Announcements Students with last names starting from A to K go to the Planetarium right now L to Z – Thursday (11:00 a.m.) 1- 3 March: Brooks Observatory tours 7:30-8:30 p.m. – extra credit Bring back your ticket with your name on the back
March 2-18 Instructor: Anatoly Miroshnichenko E-mail: email@example.com The lecture notes are available from: http://ardbeg.astro.utoledo.edu/~anatoly/astr1010/2004/materials.html
The Giant Planets: Jupiter, Saturn, Uranus, Neptune Internal Structure Atmospheres Magnetospheres Satellites and Rings Chapter 9
Jovian Planets: Basics • Distance: 5-30 AU • Much farther from Sun than terrestrial planets • Much colder (100-50 K) • Mass: 10-100 Earth masses • Much more massive than terrestrial planets • Jupiter & Saturn are similar • Size (about 10 Earth diameters) • Composition: mostly hydrogen and helium • Uranus & Neptune are similar • Smaller than Jupiter & Saturn • Less hydrogen and helium
Appearance • Jovian planets show “banded” appearance • due to atmosphere • we see only cloud tops • Rotation quite fast (hours) • Jupiter: 10 hrs • Saturn: 11 hrs • Uranus: 17 hrs • Neptune: 16 hrs
Clouds • Clouds on Jupiter & Saturn composed of ammonia ice (NH3) • different colors due to differing cloud composition Saturn’s clouds deeper; less visible • Clouds on Uranus & Neptune • composed of methane (CH4) • produces blue-green color
Axial Tilt & Seasons • Jupiter • only 3º axis tilt; no real seasons • Saturn • 27º tilt; normal seasonal variation • Neptune • 29º tilt; similar to Saturn • Uranus • 98º tilt -on its side![collision?] • extreme seasons! each 21 yrs long Seasons on Uranus
Planet Interiors Jupiter
Comparing Jovian Planet Interiors Density and size – Jovian planets have very low densities and similar radii The smallest stars are even smaller in radius than Jupiter, but ~80 times more massive Uranus and Neptune have higher densities and a different chemical composition (hydrogen compounds and rocks and less pure H and He)
Jovian Planet Atmospheres No solid surfaces Jupiter atmosphere Content: Almost entirely H and He + trace amounts of methane (CH4), ammonia (NH3), and H20. Jupiter’s weather occurs in troposphere where clouds can be formed of ammonia crystals and other compounds
Jupiter’s Atmosphere Wind is driven by the planet’s rotation. Jupiter’s rotation is so fast that the atmosphere breaks up into many swirling bands. The bands of rising air are called zones The adjacent bands of falling air are called belts Belts and Zones on Jupiter Great Red Spot is the most dramatic weather pattern in the Solar system (size of 2 Earths)
Atmospheres of Other Planets Different colors are due to trace gases or colored compounds, produced by chemical reactions Saturn has almost the same color as Jupiter Uranus and Neptune are blue (due to methane which absorbs red light and transmits blue) Saturn has belts and zones Neptune has bands and a high-pressure storm Great Dark Spot Uranus has slowly changing weather
Magnetospheres Magnetosphere consists of planet’s magnetic field and particles trapped within them. Jupiter’s magnetic field is 20,000 times stronger than Earth’s. It deflects solar wind at 40 Jupiter radii (3 million km). The charged particles from Jupiter’s magnetosphere bombard surfaces of Jupiter’s moons which leads to release of their atmospheric gases
Jovian Planet Moons There are more than 100 known moons orbiting Jovian planets (J-52, S-30, U-21, N-11) Three main groups of jovian moons: Small moons - less than 300 km in diameter Medium-size - 300-1500 km Large - more than 1500 km Medium and large moons have circular orbits that lie close to the equatorial planes of their parent planets
Jupiter Moons Pre-visit expectations: cold and geologically dead Voyager missions: the moons are active! Four Galilean moons: Io, Europa, Ganymede, Callisto Io has many volcanoes and no impact craters Europa – no craters, fractured surface, icebergs Ganymede – grooves on surface, magnetic field Callisto – a heavily cratered iceball
Io Eruptions erased all Io’s impact craters.
Reasons for Geological Activity Io has an additional heating source – tidal heating Tidal heating is due to the Io’s orbit ellipticity. Io is continuously flexed by Jupiter. Source of the orbit ellipticity – orbital resonances Periodical lining up of the three closest satellites of Jupiter (Io – 4 orbits, Europa – 2 orbits, Ganymede – 1 orbit)
Europa • Recently formed crust • No craters • tidal heating work Visible icebergs suggest the presence of an ocean below the surface. Latest news: the ocean may be made of acids
Rings and Gaps Two of Saturn’s rings can be seen from Earth In fact, there are as high as 100,000 individual rings and gaps Rings and gaps are caused by grouping of particles at some orbital distances which are being forced out at others. Gaps can be created by gap moons located within rings. They clear up gaps around their orbits.
Rings of Jupiter, Uranus and Neptune These rings are much fainter than that of Saturn and were discovered after 1977. The rings of Uranus and Neptune were discovered during a stellar occultation. Rings are similar to each other. They lie in their planet’s equatorial plane, particle orbits are almost circular, gaps are due to gap moons. Saturn’s rings have larger size, higher reflectivity, and greater number of particles.
Origin of the Rings Ring particles may not last very long. They are ground into dust in a few million years. It should be a source of new ring particles. The most likely one is collisions of small moons and impacts between meteorites and small moons. In the beginning, there were many more moons around jovian planets. Gradual dismantling of the moons created the ring systems.
Summary of Jovian Planets • Jovian planets larger, more massive than terrestrial • Composition: • mostly hydrogen (H) and helium (He) • dominated by hydrogen • also large amounts of ices (water, ammonia, methane) • Why So Large? • basic reason is distance from sun • cooler temps allowed ices (volatiles) to freeze
Role of Volatiles • Inner solar system is hot: • volatiles are gaseous; not available for planet core formation • planet cores • only rock (no ice) • smaller, less massive (1 earth mass) • Outer solar system is cold: • volatiles are solid; available for planet core formation • planet cores • both rock and ice • bigger, more massive (10 earth masses) • Massive cores have larger gravity; can capture gas • Jovian planets have massive atmospheres (lots of H and He) • Terrestrial planets have minimal atmosphere (little H and He)
Summary Jovian planets are dynamic worlds with rapid winds, huge storms, strong magnetic fields, and interiors where common materials strangely behave. Jovian moons are geologically active because of their ice compositions. Ring systems were formed from small moons. Study of jovian planets brought new concepts of ice geology, tidal heating, and orbital resonances.