Cassini MAG: Magnetometer - CERTIFIED

The Cassini Magnetometer (MAG) measured the three vector components and magnitude of the magnetic field in Saturn's magnetosphere and interplanetary space. MAG consists of two separate sensors, a Fluxgate Magnetometer (FGM) and a Vector/Scalar Helium Magnetometer (V/SHM). The V/SHM was built at the Jet Propulsion Laboratory, Pasadena, CA, while the FGM was built and managed at Imperial College, London, UK.

Scientific objectives for the MAG include the following:

• Measure the magnetic field generated in Saturn's interior
• Characterize Saturn's global magnetospheric magnetic field
• Understand the coupling between the magnetosphere and ionosphere
• Characterize the interaction between the icy moons and Saturn's magnetosphere
• Determine the magnetic state of Titan and characterize its magnetospheric interaction

MAG detectors:

• Fluxgate Magnetometer (FGM): measured magnetic field direction and magnitude. This is the primary magnetometer used by the mission because it gathered data during the entire Saturn tour.
• Vector Helium Magnetometer (VHM): measured magnetic field direction and magnitude. This detector failed in November, 2005.
• VHM Scalar Mode (SHM): high-accuracy measurements of magnetic field magnitude while FGM was measuring vector magnetic field. This detector failed in November, 2005.

The instrument returned nearly continuous magnetic field measurements throughout the entire Cassini mission and part of interplanetary cruise on the way to the Saturn system. The magnetometers were mounted on an 11 m boom to minimize interference from spacecraft generated fields. The V/SHM was mounted at the end of the boom and the FGM at the mid-point. The goal of two separate sensors was to provide two independent measurements of the local field for cross-calibration.

The helium magnetometer has two modes of operation, a vector mode (VHM) that measures the magnetic field direction and magnitude and a scalar mode (SHM) that measures the magnetic field magnitude only. The scalar mode of operation was intended to provide highly accurate measurements of the magnetic field magnitude while the FGM simultaneously measured the vector magnetic field. It was intended to be used in strong magnetic fields close to Saturn to make an accurate determination of Saturn's internal planetary field. (The helium magnetometer failed on November 17, 2005 thus data from this sensor are not available after this time.)

The magnetometer acquired data almost continuously throughout the mission, although the data rate varied based on available resources (solid state recorder space and downlink capability). The maximum data rates for each of the modes are as follows: FGM (32 vectors/s), VHM (2 vector/s) and SHM (1 value/sec).

The User's Guide includes detailed information on instrument characteristics, how to search for, calibrate and transform MAG data into various coordinate systems of interest. It also includes step-by-step instructions of how to replicate examples from the published literature. The engineering details of the MAG instrument and the science objectives it was built to address are described in further detail in the Space Science Reviews paper by Dougherty et al. (2004).

Calibrated magnetometer data that has been transformed into several different geophysical coordinate systems is available on PDS. Data is available in RTN (Radial Tangential Normal) coordinates for interplanetary cruise data and KRTP (Kronocentric body-fixed, J2000 spherical Coordinates), KSM (Kronocentric Solar Magnetospheric Coordinates), KSO (Kronocentric Solar Orbital Coordinates) for the Saturn orbits. For more on coordinate systems, see the MAG data-set information page, or download the MAG User's Guide [PDF].

These data files include the magnetic field vector components and magnitude as well as basic trajectory information appropriate for the particular coordinate system.

Calibrated magnetometer data is available on PDS at the full time resolution as well as 1-minute and 1-second averages:

• Full Resolution, organized by year and by a set of days, with the indicated coordinate data for that set of days—for example, for 2003 days 91–120 in RTN coordinates, DATA/2003/091_120_APR/03110_FGM_RTN/
• One-Second Averages, organized by year and then by days, with multiple coordinate systems available—for example, for 2006 days 36–68, DATA/2006/06036_06068_21_FGM_RTN_1S
• One-Minute Averages, organized by year, with multiple coordinate systems available—for example, DATA/2005/2005_FGM_KSM_1M/

Calibrations required by the magnetometer are described in detail in the MAG User's Guide [PDF]. Calibrations for the V/SHM consist of subtracting zero levels, multiplying by an orthogonality-sensitivity matrix, rotating from the sensor coordinates to the spacecraft coordinates, and subtracting spacecraft generated fields. A precise determination of the alignment of the magnetometer sensors with respect to the spacecraft body is accomplished by use of the Science Calibration Subsystem (SCAS) calibration coils. The SCAS consists of two coils rigidly mounted on the spacecraft body with a known alignment to the spacecraft axes. (SCAS calibration activities are described here)

Data in moon-centered coordinates for all targeted moon flybys, including the magnetic field components and magnitude, spacecraft trajectory vector, and distance.

• Titan (Temporarily unavailable)
• Enceladus (Temporarily unavailable)
• Dione (Temporarily unavailable)
• Rhea (Temporarily unavailable)
• Tethys (Temporarily unavailable)
• Iapetus (Temporarily unavailable)

• Saturn Magnetosphere Model
• Titan Induced Magnetosphere model (Temporarily unavailable)
• Enceladus Environment Model (Temporarily unavailable)
• SKR Phase Models - The phase model [TXT] for the magnetic perturbation systems and a User's Guide [PDF] has been provided by Gabby Provan.

Complete set of Conjugate Maps (Temporarily unavailable) of Cassini spacecraft in the Saturnian magnetosphere, based on an empirical magnetosphere model.

Comprehensive lists of events may be useful in selecting a timeframe to study. These events are available within the Event Calendar, or directly from the files below.

• Bow Shock and Magnetopause Crossings

Analyzing MAG Data

• A Software Package (Temporarily unavailable) is available to view and download MAG data.
• The PDS also provides a Plotting Software that runs on PCs.
• Other relevant information, can be found on the Magnetospheres Discipline website.

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For questions and comments, visit the PDS Cassini Contact Page