Terrestrial Planet Magnetic Fields
Mercury, Venus, the Earth and Mars are all “terrestrial” planets so then why do two of them have magnetic fields and two do not?
To answer this question its best to look at the characteristics of the current magnetic fields of Earth/Mercury and the remnants of fields on Venus/Mars.
Beginning with Earth and Mercury; these two planet’s magnetic fields are present and substantial. They are both generated by a dynamo effect(circulation of the planet’s iron-rich liquid core), and have similar strengths due to differences in the planet’s sizes/orbital speeds. This effect aligns the magnetic field lines with the poles which produces the bar magnetic like structure of these fields.
As for Venus and Mars, both of these bodies’ magnetic fields are so small they are considered nonexistent. While Venus has a similar iron core as Earth/Mercury; its slow rotational speed compared to its size stops the dynamo effect from creating a magnetic field. There is however an induced field on Venus due to the solar winds interaction with charged atoms in the planet’s Ionosphere — Shown Below.
As for Mars, the remnants of a pre-existing magnetic field can be found on the planet from 4 billions years ago. The Martian Magnetosphere was lost due to asteroid strikes, and intense solar wind interaction with the ionosphere; these phenomena stripped away the atoms that made up the magnetic field of Mars.
The observations above show similar characteristics for the various planetary magnetic fields. Some scientists have theorized that the differences in these fields are due to age cycles. Starting with Venus holding onto a young field before its dynamo effect phase. As it ages the core should solidify, thus speeding up the planetary rotation and starting the dynamo phase. Then onto Earth as mid dynamo and Mercury as late-mid dynamo; these planets have semi liquid cores that are currently rotating in order to produce the planetary magnetic field. Lastly we have Mars as a deceased Magnetic field long after its dynamo phase; with the majority of its magnetic field already torn from the planet.
To come to these conclusions we have used various probes such as the Solar Orbiter (Studied Venusian Magnetic field, came to the conclusion that Venus currently has an induced field) and the Mars Global Surveyor(Observed magnetic field leftovers on Martian crust and the absence of global fields).
Sources:
Ian. (2021, January 4). Earth facts: Surface, atmosphere, satellites, history & definition. The Nine Planets. Retrieved September 12, 2022, from https://nineplanets.org/earth/
Ian. (2021, January 4). Mars facts: Temperature, surface, information, history & definition. The Nine Planets. Retrieved September 12, 2022, from https://nineplanets.org/mars/
Ian. (2021, January 4). Mercury facts: Information, history, location, Size & Definition. The Nine Planets. Retrieved September 12, 2022, from https://nineplanets.org/mercury/
Ian. (2021, January 4). Venus facts: Surface, atmosphere, moons, history & definition. The Nine Planets. Retrieved September 12, 2022, from https://nineplanets.org/venus/
NASA. (n.d.). Solar mission reveals new details about Venus’ unusual magnetic field. JHUAPL. Retrieved September 12, 2022, from https://www.jhuapl.edu/NewsStory/210603-Solar-Orbiter-unveils-new-details-Venus-magnetosphere
NASA. (n.d.). Mars Global Surveyor Magnetic Field Investigation. NASA. Retrieved September 12, 2022, from https://mgs-mager.gsfc.nasa.gov/
Russell, C. T. (1993). Magnetic fields of the terrestrial planets. NASA/ADS. Retrieved September 12, 2022, from https://ui.adsabs.harvard.edu/abs/1993JGR....9818681R/abstract
Image Sources:
<a href=”https://www.freepik.com/free-vector/earth-s-magnetic-field-poster_26348837.htm#query=magnetic%20field%20earth&position=2&from_view=keyword">Image by brgfx</a> on Freepik
