Date: Apr 19 20:36 UTC
Subject: HST Neptune Dark Spot
From: NASA Space News
HUBBLE DISCOVERS NEW DARK SPOT ON NEPTUNE
The distant, blue-green planet Neptune has again surprised astronomers
with the emergence of a new great dark spot in the cloudy planet's
northern hemisphere. The feature was discovered by NASA's Hubble Space
Telescope.
Only last June, Hubble images revealed that a great dark spot in the
southern hemisphere - discovered by the Voyager 2 spacecraft during its
1989 flyby - had mysteriously disappeared.
The new dark spot is a near mirror-image of the previous feature first
mapped by Voyager 2. The northern dark spot discovered by Hubble is
accompanied by bright, high-altitude clouds. As atmospheric gases flow
up over the spot, they cool to form these methane-ice crystal clouds.
"Hubble is showing us that Neptune has changed radically since 1989,"
said Heidi Hammel of the Massachusetts Institute of Technology. "New
features like this indicate that with Neptune's extraordinary dynamics,
the planet can look completely different in just a few weeks."
Like its predecessor, the new spot might be a hole in Neptune's methane
cloud tops that gives a peek to lower levels of the atmosphere.
"We weren't surprised the other spot disappeared," said Hammel. "It
was kind of 'floppy' because it changed shape as atmospheric
circulation carried it around the planet." (By contrast, Jupiter's
Great Red Spot, which is similar to Neptune's original spot in relative
size and position, has remained stable in appearance for at least 300
years.)
Hammel points out that studying the dynamics of Neptune's immense
atmosphere might lead to a better understanding of Earth's atmosphere.
"Neptune's unusual behavior is showing us that though we can make great
models of planetary atmospheric circulation, there may be key pieces
missing."
Energy from the Sun drives Earth's weather system. However, the
mechanism must be very different on Neptune because the planet radiates
two times more energy than it receives from the dim, distant Sun.
Neptune's atmosphere might be so dynamic because the cloud tops are
warmed from below by this strong internal heat source. A slight change
in the temperature differential from cloud bottom to top might trigger
rapid, large-scale changes in atmospheric circulation.
Since the 1989 Voyager flyby, astronomers using ground-based telescopes
have not been able to resolve the subtle structures in Neptune's
variable atmosphere, particularly the low-contrast dark features.
The astronomers don't know how long the new feature will last. For the
first time in planetary history though, Hubble will allow astronomers
to follow the details of Neptune's atmospheric changes over at least a
decade.
The Space Telescope Science Institute is operated by the Association of
Universities for Research in Astronomy, Inc. (AURA) for NASA, under
contract with the Goddard Space Flight Center, Greenbelt, MD. The
Hubble Space Telescope is a project of international cooperation
between NASA and the European Space Agency (ESA).
Image files in GIF and JPEG format may be accessed via anonymous ftp
from ftp.stsci.edu in /pubinfo:
GIF format JPEG format
Neptune 3 visits: /pubinfo/gif/Nept3.gif /pubinfo/jpeg/Nept3.jpg
Neptune Dark Spot: /pubinfo/gif/NeptDS.gif /pubinfo/jpeg/NeptDS.jpg
The same images are available via World Wide Web from links in
"http://www.stsci.edu/public.html" or more directly from
"http://www.stsci.edu/EPA/Latest.html".
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- T o d d E. V a n H o o s e a r -
``'''vanhoose@lalaland.cl.msu.edu - vanhoose@msu.edu - vanhoose@lalaland.cl.msu.edu
(._.) Michigan State University - East Lansing, MI USA
(_) Computer Laboratory - Department of Communication
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