Duane H. Pontius, Jr.
Current and upcoming courses:
Courses I've taught recently at BSC include General Astronomy,
Physics of Music, General Physics I & II, Modern Physics,
Mathematical Methods for Physics, Optical Physics, Thermal Physics,
Classical Mechanics, Electricity and Magnetism, and my honors
courses, "Science, Physics, Music" and "Uncommon Sense"
- General Physics I
- Mathematical Tools for Physics
- Uncommon Sense
at Sea - Click for information about former and future
"We don't give A grades for large volumes of C
work" - John Strohl, in memorium
I study the magnetospheres
of Jupiter and Saturn and the dynamics of plasma trapped within
them. These planets are particularly interesting because both
have moons imbedded within them that continually spew huge amounts
of material into outer space. More detailed information can be
found accompanying my publications
on the topic. Io is the innermost Galilean moon of Jupiter,
and intense volcanic activity makes it spew off roughly a ton of
mass every second. Once ionized, this material is swept up into a
large cloud of gas that encircles the planet and rotates with it,
forming a huge, million-ton doughnut of gas around Jupiter. The torus is centered on Io's orbit,
which is about the same size our own moon's orbit about the
Earth. However, the ionized gas (called a plasma) rotates once
every ten hours, so centrifugal forces are overwhelmingly larger
than gravity. (Just imagine the moon going around the Earth two and
a half times a day rather than once a month!) It's a really
fascinating object for study, and we are fortunate to be able to do
so via telescopes from the Earth as well as spacecraft that visit
Jupiter. For more information, see my article on the torus, The Nebula in Our Own
Backyard, which appears in the Nov/Dec 2000 issue of Mercury,
published by the Astronomical
Society of the Pacific.
One of Saturn's moon's was recently to exhibit similar
behavior, though the discovery was quite unexpected.
Enceladus' diameter is one-seventh that of Io, though their
orbital radii are similar, so the gravitational tidal forces that
stress and flex Io and heat it internally are several orders of
magnitude weaker at Enceladus. Nevertheless, on 14 July 2005,
the Cassini spacecraft passed within 150 km of Enceladus and found
dramatic evidence that a huge cloud of material is continually
ejected from the surface. These atoms and ions are
dissociation products of water molecules, hinting that there must be
liquid water near Enceladus' surface. The mechanism for
maintaining such warm pockets in an environment that would otherwise
be hundreds of degrees below freezing is still under debate.
However, the data provide unambigous evidence and the
photographs are breathtaking.
My role in all this was in developing a theoretical model to relate
the spatial distribution of mass loading to the deflection of plasma
away from Enceladus. Those measurements were made by the
Cassini Plasma Spectrometer (CAPS), and the analysis is described in
a pair of papers, one in Science, the other in the Journal of
Geophysical Research. (Click for a preprint of Enceladus: A significant
plasma source for Saturn’s magnetosphere, by me and Tom Hill.)
Further details of my professional history are in my curriculum vitae, or you can go directly
to my publication list.
Some pre- and reprints are available. Then there are the personal photos and odd stuff.
Sites with information of occasional utility
Stuff for when work becomes overwhelming: