Interstellar%20and%20Interplanetary%20Material

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Interstellar and Interplanetary Material
HST Astrobiology Workshop May 5-9, 2002 P.C.
Frisch University of Chicago
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Outline

• The solar system is our template for
  understanding interplanetary material
• Heliosphere, solar wind, ISM
• Astrospheres
• Interstellar and interplanetary matter
• ISM affects planets inner vrs outer planets
• 3D data visualization of solar motion

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Heliosphere and ISM

• About 98 of diffuse material in heliosphere is
  interstellar gas
• Solar wind and interstellar gas densities are
  equal near Jupiter, or at 6 au

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Solar Wind

• Expanding solar corona becomes solar wind
• At 1 au and solar max n(p)4 /cc, V 350
  km/s, B 2nT (20 mG)
• SW density decreases by 1/R2 in solar system
• SW sweeps up charged particles, including ISM

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Heliosphere today

• Top Plasma Temp
• Bottom Interstellar Ho
• Ho Wall Ho and p couple
• Properties T29,000 K, N(Ho)3 x 1014 cm-2,
  dV-8 km/s
• Model 4-fluid model
• (Figure courtesy Hans Mueller)

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Heliosphere vrs Planetary System

• HELIOSPHERE
• Warm Partially Ionized ISM surrounds Sun
  nHI0.22 /cc, nHeI0.12 /cc, n0.11 /cc, T6500
  K, VHC26 km/s (ionization must be modeled)
• SW Termination Shock 75-90 au
• Heliopause 140 au
• Bow shock 250 au, M1.5 (?)
• PLANETARY SYSTEM
• Pluto 39 au
• NASA Spacecraft
• Voyager 1 84 au (in nose direction) (3.6
  au/year)
• Voyager 2 66 au (in nose direction) (3.3
  au/year)
• Pioneer 10 80 au (in tail direction)
• ESA/NASA Ulysses 15 au, over poles of Sun
• Future Spacecraft
• Interstellar Probe ? 10-20 au/year in nose
  direction (Liewer and Mewaldt 2000)

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Warm partially ionized diffuse interstellar cloud
around Sun

• Observations of interstellar Heo in solar system
  give cloud properties (Witte et al. 2002, Flynn
  et al 1998)
• nHeI0.014 /cc, T6,400 K, VHC26
  km/s
• ISM radiative transfer models give composition
  and ionization at boundary heliosphere (Slavin
  Frisch 2002, model 18)
• nHI0.24 /cc , ne0.09 /cc, H/H23,
  He/He45
• Magnetic field strength lt3 mG (but unknown)
• Over 1 of cloud mass is in interstellar dust
• Observed upstream direction towards l5o, b14o.
• This cloud referred to as Local Interstellar
  Cloud (LIC)

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Sun in Local Bubble interior 106 Years Ago

• ? Sun moves towards l28o, b32o, V13.4 km/s
• (Dehnen Binney 1998)
• ? Local Bubble densities nHIlt0.0005 cm-3
• nHII0.005 cm-3
• T106 K

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Heliosphere while in Local Bubble Plasma(Figure
courtesy Hans Mueller)

• Sun in Fully Ionized Local Bubble Plasma
• Relative V13.4 km/s
• TInterstellar106.1 oK
• n(p)IS0.005 cm-3
• n(Ho)IS0 cm-3
• No IS neutrals in heliosphere

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Solar Environment varies with Time

• ?Sun entered outflow of diffuse ISM from Sco-Cen
  Association (SCA) 103-105 years ago
• LSR Outflow 17 /- 5 km/s from upstream
  direction
• l2.3o, b-5.2o
• ISM surrounding solar system now is warm
  partially ionized gas.
• Solar path towards l28o, b32o implies Sun
  will be in SCA outflow for million years in
  future.
• Denser ISM will shrink heliosphere to radius
  ltlt100 au

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Solar Encounter with Interstellar Clouds

• Sun predicted to encounter about a dozen giant
  molecular clouds over lifetime,
• Encounters with n10 cm-3 interstellar clouds
  will be much more frequent.
• An increase to n10 cm-3 for the cloud around the
  Sun would (Zank and Frisch 1998)
• Contract heliopause to radius of 14 au
• Increase density of neutrals at 1 au to 2 cm-3
• Give a Rayleigh-Taylor unstable heliopause from
  variable mass loading of solar wind by pickup ions

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Heliosphere and IS cloud densitynHI0.22 /cc
nHI15 /cc
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Solar Encounter with Interstellar Clouds

• Sun moves through LSR at 13.4 km/s, or 13.4
  pc/106 years.
• 96 interstellar absorption components are seen
  towards 60 nearby stars which sample interstellar
  cloudlets within 30 pc of Sun (F02).
• Nearest stars show 1 interstellar absorption
  component per 1.4-1 .6 pc.
• Relative Sun-cloud velocities of 0-32 km/s
  suggest variations in the galactic environment of
  the Sun on timescales lt50,000 years.

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Astrospheres.

• Cool star mass loss gives astrospheres with
  properties determined by interactions with the
  ISM and sensitive to interstellar pressure
  (Frisch 1993)
• a Cen mass loss rate of 10-14 MSun/year (Wood et
  al. 2001)
• Heated interstellar Ho in solar heliosheath
  (25,000 K) see towards a Cen AB and other stars
  (e.g. Linsky, Wood)
• Astrospheres found around a Cen AB (1.3 pc), e
  Ind (3 pc), l And (?, 23 pc), and other stars
  (Linsky Wood 1996,Gayley et al. 1997, Wood et
  al. 1996)

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Example Sun a Cen Heliosheath

• Interstellar Lya absorption shows redward
  shoulder from decelerated Ho
• Interstellar Ho and p couple by charge exchange
• Ho heated to 29,000 K, N(Ho)3 x 1014 cm-2, dV
  -8 km/s
• Gayley et al. 1997

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Interstellar and Interplanetary Material
Observations of ISM in the Solar System

• Ho /Heo fluorescence of solar Lya/584A emission
  (1971, many satellites)
• Heo Ulysses
• Dust Ulysses, Galileo, Cassini
• Pickup Ions Ampte, Ulysses
• Anomalous Cosmic Rays e.g. Ulysses, ACE, many
  other spacecraft

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Interstellar Ho in Solar System

• Ho Solar Lya photons fluorescing on
  interstellar Ho at 4 au
• Discovered 1971 (Thomas, Krassa, Bertaux,
  Blamont)
• Ho decelerated in solar system (by 5 km/s)

• Left Interstellar Ho
• Right Geocorona
• (Copernicus data, Adams and Frisch 1977)

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Interstellar Heo in Solar System

• Heo Solar 584 A fluorescence on interstellar
  Heo at 0.5 au
• Discovered 1974 (Weller and Meier)
• Heo atoms measured directly by Ulysses
• Best data on interstellar gas inside solar system
• n(Heo)0.014 /cc, T6,400 K, V26 km/s, observed
  upstream at l5o, b14o (Witte 2002)

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Interstellar Heo in Solar System

• Interstellar He gravitationally focused
  downstream of the Sun.
• The Earth passes through the Helium focusing cone
  at the beginning of December.
• Density enhancement in cone

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Pickup Ions Gloeckler and Geiss (2002)
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Pickup ions become Anomalous Cosmic Rays (Figure
from ACE web site)
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Anomalous Cosmic RaysCummings and Stone (2002)
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Anomalous Cosmic Rays captured in Earths
magnetosphereFigure from ACE web site
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Pickup Ions, Anomalous Cosmic Rays,and the
ISM(Cummings and Stone 2002)
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Pickup Ions, Anomalous Cosmic Rays,and the
ISM(Cummings and Stone 2002)
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Interstellar Dust

• Smallest grains filtered in outer heliosphere
  (lt0.1mm)
• Medium grains filtered by solar wind (0.1-0.2 mm)
• Large grains constitute 30 of interplanetary
  grain flux with masses gt10-13 gr (or radiusgt0.2
  mm) at 1 au.
• 1 of the cloud mass in dust
• Work by Gruen, Landgraf et al.

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Entry of ISM into Heliosphere
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ISM effects on planets

• Inner versus Outer Planets (Ho)
• Cosmic rays
• ?Anomalous cosmic rays (require neutral ISM)
• ?Galactic Cosmic Rays (sensitive to heliosphere
  B)
• In principle, core samples on inner versus outer
  planets would sort solar variations from
  interstellar variations

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Inner versus Outer PlanetsHeliosphere in n15
cm-3 cloudT (K) Ho
Density (cm-3)
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Cosmic Rays and Sunspot numbersClimax, Co. data
0.5-200 GeV/nucleii(figure courtesy Cliff
Lopate)

• Cosmic ray fluxes at Earth coupled to solar cycle
  (through solar magnetic field)
• Encounter with dense interstellar cloud decreases
  heliosphere dimensions by order of magnitude and
  will alter cosmic ray flux at Earth

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Planetary climates and the interplanetary
environment.

• Galactic Cosmic Ray flux correlated with low
  level (lt3.2 km) cloud cover (Marsh Svensmark
  2002)

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Instantaneous 3D visualization of Hipparcos
catalog stars and MHD heliosphere model. Credits

• Data Hipparcos catalog of stars, A. Mellinger
  Milky Way Galaxy photage, Heliosphere MHD model
  of T. Linde (U. Chicago)
• Video A. Hanson (Indiana U., producer), P.
  Frisch (U. Chicago, scientist)
• Funding NASA AISRP grant 5-8163 (U. Chicago)

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ConclusionsKnow your astrosphere

• A stellar astrosphere and the interplanetary
  environment of an extrasolar planetary system
  depend on both the stellar wind and the
  properties of the interstellar cloud surrounding
  the star.
• Inner and outer planets see different fluxes of
  ISM over time.
• Astrospheres change when stars encounter
  different interstellar clouds.
• Star-planet coupling is function of surrounding
  ISM (and perhaps climate?)