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 P. Frisch, May 2002 2
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 3
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/R 2 in solar system SW sweeps up charged particles, including ISM P. Frisch, May 2002 4
Heliosphere today Top: Plasma Temp Bottom: Interstellar H o H o Wall: H o and p+ couple Properties: T~29,000 K, N(H o )~3 x 10 14 cm -2, dv=-8 km/s Model: 4-fluid model (Figure courtesy Hans Mueller) P. Frisch, May 2002 5
Heliosphere* vrs Planetary System HELIOSPHERE: Warm Partially Ionized ISM surrounds Sun n HI =0.22 /cc, n HeI =0.12 /cc, n + =0.11 /cc, T=6500 K, V HC =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 Ë 10-20 au/year in nose direction (Liewer and Mewaldt 2000) *Heliosphere = solar wind bubble P. Frisch, May 2002 6
Warm partially ionized diffuse interstellar cloud around Sun Observations of interstellar He o in solar system give cloud properties (Witte et al. 2002, Flynn et al 1998): n HeI =0.014 /cc, T=6,400 K, V HC =26 km/s ISM radiative transfer models give composition and ionization at boundary heliosphere (Slavin Frisch 2002, model 18): n HI =0.24 /cc, n e =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=5 o, b=+14 o. This cloud referred to as Local Interstellar Cloud (LIC) P. Frisch, May 2002 7
Sun in Local Bubble interior Ë Sun moves towards l~28 o, b~+32 o, V~13.4 km/s (Dehnen Binney 1998) Ë Local Bubble densities: n HI <0.0005 cm -3 n HII ~0.005 cm -3 T~10 6 K ~10 6 Years Ago P. Frisch, May 2002 8
Heliosphere while in Local Bubble Plasma (Figure courtesy Hans Mueller) Sun in Fully Ionized Local Bubble Plasma Relative V=13.4 km/s T Interstellar =10 6.1 o K n(p + ) IS =0.005 cm -3 n(h o ) IS =0 cm -3 No IS neutrals in heliosphere P. Frisch, May 2002 9
Solar Environment varies with ËSun entered outflow of diffuse ISM from Sco-Cen Association (SCA) 10 3-10 5 years ago Time Ë Ë Ë Ë LSR Outflow: 17 +/- 5 km/s from upstream direction l=2.3 o, b=-5.2 o ISM surrounding solar system now is warm partially ionized gas. Solar path towards l=28 o, b=+32 o 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 10
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 11
Heliosphere and IS cloud density n HI =0.22 /cc n HI =15 /cc P. Frisch, May 2002 12
Solar Encounter with Interstellar Clouds Sun moves through LSR at ~13.4 km/s, or 13.4 pc/10 6 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 13
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 M Sun /year (Wood et al. 2001) Ë Heated interstellar H o in solar heliosheath (~25,000 K) see towards a Cen AB and other stars (e.g. Linsky, Wood) Ë 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 14
Example: Sun & a Cen Heliosheath Interstellar Lya absorption shows redward shoulder from decelerated H o Interstellar H o and p + couple by charge exchange H o heated to 29,000 K, N(H o )~3 x 10 14 cm -2, dv = -8 km/s Gayley et al. 1997 P. Frisch, May 2002 15
Interstellar and Interplanetary Material Observations of ISM in the Solar System H o /He o fluorescence of solar Lya/584A emission (~1971, many satellites) He o Ulysses Dust Ulysses, Galileo, Cassini Pickup Ions Ampte, Ulysses Anomalous Cosmic Rays e.g. Ulysses, ACE, many other spacecraft P. Frisch, May 2002 16
Interstellar H o in Solar System H o Solar Lya photons fluorescing on interstellar H o at ~4 au Discovered ~1971 (Thomas, Krassa, Bertaux, Blamont) H o decelerated in solar system (by ~5 km/s) Left: Interstellar H o Right: Geocorona (Copernicus data, Adams and Frisch 1977) P. Frisch, May 2002 17
Interstellar He o in Solar System He o Solar 584 A fluorescence on interstellar He o at ~0.5 au Discovered 1974 (Weller and Meier) He o atoms measured directly by Ulysses Best data on interstellar gas inside solar system n(he o )=0.014 /cc, T=6,400 K, V=26 km/s, observed upstream at l=5 o, b=+14 o (Witte 2002) P. Frisch, May 2002 18
Interstellar He o 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 19
Pickup Ions Gloeckler and Geiss (2002) P. Frisch, May 2002 20
Pickup ions become Anomalous Cosmic Rays (Figure from ACE web site) P. Frisch, May 2002 21
Anomalous Cosmic Rays Cummings and Stone (2002) P. Frisch, May 2002 22
Anomalous Cosmic Rays captured in Earth s magnetosphere Figure from ACE web site P. Frisch, May 2002 23
Pickup Ions, Anomalous Cosmic Rays, and the ISM (Cummings and Stone 2002) P. Frisch, May 2002 24
Pickup Ions, Anomalous Cosmic Rays, and the ISM (Cummings and Stone 2002) P. Frisch, May 2002 25
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 26
Entry of ISM into Heliosphere P. Frisch, May 2002 27
ISM effects on planets qinner versus Outer Planets (H o ) qcosmic rays: Anomalous cosmic rays (require neutral ISM) Galactic Cosmic Rays (sensitive to heliosphere B) qin principle, core samples on inner versus outer planets would sort solar variations from interstellar variations P. Frisch, May 2002 28
Inner versus Outer Planets Heliosphere in n=15 cm -3 cloud T (K) H o Density (cm -3 ) P. Frisch, May 2002 29
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 P. Frisch, May 2002 30
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 31
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 32
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 33