— Computer-processed images of Pluto taken by the Hubble Space
Telescope show that it is not simply a ball of ice and rock, but a
dynamic world that undergoes dramatic atmospheric changes produced by
its seasons, NASA said Thursday.
The images show an icy and dark molasses-colored
world that is highly mottled and whose northern hemisphere is now
getting brighter.
The images show that the body — once considered the
ninth and most distant planet but now reduced to the status of dwarf
planet — also turned noticeably redder in the two years after the turn
of the millennium for reasons that are not clear, and that its equator
features a large bright spot whose origin remains a mystery.
“Around the solar system, the only things whose surfaces change by a notable amount are Earth and Mars,” said astronomer
The new images will play a key role in targeting the
The probe will pass the planet so quickly that it
will be able to image only one hemisphere at a limited number of sites.
“These (images) have been used already to help plan the encounter,”
said astronomer
More than 350 images of Pluto were taken by Hubble
in 2002 and 2003. But the object is so distant that its image in each
of the pictures is only a few pixels across. To get better resolution,
Buie cobbled together a network of 20 homemade computers that churned
continuously for four years to produce the (relatively) high-resolution
pictures. Working on a limited budget, Buie was able to build the
computers for about
“This must be one of the cheapest supercomputers you
will ever encounter,” he said at a news briefing for the National
Aeronautics and Space Administration.
The images, he said, “are comparable to what you
might see by looking at the moon with the naked eye. You can’t see
craters and geology, but it is the first step in understanding.”
Pluto is in a highly eccentric orbit whose year
lasts 248 Earth years. It reached its closest approach to the sun in
1989, becoming warm enough to begin melting its nitrogen and carbon
monoxide ice, but still remaining a frigid -396 to -378 degrees
Fahrenheit.
Comparison of the new images to those taken by
Hubble in 1994 show that its atmosphere doubled during the period.
Still, its atmospheric pressure is only about a millionth that of
Earth. An astronaut standing in the Plutonian wind would likely not
feel anything, Buie said, but “it is not so insubstantial as to give
you something that can’t do anything on the surface. It is extremely
effective at moving frosts around on the surface.”
In particular, the researchers see “a massive
conveyor belt” that moves nitrogen frost evaporated from the pole in
sunlight to the dark pole, where it refreezes.
After remaining constant “to a small fraction of a
percent” for the 50 years that astronomers have observed Pluto, its
surface color got about 20 percent to 30 percent redder over a two-year
period at the beginning of the decade, Buie said. The change is not an
artifact of the telescope, he added, because one of Pluto’s moons is in
the same image and its color has not changed. The reason for the color
change “is still a mystery to be worked out.”
One possible explanation for the red tinge is carbon
compounds on the surface. The primary gases in the atmosphere are
methane and hydrogen. When exposed to sunlight, hydrogen atoms break
off and the carbon atoms combine, producing complex chemicals that are
reddish. Eventually, when all the hydrogens have broken off, Buie said,
the material should turn black like graphite.
“The mystery is why everything out there isn’t completely and totally black,” he added.
—
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