Lunar crater and rille age comparison.... PLEASE HELP!

[bassmaster]

Hey,<br /><br />I'm doing an assignment for Earth and Space Sciences 12U and I'm just stumped at this question:<br /><br />"Consider the age of Herodotus and Schroter's Valley relative to surrounding features. Are they older or younger than Aristrachus? What is your evidence?"<br /><br />I'm quite confident that Aristarchus is younger than Herodotus and Schroter's Valley because Aristarchus is a rayed crater... and rayed craters have ejecta that are eventually removed (how?).<br /><br />But how can I prove that Schroter's Valley and Herodotus are older? I know Herodotus is a flat-surfaced crater, but isn't there a possibility that a flat-surfaced crater could be younger than a rayed crater? Or is this not possible?<br /><br />Wow, I'm just really confused. Somebody please help!

 

[MeteorWayne]

Generally, the best way to assess age is to look at the craters superimposed on the object. More craters=older.<br /><br />I'm not familiar with those specific ones, so that's all I can add at the moment.<br /><br />MW <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[bassmaster]

Unfortunately, we're dealing with individual craters here. Not an entire surface of craters. I'm trying to find the age of these individual craters... how can that be done? Are flat-surfaced craters ALWAYS older than craters with a central peak and terraces? And if so... why?

 

[MeteorWayne]

To my knowledge, flatness by itself is not an indicator of age, although it could be, I guess. Wait for one of our resident geologists to speak on that.<br /><br />In general, crater shape is indicative of impact object size and energy. Maybe google crater shape?<br /><br />Older Mare (Basins, rather than craters) are flat because when they were formed ( /> 4 billion years ago) the mantle was still molten and rose up and filled large areas.<br /><br />Older craters COULD be flatter if enough dust has filled the bowl, particularly one without a central peak, but the timescales are very long.<br /><br />I assume you have images of these craters?<br /><br />Examine them very carefully and see if there aren't tiny craters on the surface.<br /><br /><br /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[bassmaster]

The images on the assignment that was given to me are smudged up because of photocopying. Here is a good image of the three lunar features I'm concerned about. What can you tell me about them? I'm not an experienced crater observer so I can't tell if there are craters within each crater.<br /><br />Is there any obvious evidence, do you think, that Schroter's Valley is older than Aristarchus?<br /><br />

 

[MeteorWayne]

First of all, Aristarchus is a Plateu, which has numerous craters on it.<br /><br />See this APOD <br /><br />Edit, I stand corrected, it is the largest crater in the Plateau.<br /><br />My bad <img src="/images/icons/smile.gif" /><br /><br />The other crater is right next door, take a close look at the APOD image to see if it's there. <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[MeteorWayne]

Here is Schroter's Valley and Aristarchus together.<br /><br /> image <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[bassmaster]

No, but this assignment is referring to the Aristarchus crater. Look at the website you gave me. They talk about the Aristarchus crater being a separate entity. By the way, if this helps, the Aristarchus crater is approx. 450 million years old. Clearly, a VERY young crater, so I'm pretty sure it has to be younger than Herodotus and Schroter's Valley. However, this explanation won't cut it because my evidence of their age has to be based on their geologic formation.<br /><br />From what I know, flat-bottomed craters can be formed in two ways:<br /><br />1. In its early life, the crater could have been bowl-shaped. Over time, the material in the inner part of the crater's rim slumped due to gravity and the material evened out on the crater floor.<br /><br />2. The crater could have initially been a complex crater with terraces and a central peak. Cracks in the crater surface allow magma from the Moon's interior to seep up to the top and then the lava forms a pool. This pool of lava eventually hardens, creating a flat surface. <br /><br />The problem is... <b />I need to know which one of these applied to Herodotus </b>. Or is there any other way I can prove that Aristarchus is younger than Herodotus and Schroter's Valley? <br /><br />Your idea of looking at the amount of internal cratering seems good, it's just that I don't think Schroter's Valley - being a rille - will have any cratering...

 

[MeteorWayne]

Look, I have a philosophical problem in doing your homework for you. Others don't<br /><br />Look carefully at the APOD I linked above. Blow it up to 2X.<br /><br />All three features you mentioned are right there. Notice anything interesting about the relationship between Schroter's Valley and one of the craters???<br /><br />Think about it <img src="/images/icons/smile.gif" /> <br /><br />Edited to correct my misidentification of which crater was which <img src="/images/icons/frown.gif" /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[MeteorWayne]

I've been playing along with you, and the more I look at the APOD, the more obvious the answer is.<br /><br />Keep looking at the image till you can see it <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[bassmaster]

Before going on I would like to thank you for your help. And yes, I do want to figure this out for myself so just keep playing along <img src="/images/icons/smile.gif" />.<br /><br />Anyway, all I noticed is that Schroter's Valley is attached to the Herodotus crater. But what does that mean? Does that mean Schroter's Valley must have formed at the same time as Herodotus? Better yet, how can I even tell when Herodotus formed?

 

[MeteorWayne]

Well, since it follows the outline of the crater, which do you think came first?<br /><br />And notice anything on the surface of the crater? <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[bassmaster]

If it follows the outline of the crater, then I guess Herodotus came first? That isn't relevant to the question I'm being asked, though, is it?<br /><br />And I must be blind but I don't see anything on the surface. There's a partial lighter spot, however... but does this mean anything?

 

[MeteorWayne]

Where might that lighter area have come from? It there any along the edge of the valley?<br /><br />PS, I have no idea of the answer to your question, I'm just following the visual evidence <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[bassmaster]

The lighter area could have come from the lunar highlands, which existed before the maria! Right!<br /><br />Or wait... is that right?<br /><br />And does that mean that Herodotus formed when only the highlands existed on the moon?

 

[MeteorWayne]

Well, could the light material be a ray? <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[bobw]

I have had a good time lurking on this thread today. Found some more pictures!<br /><br />http://history.nasa.gov/ap15fj/photos/tt/as15-88-11980.jpg<br />http://history.nasa.gov/ap15fj/photos/tt/as15-88-12002.jpg<br />http://history.nasa.gov/ap15fj/photos/tt/as15-88-12005.jpg<br />http://lunar.gsfc.nasa.gov/images/gallery/2Craters_br-browse.jpg<br />http://www.hq.nasa.gov/alsj/a15/AS15-88-11980HR.jpg<br />http://www.hq.nasa.gov/alsj/a15/AS15-88-12005HR.jpg<br />http://www.hq.nasa.gov/alsj/a15/AS15-93-12601HR.jpg <div class="Discussion_UserSignature"> </div>

 

[bassmaster]

I highly doubt it... rays only form after meteor impact and eventually disappear (how?) over time. Rays are a result of ejecta/debris from the impact. Maybe the rays from Aristarchus fell into Herodotus because it was close by?<br /><br />But once again, how does this help in any way?

 

[MeteorWayne]

Follow the lines <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[MeteorWayne]

bobw, very interesting collection of images!!<br />Thanx VERY much. It's fascinating how different it looks under various perspectives and lighting conditions!!! <br /><br />I have chnaged part of my theory somewhat.<br /><br />BassMaster, trust me, I don't know the answer, but look at the images bobw provided, and the one I linked to. <br /><br />In the end, you are going to have to put the story together in your own mind. Believe it or not, that's the fun, and the education. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[bassmaster]

OH, I THINK I GET IT! So because the rays of Aristarchus ended up in Herodotus, then Aristarchus MUST have formed after Herodotus because if it were vice versa, then there would be no rays in Herodotus!<br /><br />Is that it?

 

[bobw]

The lightbulb comes on! Congratulations. <div class="Discussion_UserSignature"> </div>

 

[bassmaster]

Yeah, I took a look at the images and my conclusion is still the same that the rays of Aristarchus fell in Herodotus so Aristarchus must have formed after or this would not be possible.<br /><br />Do you agree?

 

[bobw]

It does really look different from Apollo than it does from earth. I thought the valley was connected to the crater when looking at the APOD picture. <div class="Discussion_UserSignature"> </div>

 

[bassmaster]

THANKS FOR YOUR HELP Meteor and Bob. I REALLY appreciate it!<br /><br />Umm... so Bob, are you sure my answer is correct now? <br />And wait, the valley isn't connected to Herodotus? So how do I explain that the valley and Herodotus formed around the same time?