Space, time & Cosmos Lecture 3: Solar system - outer planets & (a little bit) beyond

1. Space, time & CosmosLecture 3: Solar system - outer planets & (a little bit) beyond Prof. Ken Tsang Cosmos3

2. The four gas giants against the Sun: Jupiter, Saturn, Uranus, Neptune (Sizes to scale) Cosmos3

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4. Visible Planet Orbits This diagram shows the relative size of the orbits of the seven planets visible to the naked eye. All the orbits are nearly circular (but slightly elliptical) and nearly in the same plane as Earth's orbit (called the ecliptic).The diagram is from a view out of the ecliptic plane and away from the perpendicular axis that goes through the Sun. Cosmos3

5. Outer Planet Orbits This shows the relative sizes and positions of the orbits of the planets farther from the Sun than Earth. All the planets have orbits that are ellipses with the Sun at one of the foci, and the ellipses are in different planes. However, only Pluto has a noticeably noncircular orbit that lies in a different plane from the other planets. Cosmos3

6. Jupiter based on a 1979 image from the Voyager 1 spacecraft and enhanced by the U.S. Geological Survey Cosmos3

7. Jupiter The Romans named the planet after the Roman god Jupiter (the god of sky and thunder). When viewed from Earth, Jupiter is the third brightest object in the night sky after the Moon and Venus. (At certain points in its orbit, Mars can briefly exceed Jupiter's brightness.) The most massive planet in our solar system, with four planet-sized moons and many smaller moons, Jupiter forms a kind of miniature solar system. Jupiter resembles a star in composition. In fact, if it had been about eighty times more massive, it would have become a star rather than a planet. Cosmos3

8. "Jupiter et Thétis" by Jean Ingres, 1811. Jupiter or Jove was the king of the gods, and the god of sky and thunder. Cosmos3

9. Time-lapse sequence from the approach of Voyager I to Jupiter, showing the motion of atmospheric bands, and circulation of the great red spot. Cosmos3

10. Jupiter's upper atmosphere is composed of about 88-92% hydrogen and 8-12% helium by percent volume or fraction of gas molecules, or approximately 75% hydrogen and 24% helium by mass. The interior contains denser materials such that the distribution is roughly 71% hydrogen, 24% helium and five percent other elements by mass. The atmosphere contains trace amounts of methane, water vapor, ammonia, and silicon-based compounds. Jupiter is 2.5 times more massive than all the other planets in our Solar System combined. Jupiter's volume is equal to 1,317 Earths, yet is only 318 times as massive. Jupiter is thought to consist of a dense core with a mixture of elements, a surrounding layer of liquid metallic hydrogen with some helium, and an outer layer predominantly of molecular hydrogen. Beyond this basic outline, there is still considerable uncertainty. Cosmos3

11. This cut-away illustrates a model of Jupiter's interior. In the upper layers the atmosphere transitions to a liquid state above a thick layer of metallic hydrogen. In the center there may be a solid core of heavier elements. Cosmos3

12. Although Jupiter would need to be about 75 times as massive to fuse hydrogen and become a star, the smallest red dwarf is only about 30 percent larger in radius than Jupiter. This has led some astronomers to term it a "failed star“. In the novel, 2010: Odyssey Two, written by Arthur C. Clarke in 1987, Jupiter's density was mysteriously increased until the planet achieves nuclear fusion, becoming a mini-sun which Earth eventually names "Lucifer“, and destroying the American space ship Discovery entirely. Cosmos3

13. This dramatic view of Jupiter's Great Red Spot and its surroundings was obtained by Voyager 1 on February 25, 1979, when the spacecraft was 9.2 million km (5.7 million mi) from Jupiter. Cloud details as small as 160 km (100 mi) across can be seen here. The colorful, wavy cloud pattern to the left of the Red Spot is a region of extraordinarily complex and variable wave motion. Cosmos3

14. Jupiter is perpetually covered with clouds composed of ammonia crystals and possibly ammonium hydrosulfide. The outer atmosphere is visibly segregated into several bands at different latitudes, resulting in turbulence and storms along their interacting boundaries. The best known feature of Jupiter is the Great Red Spot, a persistent anti-cyclonic storm located 22° south of the equator that is larger than Earth. It is known to have been in existence since at least 1831, and possibly since 1665. Mathematical models suggest that the storm is stable and may be a permanent feature of the planet. The storm is large enough to be visible through Earth-based telescopes. Cosmos3

15. Rings of Jupiter: third ring system discovered in the Solar System, after those of Saturn and Uranus, first observed in 1979 by the Voyager 1 space probe Jupiter has a faint planetary ring system composed of three main segments: an inner torus of particles known as the halo, a relatively bright main ring, and an outer "gossamer" ring. These rings appear to be made of dust, rather than ice as is the case for Saturn's rings. Cosmos3

16. Rings of Jupiter Cosmos3

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18. Triple EclipseOn Earth, we witness a solar eclipse when our Moon's shadow sweeps across our planet's face as it passes in front of our Sun. Jupiter, however, has four moons roughly the same size as Earth's Moon. The shadows of three of them occasionally sweep simultaneously across Jupiter. The image was taken March 28, 2004, with Hubble's Near Infrared Camera and Multi-Object Spectrometer. Closer inspection by NASA's Hubble Space Telescope reveals that these spots are actually a rare alignment of three of Jupiter's largest moons - Io, Ganymede, and Callisto - across the planet's face. In this image, the telltale signatures of this alignment are the shadows [the three black circles] cast by the moons. Io's shadow is located just above center and to the left; Ganymede's on the planet's left edge; and Callisto's near the right edge. Only two of the moons, however, are visible in this image. Io is the white circle in the center of the image, and Ganymede is the blue circle at upper right. Callisto is out of the image and to the right. Seeing three shadows on Jupiter happens only about once or twice a decade. Why is this triple eclipse so unique? Io, Ganymede, and Callisto orbit Jupiter at different rates. Their shadows likewise cross Jupiter's face at different rates. For example, the outermost moon Callisto orbits the slowest of the three satellites. Callisto's shadow moves across the planet once for every 20 shadow crossings of Io. Add the crossing rate of Ganymede's shadow and the possibility of a triple eclipse becomes even more rare. Viewing the triple shadows in 2004 was even more special, because two of the moons were crossing Jupiter's face at the same time as the three shadows. Jupiter appears in pastel colors in this photo because the observation was taken in near-infrared light. Astronomers combined images taken in three near-infrared wavelengths to make this color image. The photo shows sunlight reflected from Jupiter's clouds. In the near infrared, methane gas in Jupiter's atmosphere limits the penetration of sunlight, which causes clouds to appear in different colors depending on their altitude. Cosmos3

19. Jupiter has 63 named natural satellites. Of these, 47 are less than 10 kilometres in diameter and have only been discovered since 1975. The four largest moons, known as the "Galilean moons", are Io, Europa, Ganymede and Callisto. Io Callisto Ganymede Cosmos3

20. Jupiter's four largest moons, known as the Galilean satellites. From top to bottom, the moons shown are Io, Europa, Ganymede and Callisto. The Great Red Spot, a storm in Jupiter's atmosphere, is at least 300 years old. Winds blow counter-clockwise around the Great Red Spot at about 400 kilometers per hour (250 miles per hour). The storm is larger than one Earth diameter from north to south, and more than two Earth diameters from east to west. Cosmos3

21. Facts about Jovian moons learned in the past 30 years Io is the most volcanically active body in our solar system. Ganymede is the largest planetary moon and is the only moon in the solar system known to have its own magnetic field. A liquid ocean may lie beneath the frozen crust of Europa. Icy oceans may also lie deep beneath the crusts of Callisto and Ganymede. In 2003 alone, astronomers discovered 23 new moons orbiting the giant planet, giving Jupiter a total moon count of 49 officially named -- the most in the solar system. The numerous small outer moons may be asteroids captured by the giant planet's gravity. Cosmos3

22. The Laplace resonance exhibited by three inner Galilean moons. The ratios in the figure are of orbital periods. Cosmos3

23. The Galilean moons seen with an amateur telescope Photo : Bresson Thomas Cosmos3

24. Jupiter with three of its Galilean satellites (from lower left to upper right): Io, Europa, and Callisto. Sky & Telescope's editor in chief, Rick Fienberg, recorded this scene on March 16, 2003, using a 12-inch (30-centimeter) Meade Schmidt-Cassegrain telescope and a Canon digital camera. Cosmos3

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26. Io and GanymedeDate: 01.17.2007The New Horizons Long Range Reconnaissance Imager (LORRI) took this 4-millisecond exposure of Jupiter and two of its moons at 01:41:04 UTC on January 17, 2007. The spacecraft was 68.5 million kilometers (42.5 million miles) from Jupiter, closing in on the giant planet at 41,500 miles (66,790 kilometers) per hour. The volcanic moon Io is the closest planet to the right of Jupiter; the icy moon Ganymede is to Io's right. The shadows of each satellite are visible atop Jupiter's clouds; Ganymede's shadow is draped over Jupiter's northwestern limb. Ganymede's average orbit distance from Jupiter is about 1.07 million kilometers (620,000 miles); Io's is 422,000 kilometers (262,000 miles). Both Io and Ganymede are larger than Earth's moon; Ganymede is larger than the planet Mercury. Cosmos3

27. Eruption at Tvashtar Catena, Io, in color Cosmos3

28. NASA's Galileo spacecraft caught this volcanic eruption in action on Jupiter's moon Io on November 25, 1999. This mosaic shows Tvashtar Catena, a chain of calderas, in enhanced color. It combines low resolution (1.3 kilometers, or .8 miles, per picture element) color images of Io taken on July 3, 1999 with the much higher resolution (180 meters, or 197 yards, per picture element) black and white images taken in November. The molten lava was hot enough, and therefore bright enough, to saturate, or overexpose, Galileo's camera (original image is inset in lower right corner). Cosmos3

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30. Capturing CallistoDate: 02.27.2007The New Horizons Long Range Reconnaissance Imager (LORRI) captured these two images of Jupiter's outermost large moon, Callisto, as the spacecraft flew past Jupiter in late February. New Horizons' closest approach distance to Jupiter was 2.3 million kilometers (1.4 million miles), not far outside Callisto's orbit, which has a radius of 1.9 million kilometers (1.2 million miles). However, Callisto happened to be on the opposite side of Jupiter during the spacecraft's pass through the Jupiter system, so these images, taken from 4.7 million kilometers (3.0 million miles) and 4.2 million kilometers (2.6 million miles) away, are the closest of Callisto that New Horizons obtained. Callisto's ancient, crater-scarred surface makes it very different from its three more active sibling satellites, Io, Europa and Ganymede. Callisto, 4,800 kilometers (3000 miles) in diameter, displays no large-scale geological features other than impact craters, and every bright spot in these images is a crater. The largest impact feature on Callisto, the huge basin Valhalla, is visible as a bright patch at the 10 o'clock position. The craters are bright because they have excavated material relatively rich in water ice from beneath the dark, dusty material that coats most of the surface. Cosmos3

31. Magnetosphere of Jupiter Jupiter's broad magnetic field is 14 times as strong as the Earth's, ranging from 4.2 gauss (0.42 mT) at the equator to 10–14 gauss (1.0–1.4 mT) at the poles, making it the strongest among the Solar planets. The field traps a sheet of ionized particles from the solar wind, generating a highly-energetic magnetic field outside the planet — the magnetosphere. Electrons within the magnetosphere generate a strong radio signature that produces bursts in the range of 0.6–30 MHz. Cosmos3

32. Hubble Space Telescope image of Jupiter aurora in UV Bright streaks and dots are caused by magnetic flux tubes connecting Jupiter to its largest moons-- Io: bright streak on the far left; Ganymede: bright dot below center; Europa: dot right of Ganymede dot Cosmos3

33. Saturn Cosmos3

34. A Hubble Space Telescope image of Saturn in true color. Cosmos3

35. Surely one of the most gorgeous sights the solar system has to offer, Saturn sits enveloped by the full splendor of its rings. Cosmos3

36. Saturn,named after the Roman god of agriculture and harvest, is the second largest planet in the Solar System, the most distant of the five planets known to the ancients. Saturn has a prominent system of rings, consisting mostly of ice particles with a smaller amount of rocky debris and dust. Cosmos3

37. Saturn: Rings While the other three gas planets in the solar system - Jupiter, Uranus and Neptune - have rings orbiting around them, Saturn's are by far the largest and most spectacular. With a thickness of about 1 kilometer (3,200 feet) or less, they span up to 282,000 km. Named alphabetically in the order they were discovered, the rings are relatively close to each other, with the exception of the Cassini Division, a gap measuring 4,700 kilometers (2,920 miles). The main rings are, working outward from the planet, known as C, B, and A. The Cassini Division is the largest gap in the rings and separates Rings B and A. In addition a number of fainter rings have been discovered more recently. The D Ring is exceedingly faint and closest to the planet. The F Ring is a narrow feature just outside the A Ring. Beyond that are two far fainter rings named G and E. The rings show a tremendous amount of structure on all scales; some of this structure is related to gravitational perturbations by Saturn's many moons, but much of it remains unexplained. Cosmos3

38. Saturn's system of rings is highly structured with many interesting features. Alongside the gaps between the rings there are also moons that act like shepherds keeping the rings in shape and the gaps clear of material. Cosmos3

39. Encke gap A ring Cassini Division B ring Cosmos3 C ring

40. This amazing close-up of Saturn's rings reveals their incredible variety. In some regions there are wavelike structures, while in other places the rings' structure appears to be more chaotic. This image shows (from top to bottom) the A ring with the Encke gap, the Cassini Division, and the B and C rings. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on 26 April 2005 at a distance of approximately 2.3 million kilometres from Saturn. The image scale is 14 kilometres per pixel. There are thousands of rings made up of billions of particles of ice and rock. The particles range in size from a grain of sugar to the size of a house. The rings are believe to be pieces of comets, asteroids or shattered moons that broke up before they reached the planet. Each ring orbits at a different speed around the planet. Cosmos3

41. This highly enhanced color view was assembled from clear, orange and ultraviolet frames obtained August 17, 1981 from a distance of 8.9 million kilometers (5.5 million miles). Cosmos3

42. History of Saturn’s Rings In 1610, Italian astronomer Galileo Galilei was the first to gaze at Saturn through a telescope. To his surprise, he saw a pair of objects on either side of the planet. He sketched them as separate spheres and wrote that Saturn appeared to be triple-bodied. Continuing his observations over the next few years, Galileo drew the lateral bodies as arms or handles attached to Saturn. In 1659, Dutch astronomer Christiaan Huygens, using a more powerful telescope than Galileo's, proposed that Saturn was surrounded by a thin, flat ring. In 1675, Italian-born astronomer Jean-Dominique Cassini discovered a 'division' between what are now called the A and B rings. It is now known that the gravitational influence of Saturn's moon Mimas is responsible for the Cassini Division, which is 4,800 kilometers (3,000 miles) wide. Cosmos3

43. Like Jupiter, Saturn is made mostly of hydrogen and helium. Its volume is 755 times greater than that of Earth. Winds in the upper atmosphere reach 500 meters (1,600 feet) per second in the equatorial region. (In contrast, the strongest hurricane-force winds on Earth top out at about 110 meters, or 360 feet, per second.) These super-fast winds, combined with heat rising from within the planet's interior, cause the yellow and gold bands visible in the atmosphere. Cosmos3

44. Though Saturn's magnetic field is not as huge as Jupiter's, it is still 578 times as powerful as Earth's. Saturn, the rings, and many of the satellites lie totally within Saturn's enormous magnetosphere, the region of space in which the behavior of electrically charged particles is influenced more by Saturn's magnetic field than by the solar wind. Hubble Space Telescope images show that Saturn's polar regions have aurorae similar to Earth's. Aurorae occur when charged particles spiral into a planet's atmosphere along magnetic field lines. Cosmos3

45. Saturn's Moons Saturn currently has 60 known moons, five of which have been discovered in data gathered by Cassini. Two more possible discoveries by Cassini still await final confirmation, as the objects might not be proper moons but instead are transient in nature. When Cassini-Huygens was launched in 1997 there were only 18 known saturnian moons. In addition to the Cassini discoveries, reanalysis of data from the Voyager 2 spacecraft, as well as Hubble observations and ground-based observations of Saturn have led to the further discoveries. Cosmos3

46. Cassini–Huygens is a joint NASA/ESA robotic spacecraft mission currently studying the planet Saturn and its moons. The spacecraft consists of two main elements: the NASA Cassini orbiter, named after the Italian-French astronomer Giovanni Domenico Cassini, and the ESA Huygens probe, named after the Dutch astronomer, mathematician and physicist Christiaan Huygens. It was launched on October 15, 1997 and entered into orbit around Saturn on July 1, 2004. On December 25, 2004 the Huygens probe separated from the orbiter at approximately 02:00 UTC; it reached Saturn's moon Titan on January 14, 2005 where it made an atmospheric descent to the surface and relayed scientific information. On April 18, 2008, NASA announced a two year extension of the mission. Cassini is the first spacecraft to orbit Saturn and the fourth to visit it. Cosmos3

47. A Cassini spacecraft image of Titan's thick atmosphere. Saturn has 52 known natural satellites (moons) and there are probably many more waiting to be discovered. Saturn's largest satellite, Titan, is a bit bigger than the planet Mercury. (Titan is the second-largest moon in the solar system; only Jupiter's moon Ganymede is bigger.) Titan is shrouded in a thick, nitrogen-rich atmosphere that might be similar to what Earth's was like long ago. Further study of this moon promises to reveal much about planetary formation and, perhaps, about the early days of Earth. Saturn also has many smaller 'icy' satellites. Cosmos3

48. Titan's internal structure. Cosmos3

49. Atmosphere of Titan Visible light cannot escape from the veil of orange smog that covers Titan's surface. The moon's dry cold atmosphere causes a 300 km thick layer of smog to build up. The smog, just like on Earth, forms when sunlight interacts with hydrocarbon molecules. Visit the NASA page for more detail on Titan: http://saturn.jpl.nasa.gov/multimedia/flash/Titan/index.html Cosmos3

50. Saturn and two of its moons, Tethys (above) and Dione Cosmos3