The main goal of NASA鈥檚 InSight lander, which arrived on the Red Planet聽in November 2018, is to measure underground heat flow and seismic activity. That isn鈥檛 going quite as planned, but the lander is using one of its less important sensors to make the very first measurements of Mars鈥檚 magnetic field from the surface, which may help us find water deep underground.
InSight鈥檚 main instrument, its seismometer, has not yet seen any sign of marsquakes. The heat probe, nicknamed 鈥渢he mole鈥�, is designed to burrow 3 metres below the surface before it starts gathering data, but it has hit an unexpected rock less than 50 centimetres below the surface and become stuck.
Enter the magnetometer, which isn鈥檛 even designed to study Mars directly. 鈥淚t鈥檚 not primarily there for science 鈥� it鈥檚 there to measure anything that might affect what the seismometer measures,鈥� says InSight scientist Catherine Johnson. 鈥淏ut we鈥檙e using it for science anyway.鈥� The first results were presented at the Lunar and Planetary Science Conference in Texas on 19 March.
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Unlike Earth, Mars lacks a global magnetic field, but it probably had one at some time in the past, which led to magnetised rocks in its crust. Electric currents created by charged particles from the sun can generate small magnetic fields in those rocks, which InSight鈥檚 magnetometer can measure.
鈥淲e can use it to probe how much water is locked up in those rocks,鈥� says Johnson. 鈥淗ow strongly magnetised they are is proportional to what the mineral is, how much of it is there and how strong the ancient magnetic field was.鈥�
We have been unable to do this in the past because orbiting spacecraft can only detect magnetic fields that make it all the way off the surface into space. 鈥淎lthough we have some idea from spacecraft observations, we only know about magnetic fields on scales of hundreds of kilometres or larger,鈥� says Johnson. Because of this scale bias, we thought the small magnetic fields on the surface would be 10 times weaker than InSight found them to be.
So far, we have only a few months of measurements, but as InSight鈥檚 magnetometer continues collecting data, it may be able to determine how much water there is inside minerals under the surface and how strong the primordial magnetic field was. The loss of the field is probably why Mars shed its atmosphere and became cold and dry, so learning more about it could help us understand why the planet is so different from Earth today.
