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Pioneer Plaque

(click to enlarge, source: WikiMedia)

If you look carefully near the center, each of the pulsar line segments have a gap at a specific radius. I can't find any mention of the meaning of this. Any ideas?

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    $\begingroup$ In case your hot-link breaks: here's an imgur of original i.stack.imgur.com/6HFFB.jpg at en.wikipedia.org/wiki/File:Pioneer10-plaque.jpg $\endgroup$
    – uhoh
    Oct 24, 2020 at 13:52
  • $\begingroup$ @Glorfindel I voted to reject your edit. The reason I left the post alone is that I figured the OP left it out intentionally. If they want to include it the link is available in my comment, but in this case I think it's their decision. $\endgroup$
    – uhoh
    Oct 24, 2020 at 16:16

2 Answers 2

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It is explained in the original paper from Sagan:

A Message from Earth 
Author(s): Carl Sagan, Linda Salzman Sagan and Frank Drake  
Source: Science, New Series, Vol. 175, No. 4024 (Feb. 25, 1972), pp. 881-884

I found a copy on the website of Swarthmore College: link to PDF

On page 2, it is explained:

Relevant excerpt from paper

Those radial lines for which the earth-pulsar distance is not accurately known are shown with breaks.

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Partial answer, exploring some details

It's clearly not an artefact of the SVG vectorised file on Wikipedia. A photograph of the Voyager Golden record (which features the same map), shows the same gap.

Using this to decode the pulsar map, the distance of the most similar pulsar can be established (280 parsecs)

Pioneer plaque close up with label

The gap is then around ~200 parsecs. I recognise nothing special about this distance.

It's too large to be some solar system distance, but too small to be a galactic distance.

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  • $\begingroup$ It might be the distance of the pulsars from the galactic plane. Some pulsars are about 200 parsec from the plane. $\endgroup$
    – BlueCoder
    Oct 25, 2020 at 14:45
  • $\begingroup$ Reference for 200 parsec distance, see this article, table 1: articles.adsabs.harvard.edu/cgi-bin/… $\endgroup$
    – BlueCoder
    Oct 25, 2020 at 14:45
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    $\begingroup$ Wikipedia also says that the distance to the galactic plane is encoded in those lines, although it says "The lengths of the lines show the relative distances of the pulsars to the Sun. A tick mark at the end of each line gives the Z coordinate perpendicular to the galactic plane." (I do not see a tick mark at any end so Wiki's explanation is confusing to me... but maybe they are just referring to the initial part of the line, starting from the center, before the gap - the more you are distant, the longer it would be). en.wikipedia.org/wiki/Pioneer_plaque#Sun_and_galactic_landmarks $\endgroup$
    – BlueCoder
    Oct 25, 2020 at 14:49
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    $\begingroup$ @BlueCoder All the lines have visible tick marks, although they are a bit hard to spot due to the binary written right next to them. $\endgroup$
    – SE - stop firing the good guys
    Oct 25, 2020 at 14:53
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    $\begingroup$ I was wondering if it could be the size of the central bulge, but that seems to be bigger than 200 pc. It is also odd that #7 doesn't have the gap... $\endgroup$
    – Ludo
    Oct 27, 2020 at 12:08

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