Upload
others
View
0
Download
0
Embed Size (px)
Citation preview
ASTRONOMY 340
FALL 200725 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)mv2 = (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”, Tb
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 “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
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=10 (2.7mm, 115.3 GHz)
J=21 (1.3mm), J=32 (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 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)
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
Note on Conductivity
Specific heat units are J mole-1 K-1 function of
temperature for most minerals
Example: feldspar (KAlSi3O8)
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
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 14
Apollo 12
Apollo 15
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 km2)
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 (km2 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