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(meteorobs) FWD: Meteor Trails causing dark spots?
Sandia National Laboratories
Albuquerque, New Mexico
Media contact:
Howard Kercheval,
hckerch@sandiadot gov, (505) 844-7842
Technical contact:
Mark Boslough, mbboslo@sandiadot gov,
(505) 845-8851
News Release: February 10, 1998
Sandia scientist, colleague suggest meteor plumes causing transient dark
spots in upper atmosphere
ALBUQUERQUE, N.M. -- A Sandia National Laboratories physicist and
his Texas-based research colleague have done some calculations that
may offer additional insight into a decade-old astronomical controversy
about whether up to 30,000 house-sized snowballs, or icy comets, are
striking Earth each day.
That theory has been proffered by two space scientists Louis Frank and
John Sigwarth of the University of Iowa, based on observations by the
Dynamics Explorer-1 satellite of transient dark spots, or holes, in the
upper atmosphere's far-ultraviolet dayglow emission.
Such a tremendous influx of small comets has never been observed.
These water-bearing objects would add phenomenal quantities of water
to Earth. If this could indeed be shown to be happening, much of what is
known about comet creation and the origins of the oceans, terrestrial life,
and perhaps even of the solar system might need revision.
The interpretations have been met with much scientific skepticism, but
Frank and Sigwarth weighed in last May with more evidence --
observations by the NASA satellite Polar that they said provide new
support for the existence of the dark holes. A number of former critics
became converts.
Now, however, Sandia physicist Mark Boslough and Randy Gladstone of
the Southwest Research Institute in San Antonio, Tex., have published a
study that provides a less provocative -- but still scientifically
interesting -- explanation for the so-called atmospheric holes.
They may be plumes, not holes, and meteoroids may be the source.
Their computational simulations, which make use of Sandia's shock
physics code CTH and Boslough's earlier work with Sandia colleague
Dave Crawford in successfully predicting the visible plumes from Comet
Shoemaker-Levy 9's impact into Jupiter in 1994, suggest that the entry of
ordinary meteoroids can form dark spots very similar to those reportedly
observed by the satellite instruments.
Their study is published in the Dec. 15 Geophysical Research Letters,
along with four other studies by other scientists that together the journal
say provide "five independent tracks of evidence that are entirely
inconsistent with a huge bombardment by small comets." The journal
says the five studies together "refute this [the small comets] hypothesis."
Boslough and Gladstone reject the assumption, central to the small
comets hypothesis, that the observed darkening is caused by absorption
of water vapor above the atmosphere. Instead, they believe that atomic
oxygen, which is the source of the dayglow, is momentarily displaced by
the passage of meteoroids. Normal air from lower altitudes contains
oxygen in its molecular form and is black in the wavelength that the
satellite sees.
They propose that when a stony object as small as 50 centimeters across
collides with the atmosphere and plunges into the lower layers, it ejects a
very thin plume of this "black" air to as high as 1,000 kilometers. It is
these
dark plumes, they suggest, that are being detected by the satellites.
Their work is preliminary and they acknowledge that the hypothesis
doesn't account for the observed high rate of dark hole formation. But
they say if they can show their idea is correct for large meteoroids, they
will look into the possibility that small ones have a similar effect.
The two scientists also propose a test of their hypothesis. They say if
they
are right, it is just a matter of time before Department of Defense
satellites
detect an infrared flash from a large meteor that corresponds exactly to
the time and location of one of the holes.
"We expect that satellite data on atmospheric holes in the FUV [far
ultraviolet] will confirm the existence of [high-altitude] plumes that are
continuously being generated by meteors."
The four other new papers that also undermine the small comets
hypothesis are based on lack of any evidence for frequent comet
bombardment on the moon, no sign of the high abundance of noble
gases in the upper atmosphere that would be expected from a high rate
of comet bombardment, absence of visible light observations, and
evidence that the source of dark pixels in the Polar spacecraft's
ultraviolet camera is internal to the camera system.
Three of these papers are by scientists at the Lunar and Planetary
Laboratory at the University of Arizona, and one is by scientists at the
Universities of Alabama and Washington and NASA Marshall Space
Flight Center.
Frank and Sigwarth, however, still strongly stick to their small comets
hypothesis -- they particularly dispute that the dark spots are
instrumental
artifacts -- and the controversy is likely to continue for some time.
Sandia is a multiprogram DOE laboratory, operated by a subsidiary of
Lockheed Martin Corp. With main facilities in Albuquerque, N.M., and
Livermore, Calif., Sandia has major research and development
responsibilities in national defense, energy, environmental technologies
and economic competitiveness.
PHOTO CAPTION: [http://www.sandiadot gov/media/images/jpg/discover.jpg]
The Earth as seen by the UV imager on the Dynamics Explorer 1 satellite,
showing ultraviolet dayglow and auroral emissions. University of Iowa
researchers believe that the dark spots are water vapor from house-sized
comets, but Sandia scientists argue that they could be plumes ejected by
ordinary meteors. Other workers insist that they are simply an instrumental
artifact.
---
Andrew Yee
ayee@nova.astro.utorontodot ca