Press Release Photos for May 28, 1997

(figure 1) Small Comets

This stunning nighttime image of the light emitted by the breakup of water molecules from a small comet was taken at 0410 UT on December 31, 1996. This image by the Low-Resolution Visible Camera on board the Polar spacecraft is composed of three consecutive snapshots of the event taken about six seconds apart. These intense glows are created at an altitude of less than 2,000 miles above Earth when sunlight illuminates the oxygen-hydrogen molecules formed after a comet's water molecules have been stripped of a hydrogen atom. A view of Earth at the time of the event has been superposed onto the image as there are no detectable emissions from Earth's nighttime atmosphere at the wavelength where these oxygen-hydrogen molecules glow.

(figure2) Small Comet Streak

A spectacular disruption of a small comet the size of a two-bedroom house took place 5,000 to 15,000 miles above the Atlantic Ocean at 2228 UT on September 26,1996. A view of Earth at the time of the event has been superposed onto the far-ultraviolet image as a frame of reference. This unusually bright and long-lived trail, which was captured by the Earth Camera aboard NASA's Polar spacecraft, ends over Germany. Images like this one show that there is a large population of objects in Earth's vicinity that have not been previously detected.

(figure 3) Polar Hole

An atmospheric hole appears as a cluster of pixels, or picture elements, in this global view of Earth far-ultraviolet dayglow, or sunlit atmosphere, taken by Polar at 0945:05 UT on April 6 1996. Previous images of atmospheric holes by the Dynamics Explorer spacecraft a decade ago largely showed the atmospheric holes in single pixels, leading critics to dismiss the phenomenon as an "instrumental artifact." These black spots in the image, or atmospheric holes, are caused by water vapor clouds from small comets disintegrating anywhere from 600 to 1,200 miles above Earth. These water clouds momentarily and locally absorb the Earth's dayglow as viewed from the Polar spacecraft. This dayglow, which is emitted by oxygen in our upper atmosphere, is light at ultraviolet wavelengths beyond the range of human eyes. A coastline map has been superposed on the image to better understand the position of the event.

(figure 4) Cat Eyes

A unintended swaying motion in the spacecraft's platform causes any physical object in Polar's line-of-sight to appear as "cat's eyes" or double in the images. These frames, taken on April 6, 1996, demonstrate the "double vision" effect on both a single star, Beta Chamaeleon (left), and a single atmospheric hole (right) produced by the disintegration of a small comet. Such images provide further evidence that atmospheric holes are not due to instrumental artifacts. The swaying motion in Polar's platform is caused by a misalignment of the center-of-gravity and spin axis of the spacecraft.

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