I recently read about a small Inuit village in northern Canada that will be included in the Google Street View displays available with Google Earth. Ikaluktutiak, or Cambridge Bay, is located at approximately 69º N, 105º W and is populated by fewer than 2,000 residents. There are only a few trucks in the village and no cars, and it is only accessible by air when it is snowed in during the winter months.
When it is not snowed-in and river ice has melted, the village is accessible by barges, as well. While the village’s geography and culture are very interesting, what caught my attention while reading the article was that a magnetic compass will not work at that latitude. Village residents navigate by landmark recognition and, more recently, with the assistance of GPS. Thinking about this led to some questions:
• How is it that a magnetic compass will not work, or not work correctly, at that latitude?
• What is a magnetic pole and how is it created?
• Do other planets have magnetic fields?
Planetary Magnetic Fields
Using the Earth as a model, the conditions a planet needs to meet in order to have a magnetic field would include a relatively fast rotation period, an electrically charged metallic liquid interior, and for convection to take place within that liquid interior. Convection causes the vertical rising and falling motions while the rotation pulls and stretches the convection currents, disrupting the flow patterns. Throughout all of this, charged particles, or electric currents, are flowing through a metallic material and in the process creating (inducing) our planet’s magnetic field. Are there other planets with a magnetic field? Within the terrestrial planet group, there is some variation. Mercury, despite its slow rotation speed, does have a measurable magnetic field, while the planet Venus, large enough to have a molten core, does not have a magnetic field—probably because of its extremely slow rotation speed. Mars has the remnants of a magnetic field preserved in rocks, similar to what we find preserved in rocks on either side of the mid-Atlantic Ridge. However, Mars is small enough that its core may have cooled so much that it can no longer power convection, thereby losing its magnetic field.
The giant gas planets, as a group, differ in many ways from the rocky terrestrial planets; however, the process for generating planetary magnetic fields still applies. With regard to magnetic fields, we include our Sun and stars as among the things that have planetary magnetic fields because both stars and the gas planets meet the three requirements from the Earth model for creating a magnetic field. The gas planets’ respective magnetic fields are created from interiors containing electrically conductive liquid and rapid rotation periods. All four of the giant gas planets have stronger magnetic fields than Earth. For example, Jupiter and Saturn have a liquid metallic hydrogen interior that is mixed with convection currents distorted by the rapid rotation of the planet.
(Adapted from my January 2013 Scope on the Skies column)
Next up: Part 2 – Earth’s Magnetic Field
Magnetic effects in space—http://archive.org/details/skylab_magnetic_effects
Magnetic field calculators—www.ngdc.noaa.gov/geomag- web/#declination
The Magnetic Sun—http://solar.physics.montana.edu/ypop/Spotlight/Magnetic
Motion of the magnetic pole—http://image.gsfc.nasa.gov/poetry/activity/s8.htm
Planetary magnetic fields PowerPoint—http://education.gsfc.nasa.gov/nycri/units/pmarchase/3b-magnetic_field.ppt
Click here to go to the Qué tal in the Current Skies web site for more observing information for this month.