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Home > Research > Space Plasmas > Space missions > Cassini (1997-2017) > Mission description

Mission description

First contact

The first in situ observations of Saturn’s environment and moons were made by Pioneer 11. It was in the late 70s, the probe flew past Saturn. These observations led to the first detection of the intrinsic magnetic field of Saturn.

Thereafter, flybys of Saturn were performed by the Voyager 1 and 2 probes. This gave more information about the magnetic field of the planet. As for Earth, it is assumed to be dipolar. Moreover, its dipole moment is aligned with the planet axis of rotation. However, the intensity is stronger than the geomagnetic field.

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Figure 1. Schematic of Saturn magnetosphere
Source : NASA

Pioneer 11 and Voyager 1 and 2 have also revealed the existence of Saturn’s magnetosphere, the region surrounding the planet in which the intrinsic field dominates. These missions have revealed the existence of auroras on Saturn, similar to those on Earth.

The many moons of Saturn were observed by the Pioneer 11 and Voyager missions, and also from Earth. These analyses revealed the existence of coupling between the magnetosphere of Saturn and its moons. Titan is the largest moon, orbiting at about 20 Saturnian radii of the planet. During their passage near Titan Voyager probes were able to detect the atmosphere of Titan, which reveled to be rich in nitrogen and methane. However, no intrinsic magnetic field was detected for Titan.

The conquest of a world

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Figure 2. Artistic view of Cassini probe orbiting around Saturn
Source NASA

The Voyager and Pioneer 11 missions provided important results on Saturn, Titan and their environment. They also aroused the curiosity of scientists. Note that these missions were designed to observe the outer solar system. They each have only made one flyby of Saturn. To answer the many questions about the " Saturnian world ", the need for a dedicated mission manifested. The answer to this need was the Cassini-Huygens mission.

Cassini-Huygens is the product of collaboration between Italian, American and European space agencies (NASA, ESA and ASI). The mission was launched in 1997 with the objective to study Saturn and Titan. It was then the most ambitious planetary mission. The various themes of the mission involve different branches of astronomy and astrophysics. The major questions to answer concern the energy source of Saturn, the ring structure of Saturn’s moons, Titan in particular. They also deal with the topic of the interactions between the interplanetary medium, Saturn and its moons.

And what about plasmas ?

A complete analysis of Saturn’s magnetosphere was part of the scientific objectives of the mission, which thus includes experiments dedicated to the measurement of plasma. Cassini-Huygens aims to lighten the space plasma physicists on the following points:

  • The overall configuration of the magnetosphere.
  • The dynamics and the source of Saturn’s magnetospheric plasma.
  • The phenomena of magnetospheric substorms, to which the auroras are related.
  • The interaction of Saturn’s magnetosphere with its ionized atmosphere called the ionosphere.
  • The interaction of the magnetosphere with the satellites (Titan in particular) and the rings of Saturn.

To each probe its mission

The mission consists of two separate probes: Cassini and Huygens. Both were launched simultaneously in 1997. They separated a few months after their arrival in the Saturnian environment in 2004.

The role of Cassini is to analyze Saturn, its moons and its environment. The Cassini spacecraft is orbiting Saturn and its moons. Thanks to Titan gravity assist, orbital trajectory of Cassini is regularly changed. This made it possible to explore all the key areas of the magnetosphere. The mission has been extended, in a phase called “grand finale”, from April to September 2017, which comprised twenty two orbits around Saturn, getting closer and closer, crossing the rings and finally being desintegrated in its atmosphere on September 15.

The Huygens probe is dedicated to the study of Titan. One year after separation, Huygens satellite has entered the atmosphere of Titan. It was then able to reach the surface. In this way, analysis of the atmosphere and surface were performed.
NASA: http://saturn.jpl.nasa.gov/

ESA: http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens

LESIA: http://www.lesia.obspm.fr/plasma/cassini/cassini.html

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