Space-Based Observations

Image taken by Pioneer 11

Because of the distorting effect caused by the Earth's atmosphere, even the most powerful and technologically advanced telescopes remained unable to spot many of Saturn's features. Only some rings were visible, and many smaller moons escaped detection until the advent of space-based observation.

A major breakthrough came from images taken by Pioneer 11, the first probe to reach Saturn. In September 1979, the spacecraft flew by only 22,000 kilometers (13,000 miles) from the planet's cloud top surface. From its vantage point, the spacecraft sent back amazing images of the gas giant and its rings. These first close-ups netted the discovery of two more moons and an additional ring. Instruments on board charted the planet's magnetosphere and magnetic field. Data from Pioneer 11 also led scientists to conclude that Titan, the biggest moon orbiting Saturn, is too cold to sustain life -- at least life as we know it.

While the known number of moons orbiting Saturn steadily increased with the development of better telescopes, only 11 were known to exist until 1980. Finally, in the two years following Pioneer 11 mission, two more NASA spacecraft explored the area sending back higher quality images and data.

Saturn's clouds taken by Voyager 1

Voyager 1, now the farthest spacecraft from Earth, encountered Saturn in November 1980, and its sister spacecraft, Voyager 2, in August 1981.

Data from Voyager 1 unveiled three more moons. Images from Voyager 2 suggested the possibility of three more, however, not verifiable at the time. Meanwhile, Earth-based instruments discovered three other moons, a testimonial of the technical advancement of ground-based astronomy. These two spacecraft, the last two to visit the ringed planet, provided interesting data on the atmosphere's composition. For example, scientists knew that, like Jupiter, Saturn's atmosphere is made up almost entirely of hydrogen and helium. However, the percentage of helium in Saturn's upper atmosphere is only 7 percent -- compared to Jupiter's 11 percent.

Saturn's Aurora taken by Hubble

After dreaming of a permanent telescope in orbit for decades, astronomers got their wish when the Hubble Space Telescope was launched in 1990. Named after the American astronomer Edwin Hubble, the telescope is light years ahead of the primitive tool of Galileo's time. Hubble's powerful optics scope the sky 612 kilometers (380 miles) above Earth, thus avoiding the alterations and distortions caused by our atmosphere. It also boasts different instruments capable of seeing from ultraviolet through infrared.

Traveling around Earth at 28,000 kilometers (17,500 miles) per hour, Hubble completes an orbit every 96 minutes. On a given day, it is capable of archiving between three and five gigabytes of data. The data is than distributed to astronomers and scientists worldwide.

Using its vantage point and powerful instruments, the Hubble Space Telescope contributed to our better understanding of the ringed planet. After Pioneer 11 observed traces of an ultraviolet aurora around Saturn, the two Voyager spacecraft provided a basic description of the phenomenon. In 1994, Hubble captured the first images of Saturn's aurora. These aurora investigations provide a framework for future explorations, to begin in July 2004.