Space travel and the body clock

The current medical limitations on spacecraft means that, much like on Earth, an ounce of prevention is worth a pound of cure. So keeping spacefarers in tip top condition will prolong their ability to function. And a huge part of that is maintaining circadian rhythm. Humans function best on a strict regimen, our bodies have evolved to perform certain functions based on their innate sense of the time of day. But the 24hr day that we’ve evolved to sync to doesn’t exist in space, or on the Moon, or Mars. So how much will not being on Earth affect our human bodies?  Cambridge University’s public astronomer Matt Bothwell...

Matt - It depends where we are really. The human body has obviously evolved to live on this 24 hour cycle. And really what we have to do is just do our best to simulate that 24 hour cycle because if you get too far away from that, our bodies get pretty unhappy. So astronauts on the International Space Station, for example, they zip around the Earth every 90 minutes. They have something like 16 sunrises every single day. The way they stay sane is to simulate artificially a 24 hour cycle. And so they stay on GMT, the lights get bright at six in the morning, the lights dim and get orange at night. And so even though they have 16 sunrises a day, they still get this 24 hour cycle that their brains need.

Will - With that being the case then if we are going to move further afield to the Moon and to Mars, which have time of days being longer or shorter than ours, are we going to have to put in some interesting kind of hacking our own biology in order to be able to still function in those places?

Matt - The answer is definitely yes for the Moon. I think interestingly for Mars we might be fine. There are studies of circadian rhythms; when you put humans in isolated environments and don't give them cues about what the light is doing, circadian rhythms tend to settle down onto a roughly 24 and a half hour cycle. Obviously evolution hasn't bothered to give us an exactly 24 hour circadian rhythm cycle. You get it close enough and then the cues from the sunrise and the sunset just sort of nudges us onto the schedule. So our natural circadian rhythm of a whisker longer than 24 hours is probably perfect for the Martian day, which is about 24 hours and 40 minutes. So I think we can function on Mars absolutely fine with no hacking needed.

Will - It feels like that there is a case of this kind of being trialled on earth already because we have people operating machinery on Mars that obviously have to attenuate to the Mars cycle already. That's

Matt - Exactly right. The NASA engineers that operate the Mars rovers have to live on Martian time, which is about 24 hours and 40 minutes. And so if you're living on Mars, that's fine. The sunrises and the sunsets on Mars would nudge your circadian rhythm back into schedule. But on Earth, living on a 24 hour, 40 minute period means you slowly drift out of sink with Earth. And then yeah, you blink and a couple of weeks have gone by and suddenly you are working the night shift. I think people only do this for a couple of months because I think it would drive you crazy after too long.

Will - Is the case then of finding the people with that slightly elongated circadian rhythm and shipping them off to the red planet?

Matt - Right, exactly. There was one study that came out of Harvard a few years ago that suggested that morning people have slightly shorter circadian rhythms and evening people have slightly longer circadian rhythms. So we just need to find all those people that like lying in and they'll make the perfect Martians.

Will - Delightful to have found a calling. But that's in terms of the internal human body clock. But when it comes to syncing up communications and satellites like that, are we going to have to end up creating time zones for different planets, do you think?

Matt - We absolutely will. We need time zones on earth because the earth rotates around and the Moon and Mars and anywhere we can conceivably go is all going to be spinning around in the future. So we will definitely need different time zones. I think one of the really interesting challenges that's gonna need to be solved is the fact that time doesn't behave the same on all planets. One of the big takeaways from Einstein's theory of relativity is that time goes a bit faster or slower depending on what your local gravitational field is like. And on the moon where gravity is only about a sixth of the Earth's gravity on the surface time is going to go ever so slightly faster. Not that in a way that humans would notice, but if we want any future satellites doing GPS positioning on the moon, we're going to have to take that into account.

Will - Do you think it would be better to keep people in these places so that they can fully get used to this circadian rhythm we create or keeping them there for a couple of months and then shipping them back home? Because it seems like if you're doing that, you're kind of constantly throwing people between these two things and that could potentially be worse.

Matt - That's a very good point, but I do wonder if maybe the answer is it's only about the same as being jet lagged or something. It might have the same effect of if you fly to the states or if you fly to Australia. Yeah, you feel a bit rough for a few days while your circadian rhythm catches up and then you're fine. So yeah, maybe in the future we just have to deal with Moon lag for a few days.

Will - So our ideal astronauts are businessmen that often fly between here and the states and also get up very late in the morning.

Matt - Exactly. They're, they're the future Martians, I think.

Will - Take that Matt Damon <laugh>.