A Scientific "Second" for a Saturn Moon
Scientists with the magnetometer instrument have found an atmosphere on Enceladus. This is the first time an atmosphere has been detected on a moon of Saturn other than Titan. This discovery was made from data collected on two recent close flybys of Enceladus.
How was the atmosphere detected?
When Cassini had its first encounter with Enceladus on Feb. 17, 2005, the magnetometer instrument saw a bending of Saturn's magnetic field, with the plasma being slowed and deflected as it passed Enceladus. Data collected during the March 9, 2005 flyby provided further evidence.
This bending is caused when Saturn's magnetic field lines come in contact with a conducting object (in this case an atmosphere). The magnetic field lines drape themselves around the moon.
What causes the atmosphere to form?
Unlike Titan, which is 5,150 kilometers (3,200 miles) across, Enceladus is a small moon. Its diameter is approximately 500 kilometers (310 miles). If Enceladus were on Earth, the entire moon would fit within the state of Arizona. This means the amount of gravity present on the moon is not enough to hold an atmosphere for very long. Moons and planets need a lot of gravity to support an atmosphere. Therefore, a strong source must be present on the moon to "feed" Enceladus's atmosphere.
What types of things can cause enough force to generate an atmosphere? Scientists currently hypothesize that volcanic eruptions or geysers might provide the necessary material.
Building on Previous Enceladus Explorations
Since the Voyager flyby in 1981, scientists have suspected that this moon is geologically active and is the source of Saturn's icy E ring. Enceladus is the most reflective object in the Solar System, reflecting about 90 percent of the sunlight that hits it. If Enceladus does have ice volcanoes, the high reflectivity of the moon's surface might result from continuous deposit of icy particles originating from the volcanoes.
If eruptions exist on Enceladus, this moon would join an elite group of moons with surface eruptions. Only Jupiter's moon Io and Neptune's moon Triton have shown evidence of active eruptions. That's an exciting possibility and one Cassini scientists will watch for in future Enceladus flybys.
Sounds of Enceladus
Cassini's magnetometer instrument detected an atmosphere around Enceladus during the Feb. 17, 2005, flyby and again during a March 9, 2005, flyby. This audio file is based on the data collected from that instrument.