Posted on January 16, 2019
Two South Poles?
Huh??
To understand what we mean by "two South Poles," let's think clearly what we mean by "pole."
You probably know that the Earth and other planets are mostly spherical balls that are captured by the Sun's gravity, so that they revolve around the Sun - but they are also spinning, or rotating, on their own axes.
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As you can see from this chart, the various planets don't have
identical tilts on their axes, and they don't even all spin the same
direction. |
In some ways, therefore, they are like a globe that can only spin on the axis running between mounts above and below the globe.
Some (not all) of the planets have magnetic fields. The Earth's magnetic field seems to be caused by the motion of the molten rock in the outer core; the field curves outward near the South Pole, turns "up" toward the equator and the Northern Hemisphere, and then turns down again near the North Pole, re-entering the Earth there.
Notice that I said "near" the poles. The magnetic poles are not exactly the same as the geographic poles, and the magnetic poles are always on the move. Currently, scientists tracking the magnetic field and its poles are puzzled about why the north magnetic pole is suddenly moving more quickly. Check out this breaking news here.
From 1908 until 1909, English explorer Ernest Shackleton led a small expedition that set a record for the southernmost point ever reached. During that "Great Southern Journey" Shackleton and his companions also became the first to climb Mount Erebus, the most active Antarctic volcano, and they also were the first people to reach (on this date in 1909) the Magnetic South Pole.
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On a later expedition, Shackleton's ship was trapped
in pack ice and was slowly crushed. The crew escaped,
but the men had to make their way back to civilization
on small lifeboats on a stormy ocean.
So Antarctic exploration was dangerous even for
experienced explorers! |
Actually, although Shackleton and company returned to England from the "Great Southern Journey" as heroes, they had failed to reach one of their goals. They had hoped to reach the geographic South Pole, which was even farther and more difficult than the magnetic pole - and the geographic pole was the one everyone seemed to care about.
Even though they didn't reach that goal, it turned out that Shackleton had turned back at the right time. The men were on half-rations on the trip back to the spot where they would catch their return ship, and they barely made it back in time to catch that ship! On the trek back, one of the explorers (Frank Wild) was doing so poorly that Shackleton gave Wild the only biscuit he, Shackleton, was allotted for the day, so that Wild would have two. Wild wrote in his diary, "All the money ever minted would not have bought that biscuit and the remembrance of that sacrifice will never leave me."
Of course she agreed!
In 1911, Roald Amundsen won the "race" to the geographic South Pole.
Other planets' magnetic fields:
Since Venus, Mars, and our Moon do not have magnetic fields, we think that their cores are cold and inactive.
Mercury only has a very, very slight magnetic field. From Mercury's size, scientists had assumed its core would be cold and inactive, but maybe the Sun being so nearby keeps the core a bit active?
Saturn's magnetic field is completely lined up with its geographical axis (the only planet in which this is the case). Jupiter has a magnetic field that is more normal, with its magnetic poles close but not exactly the same as its geographical poles. Scientists think that their magnetic fields are caused by layers of liquid metallic hydrogen rubbing against one another.
Uranus is entirely unique in its axial tilt. At some point in the history of the solar system, we think, another largish body must have slammed into it, leaving it to spin on an axis that is just about "flat" - in other words, its axis is pretty much on the same plane on which it moves around the Sun. So it seems to be spinning "lying down." It's been called "the tipped-over planet."
But Uranus's magnetic field has a more normal orientation than its rotational axis, which means that its Magnetic North Pole is about 60 degrees away from its Geographical North Pole (and of course the same with the South).
Neptune's magnetic field, like Uranus's, is way off-kilter from its axial tilt. In both of these planets, the magnetic field does not go through the center of the planet, but rather tips off to one side. Scientists think that the fields are caused by layers of water.
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