Planetary Science Research Discoveries

pdf version  PSRD-MarsChryse.pdf

FEATURE STORY
posted June 14, 2001

Outflow Channels May Make a Case for a Bygone Ocean on Mars
Written by Linda M.V. Martel
Hawai'i Institute of Geophysics and Planetology

MOLA for northern Mars

High-resolution elevation data from the Mars Orbiter Laser Altimeter (MOLA) onboard the Mars Global Surveyor (MGS) spacecraft have been analyzed recently in Chryse Planitia to test the hypothesis that large outflow channels emptied into an ocean in this region of Mars. Researchers Mihail (Misha) Ivanov (Vernadsky Institute of Geochemistry and Analytical Chemistry) and James Head (Brown University) collected quantitative MOLA information on channel patterns, continuity, and elevations where those patterns change or disappear into the northern lowlands. Their recently published report describes how the channels end, or become more subtle, at elevations very close to a previously mapped geologic contact interpreted by some to represent a shoreline of an ancient ocean. Ivanov and Head hypothesize that the change in channel topography is consistent with flow of water from a river into a submarine environment with possible deposition of sediments by density currents deep into the North Polar basin.

Reference: Ivanov, M. A. and J. W. Head, III (2001) 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, Journal of Geophysical Research,vol. 106, p. 3275-3295.
Chryse Planitia

Viking Lander 1 in Chryse Planitia Chryse Planitia, chosen in the mid-1970s for the landing site of Viking 1, is a relatively flat, low, broad plain just north of the Martian equator. Because many of the largest Martian outflow channels converge here, Chryse Planitia is an ideal setting to study channel patterns and depositional environments. More importantly, researchers have noticed that the distinctive textures and teardrop-shaped islands inside the channels change and disappear near the margins of Chryse Planitia. These changes have led some people to hypothesize that debris-laden rivers may have emptied their loads into a lake at Chryse Planitia or into an ocean that occupied the northern lowlands. The actual timing of this bygone ocean is unknown, but may be Hesperian to Early Amazonian.


What the MOLA Data Reveal

Ivanov and Head cite five main lines of evidence from MOLA data that support the hypothesis that large outflow channels emptied into an existing standing body of water in the northern lowlands of Mars in Hesperian-Early Amazonian times.


Relationship of the Chryse Channels with the Hypothesized Ocean

Try to picture the floods. The crashing, tumultuous torrents were large and dirty, carrying rocks, ice, and sediments through the channels. Debris-laden floodwaters scoured the landscape, cutting through the underlying rock, and when they spread out, where did the floodwaters go? Did the water merely sink underground? Did it fill the North Polar basin to make an ocean? Did it enter an existing ocean? We can only guess what happened.

We need more information on the actual volumes of water and sediments involved in the floods and the timing of the floods. Ivanov and Head refer to different estimates of channel volumes (from Michael Carr, Victor Baker and others) to try to give us a better picture. Carr's estimate of the water volume of a single large flood in a Martian outflow channel is 300,000 km3. This is enough water to flood the entire North American continent by 30 meters! It would take at least 46 of these floods to fill the Martian northern lowlands to the level of Contact 2. Other estimates suggest that each channel may have filled the North Polar basin in separate events, requiring significant water loss between floods and refilling to essentially the same level. Ivanov and Head favor the hypothesis that the channels flowed into a preexisting standing body of water whose margins were already near the level of Contact 2 and cite the striking similarity of elevations where the channels end and the proximity of these elevations to the mapped Contact 2.


Mars Ocean Still Being Debated

Whether or not Mars had large bodies of standing water remains an unanswered question and not all investigators support the notion of a vast northern ocean. Photogeologic mapping of the proposed shorelines by Michael Malin and Kenneth Edgett in 1999 using high resolution images of Mars taken with the Mars Orbiter Camera (MOC) showed no features they would attribute to the action of water in a coastal environment. Other researchers contend that ridge networks in the northern lowlands are indicative of tectonic processes related to the Tharsis volcanoes. Tectonic features in this area of Mars, however, are not inconsistent with the possible presence of an ocean. Earth's ocean basins are prime examples of tectonic features.

Confirming the presence of large bodies of standing water in Martian history will require a multifaceted approach. We'll need laser altimiters (MOLA) for topographic data, cameras for photogeologic mapping, infrared spectrometers (such as onboard 2001 Mars Odyssey) for mapping the distribution of minerals on the surface, gamma ray spectrometers (also on Odyssey) for mapping the surface distribution and abundance of chemical elements, as well as mineral and chemical studies of meteorites and rocks returned from Mars (to check for the presence of salts, for example.) If there were standing bodies of water on Mars billions of years ago they may have influenced the planet's atmosphere and climate, geology, environmental chemistry, and ultimately its capacity to support the emergence of life. These are the reasons why scientists, including Ivanov and Head, seek evidence of ancient oceans on Mars. The search may quench our collective thirst for knowledge about the Red Planet.


ADDITIONAL RESOURCES

Baker, V. R., R. G. Strom, V. C. Gulick, J. S. Kargel, G. Komatsu, and V. S. Kale (1991) Ancient Oceans, Ice Sheets and the Hydrological Cycle on Mars, Nature, vol. 352, p. 589-594.

Carr, M. H. (1996) Water on Mars, Oxford University Press, New York.

Head, J. W., III, H. Hiesinger, M. A. Ivanov, M. A. Kreslavsky, S. Pratt, and B. J. Thomson (1999) Possible Ancient Oceans on Mars: Evidence from Mars Orbiter Laser Altimeter Data, Science, vol. 286, p. 2134-2137.

Head, J. W., III, M. Kreslavsky, J. Hiesinger, M. Ivanov, S. Pratt, and M. Seibert (1998) Oceans in the Past History of Mars: Tests for Their Presence Using Mars Orbiter Laser Altimeter (MOLA) Data, Geophysical Research Letters, vol. 25, p. 4401-4404.

Ivanov, M. A. and J. W. Head, III (2001) 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, Journal of Geophysical Research,vol. 106, p. 3275-3295.

Malin, M. C. and K. S. Edgett (1999) Oceans or Seas in the Martian Northern Lowlands: High Resolution Imaging Tests of Proposed Coastlines, Geophysical Research Letters, vol.26, p. 3049-3052.

Mars Exobiology Strategy (report dated January 1995)

Mars Global Surveyor

2001 Mars Odyssey

MOLA (Mars Orbiter Laser Altimeter).

Parker, T. J., R. S. Saunders, and D. M. Schneeberger (1989) Transitional Morphology in West Deuteronilus Mensae, Mars: Implications for Modification of the Lowland/Upland Boundary, Icarus, vol. 82, p. 111-145.

Smith, D. E., and others (1999) The Global Topography of Mars and Implications for Surface Evolution, Science, vol. 284, p. 1495-1503.

Withers, P. and G. A. Neumann (2001) Enigmatic northern plains of Mars, Nature, vol. 410, p. 651. (University of Arizona press release.)



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