ASTRONOMY 340 FALL September 2007 Class #6-#7

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 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

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

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

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, T b Optically thick vs optically thin

Mars non thermal CO

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?

Spencer et al. 2000 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?

Spencer et al. 2000 Science 288 1208 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 240.0-300.0nm range -> fit linewidths T ~ 300 K N(SO 2 ) ~ 7 x 10 16 cm -2 N(S 2 ) ~ 1 x 10 16 cm -2 Pure SO 2 suggests a lack of Fe since Fe will bind with SO 2 if available

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, 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

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)

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

Note on Conductivity Specific heat units are J mole -1 K -1 function of temperature for most minerals Example: feldspar (KAlSi 3 O 8 )

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

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

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

Apollo 17 View of Earth

Earth Topographic Map

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

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

Mercury South Pole

Mercury, Scarp displacement

Luna, near side LUNA Earth Facing Side The far side

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

Lunar Highlands

Lunar Mare

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

Venus Clouds Mariner 10

Venus Topography identified

Venus Surface, Venera 13

Sapas Mons

Maat Mons

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

Mars Hubble

Mars Orbiter Laser Altimeter Topographic Map

Sojourner at Yogi Seeds Fig 23-15)

Vallis Marineris (Seeds Fig 23-17

Olympus Mons Viking 1

MOLA Generated Perspective of O.Mons

Vallis Marinaris

Fig 23-22a

Fig 23-23a

Fig 23-23b

Water in Newton Crater, Context

Evidence for recent liquid flow

Fig 23-24a

Famous Viking 1 Face

MGS view of the Face

Let s put it all together. Calculate the surface area to mass ratio (km 2 g -1 ) Moon: 5.16 10-19 Mercury: 2.26 10-19 Mars: 2.25 10-19 Venus: 9.46 10-20 Earth: 8.55 10-20