Sky's Up Summer 2016 - Page 24

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