The atmosphere of a comet comes and goes . Approaching the sun , it swells as material from the icy cometary nucleus is warmed and evaporated by increasing sunlight. Oriented with the sunward direction toward the upper right, the picture is a composite of Hubble Space Telescope images recorded on April 3 and 4, 1996. The Hydrogen data, combined with other observations, indicate that this comet's nucleus, itself only a few km across, was producing about 7 to 8 tons of water per second.
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