Astronomy and Astrophysics – Astronomy
Scientific paper
Jan 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21542307d&link_type=abstract
American Astronomical Society, AAS Meeting #215, #423.07; Bulletin of the American Astronomical Society, Vol. 42, p.327
Astronomy and Astrophysics
Astronomy
Scientific paper
We present a model to estimate the maximum self-sustained magnetic moment of a terrestrial dynamo given only the total mass and core-mass fraction of the planet. Assuming the magnetic field is self-sustained by a convectively driven dynamo we estimate the magnetic moment using a dynamo scaling law, which relies on properties of the planetary interior such as the super-adiabatic heat flux at the core-mantle boundary and size of the dynamo region. To estimate these interior properties we model the internal structure of the planet using a sub-solidus, mobile lid convection profile for the mantle and a thermal convection profile for the core. We present models for 1-10 Earth-masses and a range of core-mass fractions.
For an Earth-mass planet with a core-mass of 32.5% of the total mass (same as the Earth) we calculate an optimal heat flux of 52 TW, from which we infer an upper bound magnetic moment of 181 ZAm2 (Z=1021). For an Iron-rich Earth-mass planet with a core-mass fraction of 65% (similar to Mercury) we calculate an optimal heat flux of 24 TW, but with a larger core size we infer a larger magnetic moment of 260 ZAm2. For more massive 10 ME planets the magnetic moment could be as much as 10 times larger than the estimates given here.
Several techniques have been proposed to detect and measure the magnetic fields of extrasolar planets and the presence of a magnetic field has been claimed in about 10. Strong magnetic fields can be used to estimate the planetary rotation rate, may be easier to detect than terrestrial atmospheres, and act as a barrier to stellar radiation which is often invoked as a requirement for habitability.
Driscoll Peter E.
Olson Peter
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