The rings of Saturn, however, are not so easily viewed, and were not known to exist until Galileo Galilei (1564-1642) first saw them in 1610 using the newly developed refracting telescope. He thought the rings were actually two moons alongside Saturn. Forty-five years later, he was proven wrong when Christiaan Huygens (1629-1695) observed a “thin, flat ring” surrounding Saturn using a telescope he designed with greater magnification. In 1675 at the Paris Observatory, Giovanni Cassini (1625-1712) discovered a wide, dark gap between the rings of Saturn, known as the ‘Cassini Division’. As technology has increased visibility, nine continuous main rings and three discontinuous arcs have been observed within Saturn’s ring system.
Christiaan Huygens also discovered the first and largest of Saturn’s many moons, Titan, in 1655, while Giovanni Cassini was the first to observe four others, Iapetus (1671), Rhea (1672), Tethys and Bione (both in 1684). There are currently 62 known moons of Saturn, 53 confirmed and officially named and nine provisional moons as well as dozens to hundreds of ‘moonlets’ (small natural satellites orbiting a planet).
The Cassini Mission
An international mission to explore Saturn, its magnetosphere (region surrounding a planet that’s dominated by the planet’s magnetic field), rings and moons began more than 25 years ago, starting with seven years of development prior to the Cassini-Huygens spacecraft launch in 1997. The design of the unmanned spacecraft included a Saturn orbiter (Cassini) and a lander (Huygens) for Titan.
On December 25, 2004, Huygens separated from Cassini, and on January 14, 2005, successfully landed on Titan, while collecting and transmitting data to Earth using Cassini as a relay. It’s batteries died shortly after landing; therefore, Huygens now sits in silence on Titan’s surface.
[ESA Science: Huygens Top 10 Discoveries at Titan]
Cassini entered Saturn’s orbit on July 1, 2004, and photographs taken during the last 12+ years have led to significant discoveries. The 2012 NASA/Jet Propulsion Laboratory video, Cassini: 15 Years of Exploration, hits some of the highlights.
End of Mission: Cassini’s primary mission was completed in 2008 as it had made 74 orbits around Saturn. The mission, however, was extended to September 2010 for additional study, and extended a second time to 2017. It’s fuel supply running low, Cassini made a number of passes through the gap between Saturn and its inner ring before it was intentionally destroyed on September 15, 2017 by forcing a dive into Saturn’s atmosphere. The purpose of the deorbit was to mitigate the risk of Cassini later colliding with one of Saturn’s moons.
When & How to Find Saturn in 2017 Astronomy Essentials (5/11/2017), Bruce McClure & Deborah Byrd
NASA: Cassini Mission Overview: Planets – Saturn
European Space Agency: Cassini-Huygens
Missions to Saturn (Past, Present, Concepts)
Wikipedia: Saturn, Galileo Galilei, Christiaan Huygens, Giovanni Cassini
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Feature photo: The image of Saturn was captured on February 9, 2004 by the narrow angle camera of the Cassini-Huygens spacecraft when it was about 69 million kilometers (43 million miles) away from Saturn. A series of exposures through different filters were combined to form the colors seen in the image. The icy moon Enceladus is faintly visible on the left. Image Credit: NASA/JPL/Space Science Institute, Public Domain