Transcript Interstellar and Interplanetary Matter

Interstellar and
Interplanetary Material
HST Astrobiology Workshop: May 5-9, 2002
P.C. Frisch
University of Chicago
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: T~29,000 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
nHI=0.22 /cc, nHeI=0.12 /cc, n+=0.11 /cc, T=6500
K, VHC=26 km/s (ionization must be modeled)
SW Termination Shock: 75-90 au
Heliopause: 140 au
Bow shock: 250 au, M~1.5 (?)
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: 1—5 au, over poles of Sun
Future Spacecraft:
Interstellar Probe  10-20 au/year in nose direction
(Liewer and Mewaldt 2000)
*Heliosphere = solar wind bubble
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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):
nHeI=0.014 /cc, T=6,400 K, VHC=26 km/s

ISM radiative transfer models give composition and ionization at
boundary heliosphere (Slavin Frisch 2002, model 18):
nHI=0.24 /cc , ne=0.09 /cc, H+/H=23%, He+/He=45%




Magnetic field strength <3 mG (but unknown)
Over 1% of cloud mass is in interstellar dust
Observed upstream direction towards l=5o, b=+14o.
This cloud referred to as Local Interstellar Cloud (LIC)
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Sun in Local Bubble interior
~106 Years Ago
 Sun moves towards
l~28o, b~+32o,
V~13.4 km/s
(Dehnen Binney 1998)
 Local Bubble
densities:
nHI<0.0005 cm-3
nHII~0.005 cm-3
T~106 K
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Heliosphere while in Local
Bubble Plasma
(Figure courtesy Hans Mueller)
 Sun in Fully Ionized
Local Bubble
Plasma
–
–
–
–
Relative V=13.4 km/s
TInterstellar=106.1 oK
n(p+)IS=0.005 cm-3
n(Ho)IS=0 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
l=2.3o, b=-5.2o
ISM surrounding solar system
now is warm partially ionized
gas.
Solar path towards l=28o, b=+32o
implies Sun will be in SCA
outflow for ~million years in
future.
Denser ISM will shrink
heliosphere to radius <<100 au
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Solar Encounter with Interstellar
Clouds
 Sun predicted to encounter about a dozen giant
molecular clouds over lifetime,
 Encounters with n=10 cm-3 interstellar clouds will
be much more frequent.
 An increase to n=10 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 density
nHI=0.22 /cc
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nHI=15 /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 <50,000 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, T=6,400 K, V=26 km/s, observed
upstream at l=5o, b=+14o (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 Rays
Cummings and Stone (2002)
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Anomalous Cosmic Rays captured
in Earth’s magnetosphere
Figure 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 (<0.1mm)
 Medium grains filtered by solar
wind (0.1-0.2 mm)
 Large grains constitute 30% of
interplanetary grain flux with
masses >10-13 gr (or radius>0.2
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 Planets
Heliosphere in n=15 cm-3 cloud
T (K)
Ho Density (cm-3)
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Cosmic Rays and Sunspot numbers
Climax, 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 (<3.2
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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Conclusions:
Know 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?)
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