Rings PHYS Week 6, Part 2

Transcription

1 Rings PHYS Week 6, Part 2 PIA00335: Voyager 1 image of Saturn and its ring four days after closest approach to Saturn. The Saturnian rings, are visible because they reflect sunlight. The translucent nature of the rings is apparent where Saturn can be seen through parts of the rings. Other parts of the rings are so dense with orbiting ice particles that almost no sunlight shines through them and a shadow is cast onto the yellowish cloud tops of Saturn, which in turn, casts a shadow across the rings at right. The black strip within the rings is the Cassini Division, which contains much less orbiting ring material than elsewhere in the rings. NASA/JPL/USGS

2 PIA06193: The Greatest Saturn Portrait...Yet While cruising around Saturn in early October 2004, Cassini captured the most detailed, global natural color view of Saturn and its rings ever made. This mosaic consists of 126 images acquired in a tile-like fashion, covering one end of Saturn's rings to the other and the entire planet in between. The images were taken over the course of two hours, while Cassini was approximately 6.3 million km from Saturn. As the view seen by Cassini during this time changed very little, no reprojection or alteration of any of the images was necessary. Three images (red, green and blue) were taken of each of 42 locations, or "footprints," across the planet. Many of Saturn's splendid features are visible in this one detailed, allencompassing view: subtle color variations across the rings, the thread-like F ring, ring shadows cast against the blue northern hemisphere, the planet's shadow making its way across the rings to the left, and blue-grey storms in Saturn's southern hemisphere to the right. NASA/JPL/Space Science Institute

3 Enchanting Saturn With giant Saturn sheltering Cassini from the Sun's blinding glare, the spacecraft viewed the rings as never before, revealing previously unknown faint rings. The mosaic images were acquired as the spacecraft drifted in Saturn's shadow for about 12 hours, allowing a multitude of unique observations of the microscopic particles that comprise Saturn's faint rings. Ring structures containing these tiny particles brighten substantially at viewing angles where the Sun is almost directly behind. Cassini detected two new faint rings: one coincident with the shared orbit of the moons Janus and Epimetheus and another coincident with Pallene's orbit. The narrowly confined G ring is easily seen here, outside the bright main rings. Encircling the entire system is the more extended E ring. The icy plumes of Enceladus, whose eruptions supply the E ring particles, betray the moon's position in the E ring's left side edge. NASA/JPL/Space Science Institute

4 PIA08176: Saturn's Night Colors This rare color view of Saturn's night side shows how the rings dimly illuminate the southern hemisphere, giving it a dull golden glow. Part of the northern dark side is just visible at top -- the illumination it receives being far less than the south. The unlit side of the rings is shown here. The portion of the rings closest to Cassini is within the dark shadow of Saturn; the bright distant portion is outside the planet's shadow. A crescent Tethys (1,071 km across) appears below the rings at left. Images taken using red, green and blue spectral filters were combined to create this color view. The images were taken with the Cassini spacecraft narrowangle camera on April 2, 2006.

5 PIA06642: Amazing Icy Moons A scene straight out of science fiction, this fantastic view shows, from left to right, Saturn's moon's Mimas, Dione and Rhea, on the far side of Saturn's nearly edge-on rings. The trailing hemispheres of all three moons are sunlit here, and wispy markings can be seen on the limbs of both Dione and Rhea. NASA/JPL/Space Science Institute

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7 PIA09865: Grandeur of the Rings Cassini spies three ring moons in their travels around Saturn. Janus (181 km across) is seen at top, while Pandora (84 km) hugs the outer edge of the narrow F ring. More difficult to spot is Pan (26 km), which is a mere speck in this view. Pan can be seen in the Encke Gap, near center left. The speck seen between the A and F rings at left is a background star. Images taken using red, green and blue spectral filters were combined to create this natural color view. Bright clumps of material in the narrow F ring moved in their orbits between each of the color exposures, creating a chromatic misalignment that provides some sense of the continuous motion in the ring system. NASA/JPL/Space Science Institute

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10 PIA09890: The Orbiting Fleet A fleet of small moons patrols the outskirts of Saturn's icy rings. The shepherd moons Prometheus (102 km across) and Pandora (84 km) are seen respectively interior and exterior to the narrow F ring at lower left. Janus (181 km) appears at center right, and Mimas (397 km) is visible at lower right. A background star is faintly visible directly between Prometheus and Mimas. NASA/JPL/Space Science Institute

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12 PIA10448: F Ring Channels A train of diagonal channels in Saturn's F ring follows behind the moon Prometheus. Each of these features was created during a previous close approach of Prometheus to the ring. When the moon is at the farthest point in its orbit of the planet, it strays close to (and often into) the F ring. The resulting gravitational disturbance leaves behind the channels seen here. Atlas (30 km across) appears at lower right. NASA/JPL/Space Science Institute 12

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14 Jupiter s Rings Revealed Why does Jupiter have rings? Jupiter's rings were discovered in 1979 by the passing Voyager 1 spacecraft, but their origin has always been a mystery. Recent data from the Galileo spacecraft currently orbiting Jupiter now confirms that these rings were created by meteoroid impacts on small nearby moons. As a small meteoroid strikes tiny Adrastea, for example, it will bore into the moon, vaporize, and explode dirt and dust off into a Jovian orbit. Pictured above is an eclipse of the Sun by Jupiter, as viewed from Galileo. Small dust particles high in Jupiter's atmosphere, as well as the dust particles that compose the rings, can be seen by reflected sunlight. Credit: M. Belton (NOAO), J. Burns (Cornell) et al., Galileo Project, JPL, NASA

15 Jupiter s ring halo These images were obtained when Galileo was in Jupiter's shadow, peering back toward the Sun. The arc on the far right of the image is produced when sunlight is scattered by small particles comprising Jupiter's upper atmospheric haze. The ring also efficently scatters light, indicating that much of its brightness is due to particles that are microns or less in diameter. Jupiter's ring system is composed of a flat main ring, a lenticular halo interior to the main ring, and the gossamer ring, outside the main ring. A faint mist of particles can be seen above and below the main rings. This vertically extended "halo" is unusual in planetary rings, and is probably caused by electromagnetic forces pushing the smallest grains out of the ring plane. To accentuate faint features in the bottom image of the ring halo, different brightnesses are represented by color. Brightest features are white or yellow and the faintest are purple.

16 PIA01278: Hubble Tracks Clouds on Uranus Hubble detected the rotation of Uranus in NIR images taken 90 min apart. The five clouds visible near the right limb rotated counterclockwise during the time between both images. Another cloud rotated along the path shown by the white arrow. The rings of Uranus are extremely faint in visible light but quite prominent in the near infrared. The brightest ring, the epsilon ring, has a variable width. Its widest and thus brightest part is at the top. Two fainter, inner rings are visible. Eight of the 10 small Uranian satellites can be seen in both images. Their sizes range from 40 km (Bianca) to 150 km (Puck). These eight satellites revolve around Uranus in less than a day. NASA/JPL/STScI 16

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18 Uranus - rings This dramatic Voyager 2 picture reveals a continuous distribution of small particles throughout the Uranus ring system Voyager took this image while in the shadow of Uranus. This unique geometry allows us to see lanes of fine dust particles not visible from other viewing angles. The combination of this unique geometry and a long, 96 second exposure allowed this spectacular observation, acquired through the clear filter of Voyager's wide-angle camera The long exposure produced a noticeable, nonuniform smear as well as streaks due to trailed stars.

19 Uranus - shepherd moons Voyager 2 discovered two 'shepherd' satellites associated with the rings of Uranus. The two moons U7 and 1986U8 -- are seen here on either side of the bright epsilon ring; all nine of the known Uranian rings are visible. The image, taken Jan , was processed to enhance narrow features. The epsilon ring appears surrounded by a dark halo as a result; occasional blips seen on the ring are also artifacts. Lying inward from the epsilon ring are the delta, gamma and eta rings; then the beta and alpha rings; and finally the barely visible 4, 5 and 6 rings. The rings range in width from about 100 km at the widest part of the epsilon ring to only a few kilometers for most of the others. The discovery of the two ring moons 1986U7 and 1986U8 is a major advance in our understanding of the structure of the Uranian rings and is in good agreement with theoretical predictions of how these narrow rings are kept from spreading out. Based on likely surface brightness properties, the moons are of roughly 20- and 30-km diameter, respectively.

20 Neptune s rings In this Voyager wide-angle image taken on Aug , the two main rings of Neptune can be clearly seen. In the lower part of the frame the originally announced ring arc, consisting of three distinct features, is visible. This feature covers about 35 degrees of longitude and has yet to be radially resolved in Voyager images. From higher resolution images it is known that this region contains much more material than the diffuse belts seen elsewhere in its orbit, which seem to encircle the planet. This is consistent with the fact that ground- based observations of stellar occultations by the rings show them to be very broken and clumpy. The more sensitive wide-angle camera is revealing more widely distributed but fainter material. Each of these rings of material lies just outside of the orbit of a newly discovered moon. One of these moons, 1989N2, may be seen in the upper right corner. The moon is streaked by its orbital motion, whereas the stars in the frame are less smeared. The dark area around the bright moon and star are artifacts of the processing required to bring out the faint rings. This wideangle image was taken from a range of 2 million km, through the clear filter.

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23 Fig. 9. The known planetary ring systems are compared by making the planets radii the same size. Illustrated here are the distribution of ring material, nearby satellite locations, the synchronous orbit radius, and the Roche distances for satellites of density 1 or 2 g/cc The New Solar System ch 16

24 Fig. 9. The known planetary ring systems are compared by making the planets radii the same size. Illustrated here are the distribution of ring material, nearby satellite locations, the synchronous orbit radius, and the Roche distances for satellites of density 1 or 2 g/cc The New Solar System ch 16