Discussion in 'General Science & Technology' started by Bowser, Sep 24, 2000.

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  1. Bowser Namaste Valued Senior Member

    Bill Steigerwald Embargoed for Sept. 21, 2000
    Goddard Space Flight Center, Greenbelt, Md. 2:00 p.m. EDT

    Release No. 00-118


    The Eros asteroid could have witnessed the formation of the Earth,
    according to a preliminary analysis of its surface composition using
    NASA's Near Earth Asteroid Rendezvous (NEAR) spacecraft. Analysis of
    solar X-rays from Eros' surface indicate that it has a composition
    similar to the chondrite meteorites found on Earth, which are
    believed to be primordial agglomerations of dust grains from the
    nebula that became the Sun and planets.

    "It looks like Eros is one of the most ancient rocks in the solar
    system, according to the initial data from NEAR," said Dr. Jacob
    Trombka, NEAR X-ray Gamma-Ray Spectrometer (XGRS) Science Team
    Leader at NASA's Goddard Space Flight Center, Greenbelt, Md.
    "Exploring Eros will help us understand how the rocky planets like
    Earth formed, so we can learn more about how we came to be."

    The result will be published in the September 22 issue of the journal
    Science, as part of a special edition describing the latest results
    from the NEAR-Shoemaker mission.

    X-rays from the Sun strike Eros' surface and cause elements to
    fluoresce (to be stimulated, then glow) in specific X-ray "colors,"
    invisible to the human eye but detectable by XGRS. This is similar to
    the way a black light uses ultraviolet light to make pop-art posters
    glow in various garish colors. Each element on Eros glows in unique
    X-ray colors, allowing XGRS to build a map of the element
    distribution at and just beneath the surface of Eros.

    Discovering the composition of Eros is the key to unlocking the
    mystery of its origin. When a forming planet reaches a certain size,
    its heat and gravity become sufficient to cause differentiation of
    its elements - the planet becomes molten, and heavy elements, like
    nickel and iron, tend to sink to the center, while light elements,
    like silicon and carbon, rise to the surface. If Eros was composed
    mostly of light elements, this would indicate that it was a fragment
    from near the surface of a larger body. If it was rich in heavy
    elements, it would likely have been from the center of a larger
    object. However, instead Eros appears to be undifferentiated, like
    the chondrite meteorites found on Earth, so it probably never was
    exposed to much heat. This implies that it is a very primitive,
    unprocessed object, probably an aggregate of smaller objects from the
    early solar system nebula.

    "The result is preliminary, because we have only mapped about 20
    percent of Eros' surface so far," said Trombka. "Also, the X-ray
    spectrometer only reveals composition right at the surface, in a
    layer about the thickness of a human hair. Bombardment by cosmic rays
    or micrometeorites could have altered the surface composition."

    "However, we made the same X-ray measurements of the Moon during the
    Apollo missions," added Trombka. "The Apollo astronauts took core
    samples, and the composition of the samples agreed with our surface
    map. This gives us confidence that our surface map of Eros reflects
    its true composition. Also, later in the mission, when NEAR makes its
    closest approach to Eros, our Gamma-ray spectrometer will reveal the
    composition down to about five inches beneath the surface. This will
    let us see if the composition right at the surface is the same as the

    The NEAR mission is managed for NASA's Office of Space by the Johns
    Hopkins University Applied Physics Laboratory (APL) in Laurel, Md.

    For images and more information, refer to:


    It's all very large.
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