# How much does the gravitational and magnetic fields of a planet effect the chemistry in it?

It is known that the earth has a magnetic field and gravitational field around it, I wish to ask to what degree is the chemistry on the planet is influenced by these fields? How would the chemical reactions seen everyday on earth be different if the strengths of these fields were different?

• Magnetic fields affect chemistry, but not too much. Planets have typically a very weak magnetic field. Gravitational field does not affect it all. Indirectly it has effect, because attraction of the atmosphere makes its pressure. Pressure greatly affects chemistry (no pressure -> no liquids). – peterh Nov 18 '20 at 19:27
• That's an ...interesting view point @John – Buraian Dec 14 '20 at 8:51
• Without gravity we wouldn't have a planet to speak of. So in the sense, wholly. Once the planet has formed it does so indirectly through its geology and atmosphere. – Mozibur Ullah Dec 16 '20 at 7:36

How would the chemical reactions seen everyday on earth be different if the strengths of these fields were different?

Depends. If you're just talking about higher $$g$$ (i.e $$g>9.8\ \rm{m/s}^2$$) but the same atmospheric pressure, than not much will change on the surface of the earth.

If the atmospheric pressure changes, there could be changes to chemical reactions. There are several factors controlling chemical reactions. One being, obviously, the identity of the reactants. The other one is temperature. But also important is pressure. Because pressure on the surface of the earth is always 1 atm, no one really thinks or cares about pressure. No one, until it changes. That said, for any substantial change in chemistry, pressure has to change quite a lot, which would make earth uninhabitable for humans, so there would be no one to see that chemistry changed.

• Worth noting that without a magnetic field the earth might have far less of an atmosphere. – John Dec 14 '20 at 14:44

In the case of gravity, it depends on where you look, literally. On the surface of a typical planet gravitational fields have hardly any effect on chemistry. But if the planet is big and massive enough so that the pressure built up by gravity throughout the mass pushes it into a rounded shape, chances are that pressure is also affecting the chemistry of its rocks.

In the case of Earth, this shows up as the formation of silicate phases in the mantle that would not appear naturally on the surface, chief among them the silicate perovskites in which each silicon atom is bonded to six oxygen atoms instead of four. The illustration below shows how the silicate rocks change from the from olivine (which has the "normal" silicate bonding) into perovskite and other phases where the silicon has become bonded to the additional oxygen neighbors.

Silicates are not the only phases affected by the gravitationally generated pressure inside Earth. Carbon is affected too, leading to the (natural) formation of diamonds -- which often have inclusions of those high-pressure silicate phases trapped inside, thus providing verification of these gravity/pressure-induced phases.

The atomic structure of each of the elements is the fundamental driver of chemical reactions.

A carbon or oxygen atom on Earth is the same as a carbon or oxygen atom anywhere in the universe. A carbon atom has six protons in its nucleus and for electrical balance it has six electrons orbiting the nucleus. Isotopic differences are simply the inclusion of additional neutrons, which have no electrical charge. They add weight to the atom and can make the atom unstable, which results in radioactive decay and transformation into another element.

The electrons are arranged in defined energy levels or orbitals around the atomic nucleus. Each level can only accommodate a specific number of electrons. The number of electrons in the outermost shell and how many electrons the shell could accommodate determines how each element reacts chemically. This is defined as the valency of an element. This is what drives the potential for chemical reactions.

The strength of gravity and planetary magnetic fields is far weaker than the forces behind chemical bonding.

• Great answer, but I think you can add more to the Macro part. Is it really true that "Planets with larger gravity have significant amounts of heavy elements"? Can that be supported with a link? Mercury is pretty small, does it have proportionately less of those than Venus, Earth or Mars? (maybe it does, I don't know). – uhoh Nov 19 '20 at 0:25
• @uhoh: When I was writing the answer my thoughts were comparing Earth & Ceres, which a gravity of 0.029g, which is very low. Comparing average densities of the two 5.514 (Earth) to 2.162 (Ceres), Ceres appears to have a lot more lighter elements on its surface & in its mantle (hydrated silicates) & no metallic core. – Fred Nov 19 '20 at 0:48
• ya but you say "planets" so I thought... planets. Did Ceres form by itself, or at some point was its mass broken off from the outside part of something else where the heavier elements had already sunk to the middle? – uhoh Nov 19 '20 at 0:51
• @uhoh: There's also Ganymede & Titan, both smaller than Mars but larger than Mercury. Both have low densities & low values of gravity. Titan at least, is thought to have formed "through co-accretion, a similar process to that believed to have formed the planets in the Solar System." – Fred Nov 19 '20 at 1:07