6 ms·

Differences between Moon’s near and far sides linked to colossal ancient impact

74 points by wglb 5y ago

h2odragon 5y ago
> The nearside is home to a compositional anomaly known as the Procellarum KREEP terrane (PKT) — a concentration of potassium (K), rare earth elements (REE), phosphorus (P), along with heat-producing elements like thorium. KREEP seems to be concentrated in and around Oceanus Procellarum, the largest of the nearside volcanic plains, but is sparse elsewhere on the Moon. Bait. Big pile of things we want, placed where we can see them but not easily reach...
- JKCalhoun 5y ago
  Indeed, the Moon is a harsh mistress.
- sfblah 5y ago
  I thought Kazakhstan produced the best potassium.
  - BlueTemplar 5y ago
    No, uranium - it doesn't make for a silly joke though...
uncertainquark 5y ago
This is yet another (most welcome) hypothesis in explaining the sheer differences in our Moon’s nearside and farside. Just last month I wrote a feature article explaining the other leading theories for what caused these nearside-farside differences if anyone’s interested: https://blog.jatan.space/p/the-two-faced-moon https://blog.jatan.space/p/the-two-faced-moon The Moon is so much more interesting than most people think.
- frankohn 5y ago
  I was wondering if a possible explanation is that, due to the gravity attraction of the earth, the hot, heavy, inner part of the moon, which is richer in heavy elements, I guess, like iron is closer to the near-side surface. Since in the far-side the hot, heavy part is too far from the surface the eruption activity is small or non-existing. Because the moon is tidally locked to the earth the pull always act in the same direction. I was imagining the moon as a drop of liquid in the vacuum space with a denser core at the center. The heavier core would be at the center because of the moon's own gravity. In the presence of the earth's gravity the denser part of the "liquid drop" will be centered more closely to one side and so the volcanic activity would be strongly biased.
  - OscarCunningham 5y ago
    For the same reason there are two tides, you would expect the drop to be pulled towards Earth, but also thrown out away from Earth. https://en.wikipedia.org/wiki/Tidal_force https://en.wikipedia.org/wiki/Tidal_force
    - frankohn 5y ago
      No, because the moon is tidal-locked to the earth so the pull is always in the same direction. Tidal-locked means the moon always show the same face to the earth.
      - CorrectHorseBat 5y ago
        Won't there be centrifugal pull (push?) on the other side? Just like there is tide on the moon side and on the other side
        false-mirror 5y ago
        You're referring to the fictitious centrifugal force [0] which is actually a minor change in inertia—very much out shined by the centripetal force of gravity. For example, on earth if you weigh 200 lbs on the North Pole, you'd weigh about 199lbs on the equator. On the moon, this tiny effect would be wiped out by gravity. [0]:https://en.wikipedia.org/wiki/Centrifugal_force https://en.wikipedia.org/wiki/Centrifugal_force
JKCalhoun 5y ago
I recently took an old-school "voxel" algorithm and munged some NASA moon terrain data to try to create a game. I really have enjoyed learning about the Moon's geography just from flying around the terrain, picking locations for "lunar bases" and such. Fascinating cracks and valleys, grooves, a straight mountain range — in general things I was not expecting on a planetoid without water/erosion. It really is stark how different the far side of the Moon is from the near side. Insanely pock-marked with so many craters.... I assumed there was an Earth component to that in the same way the Earth has locked the Moon into an orbit/rotation that is always facing us. I'm become very keen to learn more about the Moon now.
- Teever 5y ago
  Can you talk more about the moon data munging? I just started some Blender tutorials and the first thing I want to try once I get some tutorials under my belt import dats from the Moon/Mars.
  - JKCalhoun 5y ago
    Sure. For the Moon the (images) data seems to be bucketed with regard to pixels-per-degree (PPD), the more coarse data set being 64ppd data (finer resolution for the Moon goes at least as high as 512ppd that I have found). Sadly, my workflow (image editors, and Blender as you mentioned) are already straining with the 64ppd data-set so I did not try to go higher resolution. It means though that my Moon is wildly small — the lunar bases that seem to be a paltry 7x7 or 9x9 voxels are in fact the size of a small town. I began with NASA's "CGI Moon Kit" [1] which, as I say, is 64ppd. There is both a "color data" image and an "elevation data" image (where the greyscale value of the image represents elevation). Polar data was garbage (and would look wildly distorted in my tile-based voxel algorithm so I confess that I tossed it — cropped everything outside 60-degrees latitude basically - I just limit fuel in the game to keep pesky kids from trying to get too deep into the polar regions). Even at 64ppd and poles cropped, I still ended up with two images that were 23040 × 11264 pixels in size. This turned out to be a challenge for most of the image editing apps I have. Blender handled it (but barely). With both color + elevation images I followed an online tutorial [2] meant for cartographers wanting to use Blender for relief shading. NASA's moon map had no shadows (probably a good thing). I was not going to try to real-time shade/light the voxel terrain so I settled on "burning in" the shadows with Blender. While my MacBook ran some 8 hours or so (over night) to generate the relief-shaded lunar map, the result was quite nice. As a result, it is near sunset everywhere on my Moon, ha ha. With a relief-shaded image representing the color and a same-sized image representing the elevation, I wrote a custom app to read both files into memory and then generate the correct number of 512 x 512 tiles that contain both the elevation data and RGB data in a single raw file. Now I have 45 x 22 raw tiles covering the entire 64ppd Moon. The voxel algorithm uses simple math to figure out which tile a given voxel is to be found, reads the elevation/color data. In hindsight, I could have output PNG files or something with alpha channel (where alpha would be interpreted as elevation). As it turned out, the Moon color was so close to greyscale that I ended up treating it as such and used only the green channel when creating my Moon tiles (so the tile data has only a single 8-bit value for elevation and a single 8-bit value for "color" per voxel — cut the raw tile size in half). Still wrapping up the game [3]. I'll put the sources up on Github end of the month, I think. [1] https://svs.gsfc.nasa.gov/4720 https://svs.gsfc.nasa.gov/4720 [2] https://somethingaboutmaps.wordpress.com/blender-relief-tutorial-blender-basics/ https://somethingaboutmaps.wordpress.com/blender-relief-tuto... [2] https://mooncraft2000.com https://mooncraft2000.com
prewett 5y ago
The article doesn't seem to answer the question of why the heat plume distributed stuff on the nearside rather than evenly, or on the top side. If the south pole was hit, it seems like the heat should flow evenly on both sides, and if anything case the deposition to happen towards the north pole, rather than the near side.
- waynecochran 5y ago
  Yes -- that is what I was wondering. The following statement is given with no explanation -- was Earth's gravity involved? As the heat plume spread beneath the Moon’s crust, that material was eventually delivered en masse to the nearside.
- andrewflnr 5y ago
  Reading the linked paper and Wikipedia, it looks like the center of the KREEP concentration is roughly antipodal to the impact crater, which itself is not exactly on the south pole. So at least the symmetry side of things is in order. But yeah, this PR article is exceptionally bad at taking a long time to say almost nothing of interest. [0] https://www.science.org/doi/10.1126/sciadv.abm8475 https://www.science.org/doi/10.1126/sciadv.abm8475 [1] https://en.wikipedia.org/wiki/South_Pole%E2%80%93Aitken_basin https://en.wikipedia.org/wiki/South_Pole%E2%80%93Aitken_basi...
mageofpanthera 5y ago
- wishawa 5y ago
  This comment sounds AI-generated. If you’re a real person can you explain the point you were trying to deliver and why you chose to write this way?
  - bdefore 5y ago
    Is that what happened here? My head went in a few orbits over this comment.
    - deleted 5y ago
      [deleted]
  - mageofpanthera 5y ago
    Machines do not have narrative-interpretation bugs associated with Superiority Complex, humans do, Arthur.
  - klyrs 5y ago
    I've met some old-school hippies who actually talk like that, and appear to completely believe the pseudoscience.
    - mageofpanthera 5y ago
      Oh, I remember that word now: "pseudoscience"; it used to be regurgitated everytime someone stepped into a pool of reality-altering facts. They never manage to pin down the 'pseudo' or the 'science', or contribute (like old-school hippies) anything to the collective.
      - klyrs 5y ago
        Yeah, but sell a finger for the price of a lid, and your hippie suddenly believes in concrete facts, scientific measurements and capitalism...
rhplus 5y ago
Why the two sides are so different is one of the Moon’s most enduring mysteries. How much can be explained by the earth shielding the moon from impacts to its near-side?
- spaetzleesser 5y ago
  That’s what I was thinking. Or that the earth gravity would cause tidal forces.
- vikingerik 5y ago
  Not much. The Earth subtends a width of only 2° in the Moon's sky - it covers only about 1/10000 of the possible approach vectors to the Moon. Think about a lunar eclipse for comparison: the Earth intercepts the Sun-Moon vector for a couple hours every few months, roughly 1/10000 of the time. The Moon is a smaller target (1/4 the diameter, 1/16 the cross section, also 1/81 the mass and gravity), so it gets hit less because of that, but not because of Earth shielding it.
  - cperciva 5y ago
    I don't think that calculation is quite right. An asteroid on a collision course with the moon doesn't need to hit the Earth in order to avoid hitting the moon -- simply coming close to the Earth will alter its course.
    - vikingerik 5y ago
      It's just as likely that the Earth will perturb an object's course away from the moon as into it. Except if the object hits Earth itself, but the point is that's a pretty small percentage of cases, the Earth occupies only a small portion of the moon's sky.
      - cperciva 5y ago
        Are the probabilities equal? I agree that they're both possible, but I don't have any clear intuition for why they should be the same -- or which would be larger if they're not the same.
getpolarized 5y ago
There's a MASSIVE impact crater on the far side of the moon which we never see. Imagine if it was inverted. It would look like a MASSIVE eyeball staring at us during our evolution. Imagine how that would have impacted religion!
- deleted 5y ago
  [deleted]
akomtu 5y ago
A wild speculation: perhaps Moon is the huge asteroid that hit and liquefied the planet that was there before Earth, so some of its material sticked to that asteroid and formed Moon, while the rest formed Earth. In this case, the two sides of Moon show the direction of the impact.
- Sharlin 5y ago
  I mean, the prevailing theory is that the Moon formed in the aftermath of the Theia–proto-Earth collision. Indeed the existence of the Moon is why the Theia hypothesis was proposed in the first place. But the bulk of Theia’s mass (which would have been ~10% of Earth’s mass) is thought to have mixed with Earth’s and sunk into the core/mantle, while most of the Moon is made of same material as the modern Earth’s crust. However, the differentiation of the Moon’s near and far sides must have happened later, presumably during what’s called the late heavy bombardment (“late” is relative here; we’re still talking ~4 Ga ago). Although I believe some recent research has cast doubt on whether the LHB actually happened at all.
JoeAltmaier 5y ago
Early fusion experiment gone awry?

74 points by wglb 5y ago

> The nearside is home to a compositional anomaly known as the Procellarum KREEP terrane (PKT) — a concentration of potassium (K), rare earth elements (REE), phosphorus (P), along with heat-producing elements like thorium. KREEP seems to be concentrated in and around Oceanus Procellarum, the largest of the nearside volcanic plains, but is sparse elsewhere on the Moon. Bait. Big pile of things we want, placed where we can see them but not easily reach...

JKCalhoun 5y ago
Indeed, the Moon is a harsh mistress.
sfblah 5y ago
I thought Kazakhstan produced the best potassium.
- BlueTemplar 5y ago
  No, uranium - it doesn't make for a silly joke though...

uncertainquark 5y ago

This is yet another (most welcome) hypothesis in explaining the sheer differences in our Moon’s nearside and farside. Just last month I wrote a feature article explaining the other leading theories for what caused these nearside-farside differences if anyone’s interested: https://blog.jatan.space/p/the-two-faced-moon https://blog.jatan.space/p/the-two-faced-moon The Moon is so much more interesting than most people think.

frankohn 5y ago
I was wondering if a possible explanation is that, due to the gravity attraction of the earth, the hot, heavy, inner part of the moon, which is richer in heavy elements, I guess, like iron is closer to the near-side surface. Since in the far-side the hot, heavy part is too far from the surface the eruption activity is small or non-existing. Because the moon is tidally locked to the earth the pull always act in the same direction. I was imagining the moon as a drop of liquid in the vacuum space with a denser core at the center. The heavier core would be at the center because of the moon's own gravity. In the presence of the earth's gravity the denser part of the "liquid drop" will be centered more closely to one side and so the volcanic activity would be strongly biased.
- OscarCunningham 5y ago
  For the same reason there are two tides, you would expect the drop to be pulled towards Earth, but also thrown out away from Earth. https://en.wikipedia.org/wiki/Tidal_force https://en.wikipedia.org/wiki/Tidal_force
  - frankohn 5y ago
    No, because the moon is tidal-locked to the earth so the pull is always in the same direction. Tidal-locked means the moon always show the same face to the earth.
    - CorrectHorseBat 5y ago
      Won't there be centrifugal pull (push?) on the other side? Just like there is tide on the moon side and on the other side
      - false-mirror 5y ago
        You're referring to the fictitious centrifugal force [0] which is actually a minor change in inertia—very much out shined by the centripetal force of gravity. For example, on earth if you weigh 200 lbs on the North Pole, you'd weigh about 199lbs on the equator. On the moon, this tiny effect would be wiped out by gravity. [0]:https://en.wikipedia.org/wiki/Centrifugal_force https://en.wikipedia.org/wiki/Centrifugal_force

JKCalhoun 5y ago

I recently took an old-school "voxel" algorithm and munged some NASA moon terrain data to try to create a game. I really have enjoyed learning about the Moon's geography just from flying around the terrain, picking locations for "lunar bases" and such. Fascinating cracks and valleys, grooves, a straight mountain range — in general things I was not expecting on a planetoid without water/erosion. It really is stark how different the far side of the Moon is from the near side. Insanely pock-marked with so many craters.... I assumed there was an Earth component to that in the same way the Earth has locked the Moon into an orbit/rotation that is always facing us. I'm become very keen to learn more about the Moon now.

Teever 5y ago
Can you talk more about the moon data munging? I just started some Blender tutorials and the first thing I want to try once I get some tutorials under my belt import dats from the Moon/Mars.
- JKCalhoun 5y ago
  Sure. For the Moon the (images) data seems to be bucketed with regard to pixels-per-degree (PPD), the more coarse data set being 64ppd data (finer resolution for the Moon goes at least as high as 512ppd that I have found). Sadly, my workflow (image editors, and Blender as you mentioned) are already straining with the 64ppd data-set so I did not try to go higher resolution. It means though that my Moon is wildly small — the lunar bases that seem to be a paltry 7x7 or 9x9 voxels are in fact the size of a small town. I began with NASA's "CGI Moon Kit" [1] which, as I say, is 64ppd. There is both a "color data" image and an "elevation data" image (where the greyscale value of the image represents elevation). Polar data was garbage (and would look wildly distorted in my tile-based voxel algorithm so I confess that I tossed it — cropped everything outside 60-degrees latitude basically - I just limit fuel in the game to keep pesky kids from trying to get too deep into the polar regions). Even at 64ppd and poles cropped, I still ended up with two images that were 23040 × 11264 pixels in size. This turned out to be a challenge for most of the image editing apps I have. Blender handled it (but barely). With both color + elevation images I followed an online tutorial [2] meant for cartographers wanting to use Blender for relief shading. NASA's moon map had no shadows (probably a good thing). I was not going to try to real-time shade/light the voxel terrain so I settled on "burning in" the shadows with Blender. While my MacBook ran some 8 hours or so (over night) to generate the relief-shaded lunar map, the result was quite nice. As a result, it is near sunset everywhere on my Moon, ha ha. With a relief-shaded image representing the color and a same-sized image representing the elevation, I wrote a custom app to read both files into memory and then generate the correct number of 512 x 512 tiles that contain both the elevation data and RGB data in a single raw file. Now I have 45 x 22 raw tiles covering the entire 64ppd Moon. The voxel algorithm uses simple math to figure out which tile a given voxel is to be found, reads the elevation/color data. In hindsight, I could have output PNG files or something with alpha channel (where alpha would be interpreted as elevation). As it turned out, the Moon color was so close to greyscale that I ended up treating it as such and used only the green channel when creating my Moon tiles (so the tile data has only a single 8-bit value for elevation and a single 8-bit value for "color" per voxel — cut the raw tile size in half). Still wrapping up the game [3]. I'll put the sources up on Github end of the month, I think. [1] https://svs.gsfc.nasa.gov/4720 https://svs.gsfc.nasa.gov/4720 [2] https://somethingaboutmaps.wordpress.com/blender-relief-tutorial-blender-basics/ https://somethingaboutmaps.wordpress.com/blender-relief-tuto... [2] https://mooncraft2000.com https://mooncraft2000.com

prewett 5y ago

The article doesn't seem to answer the question of why the heat plume distributed stuff on the nearside rather than evenly, or on the top side. If the south pole was hit, it seems like the heat should flow evenly on both sides, and if anything case the deposition to happen towards the north pole, rather than the near side.

waynecochran 5y ago
Yes -- that is what I was wondering. The following statement is given with no explanation -- was Earth's gravity involved? As the heat plume spread beneath the Moon’s crust, that material was eventually delivered en masse to the nearside.
andrewflnr 5y ago
Reading the linked paper and Wikipedia, it looks like the center of the KREEP concentration is roughly antipodal to the impact crater, which itself is not exactly on the south pole. So at least the symmetry side of things is in order. But yeah, this PR article is exceptionally bad at taking a long time to say almost nothing of interest. [0] https://www.science.org/doi/10.1126/sciadv.abm8475 https://www.science.org/doi/10.1126/sciadv.abm8475 [1] https://en.wikipedia.org/wiki/South_Pole%E2%80%93Aitken_basin https://en.wikipedia.org/wiki/South_Pole%E2%80%93Aitken_basi...

mageofpanthera 5y ago

wishawa 5y ago
This comment sounds AI-generated. If you’re a real person can you explain the point you were trying to deliver and why you chose to write this way?
- bdefore 5y ago
  Is that what happened here? My head went in a few orbits over this comment.
  - deleted 5y ago
    [deleted]
- mageofpanthera 5y ago
  Machines do not have narrative-interpretation bugs associated with Superiority Complex, humans do, Arthur.
- klyrs 5y ago
  I've met some old-school hippies who actually talk like that, and appear to completely believe the pseudoscience.
  - mageofpanthera 5y ago
    Oh, I remember that word now: "pseudoscience"; it used to be regurgitated everytime someone stepped into a pool of reality-altering facts. They never manage to pin down the 'pseudo' or the 'science', or contribute (like old-school hippies) anything to the collective.
    - klyrs 5y ago
      Yeah, but sell a finger for the price of a lid, and your hippie suddenly believes in concrete facts, scientific measurements and capitalism...

rhplus 5y ago

Why the two sides are so different is one of the Moon’s most enduring mysteries. How much can be explained by the earth shielding the moon from impacts to its near-side?

spaetzleesser 5y ago
That’s what I was thinking. Or that the earth gravity would cause tidal forces.
vikingerik 5y ago
Not much. The Earth subtends a width of only 2° in the Moon's sky - it covers only about 1/10000 of the possible approach vectors to the Moon. Think about a lunar eclipse for comparison: the Earth intercepts the Sun-Moon vector for a couple hours every few months, roughly 1/10000 of the time. The Moon is a smaller target (1/4 the diameter, 1/16 the cross section, also 1/81 the mass and gravity), so it gets hit less because of that, but not because of Earth shielding it.
- cperciva 5y ago
  I don't think that calculation is quite right. An asteroid on a collision course with the moon doesn't need to hit the Earth in order to avoid hitting the moon -- simply coming close to the Earth will alter its course.
  - vikingerik 5y ago
    It's just as likely that the Earth will perturb an object's course away from the moon as into it. Except if the object hits Earth itself, but the point is that's a pretty small percentage of cases, the Earth occupies only a small portion of the moon's sky.
    - cperciva 5y ago
      Are the probabilities equal? I agree that they're both possible, but I don't have any clear intuition for why they should be the same -- or which would be larger if they're not the same.

getpolarized 5y ago

There's a MASSIVE impact crater on the far side of the moon which we never see. Imagine if it was inverted. It would look like a MASSIVE eyeball staring at us during our evolution. Imagine how that would have impacted religion!

deleted 5y ago
[deleted]

akomtu 5y ago

A wild speculation: perhaps Moon is the huge asteroid that hit and liquefied the planet that was there before Earth, so some of its material sticked to that asteroid and formed Moon, while the rest formed Earth. In this case, the two sides of Moon show the direction of the impact.

Sharlin 5y ago
I mean, the prevailing theory is that the Moon formed in the aftermath of the Theia–proto-Earth collision. Indeed the existence of the Moon is why the Theia hypothesis was proposed in the first place. But the bulk of Theia’s mass (which would have been ~10% of Earth’s mass) is thought to have mixed with Earth’s and sunk into the core/mantle, while most of the Moon is made of same material as the modern Earth’s crust. However, the differentiation of the Moon’s near and far sides must have happened later, presumably during what’s called the late heavy bombardment (“late” is relative here; we’re still talking ~4 Ga ago). Although I believe some recent research has cast doubt on whether the LHB actually happened at all.

JoeAltmaier 5y ago

Early fusion experiment gone awry?