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

  2. 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 P. Frisch, May 2002

  3. 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 P. Frisch, May 2002

  4. 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 P. Frisch, May 2002

  5. 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) P. Frisch, May 2002

  6. 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 P. Frisch, May 2002

  7. 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) P. Frisch, May 2002

  8. 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 P. Frisch, May 2002

  9. Heliosphere while in Local Bubble Plasma(Figure courtesy Hans Mueller) • Sun in Fully Ionized Local Bubble Plasma • Relative V=13.4 km/s • TInterstellar=106.1oK • n(p+)IS=0.005 cm-3 • n(Ho)IS=0 cm-3 • No IS neutrals in heliosphere P. Frisch, May 2002

  10. 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 P. Frisch, May 2002

  11. 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 P. Frisch, May 2002

  12. Heliosphere and IS cloud densitynHI=0.22 /cc nHI=15 /cc P. Frisch, May 2002

  13. 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. P. Frisch, May 2002

  14. 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) P. Frisch, May 2002

  15. 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 P. Frisch, May 2002

  16. Interstellar and Interplanetary MaterialObservations 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 P. Frisch, May 2002

  17. 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) P. Frisch, May 2002 Left: Interstellar Ho Right: Geocorona (Copernicus data, Adams and Frisch 1977)

  18. 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) P. Frisch, May 2002

  19. 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 P. Frisch, May 2002

  20. Pickup Ions Gloeckler and Geiss (2002) P. Frisch, May 2002

  21. Pickup ions become Anomalous Cosmic Rays (Figure from ACE web site) P. Frisch, May 2002

  22. Anomalous Cosmic RaysCummings and Stone (2002) P. Frisch, May 2002

  23. Anomalous Cosmic Rays captured in Earth’s magnetosphereFigure from ACE web site P. Frisch, May 2002

  24. Pickup Ions, Anomalous Cosmic Rays,and the ISM(Cummings and Stone 2002) P. Frisch, May 2002

  25. Pickup Ions, Anomalous Cosmic Rays,and the ISM(Cummings and Stone 2002) P. Frisch, May 2002

  26. 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. P. Frisch, May 2002

  27. Entry of ISM into Heliosphere P. Frisch, May 2002

  28. 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 P. Frisch, May 2002

  29. Inner versus Outer PlanetsHeliosphere in n=15 cm-3 cloudT (K) Ho Density (cm-3) P. Frisch, May 2002

  30. 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 P. Frisch, May 2002

  31. Planetary climates and the interplanetary environment. • Galactic Cosmic Ray flux correlated with low level (<3.2 km) cloud cover (Marsh & Svensmark 2002) P. Frisch, May 2002

  32. 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) P. Frisch, May 2002

  33. 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?) P. Frisch, May 2002