Giant Planets – AtmospheresPHYS 178 – 2008 Week 5, Part 2

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Jupiter

This processed color image

of Jupiter was produced in1990 by the U.S. Geological

Survey from a Voyager

image captured in 1979.The colors have been

enhanced to bring out detail.

Zones of light-colored,ascending clouds alternate

with bands of dark,

descending clouds. The

clouds travel around theplanet in alternating

eastward and westward

belts at speeds of up to 540kilometers per hour.

Tremendous storms as big

as Earthly continents surgearound the planet. The

Great Red Spot (oval shape

toward the lower-left) is anenormous anticyclonic storm

that drifts along its belt,

eventually circling the entireplanet.

Jupiter with Io and Europa

Voyager 1 took this photo of Jupiter and two of its satellites (Io, left, and Europa) on Feb. 13, 1979. Io is about 350,000 km above

Jupiter's Great Red Spot; Europa is about 600,000 kilometers (375,000 miles) above Jupiter's clouds. Although both satellites have

about the same brightness, Io's color is very different from Europa's. Io's equatorial region show two types of material -- dark orange,broken by several bright spots -- producing a mottled appearance. The poles are darker and reddish. Preliminary evidence suggests

color variations within and between the polar regions. Europa is less strongly colored, although still relatively dark at short

wavelengths. While the dominant large-scale motions are west-to-east, small-scale movement includes eddy-like circulation withinand between the bands. Jupiter is about 20 million km from the spacecraft. (JPL)

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Figure 10.1 Jupiter

Jupiter as seen by the Cassini

spacecraft on its way to Saturn.The storm system called the

Great Red Spot is visible to the

lower right. Unlike manyspacecraft photos, the colors

here are only slightly enhanced.

(NASA/JPL)

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PIA02863: Planetwide Color Movie

The first color movie of Jupiter from NASA's Cassini spacecraft shows what it would look like to peel the entire globe of Jupiter,stretch it out on a wall into the form of a rectangular map, and watch its atmosphere evolve with time. The brief movie clip spans 24

Jupiter rotations between Oct. 31 and Nov. 9, 2000.

Various patterns of motion are apparent all across Jupiter at the cloudtop level seen here. The Great Red Spot shows itscounterclockwise rotation, and the uneven distribution of its high haze is obvious. To the east (right) of the Red Spot, oval storms,

like ball bearings, roll over and pass each other. Horizontal bands adjacent to each other move at different rates. Strings of small

storms rotate around northern-hemisphere ovals. The large grayish-blue "hot spots' at the northern edge of the white EquatorialZone change over the course of time as they march eastward across the planet. Ovals in the north rotate counter to those in the

south. Small, very bright features appear quickly and randomly in turbulent regions, candidates for lightning storms.

The clip consists of 14 unevenly spaced timesteps, each a true color cylindrical projection of the complete circumference of Jupiter,from 60 degrees south to 60 degrees north. The maps are made by first assembling mosaics of six images taken by Cassini's

narrow-angle camera in the same spectral filter over the course of one Jupiter rotation and, consequently, covering the whole planet.

Three such global maps -- in red, green and blue filters -- are combined to make one color map showing Jupiter during one Jovianrotation. Fourteen such maps, spanning 24 Jovian rotations at uneven time intervals comprise the movie. Occasional appearances of

Io, Europa, and their shadows have not been removed.

The smallest visible features at the equator are about 600 km across. In a map of this nature, the most extreme northern andsouthern latitudes are unnaturally stretched out. (NASA/JPL/University of Arizona)

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Figure 10.14 Winds on the Giant Planets

The speed and direction of the east–west winds on Jupiter, Saturn, Uranus, and Neptune, as measured by Voyager, are shown onthese photographic maps. Latitude is shown in the left column of each chart, with the equator being 0°. The dark line shows the wind

speed at each latitude (measured relative to the planet’s core). Notice that Saturn has very strong winds at the equator.

(NASA/JPL)

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The New Solar System ch 14

PIA01093: Turbulence near the Great Red Spot

True and false color mosaics of the turbulent region west of Jupiter's Great Red Spot. The Great Red Spot is on the planetary limb

on the right hand side of each mosaic. The region west (left) of the Great Red Spot is characterized by large, turbulent structures thatrapidly change in appearance. The turbulence results from the collision of a westward jet that is deflected northward by the Great

Red Spot into a higher latitude eastward jet. The large eddies nearest to the Great Red Spot are bright, suggesting that convection

and cloud formation are active there.

The top mosaic combines the violet (410 nm) and near infrared continuum (756 nm) filter images to create a mosaic similar to how

Jupiter would appear to human eyes. Differences in coloration are due to the composition and abundance of trace chemicals in

Jupiter's atmosphere. The lower mosaic uses the Galileo imaging camera's three near-infrared (invisible) wavelengths (756 nm, 727nm, and 889 nm displayed in red, green, and blue) to show variations in cloud height and thickness. Light blue clouds are high and

thin, reddish clouds are deep, and white clouds are high and thick. Purple most likely represents a high haze overlying a clear deep

atmosphere. Galileo is the first spacecraft to distinguish cloud layers on Jupiter.

Jupiter’s Great RedSpot

This dramatic view of

Jupiter's Great Red Spotand its surroundings was

obtained by Voyager 1

on Feb. 25, 1979, whenthe spacecraft was 9.2

million km from Jupiter.

Cloud details as small as160 km across can be

seen here. The colorful,

wavy cloud pattern to theleft of the Red Spot is a

region of extraordinarily

complex end variablewave motion.

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Figure 10.15 The Great Red Spot This is the largest storm system on Jupiter, as seen during the Voyager spacecraft flyby.

Below and to the right of the Red Spot is one of the white ovals, which are similar but smaller high-pressure features. The whiteoval is roughly the size of planet Earth. The colors have been somewhat exaggerated. (JPL/NASA)

The New Solar System ch 14

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Figure 10.3 Galileo Probe Fall into Jupiter

This artist’s impression shows the Galileo probe

descending into the clouds on its parachute just after theprotective heat shield separated. The probe made its

measurements of Jupiter’s atmosphere on December 7,

1995. (NASA/ARC)

PIA01259: Galileo probe’s entry point on Jupiter

[left] - The arrow points to the predicted site at which the Galileo Probe will enter Jupiter's atmosphere on December 7, 1995. At this

latitude, the eastward winds have speeds of about 110 m/s. The white oval to the north of the probe site drifts westward at 6 m/s,

rolling in the winds which increase sharply toward the equator. The Jupiter image was obtained with the high resolution mode ofHubble's Wide Field Planetary Camera 2 (WFPC2). [right] - These four enlarged Hubble images of Jupiter's equatorial region show

clouds sweeping across the predicted Galileo probe entry site, which is at the exact center of each frame (a small white dot has been

inserted at the centered at the predicted entry site). During the intervening time between the first and fourth maps, the winds have

swept the clouds 24,000 km eastward.

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PIA00582: Jupiter's Multi-level Clouds

The top left and right images, at 1.61 !m

and 2.73 !m respectively, show views of

the deep atmosphere down to a pressureabout three times that at the Earth's

surface. The middle image in the top

row, at 2.17 !m, shows only the highestaltitude clouds and hazes because of

strong absorption by H2, the main

constituent of Jupiter's atmosphere. Onlythe Great Red Spot, the highest

equatorial clouds, a small feature at mid-

northern latitudes, and thin, high

photochemical polar hazes can be seen.In the lower left image, at 3.01 !m,

deeper clouds can be seen dimly against

gaseous ammonia and methaneabsorption. The lower middle image, at

4.99 !m,shows the planet's own heat

from the deep, warm atmosphere.

The false color image (lower right)

indicates the temperature. Red areas

denote photons from the hot deepatmosphere leaking through minimal

cloud cover; green denotes cool

tropospheric clouds; blue denotes thecold upper troposphere and lower

stratosphere. The poles appear purplish,

because small-particle hazes allowleakage and reflectivity, while yellowish

regions at temperate latitudes may

indicate tropospheric clouds with smallparticles. A mix of high and low-altitude

aerosols causes the aqua appearance of

the Great Red Spot and equator.

NASA/JPL

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PIA00602: True and false color hotspot mosaic

True and false color views of Jupiter from Galileo show an equatorial "hotspot" on Jupiter and cover 34,000 km by 11,000 km.

The top mosaic combines violet and near infrared to show how Jupiter would appear to human eyes. Differences in colorationare due to trace chemicals. The bottom mosaic combines three near-infrared wavelengths to show variations in cloud height

and thickness. Bluish clouds are high and thin, reddish clouds are low, and white clouds are high and thick. The dark blue

hotspot in the center is a hole in the deep cloud with an overlying thin haze. The light blue region to the left is covered by a very

high haze layer. The multicolored region to the right has overlapping cloud layers of different heights.

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PIA01638: Jovian Lightning and the Daytime Storm

A convective storm (left) and associated lightning (right) in Jupiter's atmosphere. The left image shows the dayside view.

The right images show the box in the dayside view as it appeared 110 minutes later during the night. Multiple lightningstrikes are visible in the night side images, which were taken 3 minutes and 38 seconds apart. The bright, cloudy area in

the dayside view is similar in appearance to a region of upwelling in Earth's atmosphere. The dark, clear region to the west

(left) appears similar to a region of downwelling in Earth's atmosphere. The presence of lightning confirms that this is a siteof moist convection.

The lightning originates below the visible ammonia cloud, which acts as a translucent screen, diffusing the light over awider area. This apparent width can be used to infer the depth of approximately 75 km.

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PIA01639: Water Cloud ThunderstormNorthwest of Great Red Spot

This false-color picture shows a convective

thunderstorm 10,000 km northwest ofJupiter's Great Red Spot. The white cloud in

the center is a tall, thick cloud 1,000 km

across, standing 25 km higher than most ofthe surrounding clouds. Its base extends off

to the left and appears red in this

representation. This red color indicates thatthe cloud base is about 50 km below the

surrounding clouds. Most of the wisps and

features in Jupiter's clouds are ammonia

clouds forming at just less than Earth's sealevel pressure. On Jupiter, water is the only

substance able to form a cloud at about five

times the Earth's sea level pressure. The redbase of this thunderstorm is so deep that it

can only be a water cloud.

It is thought that this storm is analogous to an

Earth thunderstorm, with the cloud's high,

bright, white portion comparable to the

familiar anvil cloud on Earth. Light at differentwavelengths penetrates to different depths in

Jupiter's atmosphere before being reflected

by clouds. In this image, red represents datataken with the 756 nm filter, where Jupiter's

atmospheric gases are mostly transparent

and the light penetrates deeply. Blue andgreen represent data taken with the 889 and

727 nm filters, respectively, where the gases

in Jupiter's atmosphere absorb strongly, soonly high clouds can reflect the light. Thus,

the blue and green areas depict higher

clouds, while the red areas show deep cloudsas well as higher clouds.

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PIA10224: Jupiter Eruptions

Detailed analysis of two continent-sized storms that

erupted in Jupiter's atmosphere in March 2007 showsthat Jupiter's internal heat plays a significant role in

generating atmospheric disturbances. Understanding

these outbreaks could be the key to unlock the mysteriesburied in the deep Jovian atmosphere.

This visible-light image is from NASA's Hubble SpaceTelescope taken on May 11, 2007. It shows the turbulent

pattern generated by the two plumes on the upper left

part of Jupiter.

Understanding these phenomena is important for Earth's

meteorology where storms are present everywhere and

jet streams dominate the atmospheric circulation. Jupiteris a natural laboratory where atmospheric scientists

study the nature and interplay of the intense jets and

severe atmospheric phenomena.

According to the analysis, the bright plumes were storm

systems triggered in Jupiter's deep water clouds that

moved upward in the atmosphere vi gorously andinjected a fresh mixture of ammonia ice and water about

30 km above the visible clouds. The storms moved in the

peak of a jet stream in Jupiter's atmosphere at 600 km/h.Models of the disturbance indicate that the jet stream

extends deep in the buried atmosphere of Jupiter, more

than 100 km below the cloud tops where most sunlight isabsorbed.

NASA/ESA

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PIA10225: Jupiter Eruptions Captured in Infrared

This infrared image shows two bright plume eruptions obtained by the NASA Infrared Telescope Facility on April 5, 2007.

NASA/JPL/IRTF

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Figure 10.16a Storms on Jupiter

We show two versions of the same

Galileo view of the large white ovals that

are the most long-lived storms after theGreat Red Spot. The top image shows

how the scene might appear to the human

eye, while the bottom is in false color (andincludes infrared information). The left

white oval is about 3/4 the size of the

Earth. Note the cyclone-shaped stormbetween the two top ovals.

(JPL/NASA)

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Figure 10.8 Jupiter in Radio Waves This false-color image of Jupiter was made with the Very Large Array (of radio telescopes)

in New Mexico. We see part of the magnetosphere, brightest in the middle because the largest number of charged particles are inthe equatorial zone of Jupiter. The planet itself is slightly smaller than the circular green region in the center. Different colors are

used to indicate different intensities of synchrotron radiation. (Imke dePater/NRAO)

Saturn's Auroras

These images of Saturn's

polar aurora were taken by

NASA's Hubble SpaceTelescope on Jan. 24, 26,

and 28. Each of the three

images of Saturn combinesultraviolet images of the

south polar region (to show

the auroral emissions) withvisible wavelength images of

the planet and rings.

The Hubble images were

obtained during a joint

campaign with NASA'sCassini spacecraft to

measure the solar wind

approaching Saturn and theSaturn kilometric radio

emissions. The strong

brightening of the aurora onJanuary 26 corresponded

with the recent arrival of a

large disturbance in thesolar wind. These results are

presented in three papers,

which appear in the Feb. 17issue of the journal Nature.

NASA/Hubble/Z. Levay and

J. Clarke

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Figure 10.10 Saturn Over Four Years These beautiful images of Saturn were recorded by the Hubble Space Telescope between

1996 and 2000. Since Saturn is tilted by 27 degrees, we see the orientation of the rings around its equator change as the planet

moves along its orbit. Note the horizontal bands in the atmosphere. (R. French, Wellesley College, et al./ Hubble Heritage Team,STScI/NASA)

Saturn and 4 moons

This approximate natural-color image shows Saturn, its rings,

and four of its icy satellites. Three satellites (Tethys, Dione,and Rhea) are visible against the darkness of space, and

another smaller satellite (Mimas) is visible against Saturn's

cloud tops very near the left horizon and just below the rings.The dark shadows of Mimas and Tethys are also visible on

Saturn's cloud tops, and the shadow of Saturn is seen across

part of the rings.

Saturn, second in size only to Jupiter in our Solar System, is

120,660 km in diameter at its equator (the ring plane) but,

because of its rapid spin, Saturn is 10% smaller measuredthrough its poles. Saturn's rings are composed mostly of ice

particles ranging from microscopic dust to boulders in size.

These particles orbit Saturn in a vast disk that is a mere 100meters or so thick. The rings' thinness contrasts with their

huge diameter--for instance 272,400 km for the outer part of

the bright A ring, the outermost ring visible here.

The pronounced concentric gap in the rings, the Cassini

Division (named after its discoverer), is a 3500-km wide

region that is much less populated with ring particles than thebrighter B and A rings to either side of the gap. The rings also

show some enigmatic radial structure ('spokes'), particularly

at left.

This image was synthesized from images taken in Voyager's

blue and violet filters and was processed to recreate anapproximately natural color and contrast.

Saturn, Tethys and Dione

Saturn and two of its moons,Tethys (above) and Dione, were

photographed by Voyager 1 on

November 3, 1980, from 13million km. The shadows of

Saturn's three bright rings and

Tethys are cast onto the cloudtops. The limb of the planet can

be seen easily through the

3,500-km-wide Cassini Division,which separates ring A from

ring B. The view through the

much narrower Encke Division,near the outer edge of ring A is

less clear. Beyond the Encke

Division (at left) is the faintest ofSaturn's three bright rings, the

C- ring or crepe ring, barely

visible against the planet.

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Figure 10.4 Cassini Mission Drops Its ProbeIn this artist’s conception, the Huygens probe drops from the Cassini orbiter into the hazy clouds of Saturn’s

moon Titan. (NASA/JPL)

PIA09893: Beauty Marks

Two dark spots drift acrossthe northern skies of Saturn.

The shadows are cast by the

moons Tethys and Mimas.

Tethys (1,071 km across)

orbits farther from Saturn than

Mimas (397 km across) andcasts the larger of the two

shadows here.

This view looks toward the

unilluminated side of the rings

from about 46 degrees abovethe ringplane.The image was

taken in visible light with the

Cassini spacecraft wide-angle

camera on March 30, 2008.The view was obtained at a

distance of approximately 1.2

million km from Saturn. Imagescale is 66 km per pixel.

NASA/JPL/Space ScienceInstitute

PIA09831: Probing the North

The Cassini spacecraft probes

Saturn's atmosphere, peering

beneath the hazes that obscurethe flowing cloud bands at visible

wavelengths. Brighter areas in

this view generally representfeatures higher in the

atmosphere than darker areas.

This view looks toward the

unilluminated side of the ringsand was acquired from about 38

degrees above the ringplane.

The image was taken with the

Cassini spacecraft wide-angle

camera on Jan. 2, 2008 using acombination of spectral filters

sensitive to wavelengths of

polarized infrared light centered

at 728 and 705 nm. The viewwas obtained at a distance of

approximately 929,000 km from

Saturn. Image scale is 52 km perpixel.

NASA/JPL/Space ScienceInstitute

PIA08410: Hissing Storm

A bright, powerful, lightning-

producing storm churns and

coasts along the lane ofSaturn's southern hemisphere

nicknamed "Storm Alley" by

scientists.

Cassini detected this

particular tempest after nearly

two years during which Saturndid not appear to produce any

large electrical storms of this

kind. The storm appears as abright, irregular splotch on the

planet near lower right.

This storm has now beencontinuously tracked by

Cassini for several months,

whereas previous stormsobserved by the spacecraft

lasted for less than 30 days.

The view looks toward the un-illuminated side of the rings

from about 5 degrees above

the ringplane. Tethys (1,071km across) is seen here in the

foreground, and casts its

shadow onto the highnorthern latitudes.

NASA/JPL/Space Science

Institute

PIA08411: Saturn's Long-lived Storm

These two side-by-side views show the longest-lived electrical storm yet observed on Saturn by NASA's Cassini spacecraft.

The views were acquired more than three months after the storm was first detected from its lightning-produced radio discharges on

Nov. 27, 2007. See PIA08410 for an earlier color view of this storm. Cassini imaging scientists believe the storm to be a vertically

extended disturbance that penetrates from Saturn's lower to upper troposphere.

The view at left was created by combining images taken using red, green and blue spectral filters, and shows Saturn in colors that

approximate what the human eye would see. The storm stands out with greater clarity in the sharpened, enhanced color view at

right. This view combines images taken in infrared, green and violet light at 939, 567 and 420 nanometers respectively andrepresents an expansion of the wavelength region of the electromagnetic spectrum visible to human eyes. This view looks toward

the un-illuminated side of the rings from about 3 degrees above the ringplane. Janus (181 km across) appears as a dark speck just

beneath the rings in both images.

PIA09188: Saturn'sActive North Pole

This Cassini image shows

Saturn's thermal glow at 5microns. This allows the

pole to be revealed during

the nighttime conditionspresently underway during

north polar winter.

Clouds at depths about 75km lower than the clouds

seen at visible wavelengths

block this light, appearingdark in silhouette. To show

clouds as features that are

bright or white rather thandark, the original image has

been contrast reversed to

produce the image shownhere. The nested set of

alternating white and dark

hexagons indicates that the

hexagonal complexextends deep into the

atmosphere, at least down

to the 3-Earth-atmospherepressure level, 75 km

underneath the clouds

seen by Voyager. Thefeature is nearly stationary,

and likely is an unusually

strong pole-encirclingplanetary wave that

extends deep into the

atmosphere.

NASA/JPL/U Arizona

PIA08332: Looking Saturn in the Eye

Cassini stares deep into the swirling hurricane-like vortex at

Saturn's south pole, where the vertical structure of the clouds

is highlighted by shadows. The width of the shadow and theheight of the sun above the local horizon yield a crude

estimate of the height of the surrounding clouds relative to

the clouds in the center. The shadow-casting clouds tower 30to 75 km above those in the center, two to five times greater

than the tallest terrestrial thunderstorms or the height of

clouds surrounding the eye of a terrestrial hurricane. Saturn'shydrogen-helium atmosphere is less dense at comparable

pressures than Earth's atmosphere, and is therefore more

distended in the vertical dimension.

The south polar storm, which displays two spiral arms of

clouds extending from the central ring and spans the dark

area inside a thick, brighter ring of clouds, is approximately8,000 km across.

Eye-wall clouds are a distinguishing feature of hurricanes on

Earth. They form where moist air flows inward across theocean's surface, rising vertically and releasing a load of

precipitation around an interior circular region of descending

air, which is the eye itself.

Though it is uncertain whether moist convection is driving this

storm, as is the case with Earthly hurricanes, the dark 'eye' at

the pole, the eye-wall clouds and the spiral arms togetherindicate a hurricane-like system. The distinctive eye-wall

clouds especially have not been seen on any planet beyond

Earth. Even Jupiter's Great Red Spot, much larger thanSaturn's polar storm, has no eye, no eye-wall, and is

relatively calm at the center.

This giant Saturnian storm is apparently different from

hurricanes on Earth because it is locked to the pole, does not

drift around like terrestrial hurricanes and because it does not

form over liquid water oceans.

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Figure 10.11 Atmospheric Structure for the Jovian Planets In each diagram, the yellow line shows how thetemperature (see the scale on the bottom) changes with altitude. The location of the main layers on each planet is

also shown. (NASA/JPL)

Uranus in true and false colour

These two pictures of Uranus -- one in true color (left) and the other in false color -- were compiled from images returned Jan. 17,

1986, by the narrow-angle camera of Voyager 2. The spacecraft was 9.1 million km from the planet, several days from closestapproach. The picture at left has been processed to show Uranus as human eyes would see it from the vantage point of the

spacecraft. The picture is a composite of images taken through blue, green and orange filters. The darker shadings at the upper right

of the disk correspond to the day-night boundary on the planet. Beyond this boundary lies the hidden northern hemisphere ofUranus, which currently remains in total darkness as the planet rotates. The blue-green color results from the absorption of red light

by methane gas in Uranus' deep, cold and remarkably clear atmosphere. The picture at right uses false color and extreme contrast

enhancement to bring out subtle details in the polar region of Uranus. The very slight contrasts visible in true color are greatlyexaggerated here. In this false-color picture, Uranus reveals a dark polar hood surrounded by a series of progressively lighter

concentric bands. One possible explanation is that a brownish haze or smog, concentrated over the pole, is arranged into bands by

zonal motions of the upper atmosphere. The bright orange and yellow strip at the lower edge of the planet's limb is an artifact of theimage enhancement. In fact, the limb is dark and uniform in color around the planet.

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Figure 10.6 The Strange Seasons on

Uranus

(a) The orbit of Uranus as seen fromabove. At the time Voyager 2 arrived

(position 1), the south pole was facing the

Sun. As we move counterclockwise in thediagram, we see the planet 21 years later

at each step.

(b) The amount of sunlight seen at thepoles and the equator of Uranus over the

course of its 84-year revolution around the

Sun.

Uranus - clouds

Time-lapse Voyager 2 images of Uranus show the movement of two small,

bright, streaky clouds -- the first such features ever seen on the planet. The

clouds were detected in this series of orange-filtered images taken Jan. 14,1986, over a 4.6-hour interval (from top to bottom). At the time, the spacecraft

was about 12.9 million kilometers (8.O million miles) from the planet, whose

pole of rotation is near the center of each disk. Uranus, which is tipped on itsside with respect to the other planets, is rotating in a counterclockwise

direction, as are the two clouds seen here as bright streaks. (The occasional

donut- shaped features that show up are shadows cast by dust in the cameraoptics. The processing necessary to bring out the faint features on the planet

also brings out these camera blemishes.) The larger of the two clouds is at a

latitude of 33 degrees; the smaller cloud, seen faintly in the three lowerimages, lies at 26 degrees (a lower latitude and hence closer to the limb).

Their counterclockwise periods of rotation are 16.2 and 16.9 hours,

respectively. This difference implies that the lower- latitude feature is laggingbehind the higher-latitude feature at a speed of almost 1OO meters per

second (22O mph). Latitudinal bands are also visible in these images. The

faint bands, more numerous now than in previous Voyager images from longer

range, are concentric with the pole of rotation -- that is, they circle the planet inlines of constant latitude.

Neptune clouds with HST

Three images of changing weather conditions were taken in 1994 on October 10 (upper left), October 18 (upper right), andNovember 2 (lower center). 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 filters.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.

Neptune

During August 16 and 17, 1989,

the Voyager 2 narrow- anglecamera was used to photograph

Neptune almost continuously,

recording approximately two andone-half rotations of the planet.

These images represent the

most complete set of full diskNeptune images that the

spacecraft will acquire. This

picture from the sequence showstwo of the four cloud features

which have been tracked by the

Voyager cameras during the past

two months. The large dark ovalnear the western limb (the left

edge) is at a latitude of 22

degrees south and circuitsNeptune every 18.3 hours. The

bright clouds immediately to the

south and east of this oval areseen to substantially change

their appearances in periods as

short as four hours. The seconddark spot, at 54 degrees south

latitude near the terminator

(lower right edge), circuitsNeptune every 16.1 hours. This

image has been processed to

enhance the visibility of smallfeatures, at some sacrifice of

color fidelity.

Neptune’s Great Dark Spot

This bulls-eye view of Neptune's small dark spot (D2) was obtained by Voyager 2's narrow-angle camera on Aug. 24, 1989. The

smallest structures that can be seen are 20 km across. 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 yetbeen 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 cloudsmakes this observation especially valuable.

Neptune - cloud changes

The bright cirrus-like clouds ofNeptune change rapidly, often

forming and dissipating over periods

of several to tens of hours. In thissequence spanning two rotations of

Neptune (about 36 hours) Voyager 2

observed cloud evolution in theregion around the Great Dark Spot

(GDS) at an effective resolution of

about 100 kilometers (62 miles) perpixel. The surprisingly rapid changes

which occur over the 18 hours

separating each panel shows that in

this region Neptune's weather isperhaps as dynamic and variable as

that of the Earth. However, the scale

is immense by our standards theEarth and the GDS are of similar size

and in Neptune's frigid atmosphere,

where temperatures are as low as 55degrees Kelvin (360 F), the cirrus

clouds are composed of frozen

methane rather than Earth's crystalsof water ice.

Neptune bands

This image of Neptunewas taken by Voyager

2's wide- angle camera

when the spacecraftwas 590,000 km

(370,000 miles) from

the planet. The imagehas been processed to

obtain true color

balance. Additionalprocessing was used to

suppress surface

brightness of the whiteclouds. The processing

allows both the clouds'

structure in the dark

regions near the poleand the bright clouds

east of the Great Dark

Spot to be reproducedin this color photograph.

Small trails of similar

clouds trending east towest and large scale

structure east of the

Great Dark Spot allsuggest that waves are

present in the

atmosphere and play alarge role in the type of

clouds that are visible.

Neptune cloud close up

This Voyager 2 high resolution color

image provides obvious evidence of

vertical relief in Neptune's brightcloud 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 thelower left. The bright sides of the

clouds which face the sun are

brighter than the surrounding cloud

deck because they are more directlyexposed to the sun. Shadows can be

seen on the side opposite the sun.

These shadows are less distinct atshort wavelengths (violet filter) and

more distinct at long wavelengths

(orange filter). This can beunderstood if the underlying cloud

deck on which the shadow is cast is

at a relatively great depth, in whichcase scattering by molecules in the

overlying atmosphere will diffuse light

into the shadow. Because moleculesscatter 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 width of the cloud

streaks range from 50 to 200 km, andtheir shadow widths range from 30 to

50 km. Cloud heights appear to be of

the order of 50 km. This correspondsto 2 scale heights.