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Astronomy 340 Fall 2007

Astronomy 340 Fall 2007. 25 September 2007 Class # 6-#7. Review. Physical basis of spectroscopy Einstein A,B coefficients  probabilities of transistions Absorption/emission coefficients are functions of ρ , N, quantum mechanical factors, temperature Molecular spectroscopy

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Astronomy 340 Fall 2007

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  1. Astronomy 340Fall 2007 25 September 2007 Class #6-#7

  2. Review • Physical basis of spectroscopy • Einstein A,B coefficients  probabilities of transistions • Absorption/emission coefficients are functions of ρ, N, quantum mechanical factors, temperature • Molecular spectroscopy • More available quantum states – rotational, vibrational • Low energy transitions  IR, radio part of the spectrum (hν << kT) • Examples • CaI in the atmosphere of Mercury  linewidth = Δλ = Δv  (1/2)mv2 = (3/2)nkT

  3. Quantum mechanics • Principle quantum # (n)  energy • Angular momentum, l • Spin, s • Multi-electron atoms have many filled orbitals (constrained by exclusion principle)  e.g. electron with n=2 could have l=1 or l=0, and if its l=1 it could have s=1/2 or -1/2  many orbitals, many transitions, many spectral lines http://physlab2.nist.gov/PhysRefData/ASD/lines_form.html

  4. Molecules • Nuclei act as single nucleus with common potential • Multiple nuclei generate other quantum states • Electronic • Rotational • Vibrational low energy  radio/NIR part of the spectrum • Most surface and atmospheric components are molecular

  5. CO • Main product of stellar evolution • Transitions  easily excited rotational modes • J = 1 0 (2.7mm, 115.3 GHz) • J = 2  1 (1.3mm) • Observations  radiotelescopes • Measure “brightness temperature”, Tb • Optically thick vs optically thin

  6. Mars – non thermal CO

  7. Example: Mercury • What does the spectrum of Mercury look like? • Planetary reflectance spectrum • Terrestrial emission and absorption • Narrow source emission lines  wavelength shifted via Doppler • Process • What do you actually measure? • Linewidths? • Wavelength?

  8. Spencer et al. 2000Science 288, 1208 • Io is the most geological activity of anything in solar system  volcanoes discovered during Voyager flyby in ’79 • What’s coming out of that volcano?

  9. Spencer et al. 2000Science 288 1208 • Use transit of Io across Jupiter to observe plumes from volcanoes  why? • Scattered light  dust scatters photons effectively so you get a “non-thermal” continuum  effect is to fill in absorption line • Identify S2 and SO2 lines in 240.0-300.0nm range -> fit linewidths • T ~ 300 K • N(SO2) ~ 7 x 1016 cm-2 • N(S2) ~ 1 x 1016 cm-2 • Pure SO2 suggests a lack of Fe since Fe will bind with SO2 if available

  10. CO molecule • C,O main products of stellar evolution, particularly intermediate mass stars • 3He  12C or 12C + 4He  16O • On terrestrial planets CO comes from CO2 + uv photons  CO + O • Transitions • J = principle rotational quantum number • J=10 (2.7mm, 115.3 GHz) • J=21 (1.3mm), J=32 (0.87mm) • J=0 is ground state, but get to J=1 if there’s ambient thermal bath with T~5.5K it’ll get excited to J=1 level

  11. CO molecule • Photons too dang weak for CCDs, so you need a radio telescope • Characterize intensity with a “brightness temperature”  if line is optically thick the observed brightness temperature really is the thermal temperature • Tb = (λ2/2k)Bλ • Rewrite radiative transfer as: • (dTb(s)/dτλ) = Tb(s) – T(s) • Tb(s) = Tb(0)e-τ(s) + T(1-e-τ(s)) • Tb = τT (τ << 1) • Tb = T (τ >> 1)

  12. Venus Images in J=1-0 Line • Observations • 2.7mm continuum, J=1-0 CO line • 3-element interferometer • Continuum results • 10% increase in Tb from day side to night side  a change in atmospheric conditions? • CO line results • Line shape varies  broad, shallow lines on dayside; deep, narrow lines on night side

  13. Note on Conductivity • Specific heat  units are J mole-1 K-1  function of temperature for most minerals • Example: feldspar (KAlSi3O8)

  14. Transition Slide…. • Radiative transfer tells us how radiation is affected travelling through some substance (gas) • In Rayleigh-Jeans approximation we can substitute a temperature (Tb) for the radiation intensity • Now onto some fun stuff – planetary surfaces…. • Relevant reading: • Chapter 5

  15. Processes at Work • Impact cratering • Weathering/erosion • Conditions of the atmosphere • Geological activity • Volcanic activity • Tectonics

  16. Geological activity - Earth • Volcanism • Shield volcanoes • Formed via a single plume • Hawaii – crustal plate moving over a hot spot • “cone” volcanoes • Formed over subduction zones • Cascade mountains, Mount Etna • Earthquakes • At plate boundaries • Plate tectonics • Mid-ocean ridges, mountain chains, moving continents, earthquakes, “ring of fire”, global resurfacing

  17. Apollo 17 View of Earth

  18. Earth Topographic Map

  19. Mercury • Heavily cratered • No volcanoes, no mountain chains, no plate boundaries, no continents  no recent tectonics • Shrinking? • Weak magnetic field • Conclusion: one plate planet with no activity over the past several billion years; surface is shaped by impacts

  20. Mercury, Mariner 10 3/74, 9/74, 3/75

  21. Mercury South Pole

  22. Mercury, Scarp displacement

  23. Luna, near side The far side LUNA Earth Facing Side

  24. Moon from Galileo Spacecraft Apollo 15 Apollo 14 Apollo 17 Apollo 12 Apollo 11 Apollo 16

  25. Lunar Highlands

  26. Lunar Mare

  27. Venus • Lots of volcanic activity in the recent past • Characteristic feature is a “coronae” which is a circular structure like the caldera of a volcano but without the mountain to go with it • Global resurfacing about 300 Myr ago • Crater density (number per km2) • We call this a “young” surface • A couple of continent-like features • No obvious plate boundaries

  28. Venus Clouds Mariner 10

  29. Venus Topography identified

  30. Venus Surface, Venera 13

  31. Sapas Mons

  32. Maat Mons

  33. Terrestrial Planet Surface Morphology (4) • Mars • Massive Shield Volcanoes • Huge Erosion Channels • Much Cratering, much eroded • Polar Caps

  34. Mars Hubble

  35. Mars Orbiter Laser Altimeter Topographic Map

  36. Sojourner at Yogi Seeds Fig 23-15)

  37. Vallis Marineris (Seeds Fig 23-17

  38. Olympus Mons Viking 1

  39. MOLA Generated Perspective of O.Mons

  40. Vallis Marinaris

  41. Fig 23-22a

  42. Fig 23-23a

  43. Fig 23-23b

  44. Water in Newton Crater, Context

  45. “Evidence” for recent liquid flow

  46. Fig 23-24a

  47. Famous Viking 1 Face

  48. MGS view of the “Face”

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