1. A Transitional Fossil 375 Ma fish: flat nose, beginnings of limbs “Missing link” between fish and life on land.

3. Lecture 30. Jupiter and the Galilean Moons; Magnetic Moments. reading: Chapter 8

4. Ganymede

5. Ganymede, cont. Largest Moon in the solar system. Larger than Mercury (& Pluto), but half the mass. Why? Differentiated into 3 layers: Fe or Fe/S core Rocky mantle Icy shell Very old terrain heavily cratered dark regions Younger terrain fewer craters, lighter extensive array of grooves and ridges unknown how they are formed Cratering ages of 3-3.5 Ga. Are ridges young or old? Is surface older/younger than Europa? Very thin atmosphere of O 2

6. Callisto

7. Callisto, cont. Slightly smaller than Mercury, but a third of its mass. Little internal structure. About 40% ice, 60% rock/Fe Most heavily cratered surface in the solar system. Little change in over 4 Ga. Some massive craters - have smoothed out over the eons from slow movement of the ice. Valhalla, largest crater, 3000 km across. Little evidence of tectonic activity. Very thin atmosphere of CO 2 Crater chain, 620 km long

8. Jupiter 90% H, 10% He Traces: methane, water, ammonia, rock Core: rocky material of 10-14 Earth masses Main bulk: liquid metallic hydrogen, 40,000 km deep Only exists at 4 million bars. Liquid metallic hydrogen is an electrical conductor Source of Jupiter’s magnetic field. Interior of Jupiter is hot, 20,000K Convection releases heat to the surface, drives the high winds in the clouds.

9. Earth’s Magnetic Field Similar to a magnet. Van Allen belts - regions of high amounts of charged particles. Charged particles originate from the solar wind. Solar wind - comes from the Sun’s corona The T is so high is an ionized plasma - nuclei and electrons. Sun can’t hold onto it. Travels up to 900 km/sec.

10. Earth’s Magnetic Field, cont. Solar wind particles are trapped by the Van Allen belts. Particles spiral into the surface. Cause the auroras (Northern lights). Auroras: -luminous bands -up to 200 miles above the surface -solar wind particles collide with O 2 and N 2 in the atmosphere -excites the atmosphere, decays into light energy -also emits uv light and X-rays

11. Origin of the Magnetic Field Not completely understood. Motion of electrical charges. Electrical currents generated in the Earth’s core. Earth’s outer core made of liquid Fe/S metal (is conductive). Core is both spinning and convecting heat from the core to the mantle. This induces an electrical current ( the dynamo effect ).

12. Magnetosphere Solar wind varies in speed and intensity. Earth’s magnetic field shields it from most of the solar wind particles. Solar wind deflected (like water around the bow of a ship). Surface where the solar wind is deflected - bow shock. Region of space behind the bow shock - Magnetosphere Magnetic field prevents most solar wind particles from entering. Magnetosphere is not spherical.

13. Chandra X-ray image shows auroral activity, charged ions of O hitting atmosphere, 2005. Jupiter’s Magnetosphere 10x stronger and larger than Earth’s. More complex than Earth’s -more rapid rotation -larger metallic interior Extends 650 million miles, past the orbit of Saturn! Is 20x the size of the Sun. Galilean Moons lie within the magnetosphere. The environment contains high level of trapped energetic particles. Sometimes called the plasma torus. (A torus is doughnut-shaped.) Quickly fatal to humans. Destroys spacecraft hardware. High energy electrons trapped in Jupiter’s radiation belts emit radiation at radio wavelengths.

14. Jupiter’s Magnetosphere Because of rapid rotation, the belts are flattened into sheets. Plasma sheets. Field rotates with the 9 hour rotational period of the planet. Amalthea, Io, Europa, and Ganymede orbit through this region. The atmosphere and surface of Io is eroded away by collisions with plasma particles. Volcanos of Io spew sulfur into the plasma torus. Sulfur becomes ionized and are trapped in orbit around Jupiter.

15. Magnetic Fields So, what happens when you pass a conductor through a changing magnetic field?

16. Magnetic Fields, cont. Moving current also generates its own magnetic field (in red). Why is this important for Astrobiology???

17. Europa As Europa moves through Jupiter’s magnetic field, an electrical current is generated. This electrical current creates a magnetic field. So, Europa has its own magnetic field. This magnetic field changes as Jupiter rotates. It is a weak magnetic field - must be near the surface. … called an induced magnetic field (induced by Jupiter’s magnetic field). What do you need to create this induced magnetic field? Who else has an intrinsic magnetic field? Europa, Ganymede, AND Callisto! Ganymedes is 4x that of Europa

18. Intrinsic Magnetic Fields Like what the Earth and Jupiter has: Intrinsic due to a liquid iron core. Io and Ganymede appear to have liquid cores that generate their own intrinsic magnetic fields.

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