New Research Suggests the Moon Causes More Than Just Ocean Tides

April 6, 2016 | Joanne Kennell

Moon above Earth's surface
Photo credit: Beth Scupham/flickr (CC BY 2.0)

It may also protect life on Earth.

Earth’s magnetic field protects us and everything else on the planet from the harmful charged particles, mainly protons and electrons, and radiation emitted from the sun. According to the classical dynamo model, this shield is produced by the geodynamo, which is the rapid motion of enormous quantities of liquid iron alloy in Earth’s outer core.

For Earth to have maintained this magnetic field until the present day, the classical model requires Earth’s core to have cooled by 3,000 degrees Celsius (5,430 degrees Fahrenheit) over the past 4.3 billion years. However, a team of researchers from National Center for Scientific Research (CNRS) and Université Blaise Pascal suggest that its temperature has fallen by only 300 degrees Celsius (570 degrees Fahrenheit).

SEE ALSO: Strange “Weather” Observed Near the Center of the Earth

So what is keeping the geodynamo active? The moon. It is now thought that the moon has compensated for this difference to keep the geodynamo working. The study was published on March 30 in the journal Earth and Planetary Science Letters.

The classical dynamo model of the formation of Earth’s magnetic field currently involves a major paradox: For the geodynamo to work, Earth would have had to be totally molten four billion years ago, and its core would have had to slowly cool from around 6,800 degrees Celsius (12,270 degrees Fahrenheit) then to 3,800 degrees Celsius (6,870 degrees Fahrenheit) today.

However, recent modeling of the evolution of the internal temperature of the planet, coupled with geochemical studies of the composition of the oldest carbonatites and basalts, do not show this cooling.

So the researchers proposed another source of energy.

Since Earth has a slightly flattened shape, rotates on an inclined axis that wobbles around the poles, and has a mantle that deforms elastically due to tidal effects caused by the moon, the researchers were able to show that this effect could continuously stimulate the motion of the liquid iron alloy making up the outer core, generating Earth’s magnetic field.

Earth constantly receives 3,700 billion watts of power through the transfer of the gravitational and rotational energy of the Earth-Moon-Sun system, and it is believed that just over 1,000 billion watts is required to bring about the motion in the outer core. According to the press release, this energy, together with the moon, is enough to generate Earth’s magnetic field, resolving the major paradox in the classical model.

Diagram of the moon's effect on Earth's geodynamo

Photo credit: Julien Monteux and Denis Andrault

Since Earth’s rotation around its axis, the direction of its axis, and the moon’s orbit and not perfectly regular, their combined effect on motion in the core is unstable, which can cause fluctuations in the geodynamo.

The effect of gravitational forces on a planet’s magnetic field is not a new concept. This effect has already been well documented for two of Jupiter’s moons, Io and Europa, and for a number of exoplanets. Now, this new model shows that the moon’s effect on Earth may go far beyond just causing the tides.

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