[X] My Assistant

[fredk]

My, that's one big, jagged, gaping hole:

[glennwsmith]

Centsworth, thanks for digging up Fram! They DO seem remarkably similar, with perhaps the difference being age. So if Concepcion is 1K years old, how old is Fram? 10K? 100K?

And way cool to see Endurance in the background! Seems like a lifetime ago that we rolled to its edge.

[john_s]

I'm having trouble with these very young ages. Meridiani Planum is lightly cratered by Martian standards but it still has enough craters that I'd be surprised if the age of the surface we see was less than 100 million years, say. If that's the case, only one crater in 100 should be less than a million years old, and only one crater in 100,000 should be less than a thousand years old. As we've passed far fewer than 100,000 craters of Concepción's size (maybe more like 100?), the odds of it being so young seem very slim.

All these numbers are WAGs but I doubt that they are wrong by a factor of 1,000...

John

[ElkGroveDan]

As we've passed far fewer than 100,000 craters of Concepción's size (maybe more like 100?)

Craters of what age? If every impact over the history of Meridiani is the range of our sample then I'd say we've passed a whole lot more than a 100. How many "Scamanders" have we passed and not observed? I don't dispute your methodology or reasoning John but I do believe that we simply don't have enough data points or a truly thorough study and analysis. I accept that the global cratering rates and ranges are applicable on a body like the moon where erosion is essentially non-existent. With Mars in general and with Meridiani specifically, we must acknowledge however that erosion and mass-wasting ARE occurring and that the rates over a planetary time scale are far from static. Further we still have no real solid understanding of the regional variations in erosion and deposition on Mars. Evidence of impacts would erode far faster in a body of water than across a wind swept plain. Was Meridiani a long lived sea? Was that sea static or subject to eddies and currents? Or was it nothing more than a temporary swamp? I've seen some truly inspiring science and studies of Martian geomorphology over the past decade that propose intriguing answers to some of these questions, but we honestly have to admit that there are still so many unanswered questions in a region like Meridiani. I don't feel that it's possible to even estimate the absolute age of a crater like this.

I am however just an armchair observer and you are a respected professional who does this for a living so no disrespect is intended.

[john_s]

Craters of what age? If every impact over the history of Meridiani is the range of our sample then I'd say we've passed a whole lot more than a 100.

No disrespect taken! Still, I *think* my point holds. Note that my WAG age for the *surface* was 100 million years. The rocks of Meridiani are likely to be three billion years old or more, 30 times older, so if you counted every crater since the rocks formed, there would be ~30 times as many as my estimate- most of them have indeed eroded away.

Thanks to HiRISE, we do have a handle on the current rate of formation of small craters on Mars, so someone ought to be able to estimate the chance that a crater of this size would have formed in the last few thousand years on the few square kilometers that Oppy has explored...

John

[Tom Tamlyn]

>Thanks to HiRISE, we do have a handle on the current rate of formation of small craters on Mars

I thought that this understanding was based on multiple MOC observations of substantially identical targets. I think I recall Malin or Edget discussing this in the hastily-scheduled (and very moving) press conference after MGS was lost. Or has HiRISE taken the understanding substantially further?

TTT

[john_s]

I thought that this understanding was based on multiple MOC observations of substantially identical targets. I think I recall Malin or Edget discussing this in the hastily-scheduled (and very moving) press conference after MGS was lost. Or has HiRISE taken the understanding substantially further?

TTT

My apologies to MOC- yes, this was done first by MOC.

John

[mcaplinger]

My apologies to MOC- yes, this was done first by MOC.

And continued by CTX far more than by HiRISE.