nucleus of the comet might be a mile or less. Using "Comet" for the distances involved is too vague. --Smkolins (talk) 20:18, 9 December 2013 (UTC)

The article currently states that a "spectacular meteor shower" on Mars is unlikely, reference Emily Lakdawalla's blog from March. Here's a NewScientist article that quotes other experts that aren't so sure. http://www.newscientist.com/article/dn24715-fiercest-meteor-shower-on-record-to-hit-mars-via-comet.html#.UqdOEidQVeE The journal paper in Icarus is already cited as a reference in the article, minus the meteor storm. Geogene (talk) 17:30, 10 December 2013 (UTC)

How many "Comet Siding Spring"s are there? Which one is this comet? --JorisvS (talk) 18:47, 28 December 2013 (UTC)

There are 12 comets and 1 asteroid by that name. -- Kheider (talk) 18:59, 28 December 2013 (UTC)

So this one would be like ... Siding Spring 12? --JorisvS (talk) 22:25, 28 December 2013 (UTC)

Yes, the odds for impact are very low. However, if you want to report the April 2013 odds, why do it in 3 separate entries? Cheers, BatteryIncluded (talk) 18:27, 17 April 2014 (UTC)

All of those estimates are more than a year old. Removing the dates from the estimates makes them appear as if they are still current. Every time the observation arc became longer the odds dropped. There is no longer ANY chance of a direct impact by the comet nucleus. -- Kheider (talk) 19:35, 17 April 2014 (UTC)

Once more: I know there is a negligible chance of impact; I do not contest the data/models, but the format and prominence given. You reverted my edit when I merged 3 separate entries starting with "As of April X the odds of impact are...". As far as I know, this is not a timeline where you can have an argument in favor of outdated chronological estimates. Being that we agree that the odds impact are nil, we must update the article accordingly by giving proper weight (little) to the old estimates. That is what I did; a one-liner is enough; add the dates if you will. Do you still think it is better the way it was before? Why? CHeers, BatteryIncluded (talk) 23:45, 17 April 2014 (UTC)

This edit was bad because it gave the suggestion that the odds of impact from March 2013 were more recent than the odds from April 2013. -- Kheider (talk) 00:06, 18 April 2014 (UTC)

Note that there is a gambling site now taking anonymous bets on the distance at the Mars encounter; see http://bitbet.us/bet/820/comet-2013-a1-will-pass-within-100-000-kilometers/ . It should be expected that people will attempt to change the information on the wiki page in order to influence the betting odds. Because anyone can be a better, there is no one who is free of potential conflict of interest in editing the page. Should it be locked? — Preceding unsigned comment added by 173.228.13.5 (talk) 20:53, 3 May 2014 (UTC)

• JPL solution #5 with a 58 day observation arc (2013-Feb-11)
• JPL solution #17 with a 244 day observation arc (2013-Jun-08)
• JPL solution #27 with a 394 day observation arc (2013-Nov-02)
• JPL solution #42 with a 502 day observation arc (2014-Feb-20)
• JPL solution #46 with a 516 day observation arc (Davide Farnocchia 2014-Mar-14 cad=0)
• JPL solution #47 with a 612 day observation arc (Davide Farnocchia 2014-Jun-10)
• JPL solution #53 with a 662 day observation arc (Davide Farnocchia 2014-Jul-29)
• JPL solution #56 with a 676 day observation arc (2014-Aug-13)
• JPL solution #58 with a 687 day observation arc (Davide Farnocchia 2014-Aug-25)
• JPL solution #67 with a 694 day observation arc (Davide Farnocchia 2014-Sep-12)
• JPL solution #97 with a 733 day observation arc (Davide Farnocchia 2014-Oct-07)

NASA TV (Thurs, 10/09/2014@2pm/et/usa) - Enjoy! :) Drbogdan (talk) 12:17, 7 October 2014 (UTC)

FOLLOWUP - NASA VIDEO REPLAY (56:15/9 October 2014) - Space Experts Discuss "Comet Siding Spring/Mars Flyby - 19 October 2014 - Flyby" - Enjoy! :) Drbogdan (talk) 01:17, 10 October 2014 (UTC)

So, this is what the comet looks like from the surface of Mars -- 67.70.35.44 (talk) 05:52, 21 October 2014 (UTC)

closest approach distances don't match the description in the text:

Closest approach of Comet Siding Spring to Mars - maximum and minimum distances noted

correction: I see, the closest distance to the comet's orbit is separate from closest approach. image put back. the image might be clearer if it had an added line indicating closest approach of the comet's orbit to mars, 100min after the closest approach of the comet body.

Malronius (talk) 15:31, 24 October 2014 (UTC)

NASA-TV/ustream (Friday, November 7, 2014@12pm/et/usa) - experts provide initial science observations of comet C/2013 A1 close flyby of Mars on October 19, 2014 and the Martian atmosphere. - Enjoy! :) Drbogdan (talk) 03:12, 6 November 2014 (UTC)

FOLLOWUP - Space Experts Discuss the Effects on the Martian atmosphere of the Comet C/2013 A1 Flyby of Mars on October 19, 2014 - Archived Discussion => Audio (with visuals; 60:21) - Enjoy! :) Drbogdan (talk) 19:41, 7 November 2014 (UTC)

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In the article is mentioned that As seen from Mars, C/2013 A1 peaked at approximately apparent magnitude −6 with the source being a twitter post from two months before the closest encounter. I really doubt that the comet actually reached that magnitude, as it appears much, much fainter in the Mars rovers photos . We need a reliable source after the flyby for the apparent magnitude, not a prediction that could be way off reality. C messier (talk) 07:38, 12 March 2023 (UTC)

@C messier: It's always hard to estimate the apparent brightness of a fuzzy object from the low quality images, and a fuzzy comet will always appear fainter than a star of the same magnitude. As of 2025, JPL Horizons (the site they used for their information) still claims that it peaked at -5.3 mag, at about 2014-Oct-19 18:30 UT. Whether that's accurate is a different question. In fact, you're probably right that it's not, because JPL's model uses an assumed slope, in addition to an absolute magnitude that is uncertain by 2 mag. I'd say the comet most likely reached negative magnitudes at closest approach, but I doubt we can be more specific. Renerpho (talk) 01:44, 7 October 2025 (UTC)

After second thoughs it could be accurate but for the whole diffuse coma, while the nucleus alone was not very bright. C messier (talk) 12:06, 7 October 2025 (UTC)

@C messier: The number would refer to the entire comet (including nucleus, coma, and tail). The formula given by Seichi Yoshida at , which is used as a reference in the article for the comet's apparent brightness slightly brighter than +11, as seen from Earth in October 2014, gives an apparent total brightness of -5.3 mag at the time of its closest approach, as seen from Mars's surface -- close to JPL's number. I think that's a reliable source, and if we can make it work as a reference, we could say with some confidence that the comet peaked at between -5 and -6 mag (which I now believe is probably true, after having looked at the data compiled by Yoshida). I'm afraid though that the conversion may be WP:ORIGINAL RESEARCH (it is not as straight-forward as plugging in some obvious numbers). Renerpho (talk) 06:49, 8 October 2025 (UTC)