|MadSci Network: Astronomy|
Hi Chris, That's an excellent question to ask. Not all planets have a magnetosphere. To have a Magnetosphere we must have a magnetic field present for those things you mentioned such as the sun, asteroids, planets, or moons. It is thought that to posess a magnetic field you must have two essential ingredients. Those ingredients are magnetic material, such as iron, and currents circulating in that material. It must have enough of this magnetic material and currents to circulate within it. If a planet or other space body does not have enough of either of these, it will not have a magnetic field. For example, the two planets which do not have magnetic fields are Venus and Mars. Venus does not have a magnetic field due to the fact that its currents move very slowly and Mars does not have one because most of its iron is on the surface and is not molten (those moving currents...). Planets known to have a Magentosphere are Mercury, Earth, Jupiter, Saturn, Uranus, and Neptune. The sun has a Magnetosphere as well, again, due to the presence of the two essential ingredients: magnetic material and moving currents. As a side note, sunspots are the result of tremendous surface disruptions associated with intense magnetic fields in the sun. Asteroids, as you mentioned must posess those two ingredients to posess a Magnetosphere. The problems here with finding one for an asteroid are of course, is there enough magnetic material, if any, contained within it for the first requirement. Secondly, if the asteroid is frozen solid with little or no internal heat for current to form and circulate then we come up short on the second requirement. This second requirement is actually why the moon has little, if any, Magnetosphere, due to its iron core freezing solid over time. As a fun fact, the earth has the strongest Magnetosphere of all the rocky planets with a magnetic field which extends 36,000 miles out into space! This magnetosphere protects us from the solar wind and acts as a shield to its fast- moving particle emissions. I hope this answer helps you out. Thanks for the question... Tye Morancy "Mad Scientist"
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