Suppose we one day find an extraterrestrial walking on our planet that originated from another planet. The alien quickly learns all about religion and now wants to become a Jew. Do we let him?

Remember: Aliens don't have to be three-eyed, green-skinned creatures. Perhaps they will even look and function exactly like we do!

(of course, the premise of this question is that Aliens do exist)

  • 13
    Only if they're not from Meroz...
    – yoel
    Commented Jun 15, 2012 at 22:27
  • 2
    Are they similar enough to allow for successful interbreeding?
    – Double AA
    Commented Jun 15, 2012 at 22:32
  • 9
    Wouldn't it basically boil down to the question of whether halachah would consider them human? If not, then no matter how sentient they are, they could no more be considered Jewish than a golem. [I imagine - though I'd have to look for sources - that the criterion would be whether they're born from a human mother (compare Bechoros 8a, הדולפנין פרין ורבין מבני אדם), so Spock might be considered halachically human, but Deanna Troi would not.]
    – Alex
    Commented Jun 15, 2012 at 22:32
  • 1
    So I assume you don't want an answer from rabbis saying that there can't be intelligent life on other planets?
    – HodofHod
    Commented Jun 17, 2012 at 2:23
  • 2
    @HodofHod That's correct. Once you take that as a given the question doesn't start. [I would, however, accept an answer if it emerges that all Rabbis agreed there was no life -- since if true, that would be an actual answer]
    – yydl
    Commented Jun 17, 2012 at 2:48

3 Answers 3


As discussed in another question, whatever extraterrestrial life exists does not have free will, and would therefore not be capable of accepting the moral responsibility of conversion.

  • 4
    There is no pasuk that says that aliens cannot have freewill. I understand that there are various sources on the topic, but the fact of the matter is that none is better than a Gemara, and even in the Gemara this kind of thing would be דברי אגדה which we could halachically wiggle out of. There therefore is no true Jewish belief on the issue even if there is Jewish thought. To not make that distinction is to paint ourselves into a corner for no reason. The correct answer, in my opinion, is "who knows, let's wait and see and figure it out then."
    – Dov F
    Commented Jun 27, 2012 at 19:57
  • 2
    Clearly you are correct that this question is only hypothetical, and any true ruling would depend on the circumstances of the case. However, this would seem to be the most reasonable conjecture.
    – Baruch
    Commented Jun 27, 2012 at 21:06
  • See comments on that question starting here judaism.stackexchange.com/questions/9197/…
    – Double AA
    Commented Jul 1, 2012 at 7:21
  • @DoubleAA: I answered your question there.
    – Baruch
    Commented Jul 2, 2012 at 19:27

On page 50 in Moreh Ohr by Rabbi Kaplan, he concludes the following:

We see from this [starting on p. 47] that there is a singular species in the world that is capable of free will, Torah, reward and punishment which are the purpose of creation. This is mankind, to whom God has given The One Torah. It is however possible that there exists many species of living creatures on other stars i.e. planets, which may even be capable of intelligence and wisdom, just not freewill. The subject of freewill is but a very small item as it is, that cannot be verified in science [or by scientists], only by belief in our Torah. And if they do find additional species of living creatures, we have already learned from the Torah that don't have freewill.


It would depend. If there are Jewish aliens then a non Jewish alien will be able to convert. However if there are no Jewish aliens then a alien would be unable to convert. This is similar to animals. Since there are no Jewish animals therefore a animal can not convert. (Hilchos Chayos 25:10)

All kidding aside. Rabbi Avigdor Miller Zatzal clearly said many times that there is no humans or aliens on the other planets.

  • 3
    I'm confused: is Hilchos Chayos a real work?
    – Double AA
    Commented Jun 27, 2012 at 19:15
  • 2
    It is a figment of my imagination, similar to the questionnaire. Commented Jun 27, 2012 at 19:17
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    Ahh well then -1. The question clearly said it assumes they exist, and it is clear that R Miller is not the only opinion on this matter judaism.stackexchange.com/a/9203/1274
    – Double AA
    Commented Jun 27, 2012 at 19:18
  • 3
    Also, I'm quite confident that yydl exists.
    – Double AA
    Commented Jun 27, 2012 at 19:18
  • 13
    DoubleAA - Sorry that I alienated you. Commented Jun 27, 2012 at 19:33

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