What is Spectroscopy

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What is Spectroscopy?
Astronomy Observatory Public Open House June 5,
2006

• Dr. Lori Feaga
• University of Maryland
• Department of Astronomy

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BackgroundThe Making of a Scientist

• 3rd grade science project on the planets
• 5th grade Space Shuttle launch in Florida,
  science project on Saturn, and an astronaut guest
  speaker
• High school loved math and science classes
• 10th-11th grade NASA internships

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Space Shuttle Discovery
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Our Solar System

• Sun
• 9 (traditional) planets
• Moons
• Asteroids
• Comets
• Kuiper Belt Objects
• Spacecraft
• Dust

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What Is What?

• Size
• Location and orbit
• Natural or manmade
• Composition
• Temperature

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Study of Composition and Temperature

• Send landers to the bodies
• Expensive and difficult
• Special instruments from Earth and spacecraft
• Telescopes
• Cameras
• Spectrometers

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Scientific Impact

• When we know the composition and temperature of a
  body in the solar system we have insight into
  its
• History
• Formation
• Evolution
• Present State
• Physical properties
• Active processes
• Relation to the Earth and our history

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Spectroscopy

• Spectroscopy was discovered in 1859 by Gustav
  Kirchhoff and Robert Bunsen
• Spectrometer -- an optical instrument that splits
  the light received from objects into its
  component wavelengths using prisms or diffraction
  gratings
• Diffraction grating -- an immensely useful tool
  for the separation of the spectral lines acting
  as a "super prism", separating the different
  colors of light much more than the dispersion
  effect in a prism (i.e. much more detail than a
  prism)

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Fingerprints

• Every substance (atom or molecule) has a
  fingerprint
• We see the fingerprint when the atom or molecule
  has absorbed or released energy
• Substances will emit spectral lines (at a
  particular wavelength) when it is heatedbright
  line
• Substances will absorb light at the same
  wavelength when it is cooldark line

Hydrogen Visible Emission Lines
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Emission and Absorption
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Why Does Each Element Have a Different Signature
Spectrum?

• Each element has a different atomic structure,
  causing it to produce (or absorb) a different set
  of wavelengths.
• It's the actions of the electrons (tiny particles
  that surround the much heavier nucleus) jumping
  between different orbitals (the many places where
  the probability of finding an electron is the
  greatest) that produce the signature spectrum for
  an element.
• When light (or other energy) is absorbed by the
  atom, an electron jumps from a low energy orbital
  to a higher energy orbital.
• When an electron returns to a less energetic
  orbital, light (or other electromagnetic
  radiation) is generated.
• There are actually many high energy orbitals that
  an electron can move to, so you can get emitted
  light in several different wavelengths. The
  bigger the difference in energy of the orbitals,
  the shorter the wave length of the light produced
  (or absorbed).

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Atomic Response to Radiation
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Molecular Response to Radiation
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Select Spectroscopy Results in Planetary Science

• Projects that I have worked on
• Jupiters moon Io (HST)
• Comet Tempel 1 (Deep Impact Mission)
• Current NASA Missions
• Cassini at Saturn
• Messenger to Mercury (2008)
• New Horizons to Pluto (2015) and Kuiper Belt

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Jupiters Moon Io

• Orbits Jupiter in less than 2 days
• Size 3,630 km (about ¼ of the Earth)
• White, red, orange and yellow in color
• Has volcanoes and lavabut what are they made of,
  what is under the surface of Io?
• Has an atmosphereis it made up of volcanic gases
  or something else?

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Io Spectral Results

• SO2 is the primary atmospheric component
• Sulfur, oxygen, sodium, chlorine and potassium
  are also present

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Comets
Borrelly

• We dont know exactly what a comet is made of
• We can see the crusty outside, but not the inside
• We know what is in the tail and coma, mostly ice
  and carbon
• We call them dirty snowballsbut is this the
  right analogy?
• 40,000 tons of dust particles from comets land on
  the Earth each year
• A comet could hit the Earth, so we want to be
  ready (not any time soon!)

Hale-Bopp
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Characteristic Vibrations of Molecules
Many of these molecules thought to be in comets!
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Deep Impact
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July 2, 2005 Outburst
8600000 6221
H2O
8600001 75631
8600002 100221
8600003 120711
Approaching Comet Tempel 1
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Heterogeneous Coma

• Data taken 10 min before impact
• Black lines in Northern coma
• Red lines in southern coma
• Solid lines 5 10 km from nucleus
• Dotted lines 10 15 km from nucleus

Tempel 1
H2O

• Asymmetry of CO2 and H2O found in coma
• CO2 more prevalent in southern coma
• H2O more prevalent in sunward direction

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Surface Water Ice on Tempel 1

• Surface
• 3-6 water ice
• 30 10 micron size particles

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Volatile Composition in Ejecta
Tempel 1
First 0.2 sec
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Ejecta over Time Sub-surface Water Ice

• Dust
• (2 µm reflectance)
• H2O Ice Absorption
• H2O Gas Emission

Impact
Time
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Spectra off Southern Limb of Tempel 1

• Post-impact spectrum obviously different from
  pre-impact spectrum
• Initial ejecta are hot but after few seconds
  ejecta leave nucleus cool
• Water, organics and carbon dioxide are present in
  the coma and were excavated during the impact

CO2
H2O
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Summary

• Spectroscopy helps scientists on Earth detect and
  understand the composition of other astronomical
  objects
• Each atom and molecule produces a distinct
  spectrum which can be studied with a spectrometer
• Most space missions include a spectrometer
  instrument