In contrast, the other large inner worlds in our solar system – Venus, Mars and Earth’s moon – do not show any evidence for internal magnetism generated via the dynamo effect. Mercury’s magnetic field is thought to operate in the much same way however, the field is weaker than that of Earth. Together, the two fields are stronger than the original and lie essentially along the axis of the Earth’s rotation. (Heat from radioactive decay in the core is thought to induce the convective motion.) The electric current, in turn, produces a magnetic field that also interacts with the fluid motion to create a secondary magnetic field. In this dynamo mechanism, fluid motion in the Earth’s outer core moves conducting material (liquid iron) across an already existing, weak magnetic field and generates an electric current. Geologists at University of Oregon explain Earth’s magnetic field this way: Earth’s magnetic field is generated by our planet’s large iron core. This discovery now makes Mercury the only other world besides Earth in the inner solar system thought to have a magnetic field generated via a self-sustaining dynamo effect. Image via NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington Read more about this image from the Planetary Science Institute. This cartoon shows schematic magnetic field lines above the surface of Mercury from magnetized crustal rocks. Now scientists say Mercury’s magnetic field may have been much stronger 4 billion years ago than it is today. Our findings indicate that a global magnetic field driven by dynamo processes in the fluid outer core operated early in Mercury’s history. We infer a lower bound on the average age of magnetization of 3.7 to 3.9 billion years. … We have detected remanent magnetization in Mercury’s crust. Data from the Mariner 10 mission revealed that Mercury actually had a large iron core, consisting of approximately 75 percent of its total mass. Then, in 1974, the Mariner 10 probe detected a weak magnetic field, less than 1/100th the Earth’s. Magnetized rocks record the history of the magnetic field of a planet, a key ingredient in understanding its evolution.ĭecades ago, scientists believed Mercury did not have a magnetic field, due to its small size and proximity to the sun. Planetary scientist Catherine Johnson is lead author of the study. Scientists published the recent Mercury magnetic field study in the journal Science on May 7, 2015.Īs MESSENGER’s orbit was degrading, and it began orbiting Mercury closer than 60 miles (100 km) from Mercury’s surface, the spacecraft’s magnetometer, an instrument that measures magnetic field strength, was able to detect evidence of the ancient field through magnetized crustal rocks. MESSENGER’s low-altitude measurements of Mercury surface, as it came near the end of its mission, revealed the evidence of magnetization in rocks on the planet’s surface. Now – thanks to MESSENGER, which crash-landed on Mercury on April 30 – scientists are able to say that Mercury’s magnetic field has existed longer than previously speculated, clocking in at at least 3.7 to 3.9 billion years or older. But its they didn’t know its age and strength until the final months of the mission of the MESSENGER spacecraft, which orbited the planet from 2011 through 2015. Scientists learned 40 years ago that Mercury has a magnetic field. This is the site of some of the crustal magnetic signals that led to an estimate of the age of Mercury’s magnetic field. Looking west across Suisei Planitia (blue colors) on Mercury.
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