1723: Meteorite Identification
| Meteorite Identification |
 Title text: Click for an actual flowchart for identifying a meteorite. My favorite part is how 'Did someone see it fall? -> Yes' points to 'NOT A METEORITE.' This is not a mistake. |
Note: Clicking on the image on xkcd (click the date above the comic to go to the comic on xkcd) takes you to the Meteorite or meteorwrong? Self-Test Check list flow chart at the Department of Earth and Planetary Sciences at Washington University in St. Louis.
Explanation
Meteorites form when a meteoroid survives entrance through the Earth's atmosphere as a meteor. Thus, they are very rare rocks that come from space, and can stem from broken asteroids, the Moon, and sometimes (very rarely) even from Mars.
The flowchart, though facetious, would actually work the vast majority of the time a person picks up a rock and believes it to be a meteorite, since, given any single rock one finds on the surface of the earth, it is almost definitely not a meteorite.
Flowcharts are often used (in xkcd) to give the inexperienced a step-by-step process to follow (see a guide to flowcharts here: 518: Flow Charts). Meteorite identification, however, is very difficult, so the brevity of this flowchart in a way pokes fun at the need for a flowchart to identify meteorites, since laypeople are not experienced enough to confirm that a rock is indeed a meteorite. A similar short flowchart as this has been used recently in 1691: Optimization, and another only two box chart was used in 1195: Flowchart.
In the title text Randall mentions that the comic image is a link to the more detailed Meteorite or meteorwrong? Self-Test Check list flowchart at the Department of Earth and Planetary Sciences at Washington University in St. Louis. (Note that, likely due to this comic pointing to it, that server may be overloaded and the page may not come up for you right away. Since it has no ads, here is a mirror you can use if it won't load.)
The authors of those resources notes that they have received many rock samples and photos (or even personal visits) from people claiming to have discovered meteorites and thus they would likely benefit from just providing people the shortcut flowchart from Randall, as a way of saying, "leave meteorite identification to the professionals."
Randall also mentions in the title text that his favorite part of this real flowchart, which is the part where if anyone saw the "meteor" fall then it is 'NOT A METEORITE.' What he most likes about it it, that this is not a mistake.
First of all the chance of actually being near a falling meteorite is exceedingly small. From the flowchart is a link to a 64 point long checklist, which basically all ends in "..., then it's not a meteorite." In point 3 is noted the following:
- Since 1900, the numbers of recognized meteorite "falls" is about 690 for the whole Earth. That's 6.3 per year. Only 98 of those occurred in the US. That's less than 1 per year. Even when a meteorite is observed to fall, experienced meteorite hunters may find only a few stones when hunting dawn to dusk for a week.
Second, meteors that can be seen falling almost definitely cannot be found on the ground immediately after. Any meteor big enough to glow and be visible while falling all the way to the ground will leave a large impact crater, rather than simply sit on the ground as a rock. Smaller meteors do not fall fast enough to glow all the way to the ground. Either they will burn up completely (not leaving any meteorite) or they will be slowed down before they burn all the way up (but typically end up much smaller than the original meteoroid). After that they will stop glowing and will brake even further until they reach a terminal velocity due to air resistance. Their small size, and lack of glow, make them practically impossible to follow with the naked eye even in daylight. If a person stands close by the impact location of a meteor it may be possible to hear a swish and a thunk, from when it passes by and then hit the ground. It will then be possible to locate the meteorite, but such a falling stone could also have been dropped from an airplane or by a storm. But in some few cases people have actually heard a real meteor falling and found it afterwards. This is what happened with the 690 events mentioned above. All this is described on How to Identify a Meteorite from The Meteorite Market which is linked in point 48 in the table from Washington University. But they did not see it fall!
What Randall finds so funny about this part of the flowchart is that there are three arrows leading to the question "Did someone see it fall?", but from there only a "Yes" option is possible, and then this gives the result "Not a meteorite." This indicates that if you have found a rock that has no dark crust or regmaglypts (the options that by saying no takes the user to the question about seeing it fall), then it is not a meteorite, and then the only reason people might still believe it to be a meteorite must be because someone saw it fall. Since seeing it fall rules out that it could be a meteorite there only need to be this single option left.
If the rock actually has those thumbprint like impressions on the surface (that scientists call regmaglypts) then the creator of the flowchart actually asks to see the rock (photo or sample). The other features that are interesting is if it has a dark thin crust (from the melting during entry), but only if it also has either regmaglypts or if it has a lighter color inside than the outer crust.
See also 1405: Meteor about how people mistake the words meteorite with meteor. The many misspellings of meteorite is mentioned in point 63 in the table.
Transcript
- [A caption is above a flowchart with only two boxes. The first box is a diamond shaped box with an arrow down to the next rectangular box below. Each box has a text.]
- How to identify a possible meteorite:
- Start
- No, it's not a meteorite.
Trivia
- In December 2012 (almost four years before this comic) a flowchart was posted under the title Meteorite identification flowchart on mindat.org a page dedicated to sharing information about minerals. (Check the attached gif file).
- The user(s) posting this earlier flowchart (Jolyon & Katya Ralph) seems to have posted a note in the discussion on this page about the fact that Randall has "borrowed" their idea.
add a comment! ⋅ add a topic (use sparingly)! ⋅ 
refresh comments!Discussion
lol, some poor soul is now wondering why his Meteorite ID chart is being flooded with traffic! 141.101.98.59 12:08, 22 August 2016 (UTC)
I'd like to see some analysis of the linked flowchart, or a least an explanation of the title text comment. Why does "Did you see it fall" have only an "yes" option, that leads to "not a meteorite" Zeimusu (talk) 12:10, 22 August 2016 (UTC)
- Because actually seeing a meteorite fall and recovering it is an incredibly rare event (690 times since 1900), but stories about how they saw a meteor fall and went out and found a rock in the middle of a crater are a dime-a-dozen. So if someone shows up with a rock they think is a meteorite, odds are they will say they saw it fall, but odds are it's not a meteorite. --162.158.214.231 14:26, 22 August 2016 (UTC)
- You missed the "have only a yes option". It lacks a "No" path. --108.162.218.179 20:07, 22 August 2016 (UTC)
- I assume the reason for that is that the chart has run out of ideas why you'd even think it's a meteorite at that point 141.101.98.59 08:30, 23 August 2016 (UTC)
I'm wondering if this is related to the recent claims in British newspapers (Warning, Daily Mail content Link 141.101.98.83 12:27, 22 August 2016 (UTC)
Here's the chart hosted externally: http://imgur.com/a/AzQOk Also, could somebody explain the mouseover text? Why does it falling from the sky mean it's not a meteorite? (Edit: Imgur's servers are trying to give out. Here's another external hosted version: http://oi66.tinypic.com/315yazp.jpg ) NexTerren (talk) 12:47, 22 August 2016 (UTC)
Where did the 'there have only been 690 confirmed cases since 1900' factoid come from? Wikipedia says there are over 38,000 well documented finds, referring to a 2011 source. 108.162.250.161 13:03, 22 August 2016 (UTC)
- The "Some Metorite Realities" page says "Since 1900, the numbers of recognized meteorite "falls" is about 690 for the whole Earth." It looks like the author mistook that as the total number of meteorite discoveries. 173.245.54.28 13:49, 22 August 2016 (UTC)
Here's some explanation on why seeing a meteorite fall is unlikely: http://www.meteoritemarket.com/metid2.htm Located at point 48A from http://meteorites.wustl.edu/realities.htm (Linked on the full chart) 141.101.70.43 13:07, 22 August 2016 (UTC)
I just tried fixing it up FOUR TIMES, and got an edit conflict each time. The later ones didn't even change anything. I'd contribute, but not if this keeps happening. Papayaman1000 (talk) 14:50, 22 August 2016 (UTC)
- Sorry about that, but I hope my edits fixed this. There is now an extended explanation of the title text. I'm finished for now, so please improve where needed. --Kynde (talk) 14:52, 22 August 2016 (UTC)
Yeah, I can't even get on it. 162.158.75.27 (talk) (please sign your comments with ~~~~)
Well, thanks Randall for 'borrowing' my chart ....
http://www.mindat.org/forum.php?read,11,279733,279757
UPDATE: I have heard from Randall and we're sorting things out! --108.162.215.125 04:25, 23 August 2016 (UTC)
- Interesting, have included this in a trivia! What did you sort out then? Guess he just got the same idea from the chart he links to, as you had...? --Kynde (talk) 20:32, 23 August 2016 (UTC)
»Any meteor big enough to glow and be visible while falling will leave a large impact crater, rather than simply sit on the ground as a rock.« Doesn't many meteors break up and fragment while still in the air? Such an event could be highly visible on the sky yet yield meteorites sitting on the ground. --141.101.80.70 09:03, 23 August 2016 (UTC)
- The missing bit is IMHO that for finding meteorite based on seeing it fall it would need to be still visible in low attitudes. In case of breakup, you will see the breakup but will have no way to guess where the meteors landed, as the breakup will change the trajectory. -- Hkmaly (talk) 12:55, 23 August 2016 (UTC)
- I think the explanation was not clear enough and have improved. But agree with Hkmaly that also a breaking up meteor will result in lots of meteorites that while falling the last part of the way, was not visible to the naked eye (day or night). If the rock had not broken up but hit the ground, it would have been visible all the way, but would have been completely destroyed in the impact (leaving a crater) and no meteorite would have been left to find. So again you would not find a meteorite that you saw land! --Kynde (talk) 20:32, 23 August 2016 (UTC)
I think it's important to note that from a certain perspective, this graph is wrong 100% of the time. Technically, speaking from a super-geological timeframe, our planet is nothing but a big mashed up mass of meteorites... or would our planet simply be a large meteoroid and thus not a meteorite yet as we have not finished plummeting into the sun? Joshupetersen (talk)
- As Earth has now cleared it's trajectory around the sun it is deemed a planet and thus not a meteoroid. Any stone that has been molten after landing on the Earth is now part of the Earth. This thus rules out all rocks that hit the Earth before it got a solid crust in the first place. Any rock that can be determined to have fallen to Earth after that, and has never been molten after landing is a meteorite and not a part of the original Earth. So technically you comment is, from any perspective, 100% wrong all the time ;-) --Kynde (talk) 20:32, 23 August 2016 (UTC)
