Transcript Magnetic fields

Sensing techniques in planetary science
• Camera/photography: takes images in visible,
infrared and/or ultraviolet light. REMOTE
• Radar: maps objects and their surface features
(mountains/canyons, asteroids) by sending radio
signals that bounce off the surface and timing
their return. Some waves can penetrate surface 
subsurface imaging. REMOTE
• Spectroscopy/Spectrometry: see below. REMOTE
and DIRECT
• Mass spectrometry: see below. DIRECT
• Microscopy: visualizes super-small
objects/features. Light microscopes have limited
resolution; electron microscopes and scanning
probe microscopes overcome that. DIRECT
• Magnetometry: measure the strength and the
direction of a magnetic field at a point in space.
Think metal detector. DIRECT (Q: Can a magnetic
field be detected remotely? ___________________
• Gravimetry: measurement of the strength and the
direction of a gravitational field. DIRECT
Spectroscopy
• …study of interaction between
matter and radiative energy
• Radiative energy can be, for
example:
• Electromagnetic radiation (from
microwave and up)
• Particles, e.g. electrons or neutrons
• Interaction can be, for example:
•
•
•
•
Emission
Absorption
Scattering
Reflection
• Atomic or molecular composition
of the sample is deduced from the
spectrum
• Challenge: separating spectra of
different components
• Physical presence of the sample is
NOT needed but can be used: both
REMOTE and DIRECT sensing.
Mass Spectrometry
• …identification of chemicals in a sample by measuring the mass-tocharge ratio and abundance of gas-phase ions.
• Break molecules into charged fragments (=ionization)
• Flying these fragments at high speed through a magnetic or electric field
bends their trajectories: higher mass  less bend; higher charge  more
bend
• Detect particles separated by mass-to-charge ratio
• Challenge: separating spectra of different components. Gas
chromatography can be used pre-MS to separate mixtures and
simplify MS analysis.
• Physical presence of the sample is needed: DIRECT sensing
Camera examples
Instrument
Spacecraft
Properties
MArs Hand Lens
Imager (MAHLI)
MSL
Curiosity
• 1600×1200 px true-color
images
• resolution of 14.5 µm/px
• white and ultraviolet LED
illumination
• mechanical focusing
from infinite to 1mm.
High Resolution
Mars
•
Imaging Science Reconnaissance
Experiment
Orbiter
(HiRISE)
(MRO)
•
0.5 m reflecting
telescope (largest ever
on a deep space mission)
resolution of 1 μrad (=
0.3 m from H=300 km)
• three color bands: B-G,
R, and NIR
• makes stereo pairs
Optical,
Spectroscopic,
and Infrared
Remote Imaging
System (OSIRIS)
Rosetta
• narrow-angle lens 700
mm
• wide-angle lens 140 mm,
• 2048×2048 px CCD chip
Radar examples
Instrument
Spacecraft
Properties
Shallow
Mars
•
Subsurface Radar Reconnaissance
(SHARAD)
Orbiter
(MRO)
detects finely spaced
(~7m) interfaces at
depths < 1km (e.g. for
internal polar cap
structure)
• HF radio waves between
15 and 25 MHz
• horizontal resolution of
0.3 to 3 km
Comet Nucleus
Sounding
Experiment by
Radiowave
Transmission
(CONSERT)
Rosetta
• will measure
propagation of 90 MHz
EM wave between the
Philae lander and the
Rosetta orbiter through
the comet nucleus (to
study the comet's
internal structure)
Spectrometer examples
Instrument
Spacecraft
Properties
Compact
Reconnaissance
Imaging
Spectrometer for
Mars (CRISM)
MRO
• visible and NIR (370-3920 nm)
• 544 channels (each 6.55 nm
wide)
• resolution 18 m at H=300 km
• studies surface mineralogy of
Mars – iron, oxides,
phyllosilicates, and carbonates
have characteristic NIR spectra
Mars Climate
Sounder (MCS)
MRO
• 1 visible/NIR channel (3003000 nm)
• 8 far IR (12 to 50 μm) channels
• measures T, P, H2O vapor and
dust levels in the atmosphere
of Mars (watch the horizon!)
• makes daily global weather
maps
Visible and
Infrared Thermal
Imaging
Spectrometer
(VIRTIS)
Rosetta • will image comet nucleus in
the IR
• will search for IR spectra of
molecules in the coma
More spectrometer examples
Instrument
Spacecraft
Properties
Cassini's
Composite
Infrared
Spectrometer
(CIRS)
Cassini
• identifies gases glowing in the
lower layers of the atmosphere
from their IR spectra
Dynamic Albedo
MSL
• pulsed sealed-tube neutron
of Neutrons
Curiosity
source and detector
(DAN)
• measures hydrogen (= ice and
water) at or near the Martian
surface
• provided by the Russian
Federal Space Agency
Chemistry and
MSL
• high energy IR (1067 nm) laser
Camera Complex Curiosity
pulse vaporizes small amount
(ChemCam)
of rock at a distance ≤ 7 m
= Laser-Induced
• the spectrum of emitted light
Breakdown
is recorded
Spectroscopy
• provides elemental
(LIBS) + Remote
compositions of rock and soil
Micro Imager
• coupled to a high-res camera
(RMI)
Mass spectrometer examples
Instrument
Spacecraft
Properties
The Ion and
Neutral Mass
Spectrometer
(INMS)
Cassini
• studies ions and neutral
particles in the upper
atmospheres of Saturn and
moons
• analyzed Enceladus plumes by
flying directly through them
COmetary
Secondary Ion
Mass Analyzer
(COSIMA)
Rosetta • analyses the composition of
dust particles by secondary ion
mass spectrometry, after the
surface is cleaned by indium
ions
Bonus: MRO HiRISE portrait of Curiosity
Chemicals in the Solar System
Note Log scale on the y-axis
Chemicals in the Solar System
• Hydrogen (H)
• Exists as H2 gas at STP
• Elemental H constitutes ~74% of mass of the Universe
• Metallic H is a phase where it loses it electron and behaves as
an electrical conductor, @~500 Gpa; can be liquid or solid
• Helium (He) ~24% of mass of the Universe
• Oxygen
• O2 gas at STP
• Elemental oxygen is a part of many rock-forming compounds
• It is also a part of water (H2O)
• Carbon
•
•
•
•
Pure forms such as graphite and diamond
Polymerizes! Basis for life as we know it.
Carbon dioxide (CO2) gas (at STP)
Hydrocarbons: methane CH3 abundant, ethane C2H5 OK,
ethylene C2H4, propane C3H8, propylene C3H8 … higher
complexity  lower abundance
• Nitrogen
• N2 is a gas at STP
• A part of ammonia (NH3/NH4+), hydrogen cyanide (HCN),
cyanoacetylene (C3HN) etc.
• Fe and Mg (planetary cores); metal oxides and silicates,
sulfur (mantles and crusts).
Life as we know it
• Made of H, C, O, N, P, S
• Building blocks of DNA: nucleotides
• Building blocks of proteins: amino acids
• Plants convert CO2 and H2O into glucose in the presence of light… etc.
• Complexity! Although simplest organic molecules can form spontaneously
from simpler inorganic constituents in right conditions…
www.compoundchem.com/2014/07/25/planetatmospheres/
www.compoundchem.com/2014/07/25/planetatmospheres/
Interiors
• Terrestrial planets and satellites: Core, Mantle, Crust
• Giants: Core, “Mantle”, Gas layer
• Here “mantle” is an intermediate density, liquid- like
transition layer between the core and the surface.
• Interior not observable…
• Observable qualities: mass, radius, gravity field,
magnetic field, energy output, seismic activity
• Density = mass/volume
• <1 g/cm3  object is rich in ices, or is relatively porous, or
has a gaseous composition
• ~ 3 g/cm3  object is rocky
• > 3 g/cm3  object has some metal content (iron, nickel, etc)
• Shape depends on density, material strength, and
plasticity
Density of planets and selected moons
Mean density
(g/cm3)
Sun
1.409
Mercury
5.430
Venus
5.240
Earth
5.515
Moon
3.346
Mars
3.940
Ceres
2.080
Jupiter
1.330
Io
3.528
Europa
3.010
Ganymede
1.936
Callisto
1.830
Saturn
0.700
Mimas
1.150
Enceladus
1.610
Tethys
0.984
Dione
1.480
Rhea
1.230
Titan
1.880
Iapetus
1.080
Uranus
1.300
Neptune
1.760
Proteus
1.300
Triton
2.061
Pluto
2.000
SS Body
Magnetic fields
• Origins of magnetic field:
• Liquid metal in the core: differences in T & P cause convection (cool,
dense matter sinks whilst warm, less dense matter rises)  electric
currents
• Planet spin: the Coriolis force causes swirling whirlpools
• Electric current + rotation = magnetism; typically aligned with the spin
axis.
• Magnetic moments and equatorial strengths of magnetic field
(a strong refrigerator magnet is ~ 0.01 T):
• Mercury: 2-6 × 1012 Tm3, Eq. strength = 300 nT (1.1% strength of Earth)
• Earth: 7.91 × 1015 Tm3, Strength of 25-65 uT
• Jupiter: 1.56 × 1020 Tm3, 428 uT (10x stronger than Earth; magnetic
moment 18000x larger)
• Ganymede: 1.3 × 1013 T·m3 , Eq. strength = 790 nT
• Saturn: 4.6 × 1018 Tm3, 21 uT
• Uranus: 10-110 uT. Misaligned w.r.t. spin axis (59)
• Neptune: 2.2 × 1017 Tm3, 14 uT. Misaligned w.r.t. spin axis (47)
• Why is magnetic field important? ________________________
___________________________________________________
Planet interiors: terrestrial
• Earth: iron-nickel core, solid + liquid, fast spin (24h)  magnetic field; rocky
mantle and crust
• Moon: rocky mantle and crust, but possibly no iron core or strictly solid iron core
( no magnetic field)
• Mercury: ~ Earth without most of the mantle. Slow spin (58d)  magnetic
field weak but detectable
• Venus: similar to Earth, but a slow spinner (-243d, retrograde orbit)  no
magnetic field.
• Mars: lower density  more volatiles. Iron present on the surface and in the
mantle, but magnetic field very weak and scattered.
Planet interiors: giants
• Jupiter: rocky/metal core, liquid metallic H, liquid molecular H, outer
atmosphere (75%H2 / 24%He, traces of methane, water vapor, ammonia).
• Ultra strong magnetic field! (liquid metallic hydrogen layer + very rapid spin rate
= 9 hours, 50 minutes).
• Internal heat: Jupiter releases more energy than it gets from the Sun (likely from
its continuing “formation”, it has not yet cooled down).
• Saturn: ~ Jupiter but less
• Uranus/Neptune: not well understood. Possibly rocky core, icy mantle, gas
outer atmosphere with significant fraction of methane ( blue/cyan).
• Maybe a layer of conductive liquid ammonia/methane/water at a shallow depth
( magnetic field that is misaligned w.r.t. the spin axis).
Interiors: selected dwarfs and moons
• Jupiter’s “Galilean”
Moons:
•
•
•
•
Io
Europa
Ganymede
Callisto
• Saturn’s moons:
• Enceladus
• Titan
• Ceres (asteroid belt dwarf)
• Pluto (Kuiper belt dwarf)
Events this week and on
• Sun, Oct 19 – C/2013 A1 Siding Spring closest approach of Mars
• http://mars.jpl.nasa.gov/comets/sidingspring/
http://www.nasa.gov/press/2014/october/nasa-prepares-its-science-fleet-foroct-19-mars-comet-encounter/
• Nights of Oct 20-21 and Oct 21-22 - Orionids (as Earth passes the orbit
of 1P/Halley comet). Expect 20-25 shooting stars/hour.
• http://www.timeanddate.com/astronomy/meteor-shower/orionid.html
• https://solarsystem.nasa.gov/planets/orionids.cfm
• Oct 23 – a partial solar eclipse with a maximum visible in SD at 3.33pm:
• http://www.timeanddate.com/eclipse/in/usa/san-diego?iso=20141023
• http://eclipse.gsfc.nasa.gov/OH/OH2014.html#SE2014Oct23P
• Nov 12 – Philae landing
• Dec 13-14, 2014 – Geminids Meteor Shower Peak
• Dec 31, 2014 – ESA Mars Express mission ends
• Late March/early April 2015 – Dawn to arrive to Ceres
• July 2015 – closest approach of Pluto by New Horizons
References
• Siobahn M. Morgan, Univ. of Iowa, course on
Planetary Science:
• http://www.uni.edu/morgans/planets/
• Cut-away models and other images by Calvin J.
Hamilton:
• http://www.solarviews.com/cap/index/index.html
• http://www.solarviews.com/cap/index/cutawaymodels1
.html