Donald Savage
Headquarters, Washington, DC                    			April 19, 1995
(Phone:  202/358-1547)                   	 

Tammy Jones
Goddard Space Flight Center, Greenbelt, MD
(Phone:  301/286-5566)

Ray Villard
Space Telescope Science Institute, Baltimore, MD
(Phone:  410/338-4514)

RELEASE:  95-131 (53)

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).

				- end -

       NOTE TO EDITORS:  Images and a video depicting Neptune rotating 
are available to media representatives by calling NASA's Broadcast and 
Imaging Branch at 202/358-1900.  NASA photo numbers are:

                         Color:                    B&W:  
Neptune 3 visits:        95-HC-189                 95-H-193
Neptune Dark Spot:       95-HC-190                 95-H-194

       Image files in GIF and JPEG format may be accessed via anonymous 
ftp from ftp.stsci.edu in /pubinfo:

                                    GIF                        JPEG
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 URL 
http://www.stsci.edu/pubic.html or more directly from 
http://www.stsci.edu/Latest.html