APOD: Lunar Farside (2011 Apr 09)

[APOD Robot]

Lunar Farside

Explanation: Tidally locked in synchronous rotation, the Moon always presents its familiar nearside to denizens of planet Earth. From lunar orbit, the Moon's farside can become familiar, though. In fact this sharp picture, a mosaic from the Lunar Reconnaissance Orbiter's wide angle camera, is centered on the lunar farside. Part of a global mosaic of over 15,000 images acquired between November 2009 and February 2011, the highest resolution version shows features at a scale of 100 meters per pixel. Surprisingly, the rough and battered surface of the farside looks very different from the nearside covered with smooth dark lunar maria. The likely explanation is that the farside crust is thicker, making it harder for molten material from the interior to flow to the surface and form the smooth maria.

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[dbail]

It would seem that since the same side of the moon faces the earth it would be much less likely for something to hit the near side. Wouldn't the gravity of the earth reduce the chance of something hitting after trying to pass through the gravity well of the earth? From the other side there should be an assist in attracting objects toward the tidally locked moon.

[bystander]

APOD: Lunar Nearside (2011 Mar 03)
http://asterisk.apod.com/viewtopic.php?f=9&t=23063
http://asterisk.apod.com/viewtopic.php? ... 41#p144741

[stowaway]

I had always figured there were more impacts on the lunar farside because if anything "out there" was being drawn toward Earth (or even heading towards the Sun), it would have a chance of hitting the Moon first. Is that too simple?

[Chris Peterson]

It would seem that since the same side of the moon faces the earth it would be much less likely for something to hit the near side. Wouldn't the gravity of the earth reduce the chance of something hitting after trying to pass through the gravity well of the earth? From the other side there should be an assist in attracting objects toward the tidally locked moon.

The Earth provides almost no shadowing effect (it is very small in the Moon's sky), and what little shadowing it does provide is approximately offset by gravitational focusing. From the other side, the slight perturbation a meteoroid might experience from Earth's gravitational field is just as likely to deviate a body away from the Moon as towards it.

All the evidence points towards both sides having the same sort of impact history, just different geology (which is probably related to the tidal locking).

[yasgur]

Tidal locking could account for a thicker crust on the farside? That must be an interesting mechanic.

[cpjh]

Sitting back in a chair and looking at the picture there seems to be two lines of craters. One starts above the dark patch (mare?) upper left and proceeds to to the lower right.
The other starts in the large crater below the mare and also proceeds to the lower right. I am being fanciful, just dreaming or seeing things that are not really there? Is such a line of impacts possible given the impact that occurred on Jupiter a few years ago?

[jerryki]

Why do the craters on the left side of the photo look like normal craters (depressions) ant the craters on the right side look like mounds?
Zoom in and you will see what I mean.

[inertnet]

Why do the craters on the left side of the photo look like normal craters (depressions) ant the craters on the right side look like mounds?
Zoom in and you will see what I mean.

I guess it's because the left half of the image is composed of images of the moon when it was illuminated from the left side, and the right half of the image was illuminated from the right. It looks very odd indeed.

[geckzilla]

Why do the craters on the left side of the photo look like normal craters (depressions) ant the craters on the right side look like mounds?
Zoom in and you will see what I mean.

Speaking of zooming, mounds, and craters, you should try this out:
http://www.moonzoo.org/

I still see mounds even though I know they are craters. I can't get mounds out of my head. Also, it is nearly impossible to tell what zoom level you are looking at the moon except when it is very close or very far. Looking at satellite images of craters confuses our human brains.

[neufer]

It would seem that since the same side of the moon faces the earth it would be much less likely for something to hit the near side. Wouldn't the gravity of the earth reduce the chance of something hitting after trying to pass through the gravity well of the earth? From the other side there should be an assist in attracting objects toward the tidally locked moon.

The Earth provides almost no shadowing effect (it is very small in the Moon's sky), and what little shadowing it does provide is approximately offset by gravitational focusing. From the other side, the slight perturbation a meteoroid might experience from Earth's gravitational field is just as likely to deviate a body away from the Moon as towards it.

All the evidence points towards both sides having the same sort of impact history, just different geology (which is probably related to the tidal locking).

I disagree somewhat on the specifics.

Chris is always having to remind us that an optical lens can't focus an extended source, e.g. a galaxy, to make it brighter.

Likewise, the Earth can't focus an extended source, e.g. incoming asteroids & comets, to make it into a more intense source.

In any event, whatever complicated dynamics are involving vis-a-vis the Earth/Moon system such dynamics are magnified enormously in the case of the giant planets and THEIR synchronous moons. And, so far as I know, no one has pointed out a nearside/farside asymmetry involving cratering in those particular situations. (The only clear asymmetries seem to involve leading & trailing faces, e.g. Iapetus.)

[neufer]

Tidal locking could account for a thicker crust on the farside? That must be an interesting mechanic.

A thicker crust on any given hemisphere could easily result in a tidal locking of that hemisphere to be the farside.

[Magellan Starswarm]

Seems odd to refer to it as the "farside" rather than the "darkside" of the moon a la Pink Floyd's 1972 masterpiece. "Farside" relates to the hilarious Gary Larsen comic strip in my twisted mind. I'm reminded of the cartoon where the astronomer sitting at the telescope has a soot black eye and a baffled expression as a gaggle of co-workers snicker and elbow one another.

[dbplatt]

Why do the craters on the left side of the photo look like normal craters (depressions) ant the craters on the right side look like mounds?
Zoom in and you will see what I mean.

I noticed that too, only that the left side look like mounds to me, and the right side like normal craters. At first I thought the obvious dividing line down the middle of the picture was causing this illusion. But when I zoomed in again, I started to notice the shadows in the craters in the left side was on the left side of the craters, and the shadows in the craters on the right side were on the right side. I think that causes the illusion of mounds vs craters.

[owlice]

Seems odd to refer to it as the "farside" rather than the "darkside" of the moon a la Pink Floyd's 1972 masterpiece.

Darkside refers to the half of the moon that is not illuminated by the sun, not to the farside.

[neufer]

Seems odd to refer to it as the "farside" rather than the "darkside" of the moon a la Pink Floyd's 1972 masterpiece.

Darkside refers to the half of the moon that is not illuminated by the sun, not to the farside.

Farside refers to the half of the moon that is not illuminated by the Earth.

[Chris Peterson]

Chris is always having to remind us that an optical lens can't focus an extended source, e.g. a galaxy, to make it brighter.

That is not true, and I haven't said that. What I've said is that a telescope, which is an afocal optical device, cannot produce an image on the retina any brighter than the source. An objective lens certainly increases the brightness of an image, proportional to its area.

Likewise, the Earth can't focus an extended source, e.g. incoming asteroids & comets, to make it into a more intense source.

In essence, it can. Certainly, there is a cylinder of space extending from the Moon, through the Earth, and out into space, from which incoming objects can be focused by the Earth into the Moon, effectively making a more "intense" source. What complicates things is that there are impactors on paths not parallel to this cylinder, and some which would have missed will hit because of gravitational perturbation, but others that would have hit will now miss.

[Beyond]

My impression of todays picture of the moon is that it looks like a golf ball with weird dimples.
If a golf ball manufacturer were to make an exact copy of the 'dimples' on a golf ball, i wonder how it would fly when hit??

[Star*Hopper]

Is it just me, or does anyone else see a huge 'X' across the face?
And not as broad or prominent, but a vertical line as well, making it into an asterisk?

Makes me think of a carpenter marking the scrap part of lumber before he saws it.
Ya reckon maybe this side always is turned away from us for a reason?!?

~S*H

[NoelC]

I wonder about the tense of the wording in the APOD text...

"The likely explanation is that the farside crust is thicker, making it harder for molten material from the interior to flow to the surface and form the smooth maria."

Note that this is written in the present tense.

Surely we aren't expected to believe there is activity with molten material going on today?

-Noel

[owlice]

Click to play embedded YouTube video.

[bystander]

Is it just me, or does anyone else see a huge 'X' across the face?
And not as broad or prominent, but a vertical line as well, making it into an asterisk?

Ahh, you have discovered our logo, not yet complete. It's a part of our awareness program to generate interest
in the forum. Once it's complete, we plan to turn the Moon around so that what was the farside is facing Earth.

[NoelC]

But wouldn't it be better just to move the Earth over to the other side? I mean, we already have the rocket motors here on the ground...

-Noel

[Emily Windsor-Cragg]

The FACT that no hues are applied, that scale is all stretched out past the boundaries of depth perception MEANS THIS PHOTO'S processing was never completed so anybody could see anything.

But what else is new? NASA doesn't expect to see anything, so they don't.

[orin stepanek]

Is it just me, or does anyone else see a huge 'X' across the face?
And not as broad or prominent, but a vertical line as well, making it into an asterisk?

Ahh, you have discovered our logo, not yet complete. It's a part of our awareness program to generate interest
in the forum. Once it's complete, we plan to turn the Moon around so that what was the far side is facing Earth.

I never noticed the X until it was pointed out! Than, I noticed the arrow; made by the crater chain; that points to the X.

Click to view full size image