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Thread: A Near Miss for a Mars-sized Impactor?

  1. #1
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    A Near Miss for a Mars-sized Impactor?

    The author finishes a paper harbored for a long time with geological arguments for the creation of the Colorado Plateau by a grazing incidence impact from a ~ Mars-Sized rogue planet about 750 million years ago. Not the creation of the moon scenario, which was earlier, but a shallow strike. Years of geological surveying, and work produce a new argument. As always, there will be other points of view. Interesting. SEE:https://arxiv.org/pdf/1711.03099.pdf


    pete

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    Quote Originally Posted by trinitree88 View Post
    The author finishes a paper harbored for a long time with geological arguments for the creation of the Colorado Plateau by a grazing incidence impact from a ~ Mars-Sized rogue planet about 750 million years ago. Not the creation of the moon scenario, which was earlier, but a shallow strike. Years of geological surveying, and work produce a new argument. As always, there will be other points of view. Interesting. SEE:https://arxiv.org/pdf/1711.03099.pdf
    There doesn't seem to be any mention of use of the Roche limit, which would probably break this rogue object apart at several million miles from Earth. Wouldn't that have an impact on this idea? (bad pun, ok.)
    We know time flies, we just can't see its wings.

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    Quote Originally Posted by George View Post
    There doesn't seem to be any mention of use of the Roche limit, which would probably break this rogue object apart at several million miles from Earth. Wouldn't that have an impact on this idea? (bad pun, ok.)
    George. Good point. Would depend on the incoming impactor's rigidity, too....but the diagram enclosed should probably be a prolate spheroid at the least, and perhaps a rubble pile. But at 25 km/sec, the given velocity, much of it would skip back out to space. Should be a stratigraphic record created not just locally, too.
    P.S. I'm not doing the simulations. Leave that as a homework question for the readers! pete

    good pun
    Last edited by trinitree88; 2020-Jan-03 at 06:39 PM. Reason: clarify

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    Also, it would take quite awhile for Earth's gravity to destroy a Mars sized object. It would have been inside the Roche Limit for at most a few hours. Not enough time for it to be destroyed.

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    Zhang is an astrophysicist by trade, so it seems likely she has taken the Roche limit into account.

    ETA: The Roche limit lies about 1.5 Earth radii from the surface of the Earth, depending on the density of the impactor. Call it 10000km. At a velocity of 25km/s (from the paper) that's seven minutes from Roche limit to impact. The geometry of a grazing impact will make that a little farther and a little longer, but the spherical cow suggests there's not enough time for something Mars-sized to deform appreciably.

    Grant Hutchison
    Last edited by grant hutchison; 2020-Jan-04 at 02:10 AM.

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    This point of view was mentioned in an Air/Space Magazine article in 2015 by someone else.

    https://www.airspacemag.com/daily-pl...car-180956994/

    Could the Colorado Plateau Be an Ancient Impact Scar?
    Conjectures on a road trip across the American West
    By Paul D. Spudis, airspacemag.com, October 19, 2015

    QUOTE: "When I took a course in meteorites years ago, Carleton Moore (then Director of the Center for Meteorite Studies at Arizona State University) once mentioned the Colorado Plateau and asked (hypothetically) how long the Earth might “remember” such an a enormous impact scar. This off-hand remark remained with me for many years and was lit anew during my sojourn. There may be a feature on the Moon analogous to the Plateau. Most large lunar impact craters look remarkably similar to each other—deep cavities with raised rims, features that gradually erode with time as other craters form on top of them. In some cases, however, the interiors of craters are uplifted, either as a single plate or with a slight doming action, stretching and deforming the crater floor with cracks and faults. Sometimes, lava is erupted from these cracks. These features are called “floor-fractured craters” and were first recognized and discussed by my colleague Peter Schultz in 1976.

    "Floor-fractured craters on the Moon may result from the injection of magma beneath the crater floor and subsequent uplift and cracking. Gassendi (right) is an example of such a process. (Peter H. Schultz)

    "Schultz proposed that magma (liquid rock) had been injected beneath the floor of these craters and the floor (made up of an impact melt sheet and associated breccias) was uplifted as a plate. Unable to support its own weight, the floor had fractured in consequence.

    "Could the Colorado Plateau be a terrestrial floor-fractured impact crater? Admittedly, this is a fairly outrageous idea. The Plateau is much larger across (375 miles, or ~600 km) than typical floor-fractured craters on the Moon (30-60 miles, or 50-100 km). The Plateau has been dissected through erosion by running water, which obscures surface features, but extensional faults predominate (as it does in floor-fractured craters). There is evidence for considerable post-Plateau volcanism (basalt lava flows) in several areas and even evidence for the intrusion of significant volumes of magma, deforming the overlying, flat sedimentary deposits (e.g., the Henry Mountains of Utah). There is no rock evidence for the presence of a large, 600 km-diameter impact basin (e.g., shock metamorphic features in mineral grains or impact melts), but such evidence might exist far below the surface of the Earth. This impact (if real) would have occurred billions of years ago, in the Precambrian, where the rock record is spotty and poorly exposed.
    Do good work. —Virgil Ivan "Gus" Grissom

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    Astrobites article revealing a little background on Ms. Zhang and her work.

    https://astrobites.org/2018/03/07/a-...ths-geography/

    Author’s note: "The discussion in this astrobite was written from the point of view that the hypothesis in the paper is correct – which of course remains to be seen by future studies."

    "Science requires collaboration, and often that collaboration leads to projects that span across different fields of science. This paper caught my eye mainly because the Colorado Plateau is one of my favorite places to travel, and though I’m not a geologist, its unique and beautiful rock formations have always piqued my interest. As I read this paper, I was surprised to find that this author also was not a geologist by trade. Xiaolei Zhang is an astrophysicist, but decided to carry on her late father’s unfinished project to uncover the formation of the Colorado Plateau and the possibility of giant-impact-plate tectonic motion."
    Do good work. —Virgil Ivan "Gus" Grissom

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    Quote Originally Posted by grant hutchison View Post
    ETA: The Roche limit lies about 1.5 Earth radii from the surface of the Earth, depending on the density of the impactor. Call it 10000km. At a velocity of 25km/s (from the paper) that's seven minutes from Roche limit to impact. The geometry of a grazing impact will make that a little farther and a little longer, but the spherical cow suggests there's not enough time for something Mars-sized to deform appreciably.
    Yep, I muffed it. I used the traditional terms for volume (km^3) and density (kg/m^3) but failed to convert the latter to kg/km^3, so my secondary mass was off by a billion. Ug. Your result is now what I calculate.

    [Added: I meant to also say that a much lower density, say that of a comet, would only bump it to~ 2.5 Earth radii.]
    Last edited by George; 2020-Jan-08 at 07:01 PM.
    We know time flies, we just can't see its wings.

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