Question - Do planets have to spin to support life?

When most people think of a nonrotating orbital body, they tend to think of synchronous rotation.

Either way, I see no reason why a planet would need to rotate--other than the reasons planets generally rotate in the first place--but there are some adaptations Earthlike life would need to flourish.

ELMontague said:

This may be best in science fact, but it's for a fiction piece. So, do they have to spin to support life?

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For life to arise on a planet you likely need a somewhat chaotic environment. The heating and cooling caused by a planet's rotation helps with that, as does having oceans, a gaseous atmosphere, and a moon close enough and massive enough to cause tides.

But I don't think you necessarily need any of those things to support life. Certain organisms may be highly adapted to a given volatile-but-regular feature of their environment (such the hot/cold, light/dark, tidal cycles caused by planetary rotation), so they may suffer unless that feature can be induced artificially.

Note that I'm speculating here. I haven't actually tried to create or sustain life on a non-rotating planet. Yet.

Dale

Well a planet that doesn't ORBIT around a star, is likely going to fall into it. So I assume you don't mean 'rotation' as in orbit. I assume you mean 'rotation' as around it's own axis. If it's NOT rotating on it's axis - Then one 'day' on the planet will take one 'year' around it's sun. But you will eventually get day and night across the whole planet over the course of a single 'year'. IF by no 'rotation' you mean that the same face is always towards the sun - then the planet must 'spin' around it's axis to maintain this orientation.

So - what exactly do you mean?

All speculation here, because we haven't found xenolife yet. That being said....

Somewhere there could be a non-rotating planet supporting life-as-we-know-it. There could be a non-rotating planet supporting life-as-we-don't-know-it. Although Earth-like life seems to have lots of things that end up being associated with the results of rotation (a clumsy way of saying it evolved on earth and takes advantage of those features), there's no reason to think life needs those things.

But if it evolved on a non-rotating world, it's different than our organisms.

I don't know the answer, but it's an interesting question.

When speaking of planetary bodies, we use two terms: revolve and rotate. Although dictionaries are apt to say the terms are synonomous, planetary scientists make a distinction.

A body rotates about an axis, just as Earth rotates about the imaginary line that passes through the north and south pole. (See Wikipedia on rotation.)

A body that moves in a circular (or elliptical) path about another body is said to revolve about it. (See Wikipedia on orbit.)

Planets that don't orbit stars are usually called "rogue planets". I find it difficult to imagine life arising on a rogue planet, much less survive. Especially not life as we recognize it.

A planet that orbits a star gains energy from that star. The comments above regarding how that energy impacts the planet are useful in answering the original question. I think the tidal forces produced in any planetary system, however weak, will ultimately cause rotation in all the bodies therein.

It was once believed that Mercury, like Earth's moon, rotated on its axis only once per orbit, thus creating one extremely hot face and one extremely cold one, and a ring-shaped temperate zone where it was imagined live might exist. Turns out that the planet completes three rotations per orbit. It spins, but too fast, and the environment there is certainly incompatible for life.

Stars emit not only light and heat, but all sorts of other radiation, most of which is deadly to life, at least in the amounts usually emitted. Earth's rotation, coupled with its molten iron core, produces a magnetic field that protects the surface from most of the deadliest radiation but not all (we still get sunburned). If it weren't for the periodic turning away from that radiation (night), life as we know it would most likely cease to exist.

I can't offer an answer, as this is not my field, but I can offer another question...

Planetary rotation may be required to generate a magnetic field, or maybe to generate a strong one, and a magnetic field is probably required to sustain life, since a magnetic field protects the planet from dangerous solar and cosmic radiation.

I seem to recall reading about planets where life exists as you describe, EL. Maybe it was Niven. (I read a LOT of Niven.)

I think there is a possibility that even without a magnetic field (produced by relatively rapid rotation and a molten core), the region between extreme hot and extreme cold would suffer only glancing deadly solar radiation. I don't know what sorts of weather the planet might experience, especially with an unchanging temperature gradient. And I think if your planet has a moon (or moons), unless they were extremely tiny, they would have long ago altered the planet's rotation to destroy the delicate balance necessary for your scenario.

ETA: Note, Mars does rotate, but having no molten core, has no magnetic field, and apparently has no life. Solar radiation there is some 2.5 times that experienced at the International Space Station. (See Wikipedia.)

Forgive me if I am wrong but isn'tthat what keeps us on the planet? (gravity)

OK Hubby just said gravity is created by mass not rotation.
I asked if a planet needs to rotate to support life and he simply said, "No."
oh now he's elaborating. "Not like we understand it maybe. "

sassandgroove said:

Forgive me if I am wrong but isn't that what keeps us on the planet? (gravity)

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No. It's magical super glue.

sassandgroove said:

OK Hubby just said gravity is created by mass not rotation.
I asked if a planet needs to rotate to support life and he simply said, "No."
oh now he's elaborating. "Not like we understand it maybe. "

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Well, he's right, assuming he means that a planet having no equatorial rotation still has sidereal rotation with respect to its star.

I beleive that is what he meant.

ELMontague said:

In one of my WIP, there is a planet - moon actuall - that is in orbit around a planet and they together around a sun. The inhabitants of the planet have to stay in the area between day and night in order to survive; too cold in the dark, too hot in the light. My twist comes from the fact that the really scary inhabitants live in either hot or cold and dwell on the edges to feed off the good guys.

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Very cool.

I doubt it. On a non-rotating planet, One side would be hot enough to kill, and the other side would be cold and you can imagine. On the horizons, where the world is in constant twilight, it might support life. However this place would be buffeted by unimaginable winds and the life would have to be very tough.

All speculation of course, life is very tough after all.

But Nivarion, a planet that has one side always facing its star IS rotating. It just rotates once per orbit, exactly as the moon does in its orbit around Earth. Assuming that it is possible for there to be non-rotating bodies in space (a remote likelyhood), such a planet, in its orbit about a star would present all of its surface to the star, but slowly.

And for a story, that's a rather neat concept, actually. For an example, let's say that somehow Earth's rotation ceased but it continued to revolve about the sun. (Ignore for the moment the catastrophic events that would cause!) Suppose that in July the western hemisphere faces the sun. It'd be noon in Chicago all month long (talk about daylight savings!). Sunset there would occur sometime in October, midnight would happen in January and sunrise would occur in April. In other words, on such a planet, one day and one year would be the same.

Just spitballing a little, so, some space please ...

There is also the biological aspect of this question. Even the best stew has to have its ingredients mixed. A martini comes shaken or stirred (as James Bond fans will note). Point being, isn't rotation (probably more so) and revolution (maybe less so) the means of mixing the ingredients? But we're talking about support and not creation ...

So, if we're talking life created on Earth, then it's got to have access to light and a means to shield itself from light. And the other usual things. Gravity, since all Earth life is based on Earth's gravitational hold. There'd also be some psychological adjustment, as there is for people who move from Ohio to, say, Alaska and get six months of sun (and six months of darkness). And so on.

If it's life you're making up, then no rules.

ETA: "Space 1999" might offer some insight to this.

Also consider that (on Earth, at least) most land animals would need to adapt for hibernation, if it's even possible to survive six months of extreme cold. Amusingly, life might be most active year-round near the north pole.

ELMontague said:

In one of my WIP, there is a planet - moon actuall - that is in orbit around a planet and they together around a sun. The inhabitants of the planet have to stay in the area between day and night in order to survive; too cold in the dark, too hot in the light. My twist comes from the fact that the really scary inhabitants live in either hot or cold and dwell on the edges to feed off the good guys.

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There was a show on Discovery (or history channel) That I watched. It created just such a planet for speculation. They way they played it out, all life on the planet had adapted to the severe climatic changes caused by the static planet- animals adapted for life on the hot side, and animals adapted for life on the cold side and then those adapted for life in the middle. It was fascinating.

Nivarion said:

I doubt it. On a non-rotating planet, One side would be hot enough to kill, and the other side would be cold and you can imagine. On the horizons, where the world is in constant twilight, it might support life. However this place would be buffeted by unimaginable winds and the life would have to be very tough.

All speculation of course, life is very tough after all.

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I'm not an exobiologist or an astronomer, but I did just finish an intro to astronomy course so the basic stuff is fresh in my mind.

Sorry, but just a simple tour of our system shows the hot/cold side thing isn't necessarily true. It happens on the Moon—a big difference between sunside and darkside temperature—because the Moon has no atmosphere. If you look at Venus, with a rotation period of 243 days, you also see it's heated to a pretty even and toasty 730K, hot enough to melt lead. Venus has incredibly strong winds which drive the heat around the planet.

I would say the biggest difficulty with a slow or no rotation is the absence of a magnetic field (created by the dynamo effect of rotation with an iron core). The magnetic field catches high energy emissions from the Sun (radiation) which could break apart organic molecules. Breakup happens in space when naked molecules are exposed to gamma and uv radiation, and molecules can only stay together where they are shielded by dust in molecular clouds.

Kij Johnson wrote a really lovely story about a world with a very slow rotation—I think it might have even been retrograde, as I can't see how else to explain that the planet's "noon" at one location would last decades.
http://www.kijjohnson.com/horse-raiders.html

-B

jst5150 said:

ETA: "Space 1999" might offer some insight to this.

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The only thing Space 1999 can offer an insight into, is 1970s space fashion.

So the OP wants a planet with one side facing the sun? Then you have a singular annular rotation while in orbit. Yeah, generating a magnetic field might be hard to justify - and that would be needed to protect the inahbitants from all sorts of nasty particles. Also handing for keeping an atmosphere in place

I'm not an orbital mechanic - but perhaps one could stipulate an incredibly dense 'captured' moon scenario? SOooooooo..... the planet starts off with a good rotation.... primitive sorts of life starts evolving.... big collision with incredibly dense moon (much like earth)... sending crap out into space, and SLOWING the rotation of the planet (Moon comes in at the 'wrong' direction'.... The debris coagulates around the moon with dense core - and creates extremely powerful elecromagnetic field wich 'reaches out' to shield the planet, while the orbital forces slow the planet to its current annular rotation with one side facing the sun....

Which results in, what? A planet with an atmosphere, one side facing the sun, protected by the dynamo-moon? Does that seem plausible enough for the scenario? Hell, the moon might be barren or not - would have a rappidly spinning 'face' towards its planet? Are we looking at a twin 'world' scenario???

ELMontague said:

This may be best in science fact, but it's for a fiction piece. So, do they have to spin to support life?

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Well there's two answers to this question:
1) Probably. There's bacteria on earth that live deep underground, powered by radioactive decay. (Seriously. How cool is that?) So, once you actually got life, it's incredibly resilient. Unless you have a place that completely prohibits chemical reactions, you could probably get something living on it. Now, living arising there is somewhat less likely, but once it's there, it's there to stay. And that does not include all the possible but really strange form of life that could be in such a place.
2) Probably. Even a planet totally unlike earth can still have spots that are friendlier than others. A planet is really big, even earth has many many places where there's nothing (or at least not much) alive.