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The dipole magnetic field created by this permanent moment has a strength of 719 ± 2 nT at Ganymede's equator, [23] which should be compared with the Jovian magnetic field at the distance of Ganymede—about 120 nT. [95] The equatorial field of Ganymede is directed against the Jovian field, meaning reconnection is possible. The intrinsic field ...
To support an Earth-like atmosphere for about 4.6 billion years (Earth's current age), a moon with a Mars-like density is estimated to need at least 7% of Earth's mass. [20] One way to decrease loss from sputtering is for the moon to have a strong magnetic field of its own that can deflect stellar wind and radiation belts.
Ganymede is the largest natural satellite in the Solar System at 5262.4 kilometers in diameter, which makes it larger than the planet Mercury – although only at about half of its mass [42] since Ganymede is an icy world.
Planetary-mass moons larger than Pluto, the largest Solar dwarf planet. A planetary-mass moon is a planetary-mass object that is also a natural satellite. They are large and ellipsoidal (sometimes spherical) in shape. Moons may be in hydrostatic equilibrium due to tidal or radiogenic heating, in some cases forming a subsurface ocean.
The magnetic moment of an object is an intrinsic property and does not change with distance, and thus can be used to measure "how strong" a magnet is. For example, Earth possesses an enormous magnetic moment, however we are very distant from its center and experience only a tiny magnetic flux density (measured in tesla ) on its surface.
Ganymede also shows a weak magnetosphere, taken as evidence of a subsurface layer of salt water, while the volume around Rhea shows symmetrical effects which may be rings or a magnetic phenomenon. Of these, Earth's magnetosphere is by far the most accessible, including from the surface.
The magnetic field is generated by a feedback loop: current loops generate magnetic fields (Ampère's circuital law); a changing magnetic field generates an electric field (Faraday's law); and the electric and magnetic fields exert a force on the charges that are flowing in currents (the Lorentz force). [58]
The magnetic field of larger magnets can be obtained by modeling them as a collection of a large number of small magnets called dipoles each having their own m. The magnetic field produced by the magnet then is the net magnetic field of these dipoles; any net force on the magnet is a result of adding up the forces on the individual dipoles.