It’s exciting that every planet and moon that we look at in our solar system is not only strange, but stranger than we expect. That’s a lot of fun, actually.
The mysteries like the planet Saturn’s rings and its moon Titan and its atmosphere, is there life on Titan or not, is Pluto a planet or just a ball of frozen gases are yet to solved. However, another three-decade mystery about planet Mercury, the closest planet to the Sun, has such a weak magnetic field is believed to be solved by a German scientist.
When Mariner 10 passed by Mercury, it discovered that the magnetic field is 1% as strong as Earth’s. The field has an axis of inclination of 7 degrees to Mercury’s axis of rotation and forms a magnetosphere around the planet. The source of this magnetic field was quite hard to understand. One of the four rocky planets in the inner Solar System, Mercury is believed to generate its magnetism in the same way as Earth — by a dynamo, caused by the rotation of molten iron at its core. However, question is why Mercury’s magnetic field is so puny, as it amounts to just one percent of the strength of Earth’s.
If the dynamo theory is right, the planet’s magnetism should be 30 times stronger than it is.
Like many others and me, you too believed since Mercury’s interior is comprised mainly of a large iron core (about 1800 to 1900 km thick), a percentage of it must be molten for the generation of the field. Another source of the field may be from partially iron rocks that were magnetized by a much stronger magnetic field in Mercury’s younger age.
Ulrich Christensen of the Max Planck Institute too believes the answer lies in the structure of Mercury’s core but nobody paid attention to the core’s outer layer. The core’s outer layers are “stably stratified,” which means they are largely insulated from the heat of the swirling inner core. As a result, only the inner core rotates effectively to generate the magnetic field. This braking effect is relatively important because Mercury has a very slow rotation, which also affects the dynamo’s power.
I hope this mystery will be put to rest with the test of the new theory soon when two scheduled missions to Mercury by NASA’s Messenger (launched in 2004 and scheduled to rendezvous in 2008) and the European Space Agency’s BepiColombo (due for launch in 2013).
Via: Physorg
