Study: Why the Moon's Far Side Looks So Different

StartsWithABang writes 55 years ago, the Soviet probe Luna 3 imaged the side of the Moon that faces away from us for the first time. Surprisingly, there were only two very small maria (dark regions) and large amounts of mountainous terrain, in stark contrast to the side that faces us. This remained a mystery for a very long time, even after we developed the giant impact hypothesis to explain the origin of the Moon. But a new study finally appears to solve the mystery, crediting the heat generated on the near side from a hot, young Earth with creating the differences between the two hemispheres.

Comments

Cosmic Baking

[djupedal]

This is what happens when you don't read the directions on the package...

Re:Cosmic Baking

[Anonymous Coward]

See, there has always been Global Warming.

Re:Cosmic Baking

[Chas]

The Earth was Young and Hot. But later, Earth got into drugs and became like Lindsey Lohan.

Yeah, she's in the middle bingeing on a nasty piece of candy called Homo Sapiens right now. It's not pretty and could fuck her up for a few centuries to come.

Re:Cosmic Baking

[Tablizer]

But I like my buns crispy on top.

uh, don't read too much into that.

Re:Cosmic Baking

[sillybilly]

Kids, let's all learn to respect each other and live in peace and harmony!

Re:Cosmic Baking

[sjames]

Or at least lay off the crack! :-)

Re:Cosmic Baking

[davester666]

Good thing zits generally disappear once you leave your teenage years...you only get them later if you are really unlucky.

Re:Cosmic Baking

[sg_oneill]

Good thing zits generally disappear once you leave your teenage years...you only get them later if you are really unlucky.

Of course on geological/cosmic type time scales, by the time she leaves puberty, the main species on this earth will be homo-greyalien or something. We're not a species that seems like it wants to hang around too long, what with our whole "Lets invent nuclear weapons, venus out the atmosphere and then feed dolphins plastic bags" tendencies.

Re:Cosmic Baking

[smooth wombat]

But later, Earth got into drugs and became like Lindsey Lohan.

But drugs are cool. I'm always told how great it is to do drugs. Just look at Elvis, Janis Joplin, Keith Moon, Philip Seymour Hoffman, Cory Monteith, Dee Dee Ramone, Jim Morrison and whole host of others who extolled the virtues of drugs.

P.S. If Lohan would drink water instead of alcohol, she'd look (and feel) a lot better than she does.

Re:Cosmic Baking

[davester666]

From the Earth's POV, humanity hasn't exactly been a positive experience for it...

useless post

[Anonymous Coward]

I thought it was to make the dome put by the aliens easier to find.

Bright future

[Tablizer]

Earth used to be a cute little sun.

Re:Bright future

[Noah Haders]

we all are made of stars

Rotation

[SimonInOz]

The moon became tidally locked within a few million years after its formation (around 4.5 billion years ago), so it's been tidally locked for over 4 billion years.

But really, did the earth stay hot enough for "a few million years" - hot enough to affect the locked side of the moon more than the other?

The moon would have cooled somewhat faster, being smaller, but this theory requires the earth to stay hot enough to affect the "earth side" of the for a very long time after the moon has cooled enough to solidify.

Re:Rotation

[K. S. Kyosuke]

How does lunar recession affect things here? Tidal locking is one thing, but is the dampening effect that the tidal forces have on the Moon stronger than the increase in discrepancy between lunar rotation and lunar orbiting period introduced due to the lunar recession? The fact that the Moon's rotation is tidally locked right now indicates that this must have been balanced until now (otherwise "now" would have to be somehow special, which I view as unlikely), but what about a long time in the past, when the distance was much closer?

Re:Rotation

[sillybilly]

I think it was just the centrifugal force as the Moon goes round and round the Earth, it's like the Moon has hair, and it's flying outwards, on the outward side. (See if you can find what's wrong with this argument, in a gravitational field.)

Re:Rotation

[Dan East]

But really, did the earth stay hot enough for "a few million years" - hot enough to affect the locked side of the moon more than the other?

The moon has no atmosphere, thus radiation from the earth cannot affect the far side of the moon at all. So obviously, even to this day, the earth still affects "the locked side of the moon more than the other". The question is simply how much. The moon and earth were both molten after the collision, so it was not a matter of the earth being hot enough to melt the moon, but merely the earth imparting energy to prolong the cooling of the near side. No matter what, the near side must have cooled slower than the far side - it's a straightforward matter of thermodynamics. One side of the moon was receiving energy from the earth while the other side was not. The near side didn't need to stay so hot it was incandescent, but merely "softer" so that small impacts would heal more on the near side than the far side, and the duration only needed to be long enough to result in some degree of visible difference, which is what we still see today.

The whole thing sounds plausible to me.

Re:Rotation

[sg_oneill]

How does lunar recession affect things here?

Space-ron-paul was right! Convert your lunar-coins to bitcoins before the collapse!

Re:Rotation

[jfdavis668]

At the time, the Moon did have an atmosphere. It was hot enough to vaporize silicon and aluminum, components of today's crust. What the paper is proposing is that the hot Earth keep the Moon hot enough to keep these elements vaporized on the Earth facing side, while the far side was cooler and the elements precipitated out. This would cause a migration of crustal components to the far side, thickening the crust. This way it was not as susceptible to puncture by falling objects.

Re:Rotation

[jfdavis668]

Here is a better summary of the paper. http://news.psu.edu/story/3178...

Re:Another medium.com story?

[ColdWetDog]

But this one has exclamation points!!!!!!

Re:Thought Gene Shoemaker figured this out...

[mister_playboy]

No, the article itself mentions the impact difference between the two sides should be less than 1%.

The near side had much more surface in a liquid state during and after many of the impacts. The article claims heat from the Earth was the cause.

"Very Long Time?"

[Guppy06]

This remained a mystery for a very long time

Martians notwithstanding, nobody had any idea what the far side of the moon looked like before 1959. Sure, 55 years may be "a very long time" for some people, but we're not exactly talking about something that puzzled Hipparchus here.

Re:"Very Long Time?"

[Anonymous Coward]

Are you sure about that? Maybe not Hipparchus, but I'd wager someone wondered what the other side looked like.

So.... At the risk of stating the obvious: modern man has been on this planet for around 50,000 years; the mystery has been solved for 55 years, leaving it as a great unknown for the better part of 49,945 years.

I'd call that a long time. Unless you're a creationist. In which case the number is more like 6,000 years, which is still a pretty long time in my book.

Re:"Very Long Time?"

[Charliemopps]

Unless you're a creationist. In which case the number is more like 6,000 years, which is still a pretty long time in my book.

Even most creationists think the earth being 6k years old is nuts. Most think science is right for the most part and it just explains "how god did it" Keep in mind, the age of the earth is no-where in the bible. The 6k figure came from some idiots counting up begots and such... most of the christians I've talked to about the subject simply don't care and if God wanted them to make a big deal about the age of the earth they're pretty sure he'd have put a line there "and the Lord sayeth the world is 6000 years old and woe unto he who talkith about giant lizards"

Re:"Very Long Time?"

[danlip]

I think the mystery being referenced here is "why are they different?" not "what does the other side look like?". In which case we only have known they are different for 55 years and therefore can't have been wondering about it for longer.

Re:"Very Long Time?"

[techno-vampire]

As I recall, people were very surprised to find out just how different the other side of the Moon is. Right up until the pictures came back everybody expected that both sides would be much more similar than they turned out to be.

Re:"Very Long Time?"

[Tablizer]

Luna 3 was an amazing mission for the time. Give the Soviets credit where credit is due.

Re:"Very Long Time?"

[Christian Smith]

So.... At the risk of stating the obvious: modern man has been on this planet for around 50,000 years;

Australia has been colonised by "modern man" for longer than 50,000 years. Modern man left Africa more like 100,000 years ago, and if you lifted one of those babies out and plonked him in the "modern world" noone would notice the difference.

Anatomically modern humans are more like 200,000 years old, and I dare speculate that their predocessors gazed at the stars and moon.

Re:"Very Long Time?"

[T.E.D.]

Even most creationists think the earth being 6k years old is nuts. Most think science is right for the most part and it just explains "how god did it"

Don't be nit-picky. When people say "creationists", they are generally using it as shorthand for Young Earth Creationists. Nobody says that out because it is too much of a mouthful, and if they said "YEC", few would know what they are talking about.

If someone wants to talk about people who think science is right for the most part and it just explains "how god did it", they can just say "most Christians".

Re:"Very Long Time?"

[rossdee]

"Even most creationists think the earth being 6k years old is nuts."

In the US of A the term creationist means someone who believes that Got created everything in 144 hours sometime within the last 10,000 years.

In the reat of the world it just means you believe that God created the universe a long time ago, which scientists suggest is around 13.7 billion years.(the Big Bang)

Re:"Very Long Time?"

[Tablizer]

I think "YEC" is quite fitting.

Or perhaps:

CRAC - Creationists Rationalizing Age Creatively

Re:"Very Long Time?"

[david_thornley]

"Creationist" is usually used to mean people who think the Earth was created several thousand years ago, all species were specifically created by God, and often some nonsense about prehistoric animals having died in the flood Noah rode out.

Personally, I think of them as people who can't credit God with more imagination than they have.

It isn't used to mean people who think God created the universe 13.8 billion years ago (or whatever) and gently directed evolution to create humans.

I think you're confusing creationists and Christians. Most Christians are not creationists.

Re:Thought Gene Shoemaker figured this out...

[jpellino]

I'd be more inclined to trust the article if they hadn't claimed the moon is 40 earth diameters away from the earth...

The moon is hollow, it is a spaceship.

[mtthwbrnd]

https://www.youtube.com/watch?...

Discuss!

Re:The moon is hollow, it is a spaceship.

[Neil Boekend]

The moon is hollow. It's where the director for the TV show "Earth" lives.

Re:Thought Gene Shoemaker figured this out...

[__aanbvm4272]

Maybe the Earth's gravity draws out more lava or liquid to create the Marias (there is a large amount of water on the Moon NASA finally admitted) There are moonquakes too. Those actions would cover up a lot of craters and not that had to imagine... Why didn't they think of that instead of coming up with such a weird conclusion? Here's another theory of mine; the near side of the Moon is more dense, duh.. That's why it always faces the gravity (us)

Re:Thought Gene Shoemaker figured this out...

[Anonymous Coward]

I'd be more inclined to trust the article if they hadn't claimed the moon is 40 earth diameters away from the earth...

The moon wasn't always that far away, it's orbit drifts out a few centimeters every year.

Re:Thought Gene Shoemaker figured this out...

[swillden]

I'd be more inclined to trust the article if they hadn't claimed the moon is 40 earth diameters away from the earth...

Meh. A simple error in the writeup, which I'm sure is not present in the scientific papers.

http://lunarscience.nasa.gov/?question=3318

Re:Thought Gene Shoemaker figured this out...

[TapeCutter]

What error? The Moon actually is 40 Earth diameters away in round numbers.

Re:Thought Gene Shoemaker figured this out...

[swillden]

Earth is 12,742 km in diameter. The moon is 363,104 km, 28.5 diameters, away at perigee, and 405,696 km, 31.8 diameters, at apogee.

In round numbers the moon is 30 Earth diameters away.

Theory only works for perfect tidal locking

[American Patent Guy]

Yes, this theory makes sense if the moon is perfectly tidally locked. However, that isn't likely. The "far side" of the moon has been that only in human history: only a few thousand years. We're talking about billions of years. All that would be needed is a few centimeters creep per year and the far side would become the near side in the course of millions of years.

This theory doesn't explain how the marias happen to all be on the near side presently given this creep. It also does not account for the likelihood that the warming would have been across the entire moon with this creep. It also does not account for the obvious fact that there are two kinds of surfaces on the near side on the moon: if this warming had been the cause, the difference would be more semi-hemispherical in nature (warming entirely one-half of the surface of the moon) -- the marias cover a lot less than that.

My bogus detector is bleeping loudly

Re:Theory only works for perfect tidal locking

[Anonymous Coward]

You're only assuming that such a creep exists, yet measurements show that the tidal locking is perfect in agreement with the idea that the tidal locking involves a torque resisting any rotation that is not locked. A conservative estimate of the time it would take to be come locked is 200k years, after which point there would be a braking force that prevents creep (which would have been stronger in the past when the discussed effect happened, since the tidal locking scales with something like sixth power of orbital distance).

Re:Theory only works for perfect tidal locking

[American Patent Guy]

The earliest images of the Moon (that I'm aware of anyway) are those made in drawing by Galileo in the 1600's. I don't know what measurements you're referring to to show this "perfect" tidal locking. When made in perspective between the time period from Galileo (400 years) to the time period when the Earth was hot enough to affect the surface of the Moon (4,000,000,000 years), I hardly think anyone alive can show that the Moon has and will always keep the same face to the Earth.

Add to that the fact that the Moon isn't solid and has a liquid core that likely rotates at a different rate than that of the solid shell, and you wind up with a system that isn't yet explained by modern science.

The reason that a rotating bowling ball set on the floor eventually stops is because of static friction. There is no static friction to stop the rotation of the Moon entirely; the angular momentum with respect to the Earth would slow in a complex equation that would diminish over time (but never entirely stop.) The present angular momentum is most likely very slow, too slow to be detected by man over the course of a few hundred years.

My arguments still remain that the maria of the Moon don't cover the near side evenly.

These guys have a long way to go before I'll be convinced that their theory is correct.

Re:Theory only works for perfect tidal locking

[American Patent Guy]

Let's take your laser measurements a do a little back-of-the-napkin calculations.

Four billion years is 4*10^9, your presumed period of tidal locking is 2*10^5; around 1000 such periods. I'll assume that the rotational rate of the Moon slows by 2 every such period, and I'll assume an original rotational rate of 1 day (as no one knows what that original rate was). Using those assumptions, the residual rotational motion of the Moon today would be 1/(2^1000)th of its original rate, which is about 1/(10^300) which would give it a present rotational period of about 10^297 years (a really big number). That is well beyond the capability of measurement using anything available.

You can't have it both ways: either the rotation of the moon is slowing, or it's not. I believe that I've shown that what the Moon is presently doing today is of no relevance to proving this theory. Try again...

I'd like to see this evidence used to show the composition of the Moon. I understood that it was from modeling the heat radiation of the Moon. I don't think your evidence exists.

Re:Theory only works for perfect tidal locking

[American Patent Guy]

Actually, tidal locking works because the (non-)rotating object is out-of balance spherically considering density imperfections in the object. (Gravity preferring one side of the object over the other.) Tidal locking deforms the Earth, not the Moon.

Re:Theory only works for perfect tidal locking

[david_thornley]

You're providing absolutely no evidence that there is any "creep". Or that you'd expect uniform hemispheres.

Re:Theory only works for perfect tidal locking

[American Patent Guy]

And you're providing no evidence that there is not any creep, nor do you explain why there are non-uniformities in the near side of the Moon. The burden of proof is upon the one attempting to prove their theory. The fact that the Moon is tidally locked to the Earth now does not prove that it was at the time the Moon's surface that we see was formed. The fact that the surface of a lake is mirror-like calm today does not mean that there were no waves yesterday.

Someone has posited a theory. They have not proven it with sufficient evidence.

Re:Theory only works for perfect tidal locking

[david_thornley]

You said "this theory makes sense if the moon is perfectly tidally locked", and proceeded to hypothesize a small creep that would nullify the theory. In other words, I'm just going with what appears to be the accepted status, and you're claiming something else. This isn't a problem in itself, but you are providing no evidence. You can find evidence that it was tidally locked from other replies to your post. The burden of proof is indeed on those who claim it was tide-locked, and indeed they have provided some very strong evidence.

KILL ALL EXCLAMATION POINTS!!!!!

[L. J. Beauregard]

Seriously, guys, does every third sentence have to end with a bang?

Re:Thought Gene Shoemaker figured this out...

[__aanbvm4272]

BOTH sides of the moon would have an equal amount of gravitational pull is questionable. Tides are stronger on the near side of Earth right? Why not then the moon also? My theory stands. Rotation? The Moon does rotate regarding the Sun. It is a fact there is not rotation in relation to us, the good ship Earth. Just maybe the Moon is not so uniformly dense and one reason why the heaviest side faces us. Let's ask the Russians. After all they were mapping it in 1959, ha ha.