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Polar Spacecraft Images Support Theory of Comets Spraying Earth's Upper Atmosphere

Douglas Isbell
Headquarters, Washington, DC                     May 28, 1997
(Phone: 202/358-1753)

William A. Steigerwald
Goddard Space Flight Center, Greenbelt, MD
(Phone: 301/286-8955)

RELEASE:  97-112

POLAR SPACECRAFT IMAGES SUPPORT THEORY OF INTERPLANETARY 
SNOWBALLS SPRAYING EARTH'S UPPER ATMOSPHERE

     Images from NASA's Polar spacecraft provide new evidence 
that Earth's upper atmosphere is being sprayed by a steady 
stream of water-bearing objects comparable to small comets.  

     Using Polar's Visible Imaging System (VIS), a research 
team led by Dr. Louis A. Frank of the University of Iowa in 
Iowa City has detected objects that streak toward Earth, 
disintegrate at high altitudes and deposit large clouds of 
water vapor in the upper atmosphere.  Frank's research is being 
reported in a news briefing at 10 a.m. today at the spring 
meeting of the American Geophysical Union at the Convention 
Center in Baltimore, MD.

     The incoming objects, which Frank estimates to be the size 
of a small house, pose no threat to people on Earth, nor to 
astronauts in orbit. "They break up and are destroyed at 600 to 
15,000 miles above the Earth," Frank noted.  "In fact, this 
relatively gentle 'cosmic rain' -- which possibly contains 
simple organic compounds -- may well have nurtured the 
development of life on our planet."

     "This is an intriguing result that requires further scientific
investigation," said Dr. George Withbroe, science director for the Sun-Earth 
Connection program in NASA's Office of Space Science.  "We need 
to look closely at measurements from other sensors to find out 
if they see related signatures in the atmosphere, now that we 
have learned more about what to look for."

     The Polar cameras have imaged trails of light in both 
ultraviolet and visible wavelengths as the objects disintegrate 
above the atmosphere.  Using a filter that detects visible 
light emitted only by fragments of water molecules, Frank has 
shown that the objects consist primarily of water.

    "The Polar results definitely demonstrate that there are 
objects entering the Earth's upper atmosphere that contain a 
lot of water," commented Dr. Thomas M. Donahue, a noted 
atmospheric physicist and professor at the University of 
Michigan in Ann Arbor.

     "The images show that we have a large population of 
objects in the Earth's vicinity that have not been detected 
before," said Frank, who designed the VIS instrument.  "We 
detect these objects at a rate that suggest Earth is being 
bombarded by five to 30 small comets per minute, or thousands 
per day."  Comets are known to contain frozen water and are 
sometimes called "dirty snowballs".

     Frank's new observations are consistent with a 
controversial theory he proposed in 1986 to explain the 
existence of dark spots, which he termed "atmospheric holes", 
in images of the sunlit atmosphere of the Earth.  He first 
detected these holes while analyzing data from an ultraviolet 
imager flown on NASA's Dynamics Explorer 1 spacecraft.  He 
theorized that the holes were caused by the disintegration of 
small icy comets in the upper atmosphere.  The water vapor they 
produce momentarily absorbs the ultraviolet solar radiation 
scattered from oxygen atoms in the upper atmosphere, preventing 
it from reaching his camera and resulting in a dark spot on the 
image.  These holes have diameters of 15 to 25 miles.

     His theory of a new class of objects in the Solar System 
ignited a wide-ranging controversy.  Many colleagues discounted 
the appearance of the holes as an instrumental problem.  But 
the new images from Polar also include observations of 
atmospheric holes in much greater detail than before, 
suggesting that they are real.  "These results certainly 
vindicate Lou Frank's earlier observations", said Donahue.

     "These remarkable images cap a great first year for 
Polar," added Dr. Robert Hoffman, Project Scientist for Polar, 
which is operated and managed by NASA's Goddard Space Flight 
Center, Greenbelt, MD.  "I am pleased that Polar's instruments 
were able to actually detect these objects streaking towards 
the Earth and disintegrating into clouds of water vapor.  They 
give scientists a fascinating new and important phenomenon to 
take into account in theories of Solar System evolution."

     Images of the comets and the atmospheric holes can be 
found on the World Wide Web at the following URL: 

   http://pao.gsfc.nasa.gov/gsfc/newsroom/flash/flash.htm

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