Talk:Near-Earth object

Observational biases section re-write

With all due respect to the editors who worked on this admittedly important section, I found the version I saw yesterday to be very problematic:

• One of the main sources was low-quality (an article with no sources on permanent.com, the personal webpage of a somewhat cranky enthusiast) and thus needed replacing.
• There is a sentence with stats showing that most NEOs are discovered near opposition. The stats are without context, the source that was given was wrong, and I tracked down that it is original research by a user for the creation of this image on Wikimedia, and thus violates WP:OR.
• Many other sources were used inappropriately, to support claims they didn't make or with the claims they did make conflated with another.
• The description of the various biases was also too imprecise (probably still is in the new version).

Sadly, what appears to be the seminal work on observational biases, Bottke (2000), is behind a paywall, and I didn't find a good popular-science-level overview article either, so the section could probably still see significant improvement. Rontombontom (talk) 10:27, 26 January 2024 (UTC)

Diagrams showing orbital classes

The five diagrams presently included in the article are all problematic for different reasons. I made a request for a new diagram at WP:GLI. Rontombontom (talk) 17:24, 27 January 2024 (UTC)

Forgot to add: this was quickly solved, Nsae Comp found & inserted a public-domain NASA diagram instead. Rontombontom (talk) 16:55, 31 January 2024 (UTC)

Working-towards-FA feedback...

Ok placeholder here. Aim is to address as much as possible before going there. Cas Liber (talk · contribs) 19:40, 31 January 2024 (UTC)

• In lead - Most known PHOs and NEOs are asteroids, but a small fraction are comets - I'd put the percentage or percentage range here. Cas Liber (talk · contribs) 19:40, 31 January 2024 (UTC)
  • First, a thanks! Second, done. But 0.35% is such a small percentage. Rontombontom (talk)

• In body - Near-Earth objects (NEOs) are [by convention technically] defined... - could remove bracketed text without losing meaning...?
  • I replaced t with "formally", which matches what's written in the IAU source. Rontombontom (talk)

• Rejig the lead into 3 or 4 paragraphs of related material.

• The Close approaches section seems to contain similar material to the History of human awareness of NEOs section...but is waaay down the article. Could we maybe combine them?

• The Risk section would make more sense being moved further down the article to directly before what we do about these things...maybe...

• See also sections should only be populated as a last resort. In general I remove any links that can be in the body of text or at a more relevant location, or remove those entirely that are only very generally related to the article.

• Overall, the article is at the longer end - if more content needs adding it might be prudent to remove or summarise some exisiting content

• I began aligning refs to a consistent format. Doing this before FAC is prudent too.

  Yesterday I merged two paragraphs into one in the lead - was that enough?

  To reduce the length of the article, I think I can merge and shorten the Risk & Magnitude of risk sections (the wikilinked articles on the Torino & Palermo scales are fairly well detailed), and trim the Close approaches section, but it'll require careful consideration of what to keep & what to cut. Every section from History... to Artificial near-Earth objects is linked logically to the previous section, so I have to think about what could be done to fit Close approaches (and the linked Impacts) in-between. I think I'll have time over the weekend for this substantial work.

  The date formats were already consistent and in line with MOS:DATEUNIFY, but perhaps not in the way you're used to (EDIT: I realise this may sound passive-aggressive... what I meant was that you'll find this formatting in several Wikipedia articles, including some FA, but I encountered other experienced Wikipedia editors before who were unfamiliar with it): dates in the article body are all in the US date format, publication dates in citations are all in the same format as in the article text, while all access dates and archive dates are (well, were before your edit) in ISO format. Is there an FA preference here for full date format uniformity that goes beyond MOS:DATEUNIFY? As for replacing all authors with first-lasts, I started that last month but apparently forgot to finish it; can do that, too, over the weekend. Rontombontom (talk) 15:26, 15 February 2024 (UTC)

  An update on the MOS:DATEUNIFY issue. I like access & archive dates in ISO format for practical reasons: I primarily look at them to see how old they are and if an update is warranted, which is much easier to see than in the US date format; especially for some key sources (like archive.org) that use URLs with YYYYMMDD in them. On the other hand, looking at Wikipedia:Vital articles/Level/5/Physical sciences/Astronomy, the only FA I found with the same formatting choice (US for article body & publication and ISO for access/archive) is Cygnus X-1. So if this is really a factor in FA acceptance, I'll change the format of all access/archive dates over the weekend, too. Rontombontom (talk) 17:31, 15 February 2024 (UTC)

  Ah I see. Ok, I haven't been at FAC a while but we'd always line them up to be consistent. If others have been getting through like the way you have it then happy to leave it. Cas Liber (talk · contribs) 23:19, 15 February 2024 (UTC)

  I went through all your suggestions, please check how well it works now. Specifically, I have the same notion towards the See also... section as you, but there are just too many for this sprawling subject. I went through it again, and although I removed a few and put one into the article, I found the nine that remained are all relevant, but not enough to warrant addition to the article (or else the article will be really too long). For example, EURONEAR is a survey programme, but its discoveries are dwarfed by the ones already mentioned in the article, while NEOShield was a planetary defence research project which appears much less significant than what NASA has done. Rontombontom (talk) 21:55, 18 February 2024 (UTC)

  Having slept over it, I now find the new ordering even more problematic. The lead part of the History of human awareness of NEOs section and the Risk section tell different parts of the same story and should belong together. Will have to think about a better ordering. It will probably need some redundancies (for example a single-sentence re-cap of the close approachas of Halley's Comet, Hermes & Icarus in the Close approaches section after it is moved back to its original place). Rontombontom (talk) 10:17, 19 February 2024 (UTC)

  Another possible solution: keep the sequence as is, but refocus the intro of the History... section on the recognition of the extraterrestrial nature of meteors & comets + the discovery of the first NEA, and move other historical events to Close encounters & Risk. Then only the first NEA will have to be mentioned twice. Rontombontom (talk) 17:16, 19 February 2024 (UTC)

  Ugh, this was a lot of work, but finally done (I chose the second option). I'd really appreciate a second (or third or fourth...) opinion on whether the article's structure is now consistent and has good enough flow. Rontombontom (talk) 18:59, 21 February 2024 (UTC)

I think it is still jumpy - I would place the Number and classification section directly under Definition (as material similar), then all the History of human awareness of NEOs section (down to and including risk) then the Exploratory missions section. This is the best way I can think of to minimse subject matter jumping back and forth. Might also allow for some reduction Cas Liber (talk · contribs) 12:48, 6 March 2024 (UTC)

sdSds started a new section with a similar proposal at the bottom, I replied there. Rontombontom (talk) 17:55, 10 March 2024 (UTC)

So, pinging @Casliber: do you think we are ready for FAC? Rontombontom (talk) 13:54, 11 April 2024 (UTC)

Artificial vs. natural near-Earth objects

While the article has a section on "Artificial near-Earth objects" they aren't mentioned in the lead. Putting a mention there might give undue weight to the topic; perhaps merely adding the word "natural" somewhere in the lead would improve the article? (sdsds - talk) 22:07, 31 January 2024 (UTC)

• Done. Rontombontom (talk) 15:25, 1 February 2024 (UTC)

Explicitly excluding Earth's Moon

While obvious to the knowledgeable reader familiar with small solar system body topics, the article might be improved for general readers by explicitly mentioning that Earth's Moon is not considered a near-Earth object since it is a natural satellite. (sdsds - talk) 22:18, 31 January 2024 (UTC)

• I added a full sentence which also clarifies that planets & spacecraft aren't included. However, I doubt I could find an explicit source spelling this out. So I hope the "SYNTH is not explanation" section of WP:SYNTHNOT covers this. Rontombontom (talk) 15:25, 1 February 2024 (UTC)

Not necessarily near Earth

Again considering the general reader rather than the specialist, There's a key aspect captured by a sentence currently in the second section: "NEOs are thus not necessarily currently near the Earth, but they can potentially approach the Earth relatively closely." Consider moving that to be the last sentence of the lede paragraph. (— 𝐬𝐝𝐒𝐝𝐬 — - talk) 23:32, 15 February 2024 (UTC)

I left it there but added a similar sentence right after the definition in the first paragraph of the lede. Does it work for you? Rontombontom (talk) 21:55, 18 February 2024 (UTC)

Yes the current version of the lede makes it clear, and leaving the details for later makes sense. Just nit-picking now...

• the use of 'whose' is potentially problematic since NEOs can't own their orbits. Perhaps something like, "A near-Earth object (NEO) is any small Solar System body whose orbit on a trajectory around the Sun that can bring it near the Earth?" Or "...in an orbit around..." would also avoid the personification of NEOs. Since solar system bodies all follow trajectories around the Sun even when we say they are orbiting a planet makes this murky. I defer to your subject matter expertise, acknowledging it might also be best to leave it as-is.
• and is using SSSB intended to imply a hypothetical interstellar object that zips between Earth and the Moon is not an NEO? That too is counter-intuitive for the general reader. If it were an NEO, the wording could reduce to, "...on a trajectory that can bring it...."

Thanks again for implementing the suggestion. The article deserves GA status! (— 𝐬𝐝𝐒𝐝𝐬 — - talk) 00:36, 19 February 2024 (UTC)

Thanks for the nit-picking, no problem at all! I eliminated the two instances of "whose".

The problem with an interstellar object is the same as with long-period comets: the underlying intention is to find objects for which close encounters can be predicted well in advance with a good degree of confidence, but if something races in and out of the inner Solar System in a few months and returns in 50,000 years or never, you'll get neither a precise orbit nor a long-term prediction. It would be good to put this justification into the article, but sadly, even after searching for an hour, I couldn't find a worthy source that could be used for this. Rontombontom (talk) 19:22, 19 February 2024 (UTC)

Yes, retaining the current high quality of the article precludes adding content that might look like original research. Relatedly, it might seem obvious but the article is about how the phrase 'near-Earth object' is used in astronomy. Yet the article doesn't link early to astronomy, even where the term is used in the Observational biases section. Nor does it include an astronomy-related infobox. Is this intentional? Also, a link somewhere in the article to interstellar interloper might be useful for some readers, even if only in the 'See also' section. (— 𝐬𝐝𝐒𝐝𝐬 — - talk) 21:05, 19 February 2024 (UTC)

I now implemented all of that. Rontombontom (talk) 14:48, 21 February 2024 (UTC)

Been busy - gonna read through soon. Another thought - article defines as is any small Solar System body with an orbit around the Sun that can bring it near the Earth. - but is it not anything closer to the sun than earth or are there any really close objects to the sun that are not NEOs? Cas Liber (talk · contribs) 22:44, 4 March 2024 (UTC)

That's a good question, a very good question! One I would love to cover explicitly in the article, but I can't find a good source (I had one but it was an article in a sanctioned non-peer-reviewed paper). But here is the situation regarding objects close to the Sun, as a synthesis of stuff I put into the article.

For now, the official NEO definition is anything that gets within 1.3 AU (Earth orbit radius) from the Sun. So yes, theoretically, that would include objects which are always close to the Sun (say on an orbit entirely within the orbit of Mercury, the definition of Vulcanoids) and thus not really near Earth. But we don't know any such objects. What's more, theoretical simulations show that such orbits aren't stable, both due to gravitational perturbations and non-gravitational ones, so we'll probably never find such objects greater than small rocks, and even if yes, they are likely to either end up destroyed or transfer to more eccentric orbits on which they can get closer to Earth. Even if we go out a bit further, to objects entirely within Venus's orbit (ꞌAylóꞌchaxnims, of which one is known), those don't have very stable orbits, either, perturbed by both Venus and Mercury. Getting to the next group in closeness to Earth's orbit, there are the co-orbitals of Venus. But all known ones are in eccentric orbits also crossing Earth's orbit and simulations show that the population of co-orbitals in near-circular orbits is low and not too stable either.

So, if our underlying motive in cataloguing objects as NEOs is to find anything that may be predicted in advance to hit the Earth, it is unnecessary to put an inner limit on the NEO orbital region. But I doubt that you'll find this written down explicitly anywhere. (I could not even find a clear statement justifying the exclusion of long-period comets from the NEO definition.) Rontombontom (talk) 17:47, 5 March 2024 (UTC)

Unsolicited comment: you have the article on a good path by avoiding this synthesis. At the same time I'm grateful for the explanation of it here! (— 𝐬𝐝𝐒𝐝𝐬 — - talk) 23:47, 5 March 2024 (UTC)

Okay, so as it reads now - sentence 3 sorta labours the point a bit. I'd make the first sentence the official definition (now sentence 2), and then merge material from sentence 1 and 3 into a single sentence. Cas Liber (talk · contribs) 00:31, 6 March 2024 (UTC)

I edited it as per the suggestion. Rontombontom (talk) 17:53, 10 March 2024 (UTC)

Exploration mission delta-v requirements

Please review my recent edit in the Exploratory missions section. It attempts to get at the concept of delta-v being a measure of acceleration rather than velocity. Another way to do this might be to explicitly link Δv.

I further re-worded it.

I'm not sure what you mean with acceleration, and I may be missing something as I am no rocket scientist, but here is my understanding. Delta-v will be the time integral of acceleration over the time periods the rocket is fired. Low acceleration over a long time can achieve the same delta-v as high acceleration over a short time (see ion engines vs. chemical rockets). If you check the Tsiolkovsky rocket equation, using a given propellant with a specific effective exhaust velocity to deliver a given payload, delta-v is a function of only the initial total mass, whatever the acceleration. (Staging & atmospheric resistance will of course complicate things.) Rontombontom (talk) 19:58, 19 February 2024 (UTC)

Yes that's correct, delta-v is measured in units of velocity, and is the integral of acceleration over time. The current phrase 'sum total of changes in orbital speed' expresses that well. Thanks! (— 𝐬𝐝𝐒𝐝𝐬 — - talk) 21:10, 19 February 2024 (UTC)

Rename and re-frame Definitions section

I suggest renaming the 'Definitions' section to 'Cataloging' and center the focus of the section on that. (— 𝐬𝐝𝐒𝐝𝐬 — - talk) 23:54, 6 March 2024 (UTC)

Both you and Cas Liber proposed this. I can see the logic in it. However, I have other problems with it. Currently, the Number and classification section is a direct continuation of the Projects to minimize the threat section, which introduces the projects that led to the cataloguing in the first place. The very first subsection, Observational biases, is strongly tied to both of the preceding two sections (the biases stem from the methods of those surveys and indicates how the numbers of the discovered NEOs aren't necessarily representative of all NEOs). The Size distribution sub-subsection of the Near-Earth asteroids subsection also heavily builds upon the surveys introduced by Projects to minimize the threat. Meanwhile, the last sub-section, Artificial near-Earth objects, provides a bridge to the Exploratory missions section (though I can see that there is a link to Projects to minimize the threat, too).

Any ideas how these connections could be untangled without more jumpiness and duplications? I don't see a good way at the moment, will have to think about it.

Or do you have alternative ideas on how to reorder these sections? Rontombontom (talk) 17:51, 10 March 2024 (UTC)

Retitle the section and rearrange the paragraphs within. See User:Sdsds/sandbox/Near-Earth object. (— 𝐬𝐝𝐒𝐝𝐬 — - talk) 06:06, 11 March 2024 (UTC)

A quick heads-up: OK, I'll check it, but I may not have the time before Friday. Rontombontom (talk) 12:56, 12 March 2024 (UTC)

I have now read your version. Seems I misunderstood you: you just want to rewrite the existing Definitions section, without the much larger re-ordering suggested by Cas Liber (moving the entire Numbers and classification section under the first chapter, which would make even more sense if the title is Detection and cataloging). Regarding your version, I would still put at least the definition of NEO in front, before using the term. (The same in the lede is a summary, the first chapter should stand on its own.) Otherwise, I could go with it. However, I also ask your opinion about the greater re-ordering suggested by Cas Liber, and if you can think of any solutions to my problems with it – the part you propose to re-write may need another re-edit if we do the big change. Rontombontom (talk) 17:11, 15 March 2024 (UTC)

The more extensive reordering proposal presents difficulties. I applaud the desire to make the article 'flow' better.

Links are another option; one possibility would be to move some content into separate articles, maybe e.g.: Detection and cataloging of small solar system bodies or Exploratory missions to small solar system bodies. I'm confident articles like that could be further expanded, and readers of the main article could choose whether and when to follow the links. That somewhat addresses the concern Cas Liber raises, though likely not entirely. (— 𝐬𝐝𝐒𝐝𝐬 — - talk) 08:12, 19 March 2024 (UTC)

After a lot of consideration, here is my new alternative proposal: what if we do the opposite of your proposal? That is, keep the focus of Definitions strictly on definitions, and move the naming of the cataloguing bodies to the Numbers... section. (Plus, move the definition of JPL, ESA etc. acronyms to the new first instances.) A much more limited re-write, but one that I think that might also remove some of the jumpiness Cas Liber wanted to correct with that big reordering proposal (which doesn't seem to work for me or you). Rontombontom (talk) 13:30, 27 March 2024 (UTC)

Yes, that sounds like it would be an improvement! (— 𝐬𝐝𝐒𝐝𝐬 — - talk) 17:12, 27 March 2024 (UTC)

Done.

As for creating Detection and cataloging of small solar system bodies or Exploratory missions to small solar system bodies, both would make sense (especially the latter as ever more missions are done), but I would find the job overwhelming at the moment. Rontombontom (talk) 21:33, 29 March 2024 (UTC)

Impact probability explanation

I have just removed this paragraph by Eric Kvaalen, which was added to the risk scales section earlier today:

The probability of impact depends both on the true minimal distance at which an object will pass in the next 100 years and on the amount of data astronomers have been able to collect on it. Any particular object has a maximum possible probability value that depends on its orbit. For objects that will hit the earth, the maximum is 100%, but at early stages when the data are limited the probability may be deemed quite low. Other objects have zero probability of impact in the next 100 years even from the initial sighting. In general, the probability may increase with more data but will eventually decrease to zero or else, rarely, increase to 100%. Given the fact that, as mentioned earlier, asteroids more than 60 metres across are estimated to hit the earth once in 1,300 years on average, it is unlikely we will discover an object with a value of 9 or 10 on the Torino scale in the next century.

I think it's a good idea to add some further explanation to that section, so I support an addition like this in principle. However, apart from the fact that this would need citations, I find the version above needs some work before it's ready to be put into the article, as some of it is a bit vague.

Here's the place to work on it! Any help is welcome. Renerpho (talk) 22:19, 14 September 2024 (UTC)

It's all quite obvious if you think about it a bit. The fact that the category changes with further observations is stated in the first reference, and we can refer to it again in this paragraph. I tried to keep the paragraph short, but I will give here a longer explanation. Each object has a distance of closest approach in the next 100 years. When we observe an object, at first there is a large uncertainty about this distance. It's like a big disk around the point where it really will be, and the disk may or may not include the earth (which is a small disk in this picture) at the moment of that closest approach. If it doesn't, then we know the object will not hit the earth, and we give it a probability of zero. If that disk does include the position of the earth, then we can calculate the probability of collision based on the data available at that point in time. If the true distance of closest approach is large, then the probability will necessarily be small. As a function of the uncertainty, the probability is zero for small uncertainty (assuming the object is not going to hit the earth), rises with rising uncertainty to some maximum, and then with further uncertainty the probability decreases again, but does not go to zero. For an object that will hit the earth, the probability is 100% for small uncertainty and goes down to very low values for high uncertainty. As the uncertainty decreases (with more observvation), the probability goes up, until it becomes 100%. We will eventually see objects which will have a Torino rating of 8 or more, simply because there really are objects that will hit the earth. We can actually estimate how often a category 8 object will come along. Also for category 9 or 10. I won't do that calculation becausee that would be called original research since I don't have a reference handy, but as I did write, we can be sure from what is stated earlier in our article that it's quite unlikely that we discover a 9 or 10 in the next century. Eric Kvaalen (talk) 13:14, 15 September 2024 (UTC)

@Eric Kvaalen: The question is how to say it in not quite so many words (and "concise" means "clear" in this case). Maybe a picture could help? Much of what you're saying, I think, boils down to figure 2 of our paper [1], which is a comparison between a (hypothetical) impacting solution and the actual missing orbit as more data is collected. That chart is published at [2] with a CC BY 4.0 license, compatible with Wikipedia. Renerpho (talk) 06:14, 17 September 2024 (UTC)

@Renerpho: Very interesting paper. I have uploaded the graph.

It would be interesting to know how often an asteroid this big or bigger comes within 38,000 km of the centre of the earth.

Why does the graph use the uncertainty in ζ? Doesn't the probability depend also on the uncertainty in ξ?

What are the true values for ζ and ξ in 2029?

Eric Kvaalen (talk) 18:40, 18 September 2024 (UTC)

@Eric Kvaalen: ζ and ξ basically correspond to minimum distance and time, respectively. The timing of the potential impact isn't relevant for the impact probability. Compare [3], p.4, and the references linked from there. The true specific values for ζ and ξ aren't very meaningful, because we know that no impact will occur. Renerpho (talk) 19:54, 18 September 2024 (UTC)

@Renerpho: The timing of a potential impact may not be important for the impact probability, but the timing of the asteroid's position is of utmost importance for the impact probability, and that is what determines ζ. I found the values in this 2013 paper: 47684 km and 9483 km, respectively, for ζ and ξ. The MOID is, or at least will be in March 2029, therefore only 9483 kilometres. The value of ξ is so small that if ζ were 0, there would be a collision! If the asteroid were an hour or so earlier it would hit us. I suppose that's the reason why the graph ignores the uncertainty in ξ. My guess is that the "uncertainty" specified by the x-axis is the standard error, because the probability only drops to essentially zero once the "uncertainty" gets down to around 10,000 km, whereas actually there cannot be a collision if ζ is more than about 21,000 km, which is about 27,000 km less than the true value. Your paper never actually defines what is meant by the "uncertainty". Eric Kvaalen (talk) 11:36, 23 September 2024 (UTC)

@Eric Kvaalen: I suppose it doesn't! Thanks for digging up the exact values.

If we want to use it for the article, I think it may be best to adapt the image: make some changes, and remove a bit of what would just be clutter in this context (remember, it's meant to be an illustration). I'll see if I get around to do it. Feel free to give it a try yourself, too! Renerpho (talk) 14:50, 23 September 2024 (UTC)