Galerie de photos de la planète Neptune

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<h1>PIA00045: Neptune - Changes in Great Dark Spot</h1><div class="PIA00045" lang="en" style="width:400px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;">These images show changes in the clouds around Neptune's Great Dark Spot (GDS) over a four and one-half-day period. From top to bottom the images show successive rotations of the planet an interval of about 18 hours. The GDS is at a mean latitude of 20 degrees south, and covers about 30 degrees of longitude. The violet filter of the Voyager narrow angle camera was used to produce these images at distances ranging from 17 million kilometers (10.5 million miles) at the top, to 10 million kilometers (6.2 million miles) at bottom. The images have been mapped on to a rectangular latitude longitude grid to remove the effects of changing viewing geometry and the changing distance to Neptune. The sequence shows a large change in the western end (left side) of the GDS, where a dark extension apparent in the earlier images converges into an extended string of small dark spots over the next five rotations. This 'string of beads' extends from the GDS at a surprisingly large angle relative to horizontal lines of constant latitude. The large bright cloud at the southern (bottom) border of the GDS is a more or less permanent companion of the GDS. The apparent motion of smaller clouds at the periphery of the GDS suggests a counterclockwise rotation of the GDS reminiscent of flow around the Great Red Spot in Jupiter's atmosphere. This activity of the GDS is surprising because the total energy flux from the sun and from Neptune's interior is only 5 percent as large as the total energy flux on Jupiter.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA00045" onclick="window.open(this.href); return false;" title="Voir l'image PIA00045: Neptune - Changes in Great Dark Spot sur le site de la NASA">Voir l'image PIA00045: Neptune - Changes in Great Dark Spot sur le site de la NASA.</a></div>
PIA00045: Neptune - Changes in Great Dark Spot
<h1>PIA00046: Neptune Full Disk</h1><div class="PIA00046" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;">During August 16 and 17, 1989, the Voyager 2 narrow-angle camera was used to photograph Neptune almost continuously, recording approximately two and one-half rotations of the planet. These images represent the most complete set of full disk Neptune images that the spacecraft will acquire. This picture from the sequence shows two of the four cloud features which have been tracked by the Voyager cameras during the past two months. The large dark oval near the western limb (the left edge) is at a latitude of 22 degrees south and circuits Neptune every 18.3 hours. The bright clouds immediately to the south and east of this oval are seen to substantially change their appearances in periods as short as four hours. The second dark spot, at 54 degrees south latitude near the terminator (lower right edge), circuits Neptune every 16.1 hours. This image has been processed to enhance the visibility of small features, at some sacrifice of color fidelity. The Voyager Mission is conducted by JPL for NASA's Office of Space Science and Applications.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA00046" onclick="window.open(this.href); return false;" title="Voir l'image PIA00046: Neptune Full Disk sur le site de la NASA">Voir l'image PIA00046: Neptune Full Disk sur le site de la NASA.</a></div>
PIA00046: Neptune Full Disk
<h1>PIA00047: Neptune - Changes in Great Dark Spot</h1><div class="PIA00047" lang="en" style="width:430px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;">The bright cirrus-like clouds of Neptune change rapidly, often forming and dissipating over periods of several to tens of hours. In this sequence spanning two rotations of Neptune (about 36 hours) Voyager 2 observed cloud evolution in the region around the Great Dark Spot (GDS) at an effective resolution of about 100 kilometers (62 miles) per pixel. The surprisingly rapid changes which occur over the 18 hours separating each panel shows that in this region Neptune's weather is perhaps as dynamic and variable as that of the Earth. However, the scale is immense by our standards the Earth and the GDS are of similar size and in Neptune's frigid atmosphere, where temperatures are as low as 55 degrees Kelvin (360 F), the cirrus clouds are composed of frozen methane rather than Earth's crystals of water ice. The Voyager Mission is conducted by JPL for NASA's Office of Space Science and Applications.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA00047" onclick="window.open(this.href); return false;" title="Voir l'image PIA00047: Neptune - Changes in Great Dark Spot sur le site de la NASA">Voir l'image PIA00047: Neptune - Changes in Great Dark Spot sur le site de la NASA.</a></div>
PIA00047: Neptune - Changes in Great Dark Spot
<h1>PIA00048: Neptune - Great Dark Spot and Scooter</h1><div class="PIA00048" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;">This image of clouds in Neptune's atmosphere is the first that tests the accuracy of the weather forecast that was made eight days earlier to select targets for the Voyager narrow angle camera. Three of the four targeted features are visible in this photograph; all three are close to their predicted locations. The Great Dark Spot with its bright white companion is slightly to the left of center. The small bright Scooter is below and to the left, and the second dark spot with its bright core is below the Scooter. Strong eastward winds up to 400 mph cause the second dark spot to overtake and pass the larger one every five days. The spacecraft was 6.1 million kilometers (3.8 million miles) from the planet at the time of camera shuttering, and the images uses the orange, green and clear filters of the camera. The Voyager Mission is conducted by JPL for NASA's Office of Space Science and Applications.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA00048" onclick="window.open(this.href); return false;" title="Voir l'image PIA00048: Neptune - Great Dark Spot and Scooter sur le site de la NASA">Voir l'image PIA00048: Neptune - Great Dark Spot and Scooter sur le site de la NASA.</a></div>
PIA00048: Neptune - Great Dark Spot and Scooter
<h1>PIA00049: Neptune - Great Dark Spot, Scooter, Dark Spot 2</h1><div class="PIA00049" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>This photograph of Neptune was reconstructed from two images taken by Voyager 2's narrow-angle camera, through the green and clear filters. The image shows three of the features that Voyager 2 has been photographing during recent weeks. At the north (top) is the Great Dark Spot, accompanied by bright, white clouds that undergo rapid changes in appearance. To the south of the Great Dark Spot is the bright feature that Voyager scientists have nicknamed 'Scooter.' Still farther south is the feature called 'Dark Spot 2,' which has a bright core. Each feature moves eastward at a different velocity, so it is only occasionally that they appear close to each other, such as at the time this picture was taken. The Voyager Mission is conducted by JPL for NASA's Office of Space Science and Applications.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA00049" onclick="window.open(this.href); return false;" title="Voir l'image PIA00049: Neptune - Great Dark Spot, Scooter, Dark Spot 2 sur le site de la NASA">Voir l'image PIA00049: Neptune - Great Dark Spot, Scooter, Dark Spot 2 sur le site de la NASA.</a></div>
PIA00049: Neptune - Great Dark Spot, Scooter, Dark Spot 2
<h1>PIA00050: Neptune's Southern Hemisphere</h1><div class="PIA00050" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;">This photograph of Neptune's southern hemisphere was taken by the narrow-angle camera on NASA's Voyager 2 when the spacecraft was 4.2 million km (2.6 million miles) from the planet. The smallest features that can be seen are 38 km (24 miles) across. The almond-shaped structure at the left is a large cloud system that has been seen for several weeks. Internal details in the feature have become increasingly apparent as Voyager 2 has approached. Systems with similar shapes in Jupiter's atmosphere rotate about their centers, rolling in the local winds that increase toward the south. However, the wispy nature of the white central clouds in this Neptunian feature make confirmation of the system's rotation difficult. The Voyager Mission is conducted by JPL for NASA's Office of Space Science and Applications.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA00050" onclick="window.open(this.href); return false;" title="Voir l'image PIA00050: Neptune's Southern Hemisphere sur le site de la NASA">Voir l'image PIA00050: Neptune's Southern Hemisphere sur le site de la NASA.</a></div>
PIA00050: Neptune's Southern Hemisphere
<h1>PIA00051: Neptune in False Color</h1><div class="PIA00051" lang="en" style="width:650px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;">In this false color image of Neptune, objects that are deep in the atmosphere are blue, while those at higher altitudes are white. The image was taken by Voyager 2's wide-angle camera through an orange filter and two different methane filters. Light at methane wavelengths is mostly absorbed in the deeper atmosphere. The bright, white feature is a high altitude cloud just south of the Great Dark Spot. The hard, sharp inner boundary within the bright cloud is an artifact of computer processing on Earth. Other, smaller clouds associated with the Great Dark Spot are white or pink, and are also at high altitudes. Neptune's limb looks reddish because Voyager 2 is viewing it tangentially, and the sunlight is scattered back to space before it can be absorbed by the methane. A long, narrow band of high altitude clouds near the top of the image is located at 25 degrees north latitude, and faint hazes mark the equator and polar regions. The Voyager Mission is conducted by JPL for NASA's Office of Space Science and Applications.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA00051" onclick="window.open(this.href); return false;" title="Voir l'image PIA00051: Neptune in False Color sur le site de la NASA">Voir l'image PIA00051: Neptune in False Color sur le site de la NASA.</a></div>
PIA00051: Neptune in False Color
<h1>PIA00052: Neptune Great Dark Spot in High Resolution</h1><div class="PIA00052" lang="en" style="width:700px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>This photograph shows the last face on view of the Great Dark Spot that Voyager will make with the narrow angle camera. The image was shuttered 45 hours before closest approach at a distance of 2.8 million kilometers (1.7 million miles). The smallest structures that can be seen are of an order of 50 kilometers (31 miles). The image shows feathery white clouds that overlie the boundary of the dark and light blue regions. The pinwheel (spiral) structure of both the dark boundary and the white cirrus suggest a storm system rotating counterclockwise. Periodic small scale patterns in the white cloud, possibly waves, are short lived and do not persist from one Neptunian rotation to the next. This color composite was made from the clear and green filters of the narrow-angle camera. The Voyager Mission is conducted by JPL for NASA's Office of Space Science and Applications.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA00052" onclick="window.open(this.href); return false;" title="Voir l'image PIA00052: Neptune Great Dark Spot in High Resolution sur le site de la NASA">Voir l'image PIA00052: Neptune Great Dark Spot in High Resolution sur le site de la NASA.</a></div>
PIA00052: Neptune Great Dark Spot in High Resolution
<h1>PIA00057: Neptune False Color Image of Haze</h1><div class="PIA00057" lang="en" style="width:780px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;">This false color photograph of Neptune was made from Voyager 2 images taken through three filters: blue, green, and a filter that passes light at a wavelength that is absorbed by methane gas. Thus, regions that appear white or bright red are those that reflect sunlight before it passes through a large quantity of methane. The image reveals the presence of a ubiquitous haze that covers Neptune in a semitransparent layer. Near the center of the disk, sunlight passes through the haze and deeper into the atmosphere, where some wavelengths are absorbed by methane gas, causing the center of the image to appear less red. Near the edge of the planet, the haze scatters sunlight at higher altitude, above most of the methane, causing the bright red edge around the planet. By measuring haze brightness at several wavelengths, scientists are able to estimate the thickness of the haze and its ability to scatter sunlight. The image is among the last full disk photos that Voyager 2 took before beginning its endless journey into interstellar space. The Voyager Mission is conducted by JPL for NASA's Office of Space Science and Applications.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA00057" onclick="window.open(this.href); return false;" title="Voir l'image PIA00057: Neptune False Color Image of Haze sur le site de la NASA">Voir l'image PIA00057: Neptune False Color Image of Haze sur le site de la NASA.</a></div>
PIA00057: Neptune False Color Image of Haze
<h1>PIA00058: Neptune Clouds Showing Vertical Relief</h1><div class="PIA00058" lang="en" style="width:682px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;">This Voyager 2 high resolution color image, taken 2 hours before closest approach, provides obvious evidence of vertical relief in Neptune's bright cloud streaks. These clouds were observed at a latitude of 29 degrees north near Neptune's east terminator. The linear cloud forms are stretched approximately along lines of constant latitude and the sun is toward the lower left. The bright sides of the clouds which face the sun are brighter than the surrounding cloud deck because they are more directly exposed to the sun. Shadows can be seen on the side opposite the sun. These shadows are less distinct at short wavelengths (violet filter) and more distinct at long wavelengths (orange filter). This can be understood if the underlying cloud deck on which the shadow is cast is at a relatively great depth, in which case scattering by molecules in the overlying atmosphere will diffuse light into the shadow. Because molecules scatter blue light much more efficiently than red light, the shadows will be darkest at the longest (reddest) wavelengths, and will appear blue under white light illumination. The resolution of this image is 11 kilometers (6.8 miles per pixel) and the range is only 157,000 kilometers (98,000 miles). The width of the cloud streaks range from 50 to 200 kilometers (31 to 124 miles), and their shadow widths range from 30 to 50 kilometers (18 to 31 miles). Cloud heights appear to be of the order of 50 kilometers (31 miles). This corresponds to 2 scale heights. The Voyager Mission is conducted by JPL for NASA's Office of Space Science and Applications.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA00058" onclick="window.open(this.href); return false;" title="Voir l'image PIA00058: Neptune Clouds Showing Vertical Relief sur le site de la NASA">Voir l'image PIA00058: Neptune Clouds Showing Vertical Relief sur le site de la NASA.</a></div>
PIA00058: Neptune Clouds Showing Vertical Relief
<h1>PIA00063: Neptune - True Color of Clouds</h1><div class="PIA00063" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;">This image of Neptune was taken by Voyager 2's wide-angle camera when the spacecraft was 590,000 km (370,000 miles) from the planet. The image has been processed to obtain true color balance. Additional processing was used to suppress surface brightness of the white clouds. The processing allows both the clouds' structure in the dark regions near the pole and the bright clouds east of the Great Dark Spot to be reproduced in this color photograph. Small trails of similar clouds trending east to west and large scale structure east of the Great Dark Spot all suggest that waves are present in the atmosphere and play a large role in the type of clouds that are visible. The Voyager Mission is conducted by JPL for NASA's Office of Space Science and Applications.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA00063" onclick="window.open(this.href); return false;" title="Voir l'image PIA00063: Neptune - True Color of Clouds sur le site de la NASA">Voir l'image PIA00063: Neptune - True Color of Clouds sur le site de la NASA.</a></div>
PIA00063: Neptune - True Color of Clouds
<h1>PIA00064: Neptune's Dark Spot (D2) at High Resolution</h1><div class="PIA00064" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;">This bulls-eye view of Neptune's small dark spot (D2) was obtained by Voyager 2's narrow-angle camera on Aug. 24, 1989, when Voyager 2 was within 1.1 million km (680,000 miles) of the planet. The smallest structures that can be seen are 20 km (12 miles) across. This unplanned photograph was obtained when the infrared spectrograph was mapping the planet, and is the highest resolution view of the feature taken during the flyby. Banding surrounding the feature indicates unseen strong winds, while structures within the bright spot suggest both active upwelling of clouds and rotation about the center. A rotation rate has not yet been measured, but the V-shaped structure near the right edge of the bright area indicates that the spot rotates clockwise. Unlike the Great Red Spot on Jupiter, which rotates counterclockwise, if the D2 spot on Neptune rotates clockwise, the material will be descending in the dark oval region. The fact that infrared data will yield temperature information about the region above the clouds makes this observation especially valuable. The Voyager Mission is conducted by JPL for NASA's Office of Space Science and Applications.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA00064" onclick="window.open(this.href); return false;" title="Voir l'image PIA00064: Neptune's Dark Spot (D2) at High Resolution sur le site de la NASA">Voir l'image PIA00064: Neptune's Dark Spot (D2) at High Resolution sur le site de la NASA.</a></div>
PIA00064: Neptune's Dark Spot (D2) at High Resolution
<h1>PIA01142: Neptune Scooter</h1><div class="PIA01142" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;">This photograph of Neptune was reconstructed from two images taken by Voyager 2's narrow-angle camera, through the green and clear filters. The image shows three of the features that Voyager 2 has been photographing during recent weeks. At the north (top) is the Great Dark Spot, accompanied by bright, white clouds that undergo rapid changes in appearance. To the south of the Great Dark Spot is the bright feature that Voyager scientists have nicknamed "Scooter." Still farther south is the feature called "Dark Spot 2," which has a bright core. Each feature moves eastward at a different velocity, so it is only occasionally that they appear close to each other, such as at the time this picture was taken. The Voyager Mission is conducted by JPL for NASA's Office of Space Science and Applications.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01142" onclick="window.open(this.href); return false;" title="Voir l'image PIA01142: Neptune Scooter sur le site de la NASA">Voir l'image PIA01142: Neptune Scooter sur le site de la NASA.</a></div>
PIA01142: Neptune Scooter
<h1>PIA01284: Neptune in Primary Colors</h1><div class="PIA01284" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>These two NASA Hubble Space Telescope images provide views of weather on opposite hemispheres of Neptune. Taken Aug. 13, 1996, with Hubble's Wide Field Planetary Camera 2, these composite images blend information from different wavelengths to bring out features of Neptune's blustery weather. The predominant blue color of the planet is a result of the absorption of red and infrared light by Neptune's methane atmosphere. Clouds elevated above most of the methane absorption appear white, while the very highest clouds tend to be yellow-red as seen in the bright feature at the top of the right-hand image. Neptune's powerful equatorial jet—where winds blow at nearly 900 mph—is centered on the dark blue belt just south of Neptune's equator. Farther south, the green belt indicates a region where the atmosphere absorbs blue light.<p>The images are part of a series of images made by Hubble during nine orbits spanning one 16.11-hour rotation of Neptune. The team making the observation was directed by Lawrence Sromovsky of the University of Wisconsin-Madison's Space Science and Engineering Center.<p>The Wide Field/Planetary Camera 2 was developed by the Jet Propulsion Laboratory and managed by the Goddard Space Flight Center for NASA's Office of Space Science.<p>This image and other images and data received from the Hubble Space Telescope are posted on the World Wide Web on the Space Telescope Science Institute home page at URL <a href="http://oposite.stsci.edu/" class="external free" target="wpext">http://oposite.stsci.edu/</a>.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01284" onclick="window.open(this.href); return false;" title="Voir l'image PIA01284: Neptune in Primary Colors sur le site de la NASA">Voir l'image PIA01284: Neptune in Primary Colors sur le site de la NASA.</a></div>
PIA01284: Neptune in Primary Colors
<h1>PIA01285: Hubble's View of Neptune</h1><div class="PIA01285" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>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.<p>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.<p>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.<p>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.<p>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.<p>The Wide Field/Planetary Camera 2 was developed by the Jet Propulsion Laboratory and managed by the Goddard Space Flight Center for NASA's Office of Space Science.<p>This image and other images and data received from the Hubble Space Telescope are posted on the World Wide Web on the Space Telescope Science Institute home page at URL <a href="http://oposite.stsci.edu/" class="external free" target="wpext">http://oposite.stsci.edu/</a>.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01285" onclick="window.open(this.href); return false;" title="Voir l'image PIA01285: Hubble's View of Neptune sur le site de la NASA">Voir l'image PIA01285: Hubble's View of Neptune sur le site de la NASA.</a></div>
PIA01285: Hubble's View of Neptune
<h1>PIA01286: Hubble Finds New Dark Spot on Neptune</h1><div class="PIA01286" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>NASA's Hubble Space Telescope has discovered a new great dark spot, located in the northern hemisphere of the planet Neptune. Because the planet's northern hemisphere is now tilted away from Earth, the new feature appears near the limb of the planet.<p>The spot is a near mirror-image to a similar southern hemisphere dark spot that was discovered in 1989 by the Voyager 2 probe. In 1994, Hubble showed that the southern dark spot had disappeared.<p>Like its predecessor, the new spot has high altitude clouds along its edge, caused by gasses that have been pushed to higher altitudes where they cool to form methane ice crystal clouds. The dark spot may be a zone of clear gas that is a window to a cloud deck lower in the atmosphere.<p>Planetary scientists don t know how long lived this new feature might be. Hubble's high resolution will allow astronomers to follow the spot's evolution and other unexpected changes in Neptune's dynamic atmosphere.<p>The image was taken on November 2, 1994 with Hubble's Wide Field Planetary Camera 2, when Neptune was 2.8 billion miles (4.5 billion kilometers) from Earth. Hubble can resolve features as small as 625 miles (1,000 kilometers) across in Neptune's cloud tops.<p>The Wide Field/Planetary Camera 2 was developed by the Jet Propulsion Laboratory and managed by the Goddard Space Flight Center for NASA's Office of Space Science.<p>This image and other images and data received from the Hubble Space Telescope are posted on the World Wide Web on the Space Telescope Science Institute home page at URL <a href="http://oposite.stsci.edu/" class="external free" target="wpext">http://oposite.stsci.edu/</a>.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01286" onclick="window.open(this.href); return false;" title="Voir l'image PIA01286: Hubble Finds New Dark Spot on Neptune sur le site de la NASA">Voir l'image PIA01286: Hubble Finds New Dark Spot on Neptune sur le site de la NASA.</a></div>
PIA01286: Hubble Finds New Dark Spot on Neptune
<h1>PIA01287: Hubble Space Telescope Wide Field Planetary Camera 2 Observations of Neptune</h1><div class="PIA01287" lang="en" style="width:510px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>Two groups have recently used the Hubble Space Telescope (HST) Wide Field Planetary Camera 2 (WFPC 2) to acquire new high-resolution images of the planet Neptune. Members of the WFPC-2 Science Team, lead by John Trauger, acquired the first series of images on 27 through 29 June 1994. These were the highest resolution images of Neptune taken since the Voyager-2 flyby in August of 1989. A more comprehensive program is currently being conducted by Heidi Hammel and Wes Lockwood. These two sets of observations are providing a wealth of new information about the structure, composition, and meteorology of this distant planet's atmosphere.<p>Neptune is currently the most distant planet from the sun, with an orbital radius of 4.5 billion kilometers (2.8 billion miles, or 30 Astronomical Units). Even though its diameter is about four times that of the Earth (49,420 vs. 12,742 km), ground-based telescopes reveal a tiny blue disk that subtends less than 1/1200 of a degree (2.3 arc-seconds). Neptune has therefore been a particularly challenging object to study from the ground because its disk is badly blurred by the Earth's atmosphere. In spite of this, ground-based astronomers had learned a great deal about this planet since its position was first predicted by John C. Adams and Urbain Leverrier in 1845. For example, they had determined that Neptune was composed primarily of hydrogen and helium gas, and that its blue color caused by the presence of trace amounts of the gas methane, which absorbs red light. They had also detected bright cloud features whose brightness changed with time, and tracked these clouds to infer a rotation period between 17 and 22 hours.<p>When the Voyager-2 spacecraft flew past the Neptune in 1989, its instruments revealed a surprising array of meteorological phenomena, including strong winds, bright, high-altitude clouds, and two large dark spots attributed to long-lived giant storm systems. These bright clouds and dark spots were tracked as they moved across the planet's disk, revealing wind speeds as large as 325 meters per second (730 miles per hour). The largest of the giant, dark storm systems, called the "Great Dark Spot", received special attention because it resembled Jupiter's Great Red Spot, a storm that has persisted for more than three centuries. The lifetime of Neptune's Great Dark Spot could not be determined from the Voyager data alone, however, because the encounter was too brief. Its evolution was impossible to monitor with ground-based telescopes, because it could not be resolved on Neptune's tiny disk, and its contribution to the disk-integrated brightness of Neptune confused by the presence of a rapidly-varying bright cloud feature, called the "Bright Companion" that usually accompanied the Great Dark spot.<p>The repaired Hubble Space Telescope provides new opportunities to monitor these and other phenomena in the atmosphere of the most distant planet. Images taken with WFPC-2's Planetary Camera (PC) can resolve Neptune's disk as well as most ground-based telescopes can resolve the disk of Jupiter. The spatial resolution of the HST WFPC-2 images is not as high as that obtained by the Voyager-2 Narrow-Angle Camera during that spacecraft's closest approach to Neptune, but they have a number of other assets that enhance their scientific value, including improved ultra-violet and infrared sensitivity, better signal-to-noise, and, and greater photometric accuracy.<p>The images of Neptune acquired by the WFPC-2 Science team in late June clearly demonstrate these capabilities. The side of the planet facing the Earth at the start of the program (11:36 Universal Time on July 27) was imaged in color filters spanning the ultraviolet (255 and 300-nm), visible (467, 588, 620, and 673- nm), and near-infrared (890-nm) parts of the spectrum. The planet then rotated 180 degrees in longitude, and the opposite hemisphere was imaged in a subset of these colors (300, 467, 588, 620, and 673-nm). The HST/WFPC-2 program more recently conducted by Hammel and Lockwood provides better longitude coverage, and a wider range of observing times, but uses a more restricted set of colors.<p>The ultraviolet pictures show an almost featureless disk that is slightly darker near the edge. The observed contrast increases in the blue, green, red, and near-infrared images, which reveal many of the features seen by Voyager 2, including the dark band near 60 S latitude and several distinct bright cloud features. The bright cloud features are most obvious in the red and infrared parts of the spectrum where methane gas absorbs most strongly (619 and 890 nm). These bright clouds thought to be high above the main cloud deck, and above much of the absorbing methane gas. The edge of the planet's disk also appears somewhat bright in these colors, indicating the presence of a ubiquitous, high-altitude haze layer.<p>The northern hemisphere is occupied by a single prominent cloud band centered near 30 N latitude. This planet-encircling feature may be the same bright cloud discovered last fall by ground-based observers. Northern hemisphere clouds were much less obvious at the time of the Voyager-2 encounter. The tropics are about 20 % darker than the disk average in the 890-nm images, and one of these images reveals a discrete bright cloud on the equator, near the edge of the disk. The southern hemisphere includes two broken bright bands. The largest and brightest is centered at 30 S latitude, and extends for least 40 degrees of longitude, like the Bright Companion to the Great Dark Spot. There is also a thin cloud band at 45 S latitude, which almost encircles the planet.<p>One feature that is conspicuous by its absence is the storm system known as the Great Dark Spot. The second smaller dark spot, DS2, that was seen during the Voyager-2 encounter was also missing. The absence of these dark spots was one of the biggest surprises of this program. The WFPC-2 Science team initially assumed that the two storm systems might be near the edge of the planet's disk, where they would not be particularly obvious. An analysis of their longitude coverage revealed that less than 20 degrees of longitude had been missed in the colors where these spots had their greatest contrast (467 and 588 nm). The Great Dark Spot covered almost 40 degrees of longitude at the time of the Voyager-2 fly-by. Even if it were on the edge of the disk, it would appear as a "bite" out of the limb. Because no such feature was detected, we concluded that these features had vanished. This conclusion was reinforced by the more recent observations by Hammel and Lockwood, which also show no evidence of discrete dark spots.<p>These dramatic changes in the large-scale storm systems and planet-encircling clouds bands on Neptune are not yet completely understood, but they emphasize the dynamic nature of this planet's atmosphere, and the need for further monitoring. Additional HST WFPC-2 observations are planned for next summer. These two teams are continuing their analysis of these data sets to place improved constraints on these and other phenomena in Neptune's atmosphere.<p>Figure Captions:<p>These almost true-color pictures of Neptune were constructed from HST/WFPC2 images taken in blue (467-nm), green (588- nm), and red (673-nm) spectral filters. There is a bright cloud feature at the south pole, near the bottom right of the image. Bright cloud bands can be seen at 30S and 60S latitude. The northern hemisphere also includes a bright cloud band centered near 30N latitude. The second picture was compiled from images taken after the planet had rotated about 180 degrees of longitude (about 9 hours later) to show the opposite hemisphere.<p>The Wide Field/Planetary Camera 2 was developed by the Jet Propulsion Laboratory and managed by the Goddard Space Flight Center for NASA's Office of Space Science.<p>This image and other images and data received from the Hubble Space Telescope are posted on the World Wide Web on the Space Telescope Science Institute home page at URL <a href="http://oposite.stsci.edu/" class="external free" target="wpext">http://oposite.stsci.edu/</a>.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01287" onclick="window.open(this.href); return false;" title="Voir l'image PIA01287: Hubble Space Telescope Wide Field Planetary Camera 2 Observations of Neptune sur le site de la NASA">Voir l'image PIA01287: Hubble Space Telescope Wide Field Planetary Camera 2 Observations of Neptune sur le site de la NASA.</a></div>
PIA01287: Hubble Space Telescope Wide Field Planetary Camera 2 Observations of Neptune
<h1>PIA01363: 3 Images of Neptune</h1><div class="PIA01363" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>These three images of Neptune were acquired 90 minutes apart by the Voyager 2 spacecraft on April 3, 1989, from a range of 208 million kilometers (129 million miles). Several atmospheric features (clouds) are visible. In addition to the dark band encircling the south polar region, a large dark spot extends from latitude 20 S. to 30 S. and spans 35 degrees in longitude. It rotates with a period between 17 and 18 hours. Relative to the size of the planet, the spot's dimensions are similar to those of the Great Red Spot of Jupiter. These images were taken exclusively through the clear filter of the narrow angle camera, which is most sensitive to blue light. The spot is 10 percent darker than its surroundings. Resolution of the images is about 3850 kilometers (2400 miles) per line pair. Images taken 70 days earlier show either the same spot or a similar spot, which appears darker than its surroundings through the clear filter but brighter through the orange filter. Clouds visible in the orange images are thought to be at higher altitudes than those visible here, and may have different scattering properties at the two wavelengths. The Voyager cameras will be tracking these atmospheric features during the next three months in order to target them for close-up imaging in the days before the spacecraft's closest approach to Neptune on August 24, 1989. The Jet Propulsion Laboratory manages the Voyager Project for NASA's Office of Space Science and Applications.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01363" onclick="window.open(this.href); return false;" title="Voir l'image PIA01363: 3 Images of Neptune sur le site de la NASA">Voir l'image PIA01363: 3 Images of Neptune sur le site de la NASA.</a></div>
PIA01363: 3 Images of Neptune
<h1>PIA01491: Neptune and Triton</h1><div class="PIA01491" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;">This image was returned by the Voyager 2 spacecraft on July 3, 1989, when it was 76 million kilometers (47 million miles) from Neptune. The planet and its largest satellite, Triton, are captured in the field of view of Voyager's narrow-angle camera through violet, clear and orange filters. Triton appears in the lower right corner at about 5 o'clock relative to Neptune. Recent measurements from Voyager images show Triton to be between 1,400 and 1,800 kilometers (about 870 to 1,100 miles) in radius with a surface that is about as bright as freshly fallen snow. Because Triton is barely resolved in current narrow-angle images, it is too early to see features on its surface. Scientists believe Triton has at least a small atmosphere of methane and possibly other gases.<p>During its closest approach to Triton on August 25, 1989, Voyager should provide high-resolution views of the moon's icy surface and reveal whether Triton's atmosphere has clouds. JPL manages the Voyager Project for NASA's Office of Space Science and Applications.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01491" onclick="window.open(this.href); return false;" title="Voir l'image PIA01491: Neptune and Triton sur le site de la NASA">Voir l'image PIA01491: Neptune and Triton sur le site de la NASA.</a></div>
PIA01491: Neptune and Triton
<h1>PIA01492: Neptune Full Disk View</h1><div class="PIA01492" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>This picture of Neptune was produced from the last whole planet images taken through the green and orange filters on the Voyager 2 narrow angle camera. The images were taken at a range of 4.4 million miles from the planet, 4 days and 20 hours before closest approach. The picture shows the Great Dark Spot and its companion bright smudge; on the west limb the fast moving bright feature called Scooter and the little dark spot are visible. These clouds were seen to persist for as long as Voyager's cameras could resolve them. North of these, a bright cloud band similar to the south polar streak may be seen.</p><p>The Voyager Mission is conducted by JPL for NASA's Office of Space Science and Applications.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01492" onclick="window.open(this.href); return false;" title="Voir l'image PIA01492: Neptune Full Disk View sur le site de la NASA">Voir l'image PIA01492: Neptune Full Disk View sur le site de la NASA.</a></div>
PIA01492: Neptune Full Disk View
<h1>PIA01539: Post-encounter View of Neptune's South Pole</h1><div class="PIA01539" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;">Voyager 2's post-encounter view of Neptune's south pole as the spacecraft sped away on a southward trajectory.<p>JPL manages the Voyager project for NASA's Office of Space Science.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01539" onclick="window.open(this.href); return false;" title="Voir l'image PIA01539: Post-encounter View of Neptune's South Pole sur le site de la NASA">Voir l'image PIA01539: Post-encounter View of Neptune's South Pole sur le site de la NASA.</a></div>
PIA01539: Post-encounter View of Neptune's South Pole
<h1>PIA01542: Neptune's Stormy Disposition</h1><div class="PIA01542" lang="en" style="width:720px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;">Using powerful ground-and space-based telescopes, scientists have obtained a moving look at some of the wildest, weirdest weather in the solar system.<p>Combining simultaneous observations of Neptune made with the Hubble Space Telescope and NASA's Infrared Telescope Facility on Mauna Kea, Hawaii, a team of scientists led by Lawrence A. Sromovsky of the University of Wisconsin-Madison has captured the most insightful images to date of a planet whose blustery weather -- monster storms and equatorial winds of 900 miles per hour -- bewilders scientists.<p>Blending a series of Hubble images, Sromovsky's team constructed a time-lapse rotation movie of Neptune, permitting scientists to watch the ebb and flow of the distant planet's weather. And while the observations, presented here at a meeting of the American Astronomical Society's Division of Planetary Science, are helping scientists tease out clues to the planet's stormy weather, they also are deepening some of Neptune's mysteries, said Sromovsky.<p>The weather on Neptune, the eighth planet from the sun, is an enigma to begin with. The mechanism that drives its near-supersonic winds and giant storms has yet to be discerned.<p>On Earth, weather is driven by energy from the sun as it heats the atmosphere and oceans. On Neptune, the sun is 900 times dimmer and scientists have yet to understand how Neptune's weather-generating machinery can be so efficient.<p>"It's an efficient weather machine compared to Earth," said Sromovsky. "It seems to run on almost no energy."<p>In an effort to dissect the distant planet's atmosphere and monitor its bizarre weather, Sromovsky and his colleagues obtained a series of measurements and images over the span of three of Neptune's rotations.<p>From those observations, Sromovsky said it is possible to measure Neptune's circulation and view a "strange menagerie of variable, discrete cloud features and zonal bands" of weather. Moreover, the new observations enabled Sromovsky's team to probe some of the deeper features of the atmosphere and to map Neptune's cloud tops.<p>"We can show some clouds are higher than others, that altitudes vary," he said. Knowing something about the topography of Neptune's clouds, provides a direct way to measure Neptune's powerful winds.<p>A looming mystery, he said, is the fate of huge dark spots, possibly giant storms. When the planetary probe Voyager visited Neptune in 1989, it detected the Great Dark Spot, a pulsating feature nearly the size of the Earth itself. Two years ago, Hubble observations showed the spot had disappeared, and that another, smaller spot had emerged. But instead of growing to a large-scale storm like the Great Dark Spot, the new spot appears to be trapped at a fixed latitude and may be declining in intensity, said Sromovsky, a senior scientist at UW-Madison's Space Science and Engineering Center.<p>"They behave like storms, and the Great Dark Spot was an exaggerated features we haven't seen on any other planet. They seem to come and go, and rather than an exciting development of these dark spots, they dissipate."<p>Another strange aspect of the distant planet's weather are distinct bands of weather that run parallel to the Neptunian equator. The weather bands encircle the planet and, in some respects, may be similar to the equatorial region of the Earth where tropical heat provides abundant energy to make clouds.<p>"We can see regions of latitude where Neptune consistently generates bright clouds," said Sromovsky. The regions are both above and below the planet's equator, but he added that it was uncertain what their explanation is in terms of atmospheric circulation.<p>Sromovsky said that compared to the look provided by the Voyager spacecraft, Neptune is a different place: "The character of Neptune is different from what it was at the time of Voyager. The planet seems stable, yet different."<p>Sromovsky's Hubble observations were made with Wide Field Planetary Camera 2 and the Near Infrared Camera and Multi-Object Spectrometer. The different instruments allowed observations to be made in a variety of wavelengths, each providing a different set of information about Neptune's clouds, their structures and how they circulate.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01542" onclick="window.open(this.href); return false;" title="Voir l'image PIA01542: Neptune's Stormy Disposition sur le site de la NASA">Voir l'image PIA01542: Neptune's Stormy Disposition sur le site de la NASA.</a></div>
PIA01542: Neptune's Stormy Disposition
<h1>PIA01982: Neptune's Clouds</h1><div class="PIA01982" lang="en" style="width:470px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;"><p>The bright cirrus-like clouds of Neptune change rapidly, often forming and dissipating over periods of several to tens of hours. In this sequence Voyager 2 observed cloud evolution in the region around the Great Dark Spot (GDS). The surprisingly rapid changes which occur separating each panel shows that in this region Neptune's weather is perhaps as dynamic and variable as that of the Earth. However, the scale is immense by our standards -- the Earth and the GDS are of similar size -- and in Neptune's frigid atmosphere, where temperatures are as low as 55 degrees Kelvin (-360 F), the cirrus clouds are composed of frozen methane rather than Earth's crystals of water ice. The Voyager Mission is conducted by JPL for NASA's Office of Space Science and Applications<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01982" onclick="window.open(this.href); return false;" title="Voir l'image PIA01982: Neptune's Clouds sur le site de la NASA">Voir l'image PIA01982: Neptune's Clouds sur le site de la NASA.</a></div>
PIA01982: Neptune's Clouds
<h1>PIA01990: Neptune - Dark Oval</h1><div class="PIA01990" lang="en" style="width:150px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;">The large, dark oval spot in Neptune's atmosphere is just coming into view in this picture returned from the Voyager 2 spacecraft on June 30, 1989. The spacecraft was about 83 million kilometers (51.5 million miles) from Neptune. Voyager scientists are interested in the dark oval cloud system, a very large system similar to Jupiter's Great Red Spot. Contrast of the features in Neptune's atmosphere is similar to that obtained at Saturn at about this same distance and lighting, whereas the features are similar to those seen at Jupiter. The Jet Propulsion Laboratory manages the Voyager Project for NASA's Office of Space Science and Applications.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01990" onclick="window.open(this.href); return false;" title="Voir l'image PIA01990: Neptune - Dark Oval sur le site de la NASA">Voir l'image PIA01990: Neptune - Dark Oval sur le site de la NASA.</a></div>
PIA01990: Neptune - Dark Oval
<h1>PIA01991: Neptune - Three New Satellites</h1><div class="PIA01991" lang="en" style="width:545px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;">This image captured by the Voyager 2 spacecraft was used to confirm the discovery of three new satellites orbiting Neptune. The 46 second exposure was taken by Voyager 2's narrow angle camera through a clear filter on July 30, 1989, when the spacecraft was about 37.3 million kilometers (23.6 million miles) from Neptune. The large globe of the planet itself is severely overexposed and appears pure white. The image has been computer processed to accentuate the new moons, which otherwise would appear little stronger than background noise. The satellite 1989 N1, at right in this frame, was discovered by Voyager 2 in early July 1989. The new satellites confirmed this week are 1989 N2, 1989 N3 and 1989 N4. Each of the moons appears as a small streak, an effect caused by movement of the spacecraft during the long exposure. The new moons occupy nearly circular and equatorial orbits ranging from about 27,300 to 48,300 kilometers (17,000 to 30,000 miles) from Neptune's cloud tops, and are estimated to range in diameter from about 100 to 200 kilometers (about 60 to 125 miles). The Voyager Mission is conducted by the Jet Propulsion Laboratory for NASA's Office of Space Science and Applications.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01991" onclick="window.open(this.href); return false;" title="Voir l'image PIA01991: Neptune - Three New Satellites sur le site de la NASA">Voir l'image PIA01991: Neptune - Three New Satellites sur le site de la NASA.</a></div>
PIA01991: Neptune - Three New Satellites
<h1>PIA01992: Neptune - Dark Feature</h1><div class="PIA01992" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;">This clear filter image was acquired by Voyager 2 on August 14, 1989, at a range of 14.8 million kilometers (9.2 million miles). The image shows a dark feature extending westward (left) and northward (up) toward the equator from the Great Dark Spot (GDS). This puzzling phenomenon developed over a relatively short period (three rotations or about 54 hours), and continues to evolve with time. Further study may reveal whether this protrusion represents an actual flow of dark cloud material from the GDS or is a result of atmospheric disturbances associated with the western boundary of the GDS. Bright, wispy "cirrus type" clouds are seen overlying the GDS at its southern (lower) margin and over its northwest (upper left) boundary. This is the first evidence that the GDS lies lower in the atmosphere than the bright clouds, which have remained in its vicinity for several months. Increasing detail in global banding and in the south polar region is also apparent. The Voyager Mission is conducted by the Jet Propulsion Laboratory for NASA's Office of Space Science and Applications.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01992" onclick="window.open(this.href); return false;" title="Voir l'image PIA01992: Neptune - Dark Feature sur le site de la NASA">Voir l'image PIA01992: Neptune - Dark Feature sur le site de la NASA.</a></div>
PIA01992: Neptune - Dark Feature
<h1>PIA01993: Neptune - Two Images</h1><div class="PIA01993" lang="en" style="width:800px;text-align:left;margin:auto;background-color:#000;padding:10px;max-height:150px;overflow:auto;">These two images of Neptune were taken by Voyager 2's narrow angle camera when the spacecraft was about 12 million km (7.5 million miles) from Neptune. Resolution is about 110 km (68 miles) per pixel. During the 17.6 hours between the left and right images, the Great Dark Spot, at 22 degrees south latitude (left of center), has completed a little less than one rotation of Neptune. The smaller dark spot, at 54 south, completed a little more than one rotation, as can be seen by comparing its relative positions in the two pictures. The Great Dark Spot and the smaller spot have a relative velocity of 100 meters per second (220 miles an hour). The light and dark bands circling Neptune indicate predominantly zonal (east/west) motion. The diffuse white feature north of the Great Dark Spot is near Neptune's equator, and rotates with about the same period as the Great Dark Spot. Streak of bright clouds at the south edge, and just east of the Great Dark Spot, are its constant companions, and change the details of their appearance, often within a few hours. Changing brightness of the cloud streaks could be a result of vertical motions. The Voyager Mission is conducted by JPL for NASA's Office of Space Science and Applications.<br /><br /><a href="http://photojournal.jpl.nasa.gov/catalog/PIA01993" onclick="window.open(this.href); return false;" title="Voir l'image PIA01993: Neptune - Two Images sur le site de la NASA">Voir l'image PIA01993: Neptune - Two Images sur le site de la NASA.</a></div>
PIA01993: Neptune - Two Images