Announcements. Writing assignment early deadline next Tuesday!

Transcription

1 PTYS 214 Spring 2018 Announcements Writing assignment early deadline next Tuesday! Nominate Kyle for the Teaching Assistant Excellence Award! Nomination form available outside lecture hall. 1

2 Previously Why is Mars important for astrobiology? Earth-Mars similarities/differences Water on Mars Morphological evidence Mineralogical evidence 2

3 Previously ALH8001 Viking Landers Phoenix Lander Methane in Mars' Atmosphere Martian Climate Stability 3

4 Life on Mercury? 4

5 Life on Venus? 5

6 Life on Jupiter? 6

7 Amalthea JUPITER Io Thebe Jupiter has 67 confirmed satellites Europa Ganymede Satellites of Jupiter Callisto Best known are the four large Galilean satellites: Io, Europa, Ganymede, Callisto Smaller, significant satellites are Thebe, Amalthea, Adrastea, Metis, Himalia 7

8 Galilean Satellites Satellite Diameter* Density* (km) (kg/m3) Revolution & Rotation (days) Avg Surface Temperature (K) Io 3, Europa 3, Ganymede 5, Callisto 4,806 1, *Earth s Moon: diameter= 3,476 km density= 3340 kg/m3 8

9 Galilean Satellites Satellite Diameter* Density* (km) (kg/m3) Synchronous Rotation Revolution & Rotation (days) Avg Surface Temperature (K) Io 3, Europa 3, Ganymede 5, Callisto 4,806 1, *Earth s Moon: diameter= 3,476 km density= 3340 kg/m3 Locked in 1:2:4 Resonances 9

10 Synchronous rotation Most Galilean satellites always keep the same face turned toward their planet (like the Moon) This means that the satellite takes as long to rotate on its axis as it does to execute one Rotation on revolution around its its axis planet Natural consequence for any satellte that orbits close to its primary Revolution around body 10

11 Non-rotating Body Rotating Body in Synchronous Rotation Caused by tidal effects on a body 11

12 Tides Example: The Earth-Moon System Not to scale! 12

13 Tidal Friction Due to friction, the Earth drags its tidal bulge ahead of the Moon (relative to the Moon!) This friction gradually slows the Earth s rotation (1 second every 50,000 years) Also, Tides circularize orbits! What would happen if the Earth were spinning slower than the moon' orbit? 13

14 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 Does this mean the tidal bulge is static? 14

15 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 (optical libration) 15

16 Why are the Galilean satellite orbits not circular? 16

17 Laplace Resonance 1:2:4 Each time Ganymede orbits Jupiter once, Europa orbits Jupiter twice and Io orbits Jupiter 4 times Resonant forcing strongly enhances the effects of the bodies mutual gravitational influence 17

18 Why is tidal heating important? It is an important source of energy for the Jovian satellites because the solar energy flux is so weak (How weak?) Io is more volcanically active than the Earth! 18

19 Tidal heating depends on the distance from the parent planet Io (the innermost of the Galilean Satellites) is close to Jupiter and has tremendous tidal heating Callisto (the outermost) is far from Jupiter and has little tidal heating Callisto has a very old heavily cratered surface Io has a very young craterless surface 19

20 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 Image of two volcanic on Earth only reach ~20m) plumes 100 km (62 mi) high (Voyager 2) Io s surface is peppered with hundreds of volcanoes, high mountains, lava flows No impact craters! Why not? 20

21 (Feb. 2000) Io s Active Surface Eruptions at Tvashtar Catena Hot lava! (hotter than on Earth) (Nov. 1999) (Galileo Images) Eruption at Kilawea Volcano, Hawaii 21

22 Life on Io? 22

23 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 parts of the surface are frequently molten, and therefore very hot! Io receives a huge amount of radiation from Jupiter but it has little or no atmosphere to shield its surface. 23

24 Europa Second closest to Jupiter and the smallest of the four Galilean satellites Spectroscopic observations indicate a surface made of water ice Very few impact craters the surface has to be very young Pwyll (~50 km across) 24

25 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 25

26 Europa surface features Magnetic field measurements demonstrate 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 26

27 Europa s surface Mountains Ridges Chaos Mountains (Galileo images) 27

28 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) 28

29 29

30 Ridges (Galileo image) Long linear features usually a kilometer wide, a few hundred meters tall, and hundreds or thousands of kilometers long 30

31 Ridge formation: Tidal squeezing model Diurnal tides open and close cracks in ice While the crack is open, water and/or slush enter the crack and this material is then squeezed up 31

32 Europa interior model ~ -170 C ~ 0 C volcanism? 32

33 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!) 33

34 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 of available energy to sustain it On Earth, the bulk of energy comes from photosynthesis Could photosynthetic life occur on Europa? 34

35 Maybe Possibly at location of cracks, if liquid water (warmer than the surrounding ice) can get close to the surface 35

36 Ganymede Largest satellite 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 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, more radiogenic heat (larger size) 36

37 Callisto Most distant Galilean Satellite Not in Laplace resonance Highly cratered surface Like Ganymede, magnetic field measurements from Galileo suggest an ocean under a thick ice crust Essentially no tidal heating, only radiogenic heat Not much energy available for life. 37

38 Jupiter Icy Moon Explorer (JUICE) (JIME? JUIME? JUICME?) Formerly Europa Jupiter System Mission - Announced in February 2009 as a joint project between NASA and ESA - ESA de-scoped it based on NASA's expected (lousy) budget - Multiple flyby of Europa, Callisto - Orbit around Ganymede Estimated launch/arrival: 2022/2030 Some Planned Instruments: Ice-penetrating radar to detect either the ice-water boundary (Europa) or pockets of warm ice (Ganymede) Laser altimeter to detect changes in satellites shape as they orbit Jupiter Various imaging instruments 38

39 Europa Clipper - Mission to study Europa - Search for habitable conditions: Ice shell Composition Geology - 45 flybys of Europa as low as 25 km Launch date Instruments: Ice-penetrating radar Infrared Spectrometer Thermal Imager Stereo Topographic Imager Magnetometer Reconnaissance Camera 39

40 Europa Lander - Search for biosignatures on surface - Assess habitability directly - Characterize sirface for future missions Proposed Launch date 2024 Proposed Instruments: Drill w/ instruments Mass spectrometer Seismometer Stereo cameras Raman spectrometer Microscopic imager 40

41 Homework Homework #21 available shortly on the web site 41