Interstellar and Interplanetary Material

HST Astrobiology Workshop: May 5-9, 2002P.C. Frisch

University of Chicago

P. Frisch, May 2002 2

Outline:

The solar system is our template for understanding interplanetary materialHeliosphere, 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 G)

SW density decreases by 1/R2 in solar system

SW sweeps up charged particles, including ISM

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Heliosphere todayTop: 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 auBow 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 G (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 densitynHI=0.22 /cc 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)

Cen mass loss rate of ~10-14 MSun/year (Wood et al. 2001)

Heated interstellar Ho in solar heliosheath (~25,000 K) see towards Cen AB and other stars (e.g. Linsky, Wood)

Astrospheres found around Cen AB (1.3 pc), Ind (3 pc), And (?, 23 pc), and other stars (Linsky & Wood 1996,Gayley et al. 1997, Wood et al. 1996)

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Example: Sun & Cen Heliosheath

Interstellar Ly 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 Ly 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 Ly 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 RaysCummings 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 (<0.1m)

Medium grains filtered by solar wind (0.1-0.2 m)

Large grains constitute 30% of interplanetary grain flux with masses >10-13 gr (or radius>0.2 m) 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 n=15 cm-3 cloud

T (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 (<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?)