Cassini MIMI: Magnetospheric Imaging Instrument - CERTIFIED

Cassini's Magnetosphere Imaging Instrument (MIMI) was built to take global images and in-situ measurements of Saturn's magnetosphere. Its three separate sensors—the Ion and Neutral Camera (INCA), the Low Energy Magnetospheric Measurements System (LEMMS) and the Charge-Energy-Mass-Spectrometer (CHEMS)—provided data that allows scientists to investigate how Saturn's magnetosphere interacts with the solar wind, Saturn's atmosphere and Saturn's retinue of satellites, especially Titan, as well as study the overall configuration and dynamics of the Saturnian magnetosphere. MIMI is the result of collaboration among several partner institutions, including John Hopkins University's Applied Physics Laboratory, the University of Maryland, the Max-Planck-Institut für Aeronomie, the Centre d'Étude Spatiale des Rayonnments in Toulouse, France and Fundamental Technologies, LLC in Lawrence, KS.

Scientific objectives for MIMI include the following:

• Characterize the global configuration and dynamics of energetic plasma in Saturn's magnetosphere
• Search for, monitor and analyze magnetospheric sub-storm activity
• Understand the satellite-magnetosphere interactions, such as the modification of satellite surfaces and the production of neutral clouds of hydrogen, nitrogen and water products
• Study Titan's cometary interaction with the magnetosphere of Saturn
• Assess the cosmic ray albedo neutron decay in Saturn's inner magnetosphere

MIMI detectors:

• Ion and Neutral Camera (INCA): Remote sensing energetic neutral atoms and ion species
• Low-Energy Magnetospheric Measurements System (LEMMS): Ions and electrons in both forward and rear directions
• Charge-Energy-Mass-Spectrometer (CHEMS): Ion energy, mass, charge and three-dimensional anisotropy

INCA, sensitive to incident energetic neutral atoms and ion species in the range 7 keV/nuc - 3 MeV/nuc, was used as a wide-angle remote sensing instrument by detecting and mapping out incident charge-exchange neutrals, the products of an exchange between the ambient gas and magnetospheric ions, much as a visible camera records incident photons.

LEMMS detected ions and electrons in both the forward and rear directions, with the rear aperture being larger and sensitive to higher energy ions and electrons. The forward-facing detector measured ions in the energy range 0.03 - 18 MeV and electrons in the energy range 0.015 - 0.884 MeV. The rear-facing detector was sensitive to ions in the 1.6 - 160 MeV energy range and electrons between 0.5 and 5 MeV.

CHEMS measured ion energy, mass, charge and three-dimensional anisotropy in the energy range 3 - 220 keV/e.

The engineering details of the MIMI instrument and the science objectives it was built to address are described in further detail in the Space Science Reviews paper by Krimigis et al. (2004).

CHEMS Calibrated Data

• The Pulse Height Analysis (PHA) data provides a list of individually detected particles, with specific detection parameters for each event, including time-of-flight (TOF), energy deposited in the SSD, and telescope number
• The energy-per-charge and mass-per-charge spectrograms are based on CHEMS PHA data
• The energy-per-charge data for six ion species (H⁺, He⁺, H₂⁺, He⁺⁺, O⁺⁺, W⁺)
• The mass-per-charge data for five energy ranges (2.8–7.8 keV/e, 8.9–23.9, 27.4–72.6, 83.4–220.2 and 2.8–220.2 keV/e)

LEMMS Calibrated Data

• Energy-time spectrograms in units of intensity
• Plots of particle pressures
• Averaged data - minute and hourly averages for accumulator rate data and PHA data (ions and electrons)

INCA Calibrated Data

• An averaged form where the original N x N pixel images intensities are averaged to a single value for one species and TOF combination in browse product and averaged data
• Browse thumbnail Ion images, which display rows and columns of images for one species and TOF combination
• Browse averaged energetic neutral atom (ENA) image skymaps for one species and TOF combination
• Movies, which display averaged ENA image skymaps
• INCA Image Files, in differential intensity for a combination of resolution, species and energy value

Calibrated Data in Physical Units

• CHEMS Rate Channels - Information on the channel types and other details can be found in the User's guide Appendix E (page 225) and Appendix F (page 243)
• LEMMS Rate Channels - See Krimigis et al., (2004), Magnetosphere imaging instrument (MIMI) on the Cassini mission to Saturn, Space Sci. Rev., 114, 233-329 with updates to the MIMI user's guide for channel descriptions, etc. The user can access a list of the backgrounds (see elsewhere in this document).

Pitch Angle Plots and Data

• LEMMS

Once data products have been selected and retrieved, users will need to read, manipulate and display that data. Below are listed resources that will enable users to make use of MIMI data.

Data Reduction and Analysis Software

Calibration Details:

• LEMMS Dust Response Calibration Report (In preparation)
• LEMMS Detector Backgrounds (Readme file)
• INCA Flat Fielding Functions
• INCA HV History
• Updates Based on Instrument Aging
Added INCA Flat Fielding Functions
Added HV history locations

SPICE Metakernel enables users to calculate spacecraft and instrument position relative to Saturnian bodies.

• link 1
• link 2
• link 3

Ancillary Data:

• Gaps in Attitude and ephemeris data
• Gaps in INCA, LEMMS, and CHEMS Science Data
• Mode Changes for INCA (ion vs neutral mode)
• INCA Calibration State
• MIMI Spin Mode