APOD: Rotating Moon from LRO (2024 Jun 02)

[APOD Robot]

Rotating Moon from LRO

Explanation: No one, presently, sees the Moon rotate like this. That's because the Earth's moon is tidally locked to the Earth, showing us only one side. Given modern digital technology, however, combined with many detailed images returned by the Lunar Reconnaissance Orbiter (LRO), a high resolution virtual Moon rotation movie has been composed. The featured time-lapse video starts with the standard Earth view of the Moon. Quickly, though, Mare Orientale, a large crater with a dark center that is difficult to see from the Earth, rotates into view just below the equator. From an entire lunar month condensed into 24 seconds, the video clearly shows that the Earth side of the Moon contains an abundance of dark lunar maria, while the lunar far side is dominated by bright lunar highlands. Currently, over 32 new missions to the Moon are under active development from multiple countries and companies, including NASA's Artemis program which aims to land people on the Moon again within the next few years.

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[Ann]

You have to wonder why the Moon's far side is so different from its near side. Does it have anything to do with the fact that the Moon is tidally locked, and always shows the same face to the Earth?

Then again, the Earth itself also looks very different in different places.We don't often think of the Earth the way it looks in the picture below, do we?

The ocean hemisphere of the Earth. Credit: DK IMAGES/SCIENCE PHOTO LIBRARY

---

Ann

[Christian G.]

The Moon clearly shows us its best side! Its "softer" side too, which the early Earth kept warm… (while the other side was left in the cold, forced to grow a thicker crust)

[Roy]

You have to wonder why the Moon's far side is so different from its near side. Does it have anything to do with the fact that the Moon is tidally locked, and always shows the same face to the Earth?

Then again, the Earth itself also looks very different in different places.We don't often think of the Earth the way it looks in the picture below, do we?

The ocean hemisphere of the Earth. Credit: DK IMAGES/SCIENCE PHOTO LIBRARY

---

Ann

[ Premise 1 - crustal rocks are lighter than deeper rocks such as flood basalts.
Premise 2 - a tide locked body has the heavier side toward the planet ]

Let me advance a sequence of events:
A major impact event sends shock waves through and around the crust of a body, which reinforce on the opposite side, weakening the (antipodal) crust allowing the outflow of flood basalts. In the case of Luna, this makes it heavier on the side of the maria and contributes to the eventual tidal locking. Evidence: higher rough terrain and large impact craters on the far side, smoother, darker terrain eon the near side with some flooded old craters.

This sequence appears to have happened on earth. Bear in mind that continents float around slowly and were not always where they are now. The Permian extinction 251 million years ago may have been triggered by an impact on Wilkes Land (see Wikipedia article Wilkes Land crater /masscon anomaly) which unleashed the Siberian Traps flood basalt. The Cretaceous-Terciary extinction may have been triggered by the Chicxulub impact unleashing the Deccan Traps flood basalt 65 million years ago. This theory was advanced by Frese et al. In a paper in 2009.

[Chris Peterson]

You have to wonder why the Moon's far side is so different from its near side. Does it have anything to do with the fact that the Moon is tidally locked, and always shows the same face to the Earth?

Then again, the Earth itself also looks very different in different places.We don't often think of the Earth the way it looks in the picture below, do we?

The ocean hemisphere of the Earth. Credit: DK IMAGES/SCIENCE PHOTO LIBRARY

---

Ann

[ Premise 1 - crustal rocks are lighter than deeper rocks such as flood basalts.
Premise 2 - a tide locked body has the heavier side toward the planet ]

Let me advance a sequence of events:
A major impact event sends shock waves through and around the crust of a body, which reinforce on the opposite side, weakening the (antipodal) crust allowing the outflow of flood basalts. In the case of Luna, this makes it heavier on the side of the maria and contributes to the eventual tidal locking. Evidence: higher rough terrain and large impact craters on the far side, smoother, darker terrain eon the near side with some flooded old craters.

This sequence appears to have happened on earth. Bear in mind that continents float around slowly and were not always where they are now. The Permian extinction 251 million years ago may have been triggered by an impact on Wilkes Land (see Wikipedia article Wilkes Land crater /masscon anomaly) which unleashed the Siberian Traps flood basalt. The Cretaceous-Terciary extinction may have been triggered by the Chicxulub impact unleashing the Deccan Traps flood basalt 65 million years ago. This theory was advanced by Frese et al. In a paper in 2009.

Christian G above has identified the most widely accepted theory right now, that the temperature difference between the Earth side and the far side resulted in different crust composition and thickness, and that the thinner crust on the Earth side allowed for much more resurfacing from magma outflows.

The Deccan Traps began forming before the Chicxulub impact, so definitely weren't caused by them. It has been suggested that the period of flood basalts was extended by the impact, but most Earth scientists who work in this area consider that unlikely.

[Roy]

K-T boundary dating has been recalibrated to 66.1 million years ago. Earliest Deccan Trapps dating is 66.2 million years ago. Difference is well within the Ar39/Ar40 0.65% margin of dating error. (0.15% by my Casio).

[Roy]

The Moon clearly shows us its best side! Its "softer" side too, which the early Earth kept warm… (while the other side was left in the cold, forced to grow a thicker crust)

The moon rotates - currently once a month. The far side gets the same amount of sun as the near side. 4.5 billion years ago, when the earth may have been warm enough to heat the moon, it would Have been in closer orbit and rotating faster. Crust thickening would not have been different, unless there were a means of letting out the interior flood basalts. Impact shock waves would do it. Then there would be rough terrain and craters on one side and smooth heavy areas on the other. Then the heavy side could tide-lock to the planet.

[AVAO]

Then again, the Earth itself also looks very different in different places.We don't often think of the Earth the way it looks in the picture below, do we

Ann

Well, I think the natives of Polynesia were sure they lived on a water planet.

Click to view full size image

source: google earth

By the way, I like coincidences because they are so random...

Planet Earth: land area 149,430,000 km²
Planet Mars: land area 144,798,000 km²
Difference: 3%

[Chris Peterson]

K-T boundary dating has been recalibrated to 66.1 million years ago. Earliest Deccan Trapps dating is 66.2 million years ago. Difference is well within the Ar39/Ar40 0.65% margin of dating error. (0.15% by my Casio).

Nope.

[Chris Peterson]

The Moon clearly shows us its best side! Its "softer" side too, which the early Earth kept warm… (while the other side was left in the cold, forced to grow a thicker crust)

The moon rotates - currently once a month. The far side gets the same amount of sun as the near side. 4.5 billion years ago, when the earth may have been warm enough to heat the moon, it would Have been in closer orbit and rotating faster. Crust thickening would not have been different, unless there were a means of letting out the interior flood basalts. Impact shock waves would do it. Then there would be rough terrain and craters on one side and smooth heavy areas on the other. Then the heavy side could tide-lock to the planet.

The Moon was tidally locked very early on. And as you say, closer. Even now the Earth side of the Moon is significantly warmer than the far side.

[Ann]

The Moon clearly shows us its best side! Its "softer" side too, which the early Earth kept warm… (while the other side was left in the cold, forced to grow a thicker crust)

The moon rotates - currently once a month. The far side gets the same amount of sun as the near side. 4.5 billion years ago, when the earth may have been warm enough to heat the moon, it would Have been in closer orbit and rotating faster. Crust thickening would not have been different, unless there were a means of letting out the interior flood basalts. Impact shock waves would do it. Then there would be rough terrain and craters on one side and smooth heavy areas on the other. Then the heavy side could tide-lock to the planet.

The Moon was tidally locked very early on. And as you say, closer. Even now the Earth side of the Moon is significantly warmer than the far side.

I asked Gogole how close the Moon was originally, adn got the answer that it used to be seventeen times closer than it its today. That is, the Moon was originally some 22,500 kilometers (14,000 miles) from the Earth, versus some 380,000 kilometers (250,000 miles) today.

If the Earth was also considerably hotter than today when the Earth-Moon binary planet was in its infancy (and it was), then the near side of the tidally locked Moon must have been very much hotter than the far side.

Ann

[johnnydeep]

The moon rotates - currently once a month. The far side gets the same amount of sun as the near side. 4.5 billion years ago, when the earth may have been warm enough to heat the moon, it would Have been in closer orbit and rotating faster. Crust thickening would not have been different, unless there were a means of letting out the interior flood basalts. Impact shock waves would do it. Then there would be rough terrain and craters on one side and smooth heavy areas on the other. Then the heavy side could tide-lock to the planet.

The Moon was tidally locked very early on. And as you say, closer. Even now the Earth side of the Moon is significantly warmer than the far side.

I asked Gogole how close the Moon was originally, adn got the answer that it used to be seventeen times closer than it its today. That is, the Moon was originally some 22,500 kilometers (14,000 miles) from the Earth, versus some 380,000 kilometers (250,000 miles) today.

If the Earth was also considerably hotter than today when the Earth-Moon binary planet was in its infancy (and it was), then the near side of the tidally locked Moon must have been very much hotter than the far side.

Ann

Not sure of the physics of this. The magma covered Earth would have been 1500 degrees C or so. Would the Moon even at a mere 1.8 Earth diameters away receive much radiative heat from it? Would any atmosphere on the Earth serve as insulation? But of course, the Moon itself was a molten ball of magma early in its history as well: how long would it take to cool done on its own?

[Chris Peterson]

The Moon was tidally locked very early on. And as you say, closer. Even now the Earth side of the Moon is significantly warmer than the far side.

I asked Gogole how close the Moon was originally, adn got the answer that it used to be seventeen times closer than it its today. That is, the Moon was originally some 22,500 kilometers (14,000 miles) from the Earth, versus some 380,000 kilometers (250,000 miles) today.

If the Earth was also considerably hotter than today when the Earth-Moon binary planet was in its infancy (and it was), then the near side of the tidally locked Moon must have been very much hotter than the far side.

Ann

Not sure of the physics of this. The magma covered Earth would have been 1500 degrees C or so. Would the Moon even at a mere 1.8 Earth diameters away receive much radiative heat from it? Would any atmosphere on the Earth serve as insulation? But of course, the Moon itself was a molten ball of magma early in its history as well: how long would it take to cool done on its own?

When the Moon became tidally locked, the Earth surface was still about 2500°C, and the Moon was 10-20 times closer than it is today. At that time, the Moon had an atmosphere of vaporized heavy elements (basically, rock vapor). The cooler side away from the Earth would have had material condense sooner, producing a thicker crust. Thick enough that there were fewer flood basalt events following meteor impacts, and maybe fewer from tectonic activity.

[johnnydeep]

I asked Gogole how close the Moon was originally, adn got the answer that it used to be seventeen times closer than it its today. That is, the Moon was originally some 22,500 kilometers (14,000 miles) from the Earth, versus some 380,000 kilometers (250,000 miles) today.

If the Earth was also considerably hotter than today when the Earth-Moon binary planet was in its infancy (and it was), then the near side of the tidally locked Moon must have been very much hotter than the far side.

Ann

Not sure of the physics of this. The magma covered Earth would have been 1500 degrees C or so. Would the Moon even at a mere 1.8 Earth diameters away receive much radiative heat from it? Would any atmosphere on the Earth serve as insulation? But of course, the Moon itself was a molten ball of magma early in its history as well: how long would it take to cool done on its own?

When the Moon became tidally locked, the Earth surface was still about 2500°C, and the Moon was 10-20 times closer than it is today. At that time, the Moon had an atmosphere of vaporized heavy elements (basically, rock vapor). The cooler side away from the Earth would have had material condense sooner, producing a thicker crust. Thick enough that there were fewer flood basalt events following meteor impacts, and maybe fewer from tectonic activity.

So does that mean that the the still very warm Earth could have heated the near side of the Moon significantly, or not?

[Chris Peterson]

Not sure of the physics of this. The magma covered Earth would have been 1500 degrees C or so. Would the Moon even at a mere 1.8 Earth diameters away receive much radiative heat from it? Would any atmosphere on the Earth serve as insulation? But of course, the Moon itself was a molten ball of magma early in its history as well: how long would it take to cool done on its own?

When the Moon became tidally locked, the Earth surface was still about 2500°C, and the Moon was 10-20 times closer than it is today. At that time, the Moon had an atmosphere of vaporized heavy elements (basically, rock vapor). The cooler side away from the Earth would have had material condense sooner, producing a thicker crust. Thick enough that there were fewer flood basalt events following meteor impacts, and maybe fewer from tectonic activity.

So does that mean that the the still very warm Earth could have heated the near side of the Moon significantly, or not?

Absolutely. And really, just a few degrees would probably be enough. Even today the side of the Moon facing the Earth is a few degrees warmer than the side facing away, from the radiant heat received from the Earth.

[johnnydeep]

When the Moon became tidally locked, the Earth surface was still about 2500°C, and the Moon was 10-20 times closer than it is today. At that time, the Moon had an atmosphere of vaporized heavy elements (basically, rock vapor). The cooler side away from the Earth would have had material condense sooner, producing a thicker crust. Thick enough that there were fewer flood basalt events following meteor impacts, and maybe fewer from tectonic activity.

So does that mean that the the still very warm Earth could have heated the near side of the Moon significantly, or not?

Absolutely. And really, just a few degrees would probably be enough. Even today the side of the Moon facing the Earth is a few degrees warmer than the side facing away, from the radiant heat received from the Earth.

Wow, that's hard to believe!

[Chris Peterson]

So does that mean that the the still very warm Earth could have heated the near side of the Moon significantly, or not?

Absolutely. And really, just a few degrees would probably be enough. Even today the side of the Moon facing the Earth is a few degrees warmer than the side facing away, from the radiant heat received from the Earth.

Wow, that's hard to believe!

Well, you have this big area of sky, almost 2° across, at more than 300K, radiating down against a background of just a few K.

FWIW, the Earth is measurably heated by the Moon, as well. A few hundredths of a degree near the equator, to as much as a half degree near the poles.