[X] My Assistant

[Guest_AlexBlackwell_*]

Perron et al. have a new paper ("Evidence for an ancient martian ocean in the topography of deformed shorelines") in the June 14, 2007, issue Nature. There is also an accompanying News and Views piece by Maria Zuber. See the Editor's Summary for a synopsis and links.

See also:

Mystery Solved: Mars Had Large Oceans
By Dave Mosher, Space.com
posted: 13 June 2007
01:00 pm ET

[Guest_AlexBlackwell_*]

See also the following EurekAlert releases:

Study supports notion that Mars once had ocean

Mars -- Red Planet once blue planet

New evidence points to oceans on Mars

[djellison]

Dr Parker...take a bow


Doug

[Guest_AlexBlackwell_*]

I, too, am glad to see the concept of a martian Oceanus Borealis gaining a pulse again. It had taken a battering over the years.

[tglotch]

I don't know...Perron's a really smart guy, but I find the northern ocean hard to buy. I mean, I've stood out in the field in several places that geologists *know* were ancient shorelines, and they're really hard to see! And that is standing right on top of them and looking at aircraft imagery. Its an awful lot harder on Mars, especially when you consider the ~4Gy of deposition and erosion that must have occurred since then.

oops...~2Gy sounds about right..thanks dvandorn...but thats still a lot of time.

[dvandorn]

Well, Tim, I know that they're a lot more recent than 2Gy old (the estimated age of the Martian shorelines, at least according to the article at Space.com), but the shorelines of southwest North America's great inland sea have always been pretty obvious to me when I have flown in to Phoenix from the midwest. I surely don't know any other explanation for the extended wall-like structures that separate higher, slightly hillier terrain from the lower, flatter desert floor.

Granted, those shorelines are much younger, and therefore are also a lot more discernible. But any theory that even approximately accounts for the Martian dichotomy has to be at least seriously considered, IMHO.

I also find the concept of the Tharsis deposition toppling the planet over to be attractive -- if the Tharsis bulge originated well away from the equator, over billions of years the whole planet would tend to shift to place the heaviest portion of the bulge much closer to the equator. I may not be a professional geologist or planetologist, but the theory feels truthful to me...

-the other Doug

[RichardLeis]

Any suggestions on how to quickly and succinctly explain why this work is more legitimate than the "puddle" paper? To the lay public, both may be equally as legitimate. My quick attempt was "The difference with this latest news is peer review, Nature, multiple well-regarded scientists and commentators, and no obvious and immediate flaws. Still may not be the truth, but the entire approach is different from the claim of puddles. Still exciting. Still must remain skeptical as research continues."

[remcook]

A funny sentence in the 'news and views' bit, related to a discussion in another thread:

"This objection is that a shoreline must follow a line of constant gravitational potential: the 'geoid' on Earth, the 'areoid' on Mars" hmmmmm
Interesting stuff this anyway!

[dvandorn]

Yes, any shoreline must follow the "areoid" because of how water collects on a planetary surface. This is a basic element of physics.

However, it is more than obvious that the "areoid" has changed over the past couple of gigayears. The Tharsis bulge was very likely emplaced *after* any such northern ocean had dried up, evaporated and/or been incorporated into underground reservoirs. This impressive pile of volcanics reshaped the very planet -- and rebalanced it, too. For example, the great canyons of Valles Marineris were formed as rifting occurred, due to the reaction of the crust to the immense amount of lava that was poured out onto the Tharsis region. The building of the Tharsis bulge is what likely caused mars to topple on its side, to place a majority of the mass now newly distributed onto the surface as close to the equator as possible.

That kind of activity, occurring over a billion years or more, would naturally crumple the crust up in some places and tear it apart in others. It is no more reasonable to expect that the areoid is the same now as it was when conditions allowed for oceans on Mars than it is to expect that the mountaintops in the Himalayas were always uplifted to the top of Earth's sensible atmosphere. Since there are fossils of seabed creatures in the rocks at the tops of those mountains, we know for a fact that those rocks once lay under an ocean. To say that there cannot be ocean-floor rocks at the top of Himalayas because the geoid doesn't allow it is just as spurious an argument as to claim that shorelines can't exist on Mars along its dichotomy boundary because the current areoid doesn't indicate them.

-the other Doug

[remcook]

I was referring to the naming of the 'areoid' vs. geoid, see: http://www.unmannedspaceflight.com/index.p...3868&st=300

[dvandorn]

Ah, gotcha...

Well, it was worthwhile to debunk the "objection" you cited, anyway...

-the other Doug

[MahFL]

Oceans = fish = land animals.......

[centsworth_II]

Oceans = fish = land animals.......

There's a whole lot that has to happen
before the fish stage of your scenario.

[centsworth_II]

I was referring to the naming of the 'areoid' vs. geoid...

I'm with Phil Stooke on this (if I understand his position). Geo-, referring to
land, is perfectly -- and simply -- used for descriptions of land and its features,
no matter what planet it is found on.

[Guest_AlexBlackwell_*]

I don't know...Perron's a really smart guy, but I find the northern ocean hard to buy.

I've closely followed Oceanus Borealis in the literature ever since Tim Parker published his first paper and really thought the data would confirm it. The initial MGS MOLA data (ca. 1998; published in Geophysical Research Letters) looked promising for Contact 2. After that, though, things went downhill. Carr and Head [2003] revived things a bit with a nice paper in JGR-Planets; see "Oceans on Mars: An assessment of the observational evidence and possible fate" (2.2 Mb PDF reprint).

In any event, I read the Perron et al. paper and found it really interesting. It does address one of the major obstacles about the current configuration and long wavelength structure of the putative contacts. Now if someone can write a similarly convincing paper explaining the lack of shoreline features in the hires imagery, then I'll be on the way to becoming a True Believer again.

[ngunn]

I too have a long term interest in this question, but frustratingly cannot access the full text of Perron et.al. I am trying to find a good detailed map of the putative shorelines (not just a global image). Alex (or anyone) do you have a link to such a map, perhaps from earlier in this long running debate?

On a separate question - I have been wondering whether these oceans retreated due to evaporation from the liquid state or whether, rather, they might have frozen first then sublimed. In the latter case of course vertical warping of the shorelines could have occurred with some of the (frozen) ocean still in place. This would presumably alter the dynamics of the situation and would also create a time gap between when the shorelines formed and the crater-count age of the plains surfaces. Is this scenario discussed anywhere in the literature?

[dvandorn]

There is also a question as to whether shorelines might have been altered due to glaciation effects. Any liquid ocean did probably end its life as a frozen-over body of water, which could have induced glaciation effects, especially around the fringes (which happen to be the shorelines).

We shouldn't necessarily expect that ancient Martian shorelines will resemble ancient Terrestrial analogues.

-the other Doug

[Guest_AlexBlackwell_*]

The initial MGS MOLA data (ca. 1998; published in Geophysical Research Letters) looked promising for Contact 2.

This is the paper I was referring to.

[Guest_AlexBlackwell_*]

I've closely followed Oceanus Borealis in the literature ever since Tim Parker published his first paper...

For those who are interested, below are some (but certainly not all) of the key references in the Oceanus Borealis, Mars issue. I haven't bothered with LPSC or other similar conference presentations.

Transitional morphology in the west Deuteronilus Mensae region of Mars: Implications for modification of the lowland/upland boundary
Parker, T. J., R. S. Saunders, and D. M. Schneeberger,
Icarus 82, 111–145, (1989).

Coastal geomorphology of the Martian northern plains
Parker, T. J., D. S. Gorsline, R. S. Saunders, D. Pieri, and D. M. Schneeberger
J. Geophys. Res. 98, 11,061–11,078, (1993).

Oceans or seas in the Martian northern lowlands: High resolution imaging tests of proposed shorelines
Malin, M. C., and K. S. Edgett,
Geophys. Res. Lett. 26, 3049–3052, (1999).
Reprint (2.9 Mb PDF)

Oceans in the past history of Mars: Tests for their presence using Mars Orbiter Laser Altimeter (MOLA) data
Head, J. W., M. A. Kreslavsky, H. Hiesinger, M. A. Ivanov, S. Pratt, N. Seibert, D. E. Smith, and M. T. Zuber
Geophys. Res. Lett. 25, 4401-4404, (1998).
Abstract

Possible ancient oceans on Mars: Evidence from Mars Orbiter Laser Altimeter data
Head, J. W., H. Hiesinger, M. A. Ivanov, M. A. Kreslavsky, S. Pratt, and B. J. Thomson
Science 286, 2134– 2137, (1999).
Full text
Press release

The evolution of the Martian hydrosphere: Implications for the fate of a primordial ocean and the current state of the northern plains
Clifford, S. M., and Parker, T. J.
Icarus 154: 40-79, (2001).
Abstract

Chryse Planitia, Mars: Topographic configuration, outflow channel continuity and sequence, and tests for hypothesized ancient bodies of water using Mars Orbiter Laser Altimeter (MOLA) data
Ivanov, M. A. and J. W. Head, III
J. Geophys. Res. 106, 3275-3295, (2001).
Reprint (6.5 Mb PDF)

Enigmatic ridges on the plains of Mars
Withers, P. and G.A. Neumann
Nature 410, 652, (2001).
Reprint available (scroll to bottom of page)

Outflow Channels May Make a Case for a Bygone Ocean on Mars
by Linda M. V. Martel
PSRD Release (June 14, 2001)

Oceans on Mars: An assessment of the observational evidence and possible fate
Carr, M. H., and J. W. Head
J. Geophys. Res. 108 (E5), 5042, (2003).
doi:10.1029/2002JE001963
Reprint (2.15 Mb PDF)

Ancient Floodwaters and Seas on Mars
by Linda M. V. Martel
PSRD Release (July 16, 2003)

[stevesliva]

Thank you, Alex. Most especially for the PSR articles.

[ngunn]

Thanks Alex - excellent stuff there.