Subscribe free to our newsletters via your
. 24/7 Space News .

Subscribe free to our newsletters via your


Gullies coming down the south-facing wall of a trough in the Sirenum Fossae/Gorgonum Chaos region of the martian southern hemisphere. Each channel and its associated fan--or apron--of debris appears to have started just below the same hard, resistant layer of bedrock located approximately 100 meters (about 325 feet) below the top of the trough wall. The layer beneath this hard, resistant bedrock is interpreted to be permeable, which allows ground water to percolate through it and--at the location of this trough--seep out onto the martian surface. The channels and aprons only occur on the south-facing slope of this valley created by faults on each side of the trough. The depression is approximately 1.4 km (0.9 mi) across. Image: NASA/JPL/Malin Space Science Systems. Caption: MSSS
The Case For Outgassing
by Bruce Moomaw
Cameron Park - July 5, 2000 - In my previous two articles, I discussed two theories attempting to explain the startling new Mars Global Surveyor photos showing what appears to be recent water runoff on the surface of Mars -- a planet whose air pressure has traditionally been regarded as too low to allow liquid water even to exist there for more than a few seconds -- and on parts of the planet so cold that ice should be nowhere near its melting point anyway.

These theories are very different -- one involves eruptions of liquid water from underground, the other the thawing of buildups of surface ice -- but they have one major thing in common: they both do agree that the gullies are indeed water-produced.

But there are at least one, and maybe two, serious alternate theories proposing that the gullies are not water-produced -- and one of them states that the "fluid" that created them isn't even liquid!

The first was described in some detail by Dr. Michael Carr of the U.S. Geological Survey at the press conference in which the discovery was first announced.

Carr is arguably the world's leading authority on the subject of water on Mars, but he is seriously skeptical about these gullies being water-produced for the two reasons given above.

He thinks there is a serious chance that the substance responsible is not subsurface water, but subsurface carbon dioxide.

It's been recognized for a long time that Mars' subsurface -- because the planet's temperatures are so much lower than Earth's -- almost certainly contains large amounts of stored CO2, in several different possible forms: as solid frozen "dry ice"; a "clathrate" mixture of CO2 incorporated into water ice; liquid CO2 (which can exist at pressures above 5 bars); and/or gaseous CO2 "adsorbed" by Mars' cold soil (that is, chemically stuck to its grains).

There is still a lot of debate about how much there is, but Jeffrey Kargel and Kenneth Tanaka have calculated that the total amount of CO2 outgassed by Mars' geothermal vents over its history "could form a global mean layer thickness of CO2 clathrate over 200 meters -- and possibly over 1300 meters -- thick, if all the CO2 is present in hydrate form."

In reality, a great deal of that amount must either have escaped from Mars completely over the eons due to its low gravity, or been converted into carbonate minerals. But that's still a lot of underground CO2.

Since there's also a good deal of subsurface water ice on Mars, most CO2 beneath the surface is probably mixed with it as a solid frozen "clathrate".

This substance can only exist under a fair amount of pressure -- equivalent to that found under about several meters of Martian soil and/or rock -- and it must be sealed off from even any small vents to the near-vacuum of Mars' surface. However, a layer of ordinary water-ice permafrost surrounding a body of clathrate can seal it off in this way.

According to Carr's theory, if such a body of clathrate is suddenly exposed to Mars' surface by a landslide on a slope, the CO2 will explode violently out of the clathrate as gas -- and the resultant powerful blast of gas could sweep a cloud of ice and rock fragments and soil down the slope, plowing a gully which could bear a surprisingly close visual resemblance to the narrow one produced by an eruption of fluid, rather than the broader trail left by an ordinary avalanche.

This kind of traveling cloud of "gas-suspended" debris occurs fairly often in volcanic eruptions, where it's known as a "nuee ardente" (burning cloud). One such cloud from Mount Pelee killed all but one of the 30,000 inhabitants of the downslope city of St. Pierre in 1902.

Carr's Martian version, needless to say, wouldn't be glowing ash and pebbles; it might be more accurately called a "refrigerated cloud". According to this theory, these eruptions would occur only on Mars' colder slopes simply because only they would be cold enough for permafrost, and an underlying layer of CO2 clathrate, to be close to the surface and thus likely to be exposed by landslides. (It should be kept in mind that these runoff gullies are quite rare on Mars.)

However, Carr told SpaceDaily that he still has considerable doubts about the feasibility of his tentative theory on the grounds of "kinetics". The key question being whether a Martian gas blast would be powerful enough to avoid immediately dissipating into the near-vacuum atmosphere of Mars to carry debris the distances being seen in the new images.

For this reason, a variant on this theory has been suggested by Dr. Kenneth Tanaka.

  • Click For Part Two

    Thanks for being here;
    We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

    With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

    Our news coverage takes time and effort to publish 365 days a year.

    If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.

    SpaceDaily Contributor
    $5 Billed Once

    credit card or paypal
    SpaceDaily Monthly Supporter
    $5 Billed Monthly

    paypal only

    Memory Foam Mattress Review
    Newsletters :: SpaceDaily :: SpaceWar :: TerraDaily :: Energy Daily
    XML Feeds :: Space News :: Earth News :: War News :: Solar Energy News

  • The content herein, unless otherwise known to be public domain, are Copyright 1995-2016 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. Privacy Statement All images and articles appearing on Space Media Network have been edited or digitally altered in some way. Any requests to remove copyright material will be acted upon in a timely and appropriate manner. Any attempt to extort money from Space Media Network will be ignored and reported to Australian Law Enforcement Agencies as a potential case of financial fraud involving the use of a telephonic carriage device or postal service.