[X] My Assistant

[CosmicRocker]

Ok, I give up. I just read Emily's blog entry regarding the MER presentations. I don't know how she does it, because I wasn't able to take notes from these guys with as much detail as she has captured in her blog. She captured most everything I was going to post from Steve's and Matt's presentations, and more, and in pretty much their words, and while attending more sessions than I was able to attend! Everyone interested in the rovers really needs to read her notes. I think it's been obvious for a while, but Emily's blog has become _the_ blog to read for the latest summary of planetary news.

I was really sorry I could not stay to listen to Knauth's presentation. I could see the tension building up toward that in several of the previous presentations. It sounds as if I missed one of the most interesting confrontations of the entire conference. Although I was not able to stay for Knauth's presentation, my notes from Grotzinger's presentation contained several side comments to myself regarding how efficiently he blew away the basal surge hypothesis. I'm trying to keep an open mind, but I too must side with the MER team for now.

[Jyril]

It would have been a ground based image (going on his response)

Doug

If it was really a picture of halley, it must have been from 1910 given that it was the date of Halley's previous visit.

[Bob Shaw]

Interesting about "the atmosphere that was." I hadn't heard about that.

Yes - I posted it verbatim because the journalistic flim-flam was as dense as the putative ancient atmosphere! It beats me why NS at times published interesting snippets surrounded by mushy statements (yeah, right, Earth's atmospheric pressure is 1 bar, hey, news!). Perhaps the idea is to feed into the newspapers as a bit of publicity...

...anyway, I really didn't want to summarise an already over-summarised piece!

Bob Shaw

[Guest_BruceMoomaw_*]

Yep, it was a ground-based 1910 Halley photo.

I was really sorry I could not stay to listen to Knauth's presentation. I could see the tension building up toward that in several of the previous presentations. It sounds as if I missed one of the most interesting confrontations of the entire conference. Although I was not able to stay for Knauth's presentation, my notes from Grotzinger's presentation contained several side comments to myself regarding how efficiently he blew away the basal surge hypothesis. I'm trying to keep an open mind, but I too must side with the MER team for now.

Grotzinger's central argument against basal surge is nicely summed up in his abstract ( http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2254.pdf ): "A further clue to the likely subaqueous origin
for Eagle cross-laminae is provided by their festoon geometry which requires that the reconstructed ripples have three-dimensional geometry defined by highly sinuous crestlines. In terrestrial settings such bedforms are known only to develop in subaqueous, subcritical flows, with velocities of less than one meter per second. They are not known to develop in eolian deposits or in subaerial base surge deposits." The italics are his.

[elakdawalla]

Yep, it was a ground-based 1910 Halley photo.
Grotzinger's central argument against basal surge is nicely summed up in his abstract ( http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2254.pdf ): "A further clue to the likely subaqueous origin
for Eagle cross-laminae is provided by their festoon geometry which requires that the reconstructed ripples have three-dimensional geometry defined by highly sinuous crestlines. In terrestrial settings such bedforms are known only to develop in subaqueous, subcritical flows, with velocities of less than one meter per second. They are not known to develop in eolian deposits or in subaerial base surge deposits." The italics are his.

Knauth did show festoon structures that he said were the result of, I think, volcanic surge deposits. One of Grotzinger's (many) objections to his talk was that the scales of these things were an order of magnitude or so larger than the MArs ones. Knauth claimed in response that there are descriptions in the literature of smaller festoon structures in surge deposits but that they are not accompanied by pictures, and that he is working on obtaining pictures.

Sounds like a debate that won't die anytime soon.

--Emily

Ok, I give up. I just read Emily's blog entry regarding the MER presentations. I don't know how she does it, because I wasn't able to take notes from these guys with as much detail as she has captured in her blog. She captured most everything I was going to post from Steve's and Matt's presentations, and more, and in pretty much their words, and while attending more sessions than I was able to attend!

I type fast. Still, I'm sure you attended others of the MER talks -- I only got to go to those two and the Knauth one; I'd be delighted to see any notes you have from talks I didn't catch.

--Emily

[odave]

I second what CR said - you're doing a great job on your blog, Emily. Thanks for all of your hard work!

[Guest_BruceMoomaw_*]

Oh, yes.

I've got some comments on the LPSC abstracts related to the debate over basal surge, but I think I'll put them in a new topic in the "MER" section. (We're getting awfully snarled up, subject-wise, in a lot of the threads on this website -- thanks in large measure, admittedly, to me).

[nprev]

In the absence of a dedicated LPSC thread, there's an interesting article in today's New Scientist (18 March 2006, p10):

A two page spread describes a rewriting of Mars geological time, with a new period - the Pre-Noachian - inferred from MOLA data indicating a new population of ancient large-scale cratering events which have been hidden beneath later impacts. "The early impact rate was quite a lot higher than we expected" according to Herb Frey of GSFC. The article also describes a turnaround in interpretations of crater rates in more modern eras, with most small craters now being seen as secondaries from a few larger events. One of the upshots of this is a suggested three-fold reduction in cratering rates in the last three billion years as compared to previous models.

And:

"The atmosphere that was

The atmosphere of Mars, which is so thin that on Earth it would be considered a hard vacuum, was once as thick or thicker than Earth's. At least that's the accepted theory, based on the abunndant evidence of river valleys on Mars's surface, suggesting that it must once have had air thick enough to support evaporation and rainfall. However, the idea has remained controversial.

Now a study of meteorites lends further support to the theory. John Bridges and Ian Wright of the Planetary and Space Sciences Research Institute at the Open University in Milton Keynes, UK, have found that the proportion of carbonates in some of the 32 known Mars meteorites found on earth suggest that the atmosphere originally contained carbon dioxide at pressures somewhere between 2.3 and 2.6 bars, compared with roughly 1 bar at sea level on Earth today.

The meteorites also reveal that by 670 million years ago the atmospheric pressure had come down to about 50 to 100 millibars and then fell further to today's level, which varies from virtually zero to 30 millibars depending on variations in the shape of Mars's orbit. Bridges and Wright presented the work at the lunar and Planetary sciences Conference in Houston, Texas."
Bob Shaw

Wow. If accurate, then Mars had an atmosphere capable of sustaining liquid surface water until 670 my ago. Soft-bodied macrofauna had evolved on Earth by that time...

Have any Martian regions been identified with an age near this point? If so, we could do worse than to look at strata from this period for fossils.

[Guest_AlexBlackwell_*]

Wow. If accurate, then Mars had an atmosphere capable of sustaining liquid surface water until 670 my ago. Soft-bodied macrofauna had evolved on Earth by that time...

Have any Martian regions been identified with an age near this point? If so, we could do worse than to look at strata from this period for fossils.

The only "age" information comes from stratigraphic relationships, which are obscured by, among other things, depositional and exhumation events. And the chronostratigraphic systems themselves have variability depending on the authros. Aside from that, the error bars in these systems are huge; in fact, huge enough that I would suspect a 670 Myr point (or thereabouts) would not be temporally resolvable, though I guess it all depends on one's definition of "near this point." Obviously, what is needed is absolutely dating of martian samples, either in situ or returned.

The upshot is that I'd be highly skeptical of anyone pointing to a spot on Mars and saying it is 670 million years old, even if they added "plus or minus 50 million years."

[tty]

The only "age" information comes from stratigraphic relationships, which are obscured by, among other things, depositional and exhumation events. And the chronostratigraphic systems themselves have variability depending on the authros. Aside from that, the error bars in these systems are huge; in fact, huge enough that I would suspect a 670 Myr point (or thereabouts) would not be temporally resolvable, though I guess it all depends on one's definition of "near this point." Obviously, what is needed is absolutely dating of martian samples, either in situ or returned.

The upshot is that I'd be highly skeptical of anyone pointing to a spot on Mars and saying it is 670 million years old, even if they added "plus or minus 50 million years."

Wasn't that figure based on martian meteorites, for which we do have good absolute age determinations?

tty

[Phil Stooke]

"Wasn't that figure based on martian meteorites, for which we do have good absolute age determinations?"

- tty


We do have good dates for the martian meteorites... but we don't know which specific geologic units they came from. So they are no help in dating specific events in martian history. Only sample return from known locations or in situ dating (if that is ever possible) will allow that, and we will need dates from a lot of places to really tie down the history.

I know some suggestions have been made about which units - or at least regions - the meteorites come from, but nothing is firmly established.

Phil

[tty]

We do have good dates for the martian meteorites... but we don't know which specific geologic units they came from. So they are no help in dating specific events in martian history. Only sample return from known locations or in situ dating (if that is ever possible) will allow that, and we will need dates from a lot of places to really tie down the history.

I know some suggestions have been made about which units - or at least regions - the meteorites come from, but nothing is firmly established.

Phil

That date is presumably derived from the age of iddingsite in the Lafayette Nakhlite. As iddingsite is a mineral formed by water it does show that liquid water was present somewhere on Mars 670 MA ago.

tty

[Guest_AlexBlackwell_*]

Richard Kerr's LPSC coverage is in the March 31, 2006, issue of Science.