Re: Do magnets work in outer space, particularly exactly between two planets?

Good question! I will give a quick summary of magnetic fields in our solar system; for more information, see the references below. A lot of astronomers and planetary scientists work on this field, so there's a lot of information out there.

A magnetic field is usually described with "magnetic field lines." Every point in space is on one of these lines, and the direction of the line tells you in which way a compass will point. The important thing about magnetic field lines is that they are always closed. That is, they don't end anywhere - they wrap around on themselves, like a circle. In a bar magnet, they come out the north pole of the magnet and then go back in through the south pole. The earth has its own magnetic field lines, which pass from the north pole through the center of the earth and out the south pole, continue away from the earth's surface to the edge of the magnetosphere, then wrap back around to the north pole. The earth is basically a giant bar magnet, except that the our north pole is actually a magnetic south pole! On the earth's surface, the field lines point toward the south pole - compasses always point north, because they point along the direction opposite to the field lines.

In space, then, magnets won't work any differently. They will still point along field lines. The question is what the field itself is doing. The magnetic field around the earth is known as the "magnetosphere." Throughout the magnetosphere, as on the earth's surface, the magnetic field lines bend from the north pole to the south pole. So in a sense, a compass will "turn around" if you orbit the earth, but by our perspective it always points north. You can see a picture of the magnetosphere here. The earth's magnetosphere is about 40 times as large as the earth itself.

The sun has its own magnetic fields, which are considerably stronger than the earth's. (Magnetic fields on the sun cause sunspots, solar flares, and other energetic events like coronal mass ejections.) The solar wind, a stream of electrically charged particles flying away from the sun, drags the sun's magnetic field lines away from the sun. At the edge of the magnetosphere, the field lines in the solar wind hit the earth's own field lines. On the side of the earth closest to the sun, the solar wind pushes the earth's magnetosphere closer to the surface; on the far side, the earth's magnetosphere is protected from the solar wind, so it streams out behind the earth. You can see an excellent picture of this process here. At the interface (which is about forty earth radii above the earth's surface), the field lines from the earth and solar wind merge into longer lines. The interplanetary magnetic field carried along with the solar wind is much weaker than the earth's, but it keeps the earth's magnetosphere contained because of the pressure from the energetic solar wind that accompanies it.

The point is that outside of the earth's magnetosphere, the sun's magnetic field dominates, and this is completely independent of the earth. The same sort of process occurs around every planet with a reasonably strong magnetosphere (Mercury, Jupiter, Saturn, Uranus, and Neptune): the field lines from the solar wind bang into the planet's magnetosphere and connect to it where they strike. Because the magnetosphere of each planet is relatively small compared to the distance between planets, the magnetic field in the solar wind determines the field direction throughout most of the solar system (including in between two planets). The interplanetary magnetic field generally streams out from the sun toward the planets, but the rotation of the sun bends the field lines, making the general shape of the interplanetary magnetic field into a spiral. However, due to activity on the sun, there are regions even larger than the earth with unusual field structures. So the direction a compass would point can change with time!

Two good websites on these issues are http://www.oulu.fi/~spaceweb/textbook/solarwind.html and http://www-istp.gsfc.nasa.gov/Education/Intro.html. Hopefully they will have all the information you are looking for! Good luck!