Earth's magnetic field, a history of polarity
One aspect of the campaign is to study the Earth's magnetic field at the base of the Southwest Indian Ridge. The magnetic field can orient themselves in space, giving us the North but, Earth Science, the study is also crucial for understanding plate tectonics. Indeed, the magnetic field undergoes polarity changes over geological time, ie the magnetic North and South are substitutes for one another. These events are very short of a geological point of view (about 10 000 years) and recur periodically (every million to forty million years ago). On the other hand, the basalts produced at the ocean ridge have ferromagnetic minerals which are oriented along the field lines in the same way that a compass needle. They freeze upon cooling and achieved the "history" of the magnetic field. The succession of these changes in polarity causes the basalts, at the base thereof, the formation of tiny variations in the field called magnetic anomalies. At each change of polarity and thus each magnetic anomaly corresponds to a specific age that used to date the ocean floor. This timing is very important because it gives us the opening rate of the ridge, and we show that the tectonic plates are moving. The figure above shows the age of oceanic crust (in million years) derived from the study of magnetic anomalies.
We use an instrument called a magnetometer to measure magnetic field. It was towed about 350 meters behind the boat to avoid any disruptions related to the metal mass of it. The photo-cons is taken at the launch of the instrument. We have both a surface magnetometer (pictured) and a magnetometer mounted on the TOBI. TOBI being towed further, it will be closer to sources of magnetic anomalies and will provide better data.
One aspect of the campaign is to study the Earth's magnetic field at the base of the Southwest Indian Ridge. The magnetic field can orient themselves in space, giving us the North but, Earth Science, the study is also crucial for understanding plate tectonics. Indeed, the magnetic field undergoes polarity changes over geological time, ie the magnetic North and South are substitutes for one another. These events are very short of a geological point of view (about 10 000 years) and recur periodically (every million to forty million years ago). On the other hand, the basalts produced at the ocean ridge have ferromagnetic minerals which are oriented along the field lines in the same way that a compass needle. They freeze upon cooling and achieved the "history" of the magnetic field. The succession of these changes in polarity causes the basalts, at the base thereof, the formation of tiny variations in the field called magnetic anomalies. At each change of polarity and thus each magnetic anomaly corresponds to a specific age that used to date the ocean floor. This timing is very important because it gives us the opening rate of the ridge, and we show that the tectonic plates are moving. The figure above shows the age of oceanic crust (in million years) derived from the study of magnetic anomalies. 
We use an instrument called a magnetometer to measure magnetic field. It was towed about 350 meters behind the boat to avoid any disruptions related to the metal mass of it. The photo-cons is taken at the launch of the instrument. We have both a surface magnetometer (pictured) and a magnetometer mounted on the TOBI. TOBI being towed further, it will be closer to sources of magnetic anomalies and will provide better data. 
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