Date: October 28, 2010
Title: Cassini’s Amazing Voyage to Saturn, Its Moons, and Its Rings
Podcaster: Andy Poniros
Description: On July 1, 2004, the Cassini spacecraft, with the Huygens probe onboard, successfully achieved orbital insertion of the Saturn system. More than six years later, a healthy Cassini spacecraft has completed its four-year primary mission, a two-year extended mission, and has begun another extended mission that is planned be completed in 2017. Andy Poniros reviews the highlights of Cassini’s incredible discoveries in the past 6 years and discusses the extended “Solstice Mission” goals.
Bio: You can soon listen to Andy Poniros Productions podcasts at www.lift-off.us. Future and archived podcasts will also be listed on The Solar System Ambassador Event web site at www2.jpl.nasa.gov/ambassador/events.html. Andy Poniros is a JPL/NASA public outreach volunteer. When he’s not spending time with his family, he enjoys telescope building, and educating the public in the fields of astronomy and space exploration. He is currently working on other astronomy and space exploration podcasts for children and adults.
Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by — no one. We still need sponsors for many days in 2010, so please consider sponsoring a day or two. Just click on the “Donate” button on the lower left side of this webpage, or contact us at signup@365daysofastronomy.org.
Transcript:
Cassini’s Amazing Voyage to Saturn, its Rings, and its Moons
It has been more than 13 years since the Cassini spacecraft was launched from this planet and propelled into the vastness of space. On its voyage through our Solar System, Cassini received timely gravity assists from Venus, Earth, and Jupiter, before achieving orbital insertion around the Saturn System almost seven years after it was launched. During a four-year primary and two-year extended mission, Cassini collected valuable data and captured amazing images, enabling scientists to make several incredible discoveries.
On January 14, 2005, after riding piggyback on Cassini during its long voyage, the Huygens probe landed safely on Titan, Saturn’s largest moon, collecting valuable atmospheric data, and sending back a compiled image of what appeared to be a mountain, dry river channels, and a dry lake bed.
The Cassini spacecraft continued where Huygens left off, completing a total of 71 flybys of Titan, while using its infrared and radar science instruments to peer through Titan’s thick atmosphere and discover an active fluid weather system in the Northern Hemisphere. Driven by frigid temperatures of -300˚F, ethane and methane gas in Titan’s atmosphere liquefy in the form of rain, producing seasonal rivers and lakes. Other discoveries of Cassini flybys of Titan include ice volcanoes, mountains, dunes of hydrocarbons, an icy outer layer, a rocky core, and the possibility of an interior ocean.
Data and images collected before and during Cassini’s initial flyby of Saturn’s tiny icy, moon Enceladus intrigued scientists. Images of Enceladus showed geological differences between its cratered North Pole and smooth-surfaced South Pole sporting cracks or vents, which scientists termed “Tiger Stripes.” A smooth-surfaced southern region, with the warmest temperatures at the center of the Tiger Stripes, suggested that Enceladus might be geologically active. After ten additional flybys that were not part of the original mission plans, scientists determined that the Tiger Stripes are tectonic faults that are spewing out salt water and replenishing Saturn’s tenuous E-ring with hydrogen atoms. Cassini science teams also determined that Enceladus has an icy outer layer, a rocky core, and a salty ocean in between.
Several other icy moons were visited by the Cassini spacecraft on its relentless quest to unlock the mysteries of the Saturnian System. Tiny Phoebe is approximately 215km in diameter, and is believed to be an asteroid captured in a retrograde orbit around Saturn, that is rotating in an orbit opposite the natural order of the solar system, an orbit that is shared by 28 other Saturnian moons. This asymmetrical, battered world has a massive ring of dark of material in its orbit that scientists believe may be the result of an object that collided with Phoebe.
Saturn’s moon Iapetus is sometimes referred to as the “Yin Yang” moon, due to the shape of a layer of dark material on its surface. Some areas of Iapetus’ surface are white as freshly fallen snow, while other areas are as dark as charcoal. The dark areas are believed to be materials that were attracted to Iapetus’ surface from the dark ring of mater in the orbit of Phoebe. Iapetus also has a huge impact crater and a narrow icy mountain range three-quarters of the way around its equator. The highest peaks in this mountain range are higher than Mount Everest on Earth and are believed to have been caused by some type of melting of the moon’s surface at one time.
Hyperion is a very small world, with the shape that resembles an eggshell, and a surface that resembles a sponge. This spongy looking moon, also believed to be captured into orbit around Saturn, has a hard icy surface, and measures only 328km from end to end.
Rhea, the second largest moon in the Saturnian System, has a narrow band of what is believed to be patches of fresh water ice around its equator, suggesting that Rhea may have its own ring. If this hypothesis proves correct, Rhea would have the distinction of being the only known moon in the solar system to have a ring.
Mimas’ large impact crater Herschel, covers one-third of its diameter. Internal temperatures obtained from VIMS, Cassini’s Visual and Infrared Mapping Spectrometer, do not coincide with predicted temperatures, prompting scientists to take a closer look at Mimas.
As the spacecraft continued a tireless mission throughout the Saturnian neighborhood, Cassini made several passes through Saturn’s E- ring, studying its composition with the onboard Cosmic Dust Analyzer, and later repositioning its orbit to observe the planet’s ring structure, magnetic field, and surface features. Saturn’s main rings average 10m in height, and span from end to end at a distance equivalent to two-thirds the distance from the Earth to our Moon.
Cassini took a close look at the main rings designated as A, B, and C (the rings that amateur astronomers can observe with their ground based telescopes) and found that the thousands of individual ringlets within the rings are made of icy particles, consisting of 99.9% water ice and ranging in size from a small house to a grain of sugar. The instruments on the spacecraft determined that the structure of the main rings and the gaps between them are affected by the orbits of tiny icy irregular shaped Sheppard Moons: Atlas, Daphnis, and Pan, ranging in size from approximately 8-30km across, which lie within or close to the plane of the rings.
Cassini also discovered very tiny irregular shaped “Moonlets,” ranging in size from 50-400m in length, producing periodic bright arcs within the ringlets. The spacecraft’s Imaging Science Subsystem Cameras observed the co-orbital moons Epimetheus and Janus crossing orbits in the gap between Saturn’s F and G rings, and tiny potato shaped Prometheus and Pandora sculpturing the structure of the F ring. Cassini has also observed Auroras, lightning, a hexagonal structure at the North Pole, and an “eyewall” hurricane-type structure in the South Pole of Saturn’s atmosphere, providing scientists more puzzling questions.
On October 11, 2010, Cassini began the Solstice Mission, another extended undertaking that is planned to continue into the year 2017. This mission will include 22 orbits of Saturn, 56 flybys of Titan, 12 of Enceladus, and flybys of several other icy moons. One orbit of Saturn around our Sun is approximately 29.5 Earth years long…If Cassini successfully completes its seven year extended mission, it will have only studied less than one half of a Saturnian solar cycle, but has and will continue to unlock the mysteries of Saturn, its Moons, and its rings.
The best is yet to come!
You can find more information regarding the NASA’s Cassini mission on the web at, www.saturn.jpl.nasa.gov
I’m Andy Poniros and thanks for listening to this 365 Days of Astronomy podcast!
End of podcast:
365 Days of Astronomy
=====================
The 365 Days of Astronomy Podcast is produced by the Astrosphere New Media Association. Audio post-production by Preston Gibson. Bandwidth donated by libsyn.com and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at 365DaysOfAstronomy.org or email us at info@365DaysOfAstronomy.org. Until tomorrow…goodbye.
Trackbacks/Pingbacks