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EMBARGOED UNTIL: 2:00 PM EDT April 19, 1995

PHOTO RELEASE NO.: STScI-PRC95-21A

HUBBLE'S VIEW OF NEPTUNE

These NASA Hubble Space Telescope views of the blue-green planet
Neptune provide three snapshots of changing weather conditions. The
images were taken in 1994 on October 10 (upper left), October 18 (upper
right), and November 2 (lower center), when Neptune was 2.8 billion
miles (4.5 billion kilometers) from Earth.

Hubble is allowing astronomers to study Neptune's dynamic atmosphere
with a level of detail not possible since the 1989 flyby of the Voyager
2 space probe. Building on Voyager's initial discoveries, Hubble is
revealing that Neptune has a remarkably dynamic atmosphere that changes
over just a few days.

The temperature difference between Neptune's strong internal heat
source and its frigid cloud tops (-260 degrees Fahrenheit) might
trigger instabilities in the atmosphere that drive these large-scale
weather changes. In addition to hydrogen and helium, the main
constituents, Neptune's atmosphere is composed of methane and
hydrocarbons, like ethane and acetylene.

The picture was reconstructed from a series of Wide Field Planetary
Camera 2 images taken through different colored filters at visible and
near-infrared wavelengths. Absorption of red light by methane in
Neptune's atmosphere contributes to the planet's distinctive aqua
color; the clouds themselves are also somewhat blue. The pink features
are high-altitude methane ice crystal clouds. Though the clouds appear
white in visible light, they are tinted pink here because they were
imaged at near infrared wavelengths.

The farthest of the gas giant planets, Neptune is four times Earth's
diameter. Though Neptune was discovered in 1846, very little has been
known about it until the advent of space travel and advanced
telescopes.

Credit: H. Hammel (Massachusetts Institute of Technology) and NASA