NEWS: March 12 Cassini flys above Enceladus Plumes

1. NEWS: March 12 Cassini flys above Enceladus Plumes

2. Solar System Exploration MissionTypeLaunch DateMilestone Cassini Flagship 15 Oct 1997 Arrival 1 July 04 Dawn (Vesta & Ceres) Discovery 27 Sep 2007 Deep Impact Discovery 12 Jan 2005 Tempel impact 05 Mars Rovers (Spirit & Opportunity) Mars Scout Summer 2003 Land Jan 04 Mars Express (ASPERA instru) Mars Scout 2 June 2003 Arrival Dec 03 Mars Odyssey Mars Scout 7 April 2001 Arrival Oct 01 Mars Reconnaissance Orbiter Mars Scout 12 Aug 2005 Arrival Aug 05 Mercury MESSENGER Discovery 3 Aug 2004 Arrival 2011 Pluto New Horizons New Frontiers 19 Jan 2006 Arrival 2015 Phoenix Discovery 4 Aug 2007 Arrival 25 May 08 Stardust Discovery 7 Feb 1999 Sample return 06 Voyager Flagship Summer 1977 Neptune 1989

3. Apollo 16 (1972)

4. Apollo 16 Landing

5. Carbon Dating • Solar neutrons enter Earth’s atmosphere. • Neutrons collide with N14 (7p, 7n), creating C14 (6p,8n) [n + N14 p + C14 ] • Living bodies continually absorb C14 (e.g. as CO2 in photosynthesis). • When the plant or animal dies, it no longer assimilates C14. • The C14 decays (half life of 5730 yrs). [C14 N14 + e- + ve ] (n  p + e- + ve ) • The e- emission rate reveals the age. Measure ages < 70,000 yrs

6. Carbon Dating first tested Radiocarbon dating was discovered by Willard Libby in 1949. He first demonstrated the accuracy by accurately dating a the wood from an ancient Egyptian royal barge whose age was known from historical documents. In 1960, Libby received the Nobel Prize in Chemistry for his work

7. Potassium-Argon (K-Ar) Dating 40K -> 40Ar + 40Ca Half life of 1.26 billion years Because Ar is a gas, it can escape from molten rock. However after the rock solidifies 40Ar produced by potassium decay begins to accumulate in crystal lattices. The ratio of 40Ar to 40K tells us the time elapsed since the rock solidified and was able to trap Ar Can date the solidification of rocks 100,000 yrs old at 1% accuracy.

8. Radioactive Dating Systems *Time that it takes wood to have half the 14C of a living plant.

9. Swisher et al. 1992, Science

10. The Electric Force Like Charges Repel, Opposites Attract Coulomb’s Law The force between two charged objects is proportional to the product of their charges divided by the square of the distance between them. Charge unit is Coulomb, denoted C. 1 proton has a charge of 1.7x10-19 C 1 electron has a charge of -1.7x10-19 C K = 9x109 N-m2/C2 is Coulomb’s constant

11. Notice the similarity Electric Force: Gravitational Force:

12. Dipole and Monopole fields Monopole Field Dipole Field Magnetic Field Electric Field of a proton A dipole field can be created with multiple electric charges, but monopole magnetic fields do not exist.

13. Changing currents are changing electric fields Direction of current is that for a positron Direction of electron motion electrons Electric Field - + In metals like copper, electrons are free to move.

14. Electric Currents Produce Magnetic Fields While giving a lecture to introductory physics students, Hans Oersted noticed that a compass needle twitched every time that he turned on an electric circuit. Further experimentation showed that a magnetic field was produced whenever a current flowed. Shape of the magnetic field for wire arrangements.

15. Magnetic Induction Imagine a coil of wire in a magnetic field, as shown to the right. The magnetic flux is proportional to the number of lines that go through the electric circuit. If the plane of the coil of wire is 90° to the B field, then the magnetic flux is large. If the coil were rotated 90 degrees, so that no B field lines intersected the coil, the flux would be zero. If circuit contains N coils of wire rather than 1, the flux is increased by a factor of N.

16. Magnetic Induction Imagine a coil of wire in a magnetic field, as shown to the right. The magnetic flux is proportional to the number of lines that go through the electric circuit. If the plane of the coil of wire is 90° to the B field, then the magnetic flux is large. If the coil were rotated 90 degrees, so that no B field lines intersected the coil, the flux would be zero. If circuit contains N coils of wire rather than 1, the flux is increased by a factor of N. A changing magnetic flux induces a current in the wire.

17. Magnetic Induction The magnetic flux is proportional to the number of lines that go through the electric circuit hoop. As the magnet is moved closer to the hoop the flux increases and a current results. If circuit contains N coils of wire rather than 1, the flux is increased by a factor of N.

18. Summary of E&M fundamentals • Coulomb’s Law: like charges repel and opposites attract: • Oersted’s Discovery: A changing electric field creates a magnetic field. • Faraday’s law: A changing magnetic flux creates an electric field. • There are no magnetic monopoles.

19. Consider this A changing magnetic field creates an electric field. A changing electric field creates a magnetic field, which then creates another electric field, and so on in leap-frog fashion. Electricity and magnetism are two aspects of the same force – electromagnetism. What does this mean? What are these constantly changing electric and magnetic fields?

20. TheElectromagneticSpectrum Vibrating electric & magnetic fields regenerate each other and make up an electromagnetic wave.

21. Electromagnetic waves are characterized by their wavelength

22. Waves: definitions • The peak to peak distance is the wavelength, . • The time that it takes for a wave to oscillate from peak to peak is the period, T. • The number of waves that pass a point per unit time is called the frequency, v:  = 1/T • The wave’s speed, u, is: u =  / T =   

23. Velocity of light Light travels at a velocity c=2.99x108 m/s in a vacuum. Is this a little odd?

24. Light: both waves and particles Light acts like a bunch of particles: It is absorbed by molecules as discrete particle packages. Light acts likes waves: e.g. it can be refracted and can combine (or superpose).

25. Yes, very! Imagine standing on the top of a train moving at a velocity vTrain and shining a flashlight towards someone in front of the train on the ground. The velocity of light relative to the train is vLight = c. The velocity of the light received by the person on the ground is c too, not c+v! vBall vBall+vTrain vTrain vLight vLight vTrain

26. Consequences Length contraction: objects in motion are shorten in the direction of motion Time dilation: Time slows with motion but this is only apparent to someone in a different reference frame because the moving clock slows too. This has been tested by flying atomic clocks on fast planes. The flown clock recorded the passage of less time, compared to the not-flown clock!

27. Photons: the particles of light The energy of a photon depends solely on its frequency speed of light = 2.998 x 108 m/s Photon frequency Photon wavelength Planck’s constant: h = 6.626 x 10-34 J s

28. Radio Waves • Radio waves have useful properties: • Travel far through the atmosphere • Easily generated by setting up currents in metal antennas • They bounce off the ionosphere, and thus travel long distances around Earth. AM = Amplitude modulation FM = Frequency modulation

29. Microwaves Microwave photo of the Amazon Microwaves are not obstructed by clouds, haze or any other particle smaller than the microwave wavelengths (~ 1 cm). They can be used to image Earth’s surface through the clouds that cover ½ the disk. Cosmic microwave background

30. Infrared Radiation Wavelength: 1 um – 1000 um We emit IR light. In fact all the objects around us emit IR radiation. Hotter objects emit more IR radiation, which we are warmed by, and which we sense with our skin. IR photo of a man IR photo of the dust in the Solar System

31. Visible Light We see the very part of the electromagnetic that the Sun emits. That is we have detectors that are sensitive the radiation that illuminates our world. White light is made up of light from all different colors

32. Ultraviolet Light Some birds & bees can see UV as well as visible light. Ultraviolet light has just the right energy to break molecular bonds apart. For this reason it is detrimental to life. The Earth has a natural shield to Solar UV light in the form of an ozone layer (80 km above the surface). 10% of sunlight is in the UV

33. X-rays X-rays were discovered 1895 by Wilhelm Conrad Roentgen (a German scientist) by accident. A week later he took this x-ray of his wife.

34. Gamma Rays Wavelength: 10-12 – 10-13 m Gamma Rays are the most energetic of all electromagnetic waves. These EM waves are therefore emitted in the hottest events. Gamma Ray Bursts: Can release more energy in 10 seconds, then released by the Sun in 10 billion yrs. Their source is unknown.

35. Summary • Changing electric fields produce changing magnetic fields, which produce changing electric fields, which propagate as waves. • These waves are called EM waves. • EM waves behave as particles & as waves • They are characterized by their wavelength. • The energy of light particles depends on the frequency (E = hv), or equivalently, their wavelength. • Light travels at 2.99x108 m/s in a vacuum.

36. An expert is a man who has made all the mistakes, which can be made in a narrow field. Neils Bohr

37. A theory which unifies all Relativistic Quantum Theory can explain the electromagnetic, weak and strong force, as long as gravity is ignored. General relativity works when the quantum behavior of nature is ignored.