From: Amara Graps (amara@amara.com)
Date: Mon Sep 02 2002 - 01:50:00 MDT
Astrophysics, abstract
astro-ph/0208556
From: Priscilla Chapman Frisch <frisch@oddjob.uchicago.edu>
Date (v1): Fri, 30 Aug 2002 04:43:15 GMT (396kb)
Date (revised v2): Fri, 30 Aug 2002 22:41:29 GMT (396kb)
Galactic Environment of the Sun and Stars: Interstellar and Interplanetary
Material
Authors: P.C. Frisch, H. Mueller, G. Zank
Comments: STScI Astrophysics of Life conference; 15 pages; 8 figures
Interstellar material surrounding an extrasolar planetary system
interacts with the stellar wind to form the stellar astrosphere, and
regulates the properties of the interplanetary medium and cosmic ray
fluxes throughout the system. Advanced life and civilization
developed on Earth during the time interval when the Sun was
immersed in the vacuum of the Local Bubble and the heliosphere was
large, and probably devoid of most anomalous and galactic cosmic
rays. The Sun entered an outflow of diffuse cloud material from the
Sco-Cen Association within the past several thousand years. By
analogy with the Sun and solar system, the Galactic environment of
an extrasolar planetary system must be a key component in
understanding the distribution of systems with stable interplanetary
environments, and inner planets which are shielded by stellar winds
from interstellar matter (ISM), such as might be expected for stable
planetary climates.
Full-text: PostScript, PDF, or Other formats
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Conclusion (copied/pasted directly from paper):
The evolution of advanced life has occurred during a time when the
Sun was immersed in the vacuum of the Local Bubble, so that the
enlarged heliosphere would have yielded effective modulation of
galactic cosmic rays. In contrast, an encounter with a modest
density diffuse cloud (n(HI) $\sim$10 \cc) is possible within 10$^4$
-- 10$^5$ years, and would destabilize the heliosphere and modify
cosmic ray fluxes impinging on the Earth. The modulation of both
galactic and anomalous cosmic rays by solar wind magnetic fields,
and the emerging link between cosmic ray fluxes and climate forcing,
suggests that a stable heliosphere, and by analogy stable
astrospheres, are significant factors in maintaining climatic
stability as is necessary for sustainable civilization.
The Galactic environment of a star determines interplanetary medium
properties, including the distribution of cosmic rays in the
astrosphere. How does this affect the ``Astrophysics of Life'',
which is the topic of this conference? Over the past century many
suggestions have been made regarding Galactic effects on Earth's
climate. Recent work has demonstrated that the global electrical
circuit is moderated by the cosmic ray flux (Roble 1991), and that,
for instance, cloud cover in the lower troposphere ($<$3.2 km)
correlates with cosmic ray flux (Marsh \& Svensmark 2002). The fact
which is clear, however, is that at the present time the solar wind
shields the Earth from most ISM products. Relatively low fluxes of
energetic particles, including galactic cosmic rays ($>$1
GeV/nucleon) and anomalous cosmic rays ($<$0.5 GeV/nucleon), are
able to penetrate to the Earth however.
Simulations which describe the interaction between interstellar
clouds and stellar winds will provide valuable information on the
properties of the astrospheres of extrasolar planetary systems, as
well as a basis for evaluating the interplanetary environment.
Understanding the historical properties of astrospheres around
extrasolar planetary systems will provide a basis for evaluating the
climatic stability on possible Earth-like extrasolar planets. The
differences in exposure to raw ISM for inner and outer planets over
the planet lifetimes may be significant.
-- ******************************************************************** Amara Graps, PhD email: amara@amara.com Computational Physics vita: ftp://ftp.amara.com/pub/resume.txt Multiplex Answers URL: http://www.amara.com/ ******************************************************************** "Hitch your wagon to a star." --Ralph Waldo Emerson
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