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Study Explains Why Lunar Craters Are Bigger On the Near Side

samzenpus posted about 5 months ago | from the some-craters-are-bigger-than-others dept.

Moon 85

An anonymous reader writes "A new study of asteroid craters on the moon has uncovered some big differences in the composition of the crust on the two sides of the moon. 'While massive impact basins pockmark the moon's near side, its far side contains considerably smaller basins. The discrepancy in crater distribution has puzzled scientists for decades. To investigate what may have caused this difference, the team obtained data from NASA's twin GRAIL probes, which orbited the moon from January to December 2012. During its mission, the probes circled the moon, making measurements of its gravity. Zuber and her colleagues used this data to generate a highly detailed map of the moon's crust, showing areas where the crust thickens and thins; in general, the group observed that the moon's near side has a thinner crust than its far side.'"

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85 comments

fuck off (-1)

Anonymous Coward | about 5 months ago | (#45386745)

Tom Neilix you prick

impossible (0, Flamebait)

Anonymous Coward | about 5 months ago | (#45386755)

The only way to explore space is by sending people into a tin can in LEO. We can't explore space from our computer chairs.

Re:impossible (-1, Offtopic)

Anonymous Coward | about 5 months ago | (#45386865)

The only way to explore space is by sending people into a tin can in LEO. We can't explore space from our computer chairs.

blacks commit more violent crimes. they have a culture that celebrates violence. being a street criminal thug that victimizes other people is cool and earns respect.

a true racist could never do so much to bring down the blacks as what they already do to themselves. talk to a black person who grew up in the hood and struggled like hell to get out and make something of themselves. they will all tell you the same thing. they got beat up - not by white racists - but by the other black kids because studying and trying to do good in school was "acting white" and being an "uncle tom".

it's so sad what human beings will do to other human beings.

earlier paper links (4, Informative)

Trepidity (597) | about 5 months ago | (#45386773)

The paper this press release is about doesn't seem to be online, but two papers from the past few months analyzing this GRAIL data (with some of the same authors) are available:

"Gravity Field of the Moon from the Gravity Recovery and Interior Laboratory (GRAIL) Mission" [pitt.edu] , the initial report of the observations

"The Crust of the Moon as Seen by GRAIL" [ucsc.edu] , reconstructing the crust thickness and composition from the observations

Re:earlier paper links (0)

Anonymous Coward | about 5 months ago | (#45392313)

I have to wonder if the reason for the thinner crust is tidal locking of the inner core, keeping the hot molten mass closer to the earth for a long time after the initial formation of the moon. Assuming of course that the initial hypothesis of the moon being formed by an impact event with the earth...

Not really solving the puzzle. (4, Insightful)

Hans Lehmann (571625) | about 5 months ago | (#45386777)

OK, there are larger craters because the crust is thinner on this side, but why is the crust thinner on this side? Mere happenstance, or is it caused by orbital mechanics or some other reason?

Re:Not really solving the puzzle. (-1)

Anonymous Coward | about 5 months ago | (#45386805)

OK, there are larger craters because the crust is thinner on this side, but why is the crust thinner on this side? Mere happenstance, or is it caused by orbital mechanics or some other reason?

God made it that way. It is not our place to question why.

Re:Not really solving the puzzle. (1)

manu0601 (2221348) | about 5 months ago | (#45387837)

God made it that way. It is not our place to question why.

Your first sentence is obviously faith, it shall not be subject to rational discussions: people just believe or not. The second sentence raises a big question. How can you be sure God does not want you to understand the universe he created?

Re:Not really solving the puzzle. (1)

Anonymous Coward | about 5 months ago | (#45388311)

How can you be sure God does not want you to understand the universe he created?

God's first command to Adam was to name all the animals. Ie, to understand creation. Adam was the witness, created in God's own image. Everything that followed, that dominates religion, was just noise.

Similarly, notice that when people or societies in the bible are "decadent" they are destroyed by God, but when they defy God in order to know more, they are "punished" by being given a harder challenge (often with a blessing). For example, Adam and Eve ate from the tree of knowledge, in response they were made to work but sent off with a blessing and a compliment. But when subsequent society grew decadent, God destroyed it by flooding the entire world. When the descendants of flood survivors built a tower to try to reach heaven, God mixed up their language to make things harder for them. OTOH, when Sodom and Gomorrah grew decadent, God just nuked them.

Two weirdly different levels of punishment. An extreme one for "decadence" and a softer one for "challenging God". Yet most religions (such as those the previous AC parodies) would rank "challenging God" as the greater crime, when the bible suggests it's our only purpose.

Re:Not really solving the puzzle. (0)

Anonymous Coward | about 5 months ago | (#45391289)

I guess i had better reread the Genisis again. Man was created before animals? Witness? no, other way around, God was lonley, and needed a cosmic ape to entertain him. A&E were released to a world already populated by others, creatures not of gods wisdom, stealing food from the true creatures.So he was playing a joke on apes or molecules.

Re:Not really solving the puzzle. (2)

iggymanz (596061) | about 5 months ago | (#45386831)

but the moon itself believed to have been formed from a collision of a planet with the mass that became the earth. in that model, the reason why composition would be uneven as the moon tidal lock with one side facing the earth that in fact due to earth's gravity acting on object of uneven composition.

Re:Not really solving the puzzle. (2)

InfiniteLoopCounter (1355173) | about 5 months ago | (#45386995)

but the moon itself believed to have been formed from a collision of a planet with the mass that became the earth. in that model, the reason why composition would be uneven as the moon tidal lock with one side facing the earth that in fact due to earth's gravity acting on object of uneven composition.

Almost. The moon was thought to be formed in stages [youtube.com] . First by a proto-planet called Thea roughly about the size of mars hitting the earth not full on, leaving debre in space. Over time the debree formed a ring to minimize energy between the earth and the ejected material. The ring then had paricles clump together that rolled on more dust to form 2 objects. These 2 objects with different material makeups (probably from the different amounts of Earth or Thea in them) then collided after some passes around the earth, leaving one side completely different in makeup from the other side. One side is tidal locked to the Earth, so it always faces us as you already know. You can see some of this by looking at the smooth section of moon vs the rough section as well.

Re:Not really solving the puzzle. (1)

icebike (68054) | about 5 months ago | (#45387253)

Wait, that's a cute theory, but it doesn't explain anything.

First that theory assumes the the moon became instantly tidally locked from near the moment of its creation, which seems highly unlikely for a body born of an impact, followed by re-impact. (The debris impacts on the far side would occur more often, because the near side would not be shielded by the earth, but that works ONLY once the proto-moon is tidally locked.).

I'm not sure there is much in the way of evidence for exactly when the moon became tidally locked.

Re:Not really solving the puzzle. (4, Informative)

InfiniteLoopCounter (1355173) | about 5 months ago | (#45387807)

First that theory assumes the the moon became instantly tidally locked from near the moment of its creation, which seems highly unlikely for a body born of an impact, followed by re-impact. (The debris impacts on the far side would occur more often, because the near side would not be shielded by the earth, but that works ONLY once the proto-moon is tidally locked.).

I'm not sure there is much in the way of evidence for exactly when the moon became tidally locked.

This is the current leading theory. Yes, it is very recent, but in the video I linked to you'll see lots of famous physicsts that you should recognize.

It's been a while since I was in physics studying this kind of thing, but it seems to me that since it is a smaller body and formed around the earth at a much smaller distance from the earth and then moved out, that there would be only a handful of parameters that would determine how long a tidal lock would take. First would be the small mass of the moon and smaller iron core, which would lead to faster tidal lock than say a planet around a star. Second would be the distance from the Earth (smaller the distance the faster it would occur). Thirdly, the impact between the 2 'proto-moons' would directly influence the rotation rate and axis of rotation of the moon (although from a disk around the earth, the eccentricty with respect the earth would be minimal). Since the moon was very close to the earth around its formation, and it formed in orbit around the earth, I would assume that a tidal lock would have occured very soon after its formation. Probably somewhere there is a simulation to show this.

Here's an article [space.com] that explains why the composition is likely to be different for more fluid materials upon the theorised collision of the 2 'proto-moons'. This explains in principal that the less solid objects were drawn to the near side (as per the original article linked to in the summary), leaving a thinner crust on the near side. The only new interesting take-home is that the period of bombardment of comets and asteroids (due to the stabilization of the orbits of Jupiter, Saturn, Neptune, and Uranus throwing them towards the inner solar system) was likely slightly less violent than predicted before.

Re:Not really solving the puzzle. (1)

InfiniteLoopCounter (1355173) | about 5 months ago | (#45387911)

Another thing to remember is that the moon was much closer in the past and is slowly drifting away from the Earth. Tidal influences on the moon and earth system would have been much greater in the period it is thought the moon was formed.

Re:Not really solving the puzzle. (0)

Anonymous Coward | about 5 months ago | (#45388241)

What do famous physicists have to do with anything? So if the funding agencies (governments) and media control who gets famous they can determine the "leading theory"?

Shielded by earth? (1)

dutchwhizzman (817898) | about 5 months ago | (#45389277)

The chance of any object large enough to leave a crater visible from earth on the moon being shielded by earth, is very small. While the earth is roughly four times the diameter of the moon, it's at such a distance that it covers a very small part of the total area from which objects from space will hit it.

Just look at the sky at night at a full moon. Calculate roughly how much area the moon covers if it's high up in the sky and multiply the surface area by 8 (4^2 then divide that number by two because you only see half the hemisphere, high up in the sky because the atmosphere makes objects appear larger if they are close to the horizon). It may be easier to imagine the moon about 2.82 times the diameter it is to get to that size. Now picture yourself standing under an umbrella that size, pointed in any random direction and have a thousand people throwing rocks at you from all directions and all distances. How big is the chance that they'd miss because the umbrella would shield you?

You could do the actual math and not do a quick guesstimate like I just did to come up with the exact amount of hemisphere that would be shielded by earth from the moon and come up with a low percentage number. That would still not be the percentage of shielding that you'd get from earth, since the gravitational field will pull in stuff that would be in a trajectory to just pass earth. Some of it will crash on earth as a result of that, some of it will deflect the path such that it may just miss the moon and some of it will pull stuff in a trajectory that will hit the moon while it wouldn't have otherwise. Still, the amount of hemisphere being influenced positively or negatively by this field would be rather small, most of the rocks would just get through regardless.

The big thing shielding both earth and the moon currently are actually the bigger planets further out in our solar system. The main reason we don't get a lot of large objects hitting us is because most stuff getting into our solar system will start being in pulled slowly from outer belts of debris and intersect with one of the big planets gravity fields before they'd even get close. Most of the moon craters we see from here were formed long ago, when there way way more stuff flying around in our solar system, especially just after the crash that triggered the inception of the moon and it just had gotten it's shape. Earth has an atmosphere and tectonics that made any old craters disappear, the moon has kept them since it's inception.

Re:Shielded by earth? (1)

icebike (68054) | about 5 months ago | (#45389389)

The chance of any object large enough to leave a crater visible from earth on the moon being shielded by earth, is very small. While the earth is roughly four times the diameter of the moon, it's at such a distance that it covers a very small part of the total area from which objects from space will hit it.

You seem to forget that the impactors of that time were all left over debris from a large body impacting the earth, and this junk was orbiting in a loose ring mostly within the orbital path of the Earth. These weren't random asteroids or comets coming in from the oort cloud or some such place.

When the earth precedes the moon as the earth orbits the sun, it will sweep all the big impactors in its path, and only a few near-miss smaller impactors will deflected into the moon. Similarly, When the moon leads the earth in the orbit, it will be the back side of the moon that leads, not the earth facing side.

When the moon is beside the earth, you could argue that they would both be hit with the frequency dependent on their diameter.

If you insist that the earth would not shield the moon, you must com up with an alternate theory as to why the back side if the moon is more heavily cratered than the earth side.

(Also the plane of the Moon's orbit around earth is not on the same plane as the earth's orbit around the sun, and the moon would spend a considerable amount of orbit out central portion of the debris field. Moon's orbit is tilted about 5 degrees [wikimedia.org] .)

Re:Not really solving the puzzle. (0)

Anonymous Coward | about 5 months ago | (#45387257)

Debris

Re:Not really solving the puzzle. (1)

InfiniteLoopCounter (1355173) | about 5 months ago | (#45387825)

Debris

You're right. I see these speeling and grammar things all the time when I post, and it is a little embarassing. It's a habit from other sites that I post quickly without proof-reading. This is because I am used to posting, then proof-reading, and then editing. I suppose I should do better.

Re:Not really solving the puzzle. (4, Interesting)

DMUTPeregrine (612791) | about 5 months ago | (#45386839)

Probably some relation to orbital mechanics, Luna likely became tidally locked to the Earth before it had fully cooled. The tidal forces on Luna would have affected how the materials settled. I'm not an expert on this by any means, so I can't calculate what exactly would happen.

Re:Not really solving the puzzle. (1)

Anonymous Coward | about 5 months ago | (#45387005)

You would think that the near side would have the thicker crust, though.

Re:Not really solving the puzzle. (0)

Anonymous Coward | about 5 months ago | (#45387083)

Maybe the inner material was more mobile than the crust, so it squeezed the crust material to the sides as it strained toward Earth?

Re:Not really solving the puzzle. (1)

BubbaDave (1352535) | about 5 months ago | (#45387185)

Maybe the heat from the molten earth kept the near side a bit warmer, and through (...I have fuckasll idea what...) that led to the thinner crust.

Two tides (2)

Okian Warrior (537106) | about 5 months ago | (#45387461)

The Earth-Moon system orbits around a point which is not at the center of the Earth, sort of like a barbell with small and large ends will balance on a point which is not in the center of the big end. The point of rotation is still inside the Earth, just not at the center of the Earth.

This is why we have two tides [roughly] each day - the side near the moon gets attracted to the moon, while the other side gets swung around on the outside and experiences centrifugal force, pulling it away from the center.

The moon should experience this same effect. I would expect tidal forces to draw mass away from the center, resulting in more mass on the far side.

Re:Two tides (1)

DMUTPeregrine (612791) | about 5 months ago | (#45388053)

Yes, that's to be expected, but why there wouldn't also be more mass on the near side, and a low-mass region around the border is what I don't know enough to explain.

Re:Two tides (1)

wonkey_monkey (2592601) | about 5 months ago | (#45389715)

This is why we have two tides [roughly] each day - the side near the moon gets attracted to the moon, while the other side gets swung around on the outside and experiences centrifugal force, pulling it away from the center.

I heard it explained as the tidal bulge near the moon experiencing the strongest pull, the Earth in the middle a lower pull, and the bulge on the other side an even lower pull than the Earth. Does that do away with centrifugal force being needed to explain it, or is just another way of putting it?

Re:Not really solving the puzzle. (0)

Anonymous Coward | about 5 months ago | (#45387751)

more likely the centripetal forces on the cooling material was slightly higher than the tidal forces, like a giant centrifuge.

Re:Not really solving the puzzle. (0)

Anonymous Coward | about 5 months ago | (#45388117)

"Probably some relation to orbital mechanics..."

Such as the fact that planet Earth is relatively close to the near-side of the Moon (duh...), while there isn't anything for millions of miles on the other side. Perhaps the higher incidence of craters on the near-side of the Moon is a result of increased likelihood of "splash damage" resulting from meteor/comet strikes on Earth. It makes sense, in light of the fact that the far-side of the Moon is essentially immune to such "splash damage" (pardon the pun), and would therefor exhibit less cratering.

The thinner crust facing Earth might be a result of the increase in impacts on the near-Earth side, rather then the cause. Increase in impacts = increased heating from those impacts = less cooling in the crust on that side = thinner crust.

Re:Not really solving the puzzle. (0)

Anonymous Coward | about 5 months ago | (#45386955)

OK, there are larger craters because the crust is thinner on this side, but why is the crust thinner on this side?

That's my fault, when I was trying to slide it off the peel into the oven I messed up and the crust got deformed and stretched a little too thin on the one side. That's why I usually go with deep-dish or pan style, so I don't have that kind of problem.

Re:Not really solving the puzzle. (0)

Anonymous Coward | about 5 months ago | (#45387161)

It indeed solves the puzzle. And "Why" is another puzzle but that could be understood quite easily I think (or understood already)

Re:Not really solving the puzzle. (1)

The123king (2395060) | about 5 months ago | (#45387395)

My guess is that non-force that is centrifugal. As the moon split away from the earth, as stated in the Giant Impact hypothesis, the crust would cool. These bits of denser solid crust would then be forced to the far side of the moon, much like a centrifuge forces denser particles to the bottom of a test tube.

Well, that's my theory anyway, it's probably a load of bollocks.

Re:Not really solving the puzzle. (1)

camperdave (969942) | about 5 months ago | (#45390159)

How about this: Over the ages, the far side has been pelted by meteors a lot more than the near side. This has sandblasted away the big craters and has served as a source of raw material for thickening the crust on that side.

Re:Not really solving the puzzle. (0)

Anonymous Coward | about 5 months ago | (#45387937)

The heavier core solidified last, off center. For a tidally locked body like the moon, that means the heavier side will face the planet it orbits.

Re:Not really solving the puzzle. (0)

Anonymous Coward | about 5 months ago | (#45389197)

The theory, iirc, is that a major impact on the far side re-flowed the surface, creating thicker crust and obliterating the then-existing crater record.

Re:Not really solving the puzzle. (1)

Medievalist (16032) | about 5 months ago | (#45393127)

OK, there are larger craters because the crust is thinner on this side, but why is the crust thinner on this side? Mere happenstance, or is it caused by orbital mechanics or some other reason?

One way to make a crust thinner is to hit it a lot.

Works on pizza and iron, don't see why it wouldn't work on moons...

Constructed like a Hollywood set (-1)

Anonymous Coward | about 5 months ago | (#45386793)

Particleboard on the non-facing side so that construction could be done on budget.

Thinner crust = more meteor strikes there? (-1)

Anonymous Coward | about 5 months ago | (#45386797)

The percentage difference in thickness is enough to influence gravity at that distance to cause that many more strikes on that side? I call bs.

Re:Thinner crust = more meteor strikes there? (0)

Anonymous Coward | about 5 months ago | (#45387219)

The percentage difference in thickness is enough to influence gravity at that distance to cause that many more strikes on that side? I call bs.

The number of strikes are probably about the same, but the thickness of the crust makes a huge difference on what happens when a meteor strikes.

Homework for next week: Fill a bucket with some flour, drop a ball in the bucket and observe the impact. Fill the same bucket with concrete to the same level as before and drop the same ball in the bucket. Is the impact the same as before?

Re:Thinner crust = more meteor strikes there? (1)

Jay Vickery (2908369) | about 5 months ago | (#45391173)

The percentage difference in thickness is enough to influence gravity at that distance to cause that many more strikes on that side? I call bs.

I think its roughly the same number of strikes but thiner crust means a bigger crater when they hit.

liquid core? (1)

boojumbadger (949542) | about 5 months ago | (#45386905)

I would hazard a guess that if the core is more liquid than the crust then the Earth's gravity might tend to draw it towards the near side more when it gets hit on that side than the far side. Hits on the far side might be more restrained as there is not as much expansion pressure. Over millions of years the effect could become quite pronounced.

Just talking through my hat, of course, and probably full of it.

Re:liquid core? (1)

FatLittleMonkey (1341387) | about 5 months ago | (#45388479)

Tidal effects don't work like that. It's a stretching, not a one directional pull. It would elongate the core, not pull it towards Earth relative to the rest of the moon. The oceans on Earth experience two daily tides for that reason, the oceans bulge both towards and away from the moon. (So does the crust, but less obviously.)

Moreso, the closer you are to the centre of mass, the less tidal effects you experience. So the moon's core would experience less tidal force than the crust.

Re:liquid core? (1)

boojumbadger (949542) | about 5 months ago | (#45394461)

Earth rotates, the moon not so much, so while there is a high tide and a low tide in the oceans of the Earth due to the moons orbit, the gravitational pull of the Earth on the moon is always in the same direction. There may well be some stretching in the moon from centripetal forces and indeed there are other forces not being taken into account such as the rotation of the Earth-Moon system around the sun or the Solar system around the Galaxy.

I don't think you know what you are talking about any more than I do. :)

Re:liquid core? (1)

FatLittleMonkey (1341387) | about 5 months ago | (#45397069)

Tidal effects don't require axial rotation, only the orbit. For example, a tether in orbit will always point towards and away-from the centre of gravity of its primary. They quickly become tide locked because of their exaggerated shape. The two ends experience a force towards, and away from, the centre of gravity of the primary. The same thing happens with a spherical object, but takes longer. That's why the moon is tidally locked.

Essentially, the radius of orbit is the only line where gravitational and centripetal forces are in balance. Anything inside that line is travelling slower than orbital speed at that radius and is pulled towards the primary, anything outside is travelling faster than orbital speed at that radius and is pulled away from the primary. You don't see it in normal man-made objects because they are too small, but a larger object (or an elongated one like a tether) will experience it.

The moon doesn't experience "tides" in the sense of a moving wave travelling through the surface. But it does experience tidal forces, and is exactly as deformed (elongated towards and away from Earth) as its own internal gravity allows. However, as I said, the effect is always in both directions, and is weakest at the centre.

[When I said Earth has two tides per day, I didn't mean one high and one low. I meant two highs and two lows. One high tide is pointing towards the moon (lagging slightly behind), the other is on the other side of the Earth, pointing away from the moon. The two lows are in between, at 90 degrees either side. If the Earth became tide-locked to the moon (which it should in 5-7 billion years) it would still have those two high spots in the ocean and crust, one fore and one aft, and two low spots in between. The only change is that they wouldn't be moving around the Earth.]

Re:liquid core? (0)

Anonymous Coward | about 5 months ago | (#45397785)

You certainly sound like you know what you are talking about so I guess I must consider myself schooled. Thank you for your pleasant demeanor and patient explanation. :)

The moon is pizza: a haiku (1)

Anonymous Coward | about 5 months ago | (#45386927)

If the moon is cheese

Thin and original crust

Means it is pizza

Simple (1)

rossdee (243626) | about 5 months ago | (#45386975)

fewer rocks strike the Earth facing side of the moon because the earth is in the way

No (1)

dutchwhizzman (817898) | about 5 months ago | (#45389315)

See my comment elsewhere in this thread. The earth is only a very small part of the moon hemisphere. It's effectively a little less than three times as big "in the moon sky" and the rest of the hemisphere. It is actually about four times as big, but to make it easier, I'm also including the half of the hemisphere you can't see in the comparison how much it would shield you.

It's like saying a thousand people throwing pebbles at you simultaneously have less chance hitting your body because you are holding up a tennis ball. Maybe a few will miss you because their pebble will bounce off the tennis ball, but almost all will get through.

I thought this was kind of obvious (5, Interesting)

localroger (258128) | about 5 months ago | (#45387051)

If the Moon was created by a glancing collision between the Earth and a Mar-sized protoplanet, which seems to be the going theory nowadays, then the Moon was created in Low Earth Orbit during the very heavy bombardment phase of the LHB. Once the Moon became tidally locked -- which would have happened pretty quickly at such proximity -- Nearside was shielded from most further bombardment by the Earth. So Nearside is kind of a fossile from the heaviest epoch of the LHB, while Farside continued to get pelted as the big stuff was swept up, and finally got the fine dusting of the last scraps evening it out. It would also have continued to accumulate crud, which Nearside wouldn't, thus the thicker Farside crust.

Re:I thought this was kind of obvious (2)

khallow (566160) | about 5 months ago | (#45388777)

Nearside was shielded from most further bombardment by the Earth

The Earth isn't much of a shield. The vast majority of the junk that passes inside the orbit of the Moon misses the Earth. Really, if a side is sheltered to any degree from impacts, it would be the trailing side of the Moon. Googling around, that results in an interesting theory from a Mike Martinez::

It would really be interesting to find out why the back-side is so different from the front side facing earth. My own 'little ' theory is that the back side was once the leading side of the moon, the side facing orbital direction very early on---and when the moon was much closer to the earth. I believe that the moon was possibly heading into heavy 'traffic' on it's orbital swings at a much faster pace--maybe taking only days to complete one orbit instead of it's 29 days now. Later on--maybe another few 100 million years or more. other massive hits on the moon occurred--swinging it slowly to it's present position.

My pet theory is that the early Moon was in a situation similar to Enceladus, a moon of Saturn. Here, Enceladus experiences liquid water volcanism due to the stress heating from moving towards and away from Saturn in its almost circular orbit. In particular, this has resulted in the "Tiger Stripes" [wikipedia.org] , a region of substantial volcanism and very new surface (some parts being less than a thousand years old amd considerably warming that the rest of the moon's surface).

Perhaps the lunar mares were at one time the most stressed regions of the Moon while it was cooling much as the "Tiger Stripes" are thought to be for Enceladus.

Just like Mars (1)

atherophage (2481624) | about 5 months ago | (#45387089)

only different. Southern hemisphere of Mars is something like six kilometres higher in elevation than the northern half. The Electric Universe people have a lot to say about such things - none of which involve impact events: hexagonal craters? Craters within craters? Crater chains?

Re:Just like Mars (1)

danda (11343) | about 5 months ago | (#45387991)

Yes.

--
When the first space probes returned images of the Moon, they revealed a surface heavily pockmarked with craters and riddled with long-sinuous channels (or rilles). Scientists seeking to interpret these features were constrained by the traditional geologic toolkit. The "debate" over the lunar craters only included two possible causative agents: volcanism, or impact. Eventually, a consensus was reached that meteoric impacts were the primary source of lunar craters.

But more than forty years ago, the British journal Spaceflight published the laboratory experiments of Brian J. Ford, an amateur astronomer who raised the possibility that most of the craters on the moon were carved by cosmic electrical discharge. (Spaceflight 7, January, 1965).

In the cited experiments Ford used a spark-machining apparatus to reproduce in miniature some of the most puzzling lunar features, including craters with central peaks, small craters preferentially perched on the high rims of larger craters, and craters strung out in long chains. He also observed that the ratio of large to small craters on the Moon matched the ratio seen in electrical arcing.
--

http://www.thunderbolts.info/webnews/120707electriccraters.htm

Alternative explanation (0)

Anonymous Coward | about 5 months ago | (#45387135)

All hail General Zed!

Simple (0)

Anonymous Coward | about 5 months ago | (#45387381)

Everyone knows the aliens on the dark side of the moon destroyed all the big ones before they hit their bases.

Re:Simple (1)

hey! (33014) | about 5 months ago | (#45387485)

**Holds right hand inches in front of face and compares to left hand at arms length.**

Hey guys, I think the craters on the near side are bigger because they're closer.

Gravitational slingshot (2)

thisisauniqueid (825395) | about 5 months ago | (#45387439)

Wouldn't asteroids hit the moon a lot harder if they glanced past the earth, due to gravitational slingshot? Seems like a good reason for a bigger crater.

Re:Gravitational slingshot (0)

Anonymous Coward | about 5 months ago | (#45388939)

No. The impact energy depends on the distance from the earth and the sun, not the trajectory.

Impact energy high school 101 (1)

dutchwhizzman (817898) | about 5 months ago | (#45389365)

Speed times mass square. Nothing more, nothing less is what determines impact energy. Go look it up in your high school text books if you doubt this.

Distances from whatever other bodies have no significant influence whatsoever. They may slightly influence the speed at which the object travels with their gravitational fields, just as the gravitational field from the moon itself may increase the speed once an object is getting closer to the moon. Looking at what currently is flying around our solar system, almost anything is coming from the outer belts and is pulled in by the combined gravitational fields of all our planets and the sun. Anything not prematurely being sucked up by the big gas giants further out, has speeds of thousands of kilometres per second by the time it gets close to the earth and the gravitation fields from both the earth and the moon have no significant effect on the impact energy any more.

Re:Gravitational slingshot (0)

Anonymous Coward | about 5 months ago | (#45392603)

No. The additional speed the asteroid gains by just depends on the difference in the gravity potential between the place where it "starts" and where it "ends" (=impacts). If it just passes closer to the earth, it will be sped up a bit while closing in, but it will lose the same amount of speed on the "way out". Of course, there's an appropriate XKCD [xkcd.com] . It really doesn't matter which path you take, it's just the difference in height on that graph that affects the kinetic energy of an object moving from one point to the other.

Gravity slingshots [wikipedia.org] need to be aimed properly, otherwise they are just as likely to reduce speed (used e.g. for the MESSENGER probe) as they are to increase it. Given the high relative (to the earth or the moon) speed of asteroids, I wouldn't expect much of a difference with "just" the earth and random trajectories.

Earth's effect? (0)

Anonymous Coward | about 5 months ago | (#45387449)

Wouldn't object's that hit the near side get a gravitational acceleration as they pass by Earth just before hitting the moon giving them, on average, a higher impact velocity?

I have a theory. (1)

sparkeyjames (264526) | about 5 months ago | (#45387487)

When the earth and moon collided it was not a high speed affair, or at least not as high speed as most celestial collisions, and happened much later than most theories have it doing so. Part of the moons crust at the time peeled off during the collision and formed most of the land masses we now have on earth. Most of the detritus of the collision continued to rotate about the earth and moon causing many many meteor strikes on both planets. Like I said it's just a theory.

Re:I have a theory. (0)

Anonymous Coward | about 5 months ago | (#45389479)

No, it would be an hypothesis. It's a theory when it gets some supporting evidence. Start working on your evidence.

not caused by impacts. (1)

danda (11343) | about 5 months ago | (#45387925)

Gravity is not the only or the strongest force in the universe.

Most likely the craters were caused by plasma discharges, ie electrical arcs.

Too much to go into here. Do yourself a favor. Google "electric universe". Read the book "The Electric Sky".

Re:not caused by impacts. (0)

Anonymous Coward | about 5 months ago | (#45389733)

You nutjobs come out of the woodwork every few months. Go stick a fork in a lightsocket and see how that works out.

Big moon craters (0)

Anonymous Coward | about 5 months ago | (#45388171)

A headline about big craters on the moon and not a single Goatse joke? Man, this place is slipping.

mo3 0p (-1)

Anonymous Coward | about 5 months ago | (#45388327)

486/66 with 8 Won't be sho0ting

Götterdämmerung (0)

Anonymous Coward | about 5 months ago | (#45389783)

The stuff filling the larger craters were from the underground helium 3 factories created by the Nazi's on the back side of the Moon; the factories have made the surface appear thicker. The earthside is thinner from mining the rocks needed for the coming meteor blitzkrieg. What wrong with you people? Haven't you learned anything from history?

Earth acting as a gravity lens focused at moon (1)

MonsterMasher (518641) | about 5 months ago | (#45390525)

I imagine having the earth act like a gravity focus, greatly increasing volume of space and velocities that would have missed the moon completely... need to make a few diagrams to get this across well.

I can't see why this would not be pretty obvious.

Of course, I play Kerbel Space Program so have more intuitive feel for these systems.. buy it, learn it, teach it to your children. How else will they dodge space trash?

Gravity Assist (0)

Anonymous Coward | about 5 months ago | (#45390669)

Wouldnt it made sense that some of the impacts on the near side would have just swung around the earth's gravity well and increase the energy of the impact?

ny vs chi (0)

Anonymous Coward | about 5 months ago | (#45391037)

So the near side has a N.Y.-style crust, while the far side has a Chicago-style crust. I vote we send a probe to measure cheese depth A.S.A.P.!

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