PTYS 214 – Spring 2011

1. Announcements PTYS 214 – Spring 2011 • Homework #9 available for download on the class website • DUE on Thursday, Apr. 14 • Class website: http://www.lpl.arizona.edu/undergrad/classes/spring2011/Pierazzo_214/ • Useful Reading:class website  “Reading Material” http://en.wikipedia.org/wiki/Moons_of_Jupiter http://en.wikipedia.org/wiki/Tidal_acceleration

2. Quiz #8 Total Students: 19 Class Average: 3.0 Low: 1.5 High: 4 Quizes are worth 20% of the grade

3. Planetary Sciences Graduate Teaching Assistant Excellence Award • Planetary Science Department initiative to promote, recognize and reward exemplary performance among graduate teaching assistants assigned to PTYS undergraduate courses • If you think your PTYS-214 Teaching Assistant qualifies for the award, please fill out a nomination form describing: • Why you are nominating the TA • How the TA has contributed to your learning experience • Nomination forms and the drop box are located on the table outside your classroom, room 308 • The Teaching Assistants for PTYS214-2 are: • LissaOng & Devin Schrader

4. Extra Credit Presentation Genevieve Connor Kyle Thompson

5. Amalthea JUPITER Io Thebe Europa Ganymede Callisto Moons of Jupiter • Best known are the four large Galilean satellites: Io, Europa, Ganymede, Callisto • Smaller, significant moons are Thebe, Amalthea, Adrastea, Metis, Himalia • Jupiter has 63 confirmed satellites

6. Galilean Moons Synchronous Rotation *Earth’s Moon: diameter= 3,476 km density= 3340 kg/m3 Locked in 1:2:4 Resonances

7. Rotation on its axis Revolution around body Synchronous rotation • Almost all Galilean moons always keep the same face turned toward their planet (like our Moon) • This means that the satellite takes as long to rotate on its axis as it does to execute one revolution around its planet • Natural consequence for any moon that orbits close to its planet

8. Non-rotating Body Rotating Body inSynchronous Rotation Connected to tidal effects on a body

9. Example: The Earth-Moon System

10. Tidal Friction • Moon’s gravity exerts a small amount of drag on the Earth causing tidal friction • This friction gradually slows the Earth’s rotation (1 second every 50,000 years)

11. Why Synchronous Rotation Effect of Earth’s gravity is much stronger on the Moon Earth raises much stronger tides on the Moon • Tidal friction is more severe • Moon slows down its rotation much faster • End result: Synchronous rotation

12. Tidal Friction on Galilean Satellites Galilean Satellites are already locked in synchronous rotation, but: Satellites orbits are non-circular • tidal bulges vary in height (because of the change in the satellite’s distance from Jupiter) • Extra tidal friction (heating) • Some tidal heating is also produced by the varying orbital velocity (libration)

13. Why are the Galilean satellite orbits not circular?

14. 1:2:4 Resonances Each time Ganymede orbits Jupiter once, Europa orbits Jupiter twice and Io orbitsJupiter 4 times Strongly enhance the bodies mutual gravitational influence

15. Why is tidal heating important? • It is a very important source of energy for the Jovian moons since the solar energy flux is so weak How weak? Io is more volcanically active than the Earth!

16. Tidal heating depends on the distance from the parent planet • Io (the innermost of the Galilean Satellites) is too close to Jupiter and has too much tidal heating • Callisto(the outermost) is too far from Jupiter and has little tidal heating Callisto has a very old heavily cratered surface

17. Tidal Heating on Io • Tidal forces alternatively squeeze and stretch Io’s interior, generating enormous amounts of heat • Io's solid surface can rise and fall by about 100 m ! (the highest ocean tides on Earth only reach ~20m) Io’s surface is peppered with hundreds of volcanoes, high mountains, lava flows No impact craters! Image sequence of two volcanic plumes 100 km (62 mi) high (Voyager 2)

18. (Feb. 2000) Io’s ActiveSurface Eruptions at Tvashtar Catena Hot lava! (hotter than on Earth) Eruption at Kilawea Volcano, Hawaii (Nov. 1999) (Galileo Images)

19. Life on Io? Io provides an environment very hostile to life • It has practically no atmosphere, so right above the surface the temperature is very cold, but its surface, with all its volcanoes, is frequently molten, therefore it is super hot! • Io receives a huge amount of radiation from Jupiter but it has little or not atmosphere to shield its surface from it

20. Europa • Second closest to Jupiter and the smallest of the four Galilean moons • Spectroscopic observations indicate a surface made of water ice • Very few impact craters – the surface has to be very young Pwyll (~50 km across)

21. Magnetic field measurements Data from the magnetometer on board of Galileo (launched in 1989, mission terminated in 2003) show that Europa’s magnetic field varies in direction and strength in response to Jupiter’s magnetic field Europa has an induced magnetic field ! This requires a near-surface, electrically conducting global layer, consistent with a salty ocean beneath its crust (an iron-core would not produce an induced field as strong) • Similar data suggest that also Ganymede and maybe even Callisto may have subsurface oceans

22. Europa surface features Magnetic field measurements demonstrated that Europa has an ocean but how thick is the ice layer? Surface features provide strong argument in favor of relatively shallow ice layer • Ridges and bands (lineaments) • Chaotic terrain

23. “Mountains” Europa’s surface Ridges “Chaos” “Mountains” (Galileo image)

24. “Chaos” regions (Galileo image) Areas where the ice appears to have been broken apart and "rafted" into new positions (similar to the disruption of pack-ice on polar seas during spring thaws on Earth)

26. Ridges (Galileo image) Long linear features usually a kilometer wide, a few hundred meters tall, and hundreds or thousands of kilometers long

27. Ridge formation: Tidal squeezing model • Diurnal tides open and close cracks in ice • While the crack is open, water and slush enter the crack and this material is then squeezed up

28. Europa in a nutshell ~ -170°C ~ 0°C volcanism

29. Life on Europa: Surface Life on the surface of Europa is practically impossible Why? 1) Temperature: -170°C (-223°C to -148°C) too low for any psycrophile we know on Earth! 2) No atmosphere no chance for stable liquid water 3) Radiation from Jupiter a deadly dose of charged particles bombard Europa’s surface continuously (not even Deinococcus Radiodurans could survive!)

30. Life on Europa: Subsurface Life may be possible in the subsurface ocean Best location: close to hydrothermal (volcanic) vents on its ocean floor (assuming they exist!) Complexity of life: mainly limited by the amount ofavailableenergy to sustain it On Earth, the bulk of energy comes from photosynthesis Could photosynthetic life occur on Europa?

31. Maybe… Possibly at location of cracks, if liquid water (warmer than the surrounding ice) can get close to the surface

32. Magnetic field measurements from Galileo indicate a steady magnetic field, similar to Earth’s, and a varying component, similar to Europa Maybe an ocean under a thick ice crust! Less tidal heat than Europa, some more radiogenic heat (larger size) Ganymede • Largest moon of the Solar System (larger than Mercury!) • Surface is characterized by light and dark regions; bright regions appears younger than the dark, heavily cratered areas

33. Europa Jupiter System Mission! Announced in February 2009 as a joint project between NASA and ESA Two independent spacecrafts: −Jupiter Europa Orbiter: built by NASA −Jupiter Ganymede Orbiter: built by ESA Estimated launch/arrival: 2020/2026 Planned Instruments: • Ice-penetrating radars to detect either the ice-water boundary (Europa) or pockets of warm ice (Ganymede) • Laser altimeters to detect changes in satellites shape as they orbit Jupiter • Various imaging instruments