Do more impact craters always signify old age of a surface?

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Discussion Overview

The discussion revolves around the relationship between the number of impact craters on celestial bodies and the age of their surfaces, particularly focusing on the Moon, Mars, and icy moons like Callisto and Ganymede. Participants explore how atmospheric conditions and geological processes affect the preservation of craters and the implications for determining surface age.

Discussion Character

  • Debate/contested
  • Conceptual clarification
  • Exploratory

Main Points Raised

  • Some participants argue that surfaces with more impact craters are generally older, citing examples from the Moon and Mars, particularly the Noachian period on Mars.
  • Others challenge the inclusion of the Moon in discussions about weathering and erosion, noting that its lack of atmosphere means lunar craters remain pristine compared to those on Mars.
  • There is a suggestion that the presence of an atmosphere on Mars contributes to the erosion of craters, making them less pristine than lunar craters.
  • Some participants question whether it is possible to determine the age of icy bodies like Callisto and Ganymede, which lack substantial atmospheres, due to potential erosion processes that are not well understood.
  • A participant mentions that solar radiation can induce sublimation on cometary nuclei, which may also apply to icy moons, suggesting that erosion could occur despite the absence of a substantial atmosphere.
  • There is a discussion about the effects of solar activity on surface processes, particularly in relation to the interpretation of impact craters on Venus.

Areas of Agreement / Disagreement

Participants express disagreement regarding the inclusion of the Moon in discussions about crater preservation and surface age. There is no consensus on whether the number of craters can reliably indicate the age of surfaces on icy bodies or how atmospheric conditions influence this relationship.

Contextual Notes

Participants note that the discussion involves uncertainties regarding the effects of solar radiation and cryo-processes on icy bodies, as well as the complexities of interpreting impact craters on different celestial bodies.

Phys12
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TL;DR
TL;DNR In icy moons, wouldn't you not be able to tell the age because of lack of a substantial atmosphere?
I've learned that the surfaces of places like the moon and the surfaces on Mars corresponding to the Noachian period signify relatively old surfaces because weathering and erosion tend to make those cratered surfaces smooth. However, I heard a professor mention that this is also true for icy bodies like Callisto and Ganymede that do not have a substantial atmosphere. Why is that the case? If these bodies are mostly icy without a substantial atmosphere to cause erosion/weathering, then wouldn't it be the case that you could never tell whether a surface is old or young?
 
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Phys12 said:
Summary:: TL;DNR In icy moons, wouldn't you not be able to tell the age because of lack of a substantial atmosphere?

I've learned that the surfaces of places like the moon and the surfaces on Mars corresponding to the Noachian period signify relatively old surfaces because weathering and erosion tend to make those cratered surfaces smooth.

Not sure why you incorrectly included the moon in there ?
It has no atmosphere and therefore no weathering /erosion. Lunar craters are as pristine today as they were when formed
other than damage to them caused by newer impacts.
Mars, on the other hand, does have an atmosphere ( tho very thin) and maybe more of one during the impact time and the years to follow.

Earth has severe erosion and loss of craters because of wind driven dust, rain/other water and tectonic activity.
One of the youngest craters on Earth is Meteor Crater in Arizona, USA at ~ 50,000 years bp.

just some thoughts :smile: Dave
 
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davenn said:
Not sure why you incorrectly included the moon in there ?
It has no atmosphere and therefore no weathering /erosion. Lunar craters are as pristine today as they were when formed
other than damage to them caused by newer impacts.
Mars, on the other hand, does have an atmosphere ( tho very thin) and maybe more of one during the impact time and the years to follow.
Well, those examples were for surfaces that are very old, so the inclusion of moon should be correct. I mentioned the surfaces of Mars that correspond to the Noachian period, which I do believe are old. While Mars does have atmosphere that make the surfaces that correspond to the Hesperian and the Amazonian period young, not all the surface on Mars is young. Correct me if I am wrong
 
Phys12 said:
Well, those examples were for surfaces that are very old, so the inclusion of moon should be correct. I mentioned the surfaces of Mars that correspond to the Noachian period, which I do believe are old. While Mars does have atmosphere that make the surfaces that correspond to the Hesperian and the Amazonian period young, not all the surface on Mars is young. Correct me if I am wrong

Your logic is flawed for the reason I gave earlier, read it again. The Moon shouldn't be included there because of the lack of any erosion unlike the other places mentioned. This results in non-smoothed craters. Under your logic, you should have included the earth, Mercury and Venus as well :wink:

Dave
 
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davenn said:
Your logic is flawed for the reason I gave earlier, read it again. The Moon shouldn't be included there because of the lack of any erosion unlike the other places mentioned.
So you're saying that even the oldest craters on Mars are have suffered from enough erosion/weathering that they are not as pristine as the craters on the moon?
 
I think you mean newest.

One picture is the Martian crater Sciaperelli and the other is the lunar crater Clavius. Don't they look different? Isn't it obvious which is which?

1591758484132.png


1591758512947.png
 
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Phys12 said:
So you're saying that even the oldest craters on Mars are have suffered from enough erosion/weathering that they are not as pristine as the craters on the moon?

Yes, exactly, for a start, Mars has major dust storms that has completely obliterated many craters
 
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Vanadium 50 said:
I think you mean newest.
Ah, yes, you're right, I do mean newest
 
And what about my original question?
 
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davenn said:
Not sure why you incorrectly included the moon in there ?
It has no atmosphere and therefore no weathering /erosion. Lunar craters are as pristine today as they were when formed
other than damage to them caused by newer impacts.
Mars, on the other hand, does have an atmosphere ( tho very thin) and maybe more of one during the impact time and the years to follow.
I guess my initial phrasing of the statement was confusing. I should've mentioned that the heavily cratered parts of a celestial body correspond to older surfaces than compared to parts that are relatively smooth. So the Maria on the moon are younger than the highlands and the surfaces corresponding to the noachian period on Mars are older than the ones corresponding to the Hesperian/Amazonian period. If that's true then you would never be able to tell the age of a surface by looking at the amount of cratering on an icy body which is far away from the sun to not have weathering/erosion due to an atmosphere/solar wind
 
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This is uncertain, IIRC, as there are slow cryo-processes which are not well understood. Also, you do have 'solar' effects, even out on the edge of the 'deep and dark'. During solar minima, much more galactic radiation gets through. Else-when, solar mega-flares, Carrington-grade events, may brush them. Given the weak average solar flux, a little extra energy may make a lot of difference...

I suppose, for the inner system, there's Venus, much of surface apparently renewed by a cataclysmic 'overturn' rather than Earth's sedate spreading-ridge/subduction plate tectonics. But, IIRC, interpreting old Venusian impact craters is complicated by uncertainties about how much such over-turn(s) contributed to current mega-nasty atmosphere. And, are any/all 'coronae' blast-marks from 'air-bursts' ??
 
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Phys12 said:
I heard a professor mention that this is also true for icy bodies like Callisto and Ganymede that do not have a substantial atmosphere. Why is that the case? If these bodies are mostly icy without a substantial atmosphere to cause erosion/weathering, then wouldn't it be the case that you could never tell whether a surface is old or young?
In the case of cometary nuclei, solar radiation induced sublimation causes significant erosion of the surface over time. In the case of Jupiter family comets (JFC), which have periods of less than 20 years and have aphelia between 5 and 6 AU (Jupiter is 5.5 AU), sublimation is quite pronounced in the few cases of direct observation of JFC nuclei.

Of course, comets on the order of a km radius are much smaller than moons and it is believed that effects of sublimation are more pronounced on smaller bodies, however it may be worth investigating whether similar processes are at work on satellites. A brief google says it might be https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2007GL032618
 
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