Lecture 31. Galileo Mission.

1. Lecture 31. Galileo Mission. reading: Chapter 8

2. The Galileo Mission Originally proposed to be a direct mission to Jupiter, Challenger accident and cancellation of Centaur rock program meant Galileo had to use flybys of Venus and Earth to provide gravity assists. Observed Moon, Earth, and Venus. False-color image of surface (imaged at different wavelengths to provide a spectral image - different compositions reflect different wavelengths of light) Blue: Titanium-rich soils, younger basalt Red: Titanium-poor and iron-poor, older lunar highlands Purple: Apollo 17 landing site, ancient explosive volcanic deposits

3. The Galileo Mission, cont. Launched October 1989 by the Shuttle Atlantis Weighed 2380 kg (~pick-up truck) Power system: Radioisotope thermoelectric generators (RTGs), 570 watts Two spacecraft: orbiter and an atmospheric probe Probe weighted 335 kg Trajectory: VEEGA (Venus-Earth-Earth Gravity Assist) Unprecedented observations. First close-up observations of 2 asteroids Gaspra and Ida

4. Watched Shoemaker-Levy 9 Impact Jupiter July 16-22, 1994 20 fragments impacted at 60 km/sec - largest was 2 km. Sent plumes thousands of km high. Left hot bubbles of gas in the atmosphere. Dark scars that lasted for months. Impact was just out of the view from Earth. Imaged fragment W:

5. Infrared image - Mauna Kea Telescope Shows hot areas What is the brightest spot?? Dust from the asteroids absorbs solar uv light, looking like dark spots.

6. Science Objectives Probe: Determine composition of Jupiter’s atmosphere Characterize atmosphere with depth to 10 bars Investigate cloud particles, location and structure of cloud layers Examine heat balance of Jupiter Nature of lightning Measure solar wind flux with depth Orbiter: Study circulation and dynamics of Jupiter’s atmosphere Study Jupiter’s atmosphere and ionosphere Image the Galilean satellites, investigate geology and minerals Determine gravitational and magnetic fields of Galilean satellites Study atmospheres, ionospheres of Galilean sats Study interaction of Jupiter’s magnetosphere with Galilean sats Study Jupiter’s magnetosphere and plasma torus

7. Orbiter Instruments Solid-state imager updated technology from Voyager basically a telescope with a very sensitive CCD sensor images recorded, compressed, sent back to Earth protected with 1 cm thick tantalum shield Ultra-violet Spectrometer measured uv albedo of Venus (measures SO2, H, O, C, and CO) Earth & Moon (ozone, lunar atmosphere) asteroids (compare to Moon) Jupiter’s clouds (hazes and aerosols, variability, hydrocarbons) Jupiter’s auroras UV emissions from the hot interior of Jupiter Io torus (abundance of neutral and charged atoms)

8. Orbiter Instruments, cont. Near Infra-red Mapping Spectrometer mapped infra-red radiation reflected or emitted from bodies composition and cloud structure and temperature Dust Detector measures mass & speed of dust Heavy Ion Counter Monitored the environment to protect spacecraft electronics Studied composition of ions around Jupiter, solar flares, cosmic rays. Magnetometer measures magnetic fields on an arm away from the spacecraft

9. Orbiter Instruments, cont. Plasma Instrument measure density, T, velocity, composition of plasma Plasma Wave Subsystem an antenna to measure electrical and magnetic fields of the plasma Radio perform experiments on celestial mechanics and relativity occultation with Earth - measures P and T of the atmosphere with depth

10. Probe Instruments Atmospheric Structure Instrument T, P Mass Spectrometer composition of atmosphere Nephelometer uses a laser beam to detect atmospheric particles Energetic Particle Investigation measures electrons, protons, alpha particles, heavy ions from magnetosphere Net Flux Radiometer measures radiation of light from the atmosphere Lightning and Radio Emission Instrument Helium Abundance Interferometer

11. Gaspra 19 km long, rotates every 7 hours Some regions are brighter Blue: brighter regions, around craters, blue due to the Fe-containing mineral olivine Red: regolith accumulations no large craters abundant smaller craters likely recent origin from the break-up of a larger body

12. Ida Asteroids have Moons! Ida covered with regolith. Bright regions near craters. Compositional differences in Fe-bearing minerals. Rotates every 4.5 hours, 56 km long. Dactyl is a different color - has a different spectral properties Made of similar rock types. 1.5 km long.

13. Discoveries An intense interplanetary dust storm! Lasted 3 weeks, counted 20,000 dust particles/day (Normal: 1 particle/3 days) Traveling 90,000-450,000 mph! May have: -come from Io -from Jupiter’s thin rings -from comet Showmaker-Levy 9

14. Discoveries, cont. Jovian wind speed of 600 kph Far less lightning activity than anticipated, although they were still 10x Earth He abundance very similar to the Sun Extensive resurfacing of Io since Voyager flybys in 1979. Intrinsic magnetic fields for Io and Ganymede Evidence for liquid water oceans underneath Europa and Ganymede (induced magnetic fields).

15. How Thick Is Europa’s Crust? We don’t really know. Examine impact craters. Shapes of largest craters different than those on Ganymede & Callisto Due to warmth of lower part of the ice shell. Strength of ice is dependent upon T and P. Ganymede & Callisto scale= 30 km Ice appears thicker Europa scale = 10 km ice appears thinner

16. Smaller craters: rim and central peak >30km: no rims or peaks surrounded by concentric rings likely melted the icy crust

17. There Are 2 Main Models Crust thickness estimated to be 20-30 km. If there is a lot of heat, the ocean may be liquid. If less heat, there may be a layer of soft convecting ice. Magnetometer data suggests it is liquid. (But is not proof).

18. If we could melt through the ice, we could explore the ocean below (IF it is liquid). Predict there should be hydrothermal vents at the bottom of the ocean.

19. How to Look for Life on Europa Europa Orbiter/Jupiter Icy Moon Orbiter Was scheduled to arrive on Europa in 2010 Mission has been repeatedly bumped. As of February: Missing from the President’s 2007 budget. Proposing a nuclear reactor to power ion thruster engines (Prometheus) Mike Griffin, NASA Administrator, told a Senate subcommittee that the mission was too ambitious, and was not well-formed. Now launch date is 2015 (??). Radar will map the thickness of the ice crust. Determine if there is a liquid ocean. Map the surface and measure topography. Try to detect signs of recent geologic activity.

20. How to Look for Life on Europa, cont. Do we have the 5 things you need for life?? Surface T of Europa is -160˚C

21. Lake Vostok, Antarctica One of the world’s largest freshwater lake Lake under 3,700 m of ice Lake is ~1 million years old Are over 145 similar lakes under the ice What Lake Vostok! looks like: Coldest Recorded T on Earth: -89˚C

22. Lake Vostok, Antarctica Drilling of the ice began at a Russian Research facility. Drilling Stopped in 1998 to avoid contaminating the lake. Retrieved a 420,000-year ice core! Lowest layers of ice is frozen lake water (accreted lake ice). This ice contained a few microbes. Lake water is constantly removed by freezing - must be a source of freshwater. animation

23. Oceans on Ganymede and Callisto Are likely deep, below 100-200 km of ice.

24. Probe Discoveries Entered Jupiter’s atmosphere Dec. 1995 Relayed data for 57 minutes to a depth of 156 km Atmosphere drier than expected. Didn’t detect 3-tiered cloud structure, only found one thin cloud layer Top: ammonia crystals Middle: ammonium hydrosulfide Lower: thick layer of water and ice crystals Significantly lower helium, neon, C, O, S Minimal organic compounds Absence of lightning (no water ice) Found extremely strong winds and turbulence, even at depth Found a new radiation belt 31,000 miles above the cloud tops Entered a cloud-free region - a “hot spot”

25. Probe Site

26. Lecture 32. Titan and its Atmosphere. reading: Chapter 8