Chapter 11 The Jovian Planets

Transcription

1 Chapter 11 The Jovian Planets The Jovian planets: Jupiter, Saturn, Uranus and Neptune Using Venus transit it was possible to get a good value of the AU (1639). Knowing the AU, it is possible to calculate the size of the planets. Their physical size can be calculated using their angular size and the distance Physical size = angular size x (2 π x distance)/360 (Read textbook page 30) Once the distances have been determined it is possible to calculate the orbital radius of the satellites. The mass of the planets can be calculated by measuring the orbital radius and the orbital period of the satellites (and using Newton s modified 3 rd Kepler law) Knowing the mass and diameter, allows to calculate the densities, proving that the Jovian planets are very different from the terrestrial planets

2 The Jovian planets: Jupiter, Saturn, Uranus and Neptune Their masses are large compared with terrestrial planets, from 17 to 320 times the Earth s mass They are gaseous Low density All of them have rings All have many satellites All that we see of these planets are the top of the clouds No solid surface is visible The density increases toward the interior of the planet All of them located a larger distances from the Sun, beyond the orbit of Mars The Jovian Planets

3 Distance from Sun: 5.2 AU Diameter: 11 diameter of Earth Mass: 318 mass of Earth Density: 1,3 g/cm^3 Escape velocity: 60 m/s Surface temperature: 120 K Composition: mostly H and He Jupiter Named after the most powerful Roman god It is the third-brightest object in the night sky (after the Moon and Venus) It is the largest of the planets Atmospheric cloud bands - different than terrestrial planets The image shows the Great Red spot, a feature that has been present since it was first seen with a telescope more than 350 years ago Many satellites, about 66. The four largest are called Galilean satellites. Discovered by Galileo in 1610 A faint system of rings. Too faint to see them with ground -based telescopes

4 Saturn The second largest planet Visible with the naked eye Named after the father of Jupiter Almost twice Jupiter s distance from the Sun Similar banded atmosphere Uniform butterscotch hue Many satellites. The largest is Titan, the only satellite to have a permanent atmosphere Spectacular ring system seen with even small telescopes This was the last planet know to the ancients Distance from Sun: 9.24 AU Diameter: 9.5 Earth diameter Mass: 95 Earth mass Density: 0.71 g/cm^3 Escape velocity: 36 km/s Surface temperature: 97 K Composition: mostly H and He

5 Uranus Distance from Sun: 19.2 AU Diameter: 4.0 Earth diameter Mass: 14 mass of Earth Density: 1.24 g/cm^3 Escape velocity: 21 m/s Surface temperature: 58 K Composition: H compounds, H, Discovered by William Herschel in 1781 Named after the father of Saturn Barely visible to naked eye, even under dark skies Featureless atmosphere Green, bluish color due to presence of methane in the atmosphere Methane absorb the red part of the spectrum and reflect the blue It showed small deviations in the expected orbit. Was another planet influencing its motion? The deviation led to the discovery of Neptune Faint ring system not visible with ground-based telescopes

6 Neptune This is the other planet whose gravitational pull is influencing the orbit of Uranus It s mass and orbit were determined first, in 1845 by the English John Adams and a bit later by the French astronomer Urbain Leverrier In 1846 it was discovered by the German astronomer Johann Galle Too faint, cannot be seen with naked eye It has a bluish color due to the presence of methane in the atmosphere Faint ring system, not visible with ground-based telescopes Distance from Sun: 30.1 AU Diameter: 3.9 Earth diameter Mass: 17 Earth mass Density: 1.67 g/cm^3 Escape velocity: 24 km/s Surface temperature: 59 K

7 Spacecraft Exploration of Jovian Planets Pioneer 10 and 11. Reached Jupiter around 1973 Voyager 1and 2 left Earth in 1977 Reached Jupiter in March and July of 1979 Used Jupiter s strong gravity to send them on to Saturn - gravity assist Voyager 2 used Saturn s gravity to propel it to Uranus and then on to Neptune Studied planetary magnetic fields and analyzed multi-wavelength radiation Both are now headed out into interstellar space!

8 Space Craft Exploration of Jovian Planets, more recent missions Galileo - launched in 1989 and reached Jupiter in December 1995 Gravity assists from Venus and Earth Spacecraft has two components: atmospheric probe and orbiter Probe descended into Jupiter s atmosphere Orbiter entered orbit, went through moon system Juno mission: On it way to Jupiter. Scheduled to arrive at Jupiter in July 2016 Cassini mission to Saturn arrived June 30, 2004 It consist of the orbiter and the Huygens probe Orbiter will orbit Saturn and its moons for 4 years (at the present it is active and returning data) Huygens probe launched from the orbiter. Descended on Titan January 14, 2005 to study Saturn s moon.

9 The mass-radius dependence for a H and He planet Notice that Jupiter is slightly larger than Saturn even if it is about 3 times more massive Adding more mass, compress the planet increasing its density but not its size

10 Distortion of Jovian planets due to fast rotation Rapid rotation creates a bulge around the equator. The shape departs from a perfect sphere Saturn is distorted, 10% larger at equator Jupiter shape is also distorted, about 7% larger at equator. Caused by fast rotation, large radius

11 Jupiter s Interior (And Earth for comparison) Metallic hydrogen is a superconductor. A superconductor conduct electricity with minimum or no resistance

12 Jovian planets interiors There is no data on direct measurements of the interior of the Jovian planets The structure of the interior of the Jovian planets is obtained through modeling based on the composition and the mass

13 Jupiter s Atmosphere Characterized by two main features: Colored bands (zones and belts) and the Great Red Spot Atmospheric content: molecular hydrogen 86% helium 14% small amounts of methane, ammonia, and water vapor The Great Red Spot seems to be a hurricane that has lasted for more than 350 years The bands are caused by convections and high wind velocity at the top of the clouds Darker belts lie atop downward moving convective cells Lighter zones are above upward moving cells Belts are low-pressure, zones are high pressure Jupiter s rapid rotation causes wind patterns to move East/West along equator The color of the bands may be due to the presence of trace elements sulfur and phosphorus and compounds of molecules of these elements The formation of these molecules is sensitive to temperature and that may account for the different colors of Belts and Zones

14 Weather on Jupiter Main weather feature : Great Red Spot! Swirling hurricane winds Has lasted for more than 350 years! Diameter twice that of Earth Rotates with planet s interior The spot appears to be confined and powered by the zonal flow. Not much change in the latitude of the Great Red Spot Smaller storms look like white ovals (this one is over 40 years old) Why do the storms last so long? On Earth, hurricanes loose power when then come upon land No solid surface on Jupiter, just gas. Nothing to stop them once they start

15 Temperature profile of Jovian planets

16 Jovian planets - The axis tilt and magnetic fields All Jovian planets (and the Earth) have strong magnetic fields. They are caused by the rapid rotation and liquid conductive cores or mantles. All of them emit low frequency radio emission. The emission is caused by the interaction of electrons with the magnetic field The magnetic fields are offset from the center and have different tilt respect to the rotational axis Uranus has the most inclined rotational axis: It has extreme seasons!

17 Jupiter s Magnetosphere Auroral emission

18 Jupiter magnetic field and the low frequency emission Jupiter has the strongest magnetic field of all the planets Jupiter produces strong radio emission at short wavelength or low frequencies (Less than 39 MHz) The radio emission is generated by electrons accelerated in the magnetic field lines connecting Io and the Jupiter This radio emission can be received with a simple antenna Two types of radio emission are common: L (long) bursts and S (Short) bursts

19 Jovian Magnetospheres All the Jovian planets have relatively strong magnetic fields All emit low frequency radio emission Jupiter has the strongest magnetic field Jupiter emit low and high frequency emission (two different mechanisms) The cutoff of Jupiter low frequency radio emission is around 40 MHz, the highest frequency of all the planets. It is the only planet from which we can receive the low frequency emission in ground-based radio telescopes The rest of the Jovian planets emit low radio emission but it cannot be received in ground-based radio telescopes. The frequency is too low and cannot propagate through the

20 Weather on Saturn Computer enhanced image shows bands, oval storm systems, and turbulent flow patterns like those seen on Jupiter The colors in the image are not the natural colors of Saturn

21 The Atmospheres of Uranus and Neptune The atmospheric content: molecular hydrogen 84% helium 14% methane 2% (Uranus) 3% (Neptune) Abundance of methane gives these planets their blue color Methane absorbs longer wavelength light (red) and reflects short wavelength light (blue)

22 Uranus and Neptune bluish color and presence of methane in their atmospheres

23 Weather on Uranus and Neptune Uranus Few clouds in the cold upper atmosphere featureless Upper layer of haze blocks out the lower, warmer clouds Neptune Upper atmosphere is slightly warmer than Uranus (despite its further distance from Sun) More visible features (thinner haze, less dense clouds lie higher) Storms Great Dark Spot Seen in 1989 (Images taken by Voyager spacecraft) gone in 1996 (Hubble telescope)

24 A Summary of the Jovian Planet Properties Most of their mass is Hydrogen and Helium light elements = low densities High surface gravity allows their atmospheres to retain these light elements Dense compact core at the center No SOLID surface The gaseous atmosphere becomes denser (eventually liquid) at core Differential Rotation outer regions rotate at a different rate than the inner regions

25 The moons or satellites of the Jovian planets

26 Jovian Planet Moons There are: Six large moons, similar in size to our Moon 12 medium-sized to 1500km Many small moons Jupiter - 67 moons Saturn - 62 moons Uranus - 27 moons Neptune - 13 moons Jupiter s Galilean satellites: Io - Jupiter s moon with active volcanoes! Europa - Jupiter s moon covered with frozen water - possible an ocean of liquid water beneath Ganymede and Callisto - similar in size to our moon, a bit larger. Ganymede is the largest moon in the solar system Four largest Jupiter moons - Galilean Moons

27 Jupiter Medium & large moons Saturn Uranus Neptune All these moons have enough self-gravity to be spherical Some are now or were in the past geologically active. Most of them have substantial amounts of ice.

28 Jupiter s Galilean Moons An Unusual Family Moon Io Europa Ganymede Callisto

29 What makes Jupiter s Galilean moons unusual? Io has several active volcanoes. Europa may have an ocean of liquid water under its ice. Ganymede & Callisto may also have sub-surface oceans? How can we account for the unusual features? Shouldn t they be cold & dead?

30 Io s Volcanoes So far about 80 active volcanoes have been identified using data mainly from Voyager and Galileo spacecrafts Volcanic eruptions mainly composed of sulfur & sulfur dioxide Volcanic plumes about 150 km high and 300 km wide Variety of volcanic hot spots Large lava lakes made of liquid sulfur Tidal heating provides the source of volcanic activity. Io orbit is elliptical. Compressing and stretching of Io release heat.

31 Io: Two images separated by 15 years

32 A better view of Io s volcanoes

33 Tidal Heating Io is squished and stretched as it orbits Jupiter. This releases of heat and rises the internal temperature Why is its orbit so elliptical?

34 The Jovian Moons Orbital resonance between the orbital periods of Io, Europa and Ganymede The 3 closest moons line up every 7 Earth days (resonance) Tugging in the same direction distorts the orbit from a circle to an ellipse 1 orbit of Ganymede = 2 orbits of Europa = 4 orbits of Io

35 Smooth Europa Icy surface covering a large rocky core: Surface is very smooth & young. Fractured into ice rafts & floes a few kilometers across, Repaved by water or geysers through the cracks in the ice.

36 Europa Surface is ice covered Extensive & complex network of cracks in icy crust internal geologic activity

37 Europa (200km square)

38 Europa Salt water oceans below thick layer of ice? (Calculations show it may have twice as much water as Earth!!) Mostly salt water, some magnesium sulfate, sulfurs (red color)

39 Does Europa have liquid water? What lies beneath Europa s surface? One possibility: km of convective ice above a rocky core The most probably scenario based on measurement of Europa s magnetic field: Thin ice crust a few km thick over a 100 km deep water ocean.

40 Europa How Europa can maintain liquid water? Heat in the interior come from interaction (tidal heating) with Jupiter and distortion of the orbit (elliptical) by interaction with nearby satellites Thermal vents may bring the heat from the core. Heat may keep the interior temperature above freezing point Possibility of life? The existence of liquid water does not imply the emergence of life. The salty water is a hostile environment. But we have seen on Earth that life can be present in environment that were considered hostile

41 Tidal stresses crack Europa s surface ice. Similar to icebergs, large chunks of ice that have been broken and reassembled

42 Titan, Saturn largest satellite Titan is the only satellite in the solar system to have an atmosphere. It has a methane-ammonia atmosphere It was recently visited by Cassini (at the present in orbit around the planet) and the Huygens probe. Rocky surface and evidence of erosion by liquid/slush.

43 Titan Properties: Mass: ~0.02 Earth-mass Radius: 0.4 R Earth Density: ~1.9 g/cm^3 Icy mantle over a rocky core. This is the only satellite (moon) in the solar system that has heavy atmosphere

44 Titan s Atmosphere Composition: ~80% N 2 (nitrogen) ~3% CH 4 (methane) Argon Hydrocarbons like: Ethane = C 2 H 6 Acetylene = C 2 H 2 Ethylene = C 2 H 6 Propane = C 3 H 8 Clouds of methane & N 2 ices

45 The Huygens probe The Huygens lander was carried by the Cassini spacecraft mission. The image to the right is an image from the surface of Titan returned by the Huygens probe

46 The methane/ethane lakes in Titan. Radar images taken by Cassini

47 Lakes on Titan (radar maps) Titan s Liquid Lakes Cassini radar have been able to image several smooth regions that have been identified as lakes of liquid methane/ethane

48 Titan, a reflection of sunlight in a methane/ethane lake. (Image taken by Cassini spacecraft)

49 Titan interior

50 Saturn satellite Mimas and Star Wars Death Star

51 Triton - Neptune s large moon It has a retrograde orbit. It orbit in direction opposite to Neptune rotation Voyager 2 detected geysers of nitrogen gas rising several km high The gas jets of nitrogen comes from liquid nitrogen heated by some internal source of heat A very thin atmosphere of nitrogen Temperature about 37 K Triton

52 The Jovian Planets rings

53 Rings All of the Jovian planets have rings The most spectacular are Saturn s rings They are very thin, less than a few km Rings are not solid objects They are comprised of many small solid particles All the particles are in orbit around the planet Water ice is the primary constituent Why do rings form? Tidal forces (differential gravitational forces) of the large planet can break apart a close enough moon.

54 Rings Rings consist of billions of small particles or moonlets orbiting close to their planet size of particle ranges from grain of sand to housesized boulders

55 Rings Particles follow Kepler s laws inner particles revolve faster than those farther out ring are not rotating, rather individual moonlets revolving if ring particles widely spaced - move independently if particles are close - gravitationally interact moons clear gaps in rings

56

57 Saturn s ring in false colors to enhance the composition

58 Saturn rings, gaps and shepherding moons

59 Origin of Rings Breakup of shattered satellite Remains of particles that were unable to come together and form satellite Gravity plays important role differential force of gravity -- tidal forces tear bodies apart inhibit loose particles from coming together

60 DF g DF g DF g

61 Roche Limit Roche Limit - the closest distance an object can come to another object without being pulled apart by tidal forces

62 Comparing Jovian Ring Systems Compared to Saturn, the ring system of other Jovian planets: have fewer particles are smaller in extent have darker particles The rings of Uranus were discovered in 1977 when the planet passed in front of a star and the rings dimmed the light from the star The rings of Jupiter and Neptune were discovered by the Voyager spacecrafts Other unsolved mysteries: Uranus rings are eccentric and slightly tilted from its equatorial plane. Neptune has partial rings.

63 Jovian Rings

64 An example: Comet Shoemaker-Levy 9. It broke into 23 pieces after coming inside the Roche limit of Jupiter in 1993 Collided with Jupiter in July 1994

65 Comet S-L 9 The string of pieces of the comet on their way to Jupiter