Sorry for the click-bait-y title. In the light of recent rumblings and rumours from NASA and SpaceX, people are once again thinking about the possibility of putting a man on Mars. And if they can send one, why not lots?

Granted, the idea of a self sustaining colony is for now firmly in the realms of science fiction, but that’s where I’m comfortable, so let’s discuss this a bit. I’m sure there are a million implications but the first religious one I thought about was time. Imagine for a moment a successful human colony on Mars (and it doesn’t have to be Mars, or even in our solar system) where humans live happy lives under the clear red sky, send kids to school and dream of making it big in the Martian dust-skiing Olympic team. In this colony there is a congregation of religious Jews (or Muslims would work well for this discussion too). How do they pray?

I don’t mean which direction do they pray, although that might be an interesting discussion too, I mean when and what? Mars has a day which is (in Earth terms) about 24 hours and 40 minutes long. It’s really pretty close to our day, and there is a sunrise and a sunset which make sense to people. One can imagine that people living on Mars would be happy to call a Martian day a “day” and be done. (In The Martian, Mark Watney distinguishes the Martian day as a “sol” – that’s fine too). It’s reasonable to assume people would wake up in Martian morning and go to sleep in Martian night.

If you are a religious Jew, would you consider time for shacharit (morning prayers) is simply worked out by using Martian hours and Martian days? It sounds kind of reasonable initially, because Judaism anyway deals with variable length days and nights (in summer and winter) by simply dividing the day or night (whether sunrise to sunset or dawn to dusk) into 12 periods and declaring those hours for today. 3 hours into the day is the end of the time for reciting Shema. 4 hours in is the end of the time for morning prayer et cetera. But does this follow through?

The first wrinkle is that you will be continuously sliding out of sync with anywhere on Earth. If today your morning prayers lined up with Jerusalem, tomorrow they will be 40 minutes out of sync, and within a couple of weeks you will be on New York time.

Slightly worse than that is what do we mean by “weeks”?  Do seven “sols” make a Martian week? Will we keep Shabbat on Mars every seven sols? Or will we try to keep track of what’s happening back on Earth and have a 6 and a bit sol week? And what happens if we lose track? There’s a  gemara in Shabbat (69b)

R. Huna said: if one is travelling on a road or in the wilderness and does not know when it is the Sabbath, he must count six days [from the day he realises he has forgotten] and observe one. R. Hiyya b. Rav said: he must observe one, and then count six [week] days. On what do they differ? One master holds that it is like the world’s creation. The other holds that it is like [the case of] Adam.

It sounds to me (you may disagree) that we would count six days as we see them (sols) and make Shabbat. That’s good – and the implication is that you do the best you can, and when you get back to civilization (or Earth) you readjust your clock. But it leads me to my next question.

Assuming we are keeping seven-sol weeks, what do we do about months? Nobody every suggested we keep months according to how we feel or keep count.  Mars’s moons Phobos and Deimos are tiny, one orbits Mars 3 times a day and one in slightly more than a day. We’re not getting any useful months out of them.  All we can sensibly do is count the months as they are on Earth. But how? Do we keep a clock going tracking what day and time it is on Earth now (out of sync with the weeks we are observing). Here’s where I see a problem. Our current Jewish calendar is specifically set out so that certain festivals cannot fall on certain days of the week. It’s a fixed calendar now, but it seems clear that the same rules where in force when the sages would declare each new month on the fly. They would still make sure to work things out so that festivals would work out right.

Basically – Yom Kippur, where we are restricted like Shabbat such that we cannot cook or light a flame can’t be allowed to work out on a Friday or a Sunday. If it does you will have 2 days without food (if it’s a Friday) and/or light (if it’s a Sunday). So, ok, nowadays we have lights which last longer than a few hours, and food which will stay good for a few days, but the rule hasn’t changed. In addition, Hoshana Rabba, the seventh day of Sukkot (Tabernacles) cannot be allowed to work out on a Shabbat because that would make us unable to do the “custom of the prophets” and beat a willow branch on a Shabbat. This is also still in force today. Since Yom Kippur and Hoshana Rabba are both in the month of Tishrei, the rule is that this month cannot start (first day of Rosh Hashana cannot be)  on Sunday, Wednesday or Friday. This is abbreviated by saying “Lo Adu Rosh” (לא אד”ו ראש).

So, if I’m counting weeks according to local Martian time, and months according to Earth, it’s only a short matter of time until I end up with the first day of Rosh Hashana landing on a “wrong” day. Will we make out own adjustments then pull back to be more in keeping with the Earth calendar? Or will we make our calendar completely independent and then leave things to sort themselves out when we get back to Earth?

I’ve mentioned hours, days, weeks and months. Years seem to me less worrisome, but sure, why not ask – how old would a kid born on Mars be when we count his barmitzvah? How long would a tree grow before we could eat its fruit?

My knowledge of Islam is minimal, but I imagine you could ask some questions about when the 5 daily prayers are, when you have Ramadan, and what times to fast during Ramadan. When to have Eid el-fitr and Eid el-adha? Excuse my ignorance and expound on anything you know about.

Please comment and tell me what you think.

Before commenting, please have a quick look at the ground rules

22 thoughts on “Is there (halachic) life on Mars?

  1. I read a book many. many years ago (in my Junior High School library!) called something like Jewish Science Fiction, which was a collection of great short stories on this theme. I think that Robert Silverberg was either the editor or one of the better-known authors in the book.

    On a related topic, I’ve always wondered how government statistics in the various Muslim countries count the ages of their citizens. I’d like to hope that someone is applying correction factors but, if not, they will be over-reporting lifespan by a few years!


    1. I like Robert Silverberg, but I don’t remember reading anything of his that was deeply Jewish in the sense of being rooted in Jewish knowledge. I think I read a short story (might have been Silverberg) of a Jewish girl bringing home an alien who it turned out was studying to be a rabbi….I’ll see if I can dig that one out, but again it was a nice cultural Jewish piece without a deep connection to how the religion really works in an orthodox sense.
      As for Muslim ages, are they counted via Islamic years? If they are, then you are right, there is about a 3% discrepancy vis-a-vis how everyone else counts.


      1. That may be the book David is referring to. I’ve definitely heard the title “The Dybbuk of Mazel Tov IV”, but I think , if anything, the story I remember was “Look, you think you’ve got troubles” by Carol Carr in the same collection. anyway, nice stories, and the one “On Venus have we got a Rabbi” is a great Sholom Aleichem pastiche, but it’s not what I’m looking for here.


  2. Love the fact that you are applying halacha to alien situations – who knows, maybe this blog will be a most precious resource in 100 years’ time and everyone will be calling you a prophet.
    I don’t think Mars would need to line up with earth time – just as Jerusalem and NY are on different clocks and we don’t care about that, so Mars would be on its own clock and shaot zmaniyot. The month thing is more of a problem – one option would be to say to keep the same calendar as on Earth with the same Hebrew named months, and then to skip some days so as to get back in sync when it is out of sync. Remember that Jews would be travelling back and forth. We already manage with the international dateline so we would find a way.
    By the way, Ramadan can vary in its start date from country to country, by one day, due to the moon. So the Muslims worldwide can be a tad out of sync with each other. We get the same effect for a few hours for Shabbat in terms of USA-Israel-Australia (LA and Melbourne are almost a day off); and we Jerusalemites get a day’s difference on Purim. And I must say it’s very weird to be so out of sync. So if Mars and Earth were in communication, it would be weird for the Jews as keeping in sync would be very difficult.


    1. Mars is a test case but maybe I’m thinking too small – imagine we are somewhere further away, where communication with Earth was severely limited, or non-existent for a while.

      The question is (maybe)- are we keeping some sort of Earth based calendar in order to keep up with Earth, or are we doing it to remind ourselves of what it would be like on Earth or are we gaining some I don’t know, spiritual benefit from observing Sabbaths and festivals at specific times.

      I don’t know what seasons, if any Mars has, but let our new alien planet have its own seasons and a year of whatever 300 days. Or 400 – neither of which matches earth closely… My guess is we wouldn’t make a point of making Pesach in the spring, since even on Earth the whole Southern hemisphere doesn’t do that. The point of Islamic years, both you and David made is well taken though – it’s perfectly believable that someone can say “it’s my birthday” even if they were born in summer and now it’s winter. I do wonder though, if Jewish majority would revert somewhat to evidence of puberty more than simple day counting.


  3. Are we required to keep any of these halachot up on Mars? Surely the moon means Earth’s moon and only Earth’s moon and the same for the Sun (if we decide to travel into a different universe).

    What are the halachot of going to the ISS? Surely that is a more likely situation?


    1. Required? People have asked the same question about keeping halachot outside of Israel. I think the general consensus is that (even if it’s only to keep up good habits) we do need to keep the halachot.
      I’m in total agreement that the moon is only Earth’s moon, and the Sun (assuming a different solar system) is really only the Earth’s sun. But accepting that, how would a serious Jew in all good conscience feel was correct to act on a planet with a different sun and moon (or no moon).
      I deliberately didn’t mention something like the ISS. Yes, it’s more likely, but doesn’t give much food for thought because it’s the sort of situation where you are unlikely to divorce yourself from an Earth based chronology. ISS orbits the Earth about 15 times a day. It’s not reasonable in anybody’s book to suggest that halacha would say 15 days are actually passing for that person – and they don’t go to sleep and wake up 15 times in 24 hours. So you are forced to say something simple and safe like “measure time from where you took off or where you will land.” Astronauts or cosmonauts can happily keep mission control time (whether that is Florida or somewhere in Russia) and once you have a day arbitrarily decided by fiat, all the rest of the times fit in simply. On a real planet with real sunrise and sunset it becomes odd (in my mind) to say “it’s 8 am in Israel, I ought to say morning prayers” when the whole city around you is perhaps getting ready for sleep.


  4. There are a lot more issues that would be hard to make sense in Judaism, not all halachic more principles. What happens on mars if the Messiah comes on earth? How do you relate to a promised land on a different planet. What about a temple in Jerusalem? Moses climbing up to Heaven. etc. When we add AI and transhumanism to the mix more stuff falls away again. will Judaism survive? Hopefully, with some transhumanism thrown in, we will live to find out.


    1. Wait wait! Time for all those questions (well, at least the ones I understand) eventually. Starting off in a simple format, so anyone who is familiar with regular Jewish practice can have a go. I have no idea if there’s a right answer to any of this – I’m interested in where the questioning leads us. Maybe I’m wrong, but my feeling is that if we can really put our finger on what would need to be done in an unusual case like this, we will have a bit more understanding of what we are doing here and now too.


  5. Since our Halachic days are quite flexible (take the hours of daylight and divide by 12) I think the same would apply no matter upon what celestial body one finds oneself on so davening times and even Shabbat would be fairly straightforward.
    The difficulties start when counting cycles of the moon or trips around the sun, however, as the Rabbanim have already establish a fixed calendar I think the same could be applied to life on Mars.


    1. That sounds good. So the question I have is, since the week is counted as per Martian days,and these are out of sync with Earth days, what do we do when the day we are up to is Friday but the Jewish date (from the fixed calendar) says it’s Yom Kippur? It’s supposed to be impossible to have Yom Kippur on a Friday.
      Or are you suggesting we just merrily count the days of the month as Martian days – so after one month our Rosh Chodesh is already a day or so out of sync with Earth. In one sense that’s nice and consistent, but it rapidly moves different groups of Jews to be on completely different calendars.
      It’s this which I’m trying to understand. If we say in our prayers that Pesach (Passover) is the “time of our freedom” (z’man cheruteinu זמן חירותינו) we normally (on Earth) are referring to more than just a simple anniversary of leaving Egypt. Numerous Jewish sources state that the month of Nissan is a time which is suited for freedom, and the exodus happened then because it was an appropriate time for freedom, rather than simply we celebrate freedom because it happened to come out on that day. Rav S. R . Hirsch has a whole long essay on why spring is a time when we are spiritually affected by the physical sense of renewal and freedom. Once we are too arbitrary about the calendar, we lose that connection almost immediately. Of course it may be impossible to have it all ways. But what is more important? Is it a higher halachic principle that all Jews should be on more or less the same timetable (allowing, as Yael has already mentioned, for a day or so slopover due to timezones etc) or would we care about seasons on our new planet? Or would we just care about day counts? None of the answers is perfect…but which one is “right”?


  6. As I posted on your FB page on this, Mars offers no great halachic challenge. How about a planet which does not rotate, so there’s no night and day? IMO that’s easy – arbitrarily set up 24 hour days and have “night” at 6pm. But what about a planet that rotates slowly, so that a full day is say 40 hours. Do you fast 41 hours on Yom Kippur? surely not. I think in this case – assuming we have a dating for YK, you start fasting at an appropriate time before “sun”down and continue fasting for 25 hours. The last solution may be more appropriate if you’re on a spaceship.

    However, if you base your calendar on what time it is in Israel – which initially seems plausible – then you have the problem with time dilation if your spaceship is travelling fast enough – days in Israel will be longer than 24 hours on your spaceship. Hence the solution here must be an onboard calendar – and that rule can therefore also apply to planets whose days and years are very out of synch with Earth.

    I’m sure Rabban Gamaliel would have been able to devise a practical solution – not so sure about some of the other Mishnaic rabbis.

    To add to my earlier comments reposted above, there would bound to be at least one rabbi who would argue that if a place is such that it is not possible to adhere to the Jewish calendar there, then that place should be forbidden for Jews.

    There is a good Bereshit-grounded general solution, I think. In Bereshit 1:14 we’re told that the celestial bodies can be used “for signs and for appointed seasons and for days and years” and the sun and moon are the great beacons for the Earth. It would be perfectly consistent to identify a different celestial object in an alien sky to acted as a source of the calendar on our rocketship or new planet.


    1. I agree with you that a non rotating planet, or a spaceship in transit is less of a problem. Time is perforce arbitrarily decided there, so why not simply make it Earth standard? 40 hour days may or may not hit a limit where people would ignore the sun’s movement and simply live off clocks….who would be able to live with a regular 30 hours between sleeps? That’s why I chose something like a 25 hour day, which I imagine people could live with, but would rapidly lose sync with Earth.

      As for your later point, sure you’ll find someone somewhere who’ll say any old thing. Still, while all the major Jewish sources concur that the right place for a Jew is Israel, 2500 years of diaspora have lent us a broad spectrum of ideas to choose from in how to deal with a less than ideal situation. I’m happy to stipulate that living on Mars is not ideal, but who knows what circumstances a person might find themselves in?
      As for the quote from Bereshit……well, yes, but if you’re going down that path, try to explain how it would work. Some planets might have a tidally locked moon which is relatively large compared to its primary…. other’s might not. Mars certainly doesn’t. How does your idea play out?


  7. IMHO the way humans (in general) choose to mark time on Mars (or on a generation ship making a voyage to another system) will probably be an important and deciding factor, on which any workable halachic answer is based.

    My reasoning:
    1. The Bible did not invent the concept and units of marking the passage of time. Humans had already been counting days, weeks, months and years for millennia.
    2. The “modern” (i.e. fixed, since 359 CE) Jewish calendar is not even of Biblical design — it is adapted from the Babylonian calendar whose innovative feature was the leap-month to keep the lunar year in sync with the solar year, and we still even use the Babylonian names for the months.
    3. Therefore, Judaism is open to using useful and/or universally accepted methods and systems for measuring and marking time.

    In addition, trying to synchronise any events with a place on earth, e.g. Jerusalem, becomes meaningless over the large distances and high speeds attained in space travel — as we learned from Einstein, everything is relative: there is no objective concept of time.


    1. Let’s see if I understand you. Imagine there’s a reasonable size, stable Martian population, and they start using sols as days and count a seven-sol week. So then you’d be OK with counting a seven sol week for the Jews on Mars? On the whole that seems sensible to me, but think of it another way .What if (for reasons unknown) the general Martian populace decides to have 6-sol weeks or 8-sol weeks? 7 is after all an entirely arbitrary number, which we use merely because of the Bible (unless you have some other source). The Etruscans had an eight day week which was adopted by ancient Rome. In fact Rome didn’t fully adopt the seven day week until the time of Constantine. There are hints in the Talmud that ‘Shabbat” issues our forefathers had were partly due to conflicts with the Nundinum system. If that’s so, I think that your statement about Jews adapting to local calendars can only be taken so far.
      After the issue with days and weeks, I wonder if the population in a system without a moon would adopt the concept of months in anything other than a nostalgic way. It seems unlikely to me that Martians with no “useful” moon would have any interest in the concept of a month. If they used Martian years (a Martian year is 687 days or 668.5 or so sols) I can imagine they might work with any other arbitrary division – 20 sols, 30 sols, 60 sols – who knows? We might have adopted a Babylonian calendar, based on the sun and the moon…but we have not in 2000 years adopted the Julian/Gregorian 12 months in a year system, despite it being in almost universal use. So, do you really think any local system would be adopted in a reasonable amount of time?

      I agree with you that it’s not possible to really synchronize people moving in different frames of reference (for this discussion I would say at different speeds) but I’m unsure how common a relativistic speed difference is. There’s certainly nothing worth mentioning between here and Mars and I imagine even between here and Alpha Centauri the difference is negligible. You would need to constantly accelerate at 1 g for about 1 year to get to relativistic speeds – that’s a hell of a barrier. If you’re going to handwave and say we could somehow reach relativistic speeds faster, I’ll handwave and say we’ll sidestep acceleration entirely and obviate the relativity problem.


      1. Thanks for educating me about the origin of the 7-day week. I thought it preceded the Bible, but it seems that it is actually one of its innovations. It’s quite amazing that it eventually became universal worldwide — even outside the Judaeo-Christian world.

        Regarding Jewish law — I think it is eventually going to have to adapt to new realities. Many things work only on Earth (some are even specific to the Northern Hemisphere) and won’t necessarily have suitable analogues elsewhere.

        I know that the current Jewish orthodoxy is very resistant to changing the rules, but one small change to our calendar is inevitable even without solving the question of space travel. Although the leap-month concept keeps the lunar calendar in sync with the solar year, there is a small inaccuracy that causes us to “lose” a day every thousand years or so. After 20,000 to 30,000 years, Pesach will no longer be in the spring (in Israel) unless a slight tweak is made to the rules.


      2. As regards the Biblical origin of the 7 day week. I have to declare my pro-Biblical bias. I did read somewhere (not sure where, though I found a similar thing here from the BBC ) saying that it’s based on a Babylonian understanding that there were 7 heavenly bodies (Sun, Moon, Mars, Mercury, Jupiter, Venus, Saturn). Wikipedia quotes people who say Judaism is the more likely source.

        Jews have been living in the Southern Hemisphere for many many years and have not changed Pesach to be in October yet, so my guess is that this is not going to happen any time soon.

        As far as the losing a day every thousand years is concerned, it may be a bit of a ret-con but I’ve read that this is not considered a problem since the fixed calendar is simply a stopgap measure until the Messiah comes and we go back to declaring new moons / leap years by word of the Sanhedrin. Certainly before the fixed calendar came about the leap years were handled in a much more relaxed fashion,and adding an extra day to a month was done for all sorts of reasons, so if we’re out a day once a thousand years, it will be easily cleaned up. Of course that doesn’t help me with my problem which is working out a calendar for our poor Martians who just want to know when to make Pesach….


      3. Kibi, I never thought you would play the Messiah card for an issue as simple as this! IMHO overuse of the Messiah card discourages problem-solving. It’s God’s business if and when to send a Messiah, and it’s our business to make decisions on the ground in the interim.

        I think the human race is at an inflection point during the last few hundred years – the future way of life is going to be very different from anything in the past, and any religion based on concepts from another (bygone?) world is going to have to be reinterpreted or adjusted, unless its followers want to withdraw from society as some groups have already done.


      4. I’m not playing the Messiah card, merely saying over something I heard. To be honest, if the recorded history of the Jewish people using a fixed calendar is 2000 years, and we’re worried it will be badly in need of repair in another 10,000 years, I’m prepared to just let it slide for now, Messiah or not.
        Yes, we are going to reinterpret and adjust…after all, it’s what we’ve been doing for 3000 years. The question, now as before when I asked it, is what adjustment should we make.


  8. Judaism, for me at least, is about what it means to comport yourself as a human being making your way in the world (whichever world that happens to be). The laws, didactic as they so often seem to be, all should – in theory – bend to that overarching concept. This is the long way of saying that the answers eventually arrived at for all their circuitous perambulations, should have as their north star (the irony of that metaphor not being lost on me) the following question: Does the suggested answer make me a better human being in the eyes of man and the eyes of G-d? If we get stuck in the minutiae of the law (as is our wont) but lose site if its intent than we end up as true aliens to a religion we claim to love. Not a satisfying answer, I know, but a precious criteria for arriving at one nonetheless.

    Liked by 1 person

    1. No argument from me there. In many cases, I can see how this guiding principle would be useful to perhaps fend off the tendency to over legislate in a way which would tend to dehumanize or reduce comapssionate action.
      Still and all, Orthodox Jews are not going to divest themselves of ritual so quickly, even if some of it is overdone. To maintain the semblance of a Jewish lifestyle (Shabbat dinner! Seder night! Channuka candles!) there needs to be a broad consensus at least among the putative Martian congregation of what day it is, no?
      So, let’s assume we’re all people of good will, who want to make things work out in a good human being way. What day should we agree on for all these things?


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