The US Mars space probe is supposed to go witching and digging for water at the South Pole of that planet in December.
My ignorance of astronomy/geo-geometry leads me to ask the question: How is it determined which pole of a rotating body, at least in the solar system, is to be labeled ‘North’/‘South’? Is this another application of the Right-Hand Rule, argued at length here previously? Or does this determination relate to the orientation of the given body with respect to others, such as in the case of a planet in the more-or-less plane of all the planets?
Given that Santa Clauses are prone to hang out at North Poles, and that they probably require a certain amount of water, wouldn’t it be most probable that there be water at Mars’ North Pole?
Your speculation was correct. North/south on distant planets is based on north/south here on earth. Wrap your right hand around the planet at the equator, with your fingers pointing in the direction of rotation. Your thumb points north.
In fact, for most planets in the solar system their north poles do point more or less north as measured here on earth. Their orbits are (nearly) co-planar with earth’s and their orientation with their orbits doesn’t vary widely. Notable exceptions are Uranus, which is more or less sideways to the rest of the planets, and Pluto, which has a notably non-co-planar orbit.
“non sunt multiplicanda entia praeter necessitatem”
For the record, there are actually
(let’s see if i get this italics thing to work * two * competing definitions of “north” in planetary science:
The right hand rule definition, favored by almost everyone, which is geophysical in origin, I think. In this scheme, all planets rotate in a prograde direction.
The north pole of a planet is the one “above” the plane of the ecliptic. This is astronomical in origin. In this scheme, planets can have retrograde rotation, and Venus (and Uranus? Pluto? both?) and roughly half the asteroids do so. I think officially the IAU still prefers this definition.
I always assumed that the poles on the planets were determined by magnetic north. Are there any instances where magnetic north is opposite of “astronomical” (for want of a better term) north in the solar system?
Well, I know the Right-Hand Rule relates an electric-current-produced magnetic north pole to the conventional direction of current, but how is a permanent ferromagnetic magnet’s poles – the case of astronomical bodies, I presume – determined as to north and south?
The north end of a magnet is simply the side of a magnet that will point towards magnetic north when free to do so, as in a compass.
Somewhat ironically, that would mean that if we treat the Earth as a magnet, the “magnetic north pole” of the Earth would be the south end of the magnet.
Defining poles magnetically doesn’t work because periodically the polarity of the earth’s field swaps sign-- one of the clinchers for many scientists as far as plate tectonics was seeing the evidence for field reversals on the ocean floor, though that’s another story.
Furthermore, IIRC, there are at least two planets (Uranus and Neptune) whose magnetic axis does not intersect the spin axis (if that makes any sense)-- the line connecting the north and south magnetic poles does not go through the center of the planet!
I freely admit, though, that magnetohydrodynamics is not my strong suit.
Well, again, magnetohydrodynamics isn’t my strong suit, but…
If I remember right, it’s because in Uranus and Neptune, the magnetic fields are generated not in a metallic core, but in a conducting shell farther out from the center of the planet.
In Earth, the liquid part of the core generates the field. In Jupiter and Saturn (shameless guessing begins the pressures are high enough in their centers for metallic hydrogen to form, and again this metallic liquid generates the fields. (end of shameless guessing)
It seems that the planets closer to Ole Sol keep a fairly vertical axis ( even Venus, which is flipped ALMOST 180 degrees north v.s. south ).
SO… this is one for my Dad, or Unc Cecil ( Dad was a science writer…). Does proximity to a star predicate the degree to which a planet will have a “vertical” polar alignment? If I am …say…third rock from the sun, opposed to 18th, will I be any more or less straight up and down in terms of my polarity?
And, how does this relate do my magnetic personality??
Typer
Wouldn’t it have been strange had the Earth’s magnetic pole been in flux when the use of the compass had first been introduced.
All of the sudden, compasses would be pointing the opposite direction. Mankind might have given up on the magnetic compass as an unreliable navigation aid. Exploration of the globe may have been slowed by decades or even centuries.
Also, I’m led to believe that Venus’s rotation is in the opposite direction of the other planets. If I’m correct about that, then Venus is also a planet whose North and South would be the opposite of Earth’s if we measured that by the planet’s own rotation rather than by using the plane of Earth’s orbit.
“Sherlock Holmes once said that once you have eliminated the
impossible, whatever remains, however improbable, must be
the answer. I, however, do not like to eliminate the impossible.
The impossible often has a kind of integrity to it that the merely improbable lacks.”
– Douglas Adams’s Dirk Gently, Holistic Detective
* two * competing definitions of “north” in planetary science: