When
3:45 p.m., April 14, 2015
Where
Kuiper Space Sciences 312
Dr. Catherine Johnson
Professor
University of British Columbia
Mercury's Magnetic Field: Stories from the Planet, Present and Past
Mercury is the only inner solar system body other than Earth to possess an active core dynamo-driven magnetic field, and the only planet with a highly dynamic, small magnetosphere. Measurements made by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft have provided a wealth of data on Mercury's magnetic field environment. Mercury's weak magnetic field was discovered 40 years ago by the Mariner 10 spacecraft; but its large-scale geometry, strength and origin could not be definitively established. MESSENGER data have shown that the field is dynamo-generated and can be described as an offset axisymmetric dipole field: the magnetic equator lies ~0.2 RM (RM = 2440 km) north of the geographic equator and the dipole moment is 0.03% that of Earth's. Re-analysis of the Mariner 10 observations has established that there has been no measurable secular variation in the internal field over 40 years. The spherical harmonic degree power spectra for the field and its secular variation provide critical constraints for viable dynamo models. Induced core fields result from time-varying magnetopause fields and their magnitude confirms the core radius estimated from MESSENGER gravity and Earth-based radar data. Field-aligned currents have been identified, that likely close in the planetary interior at depths below the base of the crust. Recent magnetic field measurements at altitudes below 50 km have the potential to resolve fields of crustal origin, which have not been seen at higher altitudes.
Professor
University of British Columbia
Mercury's Magnetic Field: Stories from the Planet, Present and Past
Mercury is the only inner solar system body other than Earth to possess an active core dynamo-driven magnetic field, and the only planet with a highly dynamic, small magnetosphere. Measurements made by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft have provided a wealth of data on Mercury's magnetic field environment. Mercury's weak magnetic field was discovered 40 years ago by the Mariner 10 spacecraft; but its large-scale geometry, strength and origin could not be definitively established. MESSENGER data have shown that the field is dynamo-generated and can be described as an offset axisymmetric dipole field: the magnetic equator lies ~0.2 RM (RM = 2440 km) north of the geographic equator and the dipole moment is 0.03% that of Earth's. Re-analysis of the Mariner 10 observations has established that there has been no measurable secular variation in the internal field over 40 years. The spherical harmonic degree power spectra for the field and its secular variation provide critical constraints for viable dynamo models. Induced core fields result from time-varying magnetopause fields and their magnitude confirms the core radius estimated from MESSENGER gravity and Earth-based radar data. Field-aligned currents have been identified, that likely close in the planetary interior at depths below the base of the crust. Recent magnetic field measurements at altitudes below 50 km have the potential to resolve fields of crustal origin, which have not been seen at higher altitudes.
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