The CNET article Interstellar comet Borisov looks ordinary, making Oumuamua even weirder says:

A paper published Monday in Nature Astronomy lays out the early data on Borisov, which is just the second-ever object seen visiting our solar system from beyond. While scientists will get a better look as the comet comes closer to Earth over the next several weeks, so far it looks to be the same color and size as most ordinary comets. Earlier research also revealed it's behaving in familiar ways with a tail containing some of the same toxic gases we expect from intrastellar comets.


Is the word intrastellar commonly used to refer to objects within our solar system by astronomers, or is it just the editors creative reversal of interstellar.

Along the same lines, would extrasolar be used by astronomers to refer to objects outside of our solar system?

  • $\begingroup$ Link to the arXiv version of the Nature Astronomy paper: arxiv.org/abs/1909.05851 $\endgroup$ Oct 15, 2019 at 8:32
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    $\begingroup$ Note that the linked paper uses the phrase "Solar System comets" rather than"intrastellar comets". The latter phrase appears to be the invention of the author of the CNET article. $\endgroup$ Oct 15, 2019 at 11:01
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    $\begingroup$ I would argue that "interstellar comet" is also incorrect, at least with respect to 21/Borisov. It was within the bounds of the solar system at the time of its discovery. Perhaps "rogue comet", to parallel "rogue planet"? $\endgroup$ Oct 15, 2019 at 11:08
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    $\begingroup$ @DavidHammen It's a comet which traveled through interstellar space (and will continue on beyond the bounds of the Solar System), so I think "interstellar comet" is OK. (And people are happy to write review articles about "Interstellar Dust in the Solar System", so... $\endgroup$ Oct 15, 2019 at 19:56

1 Answer 1


No. (I'll note that this usage is arguably erroneous, since the nominal meaning of "intrastellar" is "within or inside a star".)

First, I personally have never heard anyone use that term in my twenty-five-odd years as an astronomer.

Second, a full-text search of the astronomical literature on the NASA Astrophysics Data System turns up a grand total of 51 sources that use "intrastellar" (as opposed to, say, 325,000 hits for "intracluster"). None of these has anything to do with the Solar System. Quick checks of a few of them show a mixture of simple typos (i.e., "intrastellar" used when "interstellar" is clearly meant), awkward/failed attempts at synonyms for "intracluster stellar light", and actually correct uses meaning "inside a star".

would extrasolar be used by astronomers to refer to objects outside of our solar system?

You mean like "extrasolar planets", the discovery of which shared the Nobel prize in physics this year? In practice, "extrasolar" seems to be used mainly to refer to other solar systems and the components thereof, rather than just anything at all outside the solar system. (Though I have seen "extrasolar dust" used to refer to dust grains found in the Solar System but thought to have originated outside it.)

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    $\begingroup$ thanks for the thorough answer! $\endgroup$
    – uhoh
    Oct 15, 2019 at 7:54

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