other planetary systems, we gain
perspective. By understanding our
neighbors, we better understand our
home.
Everyone who has looked at the
Moon through a telescope or visited
Meteor Crater in Arizona knows
what an impact crater looks like.
Spacecraft studying other hard
surfaces in the Solar System usually
find craters. At first blush, they look
the same. But a little more careful
examination shows that there are
differences in forms and internal
structure. Nature has provided us
with samples of cratering on icy and
rocky surfaces and the differences
in the craters’ appearances
bear witness to the surface and
subsurface materials and their
physical behavior under stress and
in the temperature regime at their
distances from the Sun.
These are just a few examples
of what we observe of Nature’s
experiments.
Our exploration of the planets,
exoplanets and beyond will
continue. Our robots extend our
reach and soon humans will be
seeing new planetary vistas with
their own eyes. We are fortunate to
be able to share this exploration and
to ponder it.
ooo
Steve Edberg is an astronomer at
JPL and an amateur astronomer
at home and at his observatory
in California. He has worked
on Galileo to Jupiter, Cassini to
Saturn, and other NASA projects.
He served as Coordinator for
Amateur Observations for the
International Halley Watch. He
is an avid eclipse chaser and
expedition organizer and was
Executive Director of the Riverside
Telescope Conference, Inc. for 22
years. He has been honored by
the International Astronomical
Union with the formal naming of
the asteroid 1985QQ as (3672)
Stevedberg.
24
Cosmic commonalities:
Dunes
Erosion of one or more types
on a planet or satellite creates
sand. With an atmosphere, thick
or thin, present, the sand can
form dunes. Sand dunes inform
us of wind speed and direction
on places like Venus, Mars and
Saturn’s satellite Titan. Top right,
optical images of dune fields on
Earth show a good match with
radar images of dune fields on
Saturn’s satellite Titan, middle
right, and radar images of Venus,
bottom right. Far right, optical
images of Mars match another
type of dune field found on
Earth. Note the “ripples” near
the bottom right section. Wind
direction in dune fields is usually
perpendicular to the nearparallel lines of dune peaks and
valleys.
Volcanoes
— By Steve Edberg
Mars
Earth
Deltas
Earth
COURTESY OF NASA/JSC
Titan
COURTESY OF NASA
Mars
COURTESY OF NASA/JPL
Venus
COURTESY OF NASA/JPL
COURTESY OF Malin Space Science Systems/MGS/JPL/NASA
COURTESY OF NASA/JPL
Flowing rivers often
produce deltas at
their ends. On Earth
and Mars the rivers
were water. On Titan,
the liquid is a mix
of liquefied gases,
methane and ethane.
The landforms look
similar. Top left,
Earth’s Okavango
Delta in Botswana
is the largest inland
delta in the world.
COURTESY OF NASA/JPL-Caltech/ASI
The river does not
empty into the ocean. Bottom left, Mars displays
several ancient river deltas. Above, the synthetic
aperture radar on NASA’s Cassini shows two river
deltas on the western shoreline of Titan’s Lake
Ontario caused by liquefied gases flowing over
and eroding the surface of water ice.
Venus
Mars
Earth
Volcanoes are found on Earth in a variety of
forms such as the Hawaiian shield volcanoes
Mauna Loa and Mauna Kea, pictured to the
right. Although these are giant, they are small
compared to Mars’ shield volcano Olympus Mons,
pictured in the middle. The first active volcanism
found elsewhere in the Solar System was found
and studied by NASA’s Voyager spacecraft. Old
volcanism and new types of volcanoes have been
recognized on Venus and there is some evidence
COURTESY OF Steve Edberg
that Venus may still be volcanically active. Far
right top, a large volcano on Venus (with its height
Io
exaggerated in this radar view) shows lava flows.
Far right bottom, Venus exhibits other novel types
of volcanoes including these “pancakes” found
during radar mapping. Bottom left, Jupiter’s
innermost Galilean satellite, Io, is now known
to be the most volcanically active place in the
COURTESY OF NASA/JPL/University of Arizona
Solar System. Some of its active volcanoes can be
monitored with Earth-based telescopes. Io’s active volcanoes are constantly changing its appearance. This
set of three images from NASA’s Galileo spacecraft show dramatic changes in Io’s Pillan Patera region. The
first image was taken in April 1997, the second in September 1997 and the third in July 1999.
Sky’s
Up
Sky’s
Up
Explorations have
shown similarities
in our Solar System
COURTESY OF NASA/JPL
Venus
COURTESY OF NASA
COURTESY OF NASA
25