Atmospheres in the Solar System: Comparative Aeronomy

Geophysical Monograph Series
Volume 130 

Editors: Michael Mendillo, Andrew Nagy, and J.H. Waite  

Published in 2002


Michael Mendillo, Andrew Nagy, and J. H. Waite

Michael Mendillo, Andrew Nagy, and J. H. Waite

I. Overviews

1 Aeronomic Systems on Planets, Moons, and Comets
Darrell F. Strobel

2 Solar System Upper Atmospheres: Photochemistry, Energetics and Dynamics
G. Randall Gladstone, Roger V. Yelle and T. Majeed

3 Solar System Ionospheres
Andrew F. Nagy and Thomas E. Cravens

4 Auroral Processes in the Solar System
Marina Galand and Supriya Chakrabarti

5 Airglow Processes in Planetary Atmospheres
Thomas Slanger and Brian Wolven

II. Interactions Between Planetary and Small Body Atmospheres with the Surrounding Plasma Medium

1 Magnetosphere-Ionosphere Coupling at Earth, Jupiter, and Beyond
B. H. Mauk, R. M. Thorne and B. J. Anderson

2 Comparison of Auroral Processes: Earth and Jupiter
J. H. Waite and D. Lummerzheim

3 Numerical Techniques Associated with Simulations of the Solar Wind Interactions with Non Magnetized Bodies
Stephen H. Brecht

4 Plasma Flow Past Cometary and Planetary Satellite Atmospheres
Michael R. Combi, Tamas I. Gombosi and Konstantin Kabin

III. Chemistry, Energetics and Dynamics

1 Wave Coupling in Terrestrial Planetary Atmospheres
Jeffrey M. Forbes

2 Exospheres and Planetary Escape
Donald M. Hunten

3 Surface Boundary Layer Atmospheres
R. E. Johnson

4 Solar Ultraviolet Variability Over Time Periods of Aeronomic Interest
Thomas N. Woods and Gary J. Rottman

5 Meteoric Material - an Important Component of Planetary Atmospheres
Joseph M. Grebowsky, Julianne I. Moses and W. Dean Pesnell

6 Current Laboratory Experiments For Planetary Aeronomy
David L. Huestis

IV. Models of Aeronomic Systems

1 Simulations of the Upper Atmospheres of the Terrestrial Planets
Stephen W. Bougher, Raymond G. Roble and Timothy Fuller-Rowell

2 Thermospheric General Circulation Models for the Giant Planets: The Jupiter Case
G.H. Millward, S. Miller, A.D. Aylward, I. C. F. Müller-Wodarg, and N. Achilleos

3 Ionospheric Models for Earth
R. W. Schunk

4 The Application of General Circulation Models to the Atmospheres of Terrestrial-Type Moons of the Giant Planets
I. C. F. Müller-Wodarg

5 The Extreme Ultraviolet Airglow of N2 Atmospheres
Michael H. Stevens

V. Observational Applications

1 The Application of Terrestrial Aeronomy Groundbased Instruments to Planetary Studies
Michael Mendillo, Fred Roesler, Chester Gardner and Michael Sulzer

2 Ultraviolet Remote Sensing Techniques for Planetary Aeronomy
John T. Clarke and Larry Paxton

3 Mass Spectrometry for Future Aeronomy Missions
D. Young

VI. Atmospheres of Other Worlds

1 A Possible Aeronomy of Extrasolar Terrestrial Planets
W. A. Traub and K. W. Jucks

2 Can Conditions For Life Be Inferred From Optical Emissions of Extra-Solar-System Planets?
Harald U. Frey and Dirk Lummerzheim


Atmospheres are crucial components of our universe. They are the only observable regions of stars and giant planets, both within and beyond our solar system. Some terrestrial-size bodies (Venus, Earth, Mars, Titan and Triton) have permanent atmospheres while others (e.g., Mercury, Moon, Io, and Europa) have tenuous gaseous envelopes that change daily. Comets are tiny bodies by planetary yardsticks, but their atmospheres can be the largest visible objects in the night sky. Atmospheric science strives to understand how such a diverse set of atmospheres form, evolve and disappear.

Our current understanding of the mystery of life links atmospheres to biology via such terms as "biosphere" and "astrobiology." But even aside from the question of life beyond Earth, the study of solar system atmospheres is, in its own right, an exciting and exploration-rich field of modern space science. The origin of this monograph is based on that fact. While the laws of physics are the same for each member of the solar system, the chemical constituents are not, nor are their magnetic fields, or amount of energy received from the Sun.

Within this context of diversity in solar system membership, the comparative-studies approach has emerged as the framework best suited to understanding the coupling, energetics and dynamics of multiple atmospheric systems. To avoid a mere survey of intrinsic characteristics, to move beyond classification nomenclature being a stand-in for progress, and to probe the depth and breadth of our understanding requires a timely and comprehensive approach to a rapidly changing field. We have addressed this need with an eye towards tutorial overviews and state-of-the-art descriptions for graduate students and young professionals drawn to aeronomy. We couple this to an agenda of synthesis for veterans in the field. Thus, the six sections of this monograph (each with multiple chapters) are so structured, and all contain an excellent set of references to enrich and guide additional research.

The specific origin of this book derives from a series of workshops at the annual meeting on Coupling, Energetics and Dynamics of Atmospheric Regions (CEDAR) held each summer in Boulder, Colorado. Comparative mesospheres, gravity wave signatures, aurora and airglow, and exospheres were the principle topics discussed over a several year period. From these workshops, a clear need emerged: a comprehensive meeting devoted exclusively to Comparative Aeronomy in the Solar System. With support from NASA and NSF and organizational expertise from the Southwest Research Institute (SwRI), a Yosemite Conference was held on 8-11 February 2000 on that topic. The current work incorporates the basic topics treated at Yosemite with additional invited contributions. In brief, we engaged the best possible set of authors to treat the core topics needed for the research fields of major current activity. Cross references by section and chapter designations bring a unity to the material presented.

In addition to the authors' expertise and the development and careful preparation of their manuscripts, we acknowledge the valuable contributions of Ms. Cynthia Farmer and Dr. William Lewis of SwRI for organizing the Yosemite Meeting and Dr. Marina Galand (Boston University) and Dr. Steven Bougher (University of Arizona) for their co-convening of pre-cursor CEDAR workshops. Ms. Maria Stefanis O'Connell (Boston University) served as Editorial Assistant with care, devotion and competence, factors of crucial importance in assembling a monograph from author-produced copy. Similarly, we thank our AGU acquisitions editor, Allan Graubard, and production editor, Bethany Matsko for their expertise on a host of development and production details and schedules. Most importantly, we thank the referees for the chapters contained in this volume. With their generous contributions of time and thoughtful suggestions on content, the colleagues listed below truly share in the success of the chapters that follow.

Several colleagues provided illustrations and images used on the cover and on the section heading pages, including J. Forbes (Section I), J. Spencer (Section II), I. Müller-Wodarg (Section IV), J. Clarke (Section V), and M. Mendillo (Frontispiece, Section III, Section VI).

Finally, in recognition of her fundamental contributions to the field of comparative aeronomy, and in acknowledgement of her enthusiastic participation in the CEDAR Workshops and Yosemite meeting dedicated to these topics, we dedicate this volume to Dr. Jane Fox with best wishes for a continuing career of active research and professional service.

Michael Mendillo
Center for Space Physics
Boston University

Andrew Nagy and J. H. Waite
Space Physics Research Laboratory
University of Michigan

Geophysical Monograph Series Volume 130


Michael Mendillo
Center for Space Physics, Boston University

Andrew Nagy and J. H. Waite
Space Physics Research Laboratory, University of Michigan

When asked about the age of the solar system, the standard response is to say that the Sun and planets formed about 4.6 billion years ago. What this response fails to convey is a sense of continuity or, perhaps better stated, of evolution from then to now. We have in the membership of the solar system nine wonderful experiments in planet formation, dozens of cases for moons, and countless asteroid and comet scenarios. While we can say rather com-fortably that our Sun is a "typical" main sequence star, we cannot point to a "typical" planet. There is a lesson in that statement and a research challenge of considerable complexity. This monograph deals with a central component of this challenge, namely, to describe the basic structure and dynamics of the upper atmospheres and ionospheres in our solar system and, moreover, to understand their differences.
Atmospheric scientists tend to divide the gaseous regions above a planet into two broad categories called simply lower and upper atmosphere. For Earth, the study of the lower regions (troposphere and strato-sphere) form the discipline of meteorology. The study of the upper regions (mesosphere, thermosphere, exosphere) and their ionized components (the ionosphere) form the discipline of aeronomy. The negative aspect of such a two-fold division is that it encourages thinking of the various atmospheric-spheres as isolated regions of self-contained physics, chemistry, and (in the case of Earth) biology. In reality, there is consider-able coupling from lower to upper regions, an aspect of aeronomy fully appreciated only in the last decade. Com-plimenting this external influence from below, an upper atmosphere has long been known to experience forcing and coupling to and from regions far above it. Aeronomy thus deals with one of the most highly coupled systems in space science --- with neutrals, plasmas, and electromagnetic processes that link the planets, moon, and comets from their surfaces to the solar wind and ultimately to the Sun itself.
The key questions posed in solar system aeronomy are:
1. What are the constituents of each atmosphere encountered?
2. How do they absorb solar radiation?
3. What are the thermal structures resulting from heating versus cooling processes?
4. What types of ionospheres are formed?
5. What are the roles of atmospheric dynamics at each site?
6. Does a planetary magnetic field shield the ionosphere from solar wind impact?
7. How do trapped energetic particles and electrodynamics affect the atmospheric system?
If all planets were the same, the answers to these questions would depend primarily on distance from the Sun. Such "seen-one, seen-them-all" space science would indeed render the solar system a boring cosmic neighborhood. Happily, space exploration has led to precisely the opposite situation. Distance from the Sun matters, but so do local conditions. Consider Figure 1 where the temperatures of each planet's upper atmosphere are plotted versus distance from the Sun. The temperatures at Venus, Mars, and Saturn fall well below the values that might be estimated via a simple interpolation between neighbors. Composition and local energetics matter!

Figure 1: A comparison of the neutral exospheric temperature of the upper atmospheres of the planets

Figure 2: A comparison of the peak electron density (left axis) and its height (right axis) of the planets.

Using the same format, Figure 2 gives the peak electron density and its altitude for the ionosphere on each planet. Excluding Mercury's weakly ionized component of a thin transient atmosphere, it is the Earth that breaks the pattern. Again, composition (atomic vs. molecular ions) matters! Finally, in Figure 3, the magnetic field strength, orientation, and solar wind stand-off distance are given for the six planets with intrinsic dipoles. The patterns of magnetic pressure balancing solar wind kinetic energy density scale appropriately with dipole strength and distance from the Sun, with the result of all six ionospheres being well inside their planet's magnetopause. Magnetosphere-ionosphere-atmosphere coupling is thus of fundamental importance for these cases. Does the absence of auroral heating at Venus or Mars lead in any way to their low neutral temperatures in Figure 1?

Figure 3: A comparison of the magnetic field dipole strength (normalized to Earth, left axis), dipole tilt (shown with respect to rotation axis), and magnetopause distance (in planetary radii, right axis) for the planets with known global magnetic field.

In the chapters that follow, experts in aeronomy and in the fields that couple to it present up-to-date summaries of the major accomplishments and outstanding issues in the field. Tutorial reviews appear in Part I, with an emphasis on the basic principles underlying key systems. That each ionosphere/atmosphere encountered has important interactions with a surrounding plasma medium (solar wind or magnetospheric) is treated in Part II. The chemistry, energetics and dynamics of atmospheric systems are treated in Part III, and a description of modeling capabilities appears in Part IV. The roles of new observing techniques are described in Part V. Looking beyond our heliospheric members to the emerging field of extra-solar-system planets, Part VI concludes with views of worlds unseen.


Bougher, S. W., S. Engel, R. G. Roble, and B. Foster, Comparative terrestrial planet thermospheres: 2. Solar cycle variation of global structure and winds at solstices, J. Geophys., Res., 105, 18669-17692, 2000.
Fox, J. L., P. Zhou, and S. W. Bougher, The Martian thermosphere/ionosphere at high and low solar activities, Adv. Space Res., 17, 11, 203-218, 1996.
Fox, J. L. and A. J. Kliore, Ionosphere: Solar cycle variations, in Venus II, edited by S. W. Bougher, D. M. Hunten and R. J. Phillips, The University of Arizona Press, Tucson, 1997.
Killen, R. M., A. Potter, A. Fitzsimmons, and T. H. Morgan, Sodium D2 line profiles: clues to the temperature structure of Mercury's exosphere, Planet. Space Sci., 47, 1449-1458, 1999.
Kivelson, M. G., and F. Bagenal, Planetary magnetospheres, in Encyclopedia of the Solar System, edited by Weissman, Academic Press 477-498, 1997.
Nagy A. F. and T. E. Cravens, Solar System Ionospheres, this volume, 2002.
Ogilvie, K. W., J. D. Scudder, V. M. Vasyliunas, R. E. Hartle, and G. L. Siscoe, Observations at the planet Mercury by the plasma electron experiment - Mariner 10, J. Geophys. Res., 82, 1807-1824, 1977.
Summers, M. E., D. F. Strobel and R. G. Gladstone, Chemical models of Pluto's atmosphere, in Pluto and Charon, Univ. Arizona Press (S. A. Stern and D. J. Tholen, editors), 391-434, 1997.
Yelle, R. V., and J. Elliot, Atmospheric structure and composition: Pluto and Charon, in Pluto and Charon, Univ. Arizona Press (S. A. Stern and D. J. Tholen, editors), 347-390, 1997.
Yung, Y. L., and W. B. De More, Photochemistry of Planetary Atmospheres, Oxford University Press, 1999.

Nb: If you are interested to get this volume, contact AGU (1800-966-2481 or orders at
The order number is GM130-989-2. The book should be off press by May 24, 2002

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