ASTRONOMY 340 FALL September 2007 Class #6-#7

Transcription

1 ASTRONOMY 340 FALL 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)mv 2 = (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

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, GHz) J = 2 1 (1.3mm) Observations radiotelescopes Measure brightness temperature, T b 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 Science 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 Science Use transit of Io across Jupiter to observe plumes from volcanoes why? Scattered light dust scatters photons effectively so you get a nonthermal continuum effect is to fill in absorption line Identify S 2 and SO 2 lines in nm range -> fit linewidths T ~ 300 K N(SO 2 ) ~ 7 x cm -2 N(S 2 ) ~ 1 x cm -2 Pure SO 2 suggests a lack of Fe since Fe will bind with SO 2 if available

10 CO molecule C,O main products of stellar evolution, particularly intermediate mass stars 3He 12 C or 12 C + 4 He 16 O On terrestrial planets CO comes from CO 2 + uv photons CO + O Transitions J = principle rotational quantum number J=1 0 (2.7mm, 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 T b = (λ 2 /2k)B λ Rewrite radiative transfer as: (dt b (s)/dτ λ ) = T b (s) T(s) T b (s) = T b (0)e -τ(s) + T(1-e -τ(s) ) T b = τt (τ << 1) T b = 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 T b 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 (KAlSi 3 O 8 )

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 (T b ) 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 LUNA Earth Facing Side The far side

24 Moon from Galileo Spacecraft Apollo 15 Apollo 14 Apollo 12 Apollo 17 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 km 2 ) 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

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

35 Mars Hubble

36 Mars Orbiter Laser Altimeter Topographic Map

37 Sojourner at Yogi Seeds Fig 23-15)

38 Vallis Marineris (Seeds Fig 23-17

39 Olympus Mons Viking 1

40 MOLA Generated Perspective of O.Mons

41 Vallis Marinaris

42 Fig 23-22a

43 Fig 23-23a

44 Fig 23-23b

45 Water in Newton Crater, Context

46 Evidence for recent liquid flow

47 Fig 23-24a

48

49 Famous Viking 1 Face

50 MGS view of the Face

51 Let s put it all together. Calculate the surface area to mass ratio (km 2 g -1 ) Moon: Mercury: Mars: Venus: Earth: