Mercury May Have Molten Hot Magma at its Core

mattatwork writes "According to ScienceDaily, NASA has come to the conclusion that the planet Mercury may have a molten core after all, based on high-precision planetary radar readings. You may (or may not) remember the Mariner 10 probe making 3 passes by Mercury between March 29th, 1974, September 21st 1974 and March 16, 1975."

Re:liquid core but little magnetism

[largesnike]

You know that Mercury is in tidal lock with the sun? so it only rotates (I think) once every 87 days or so. This slow rotation rate may explain the weakness of the field. Perhaps its high orbital eccentricity (0.2) and proximity to the sun, and the resultant tidal wrenching would explain the liquid mantle?

Re:liquid core but little magnetism

[wizardforce]

mercury has a 3:2 resonance orbit:rotation which could very well explain a very slow fluid core rotation and thus the weak field since eventually the core will sync with the rotation of the outside of the planet.

Re:liquid core but little magnetism

[dryeo]

You're reading it wrong. It is Mercury has quite a strong field compared to Mars or Venus.
Heres a short blurb which mentions that Mercury probably has a molten core written in 2003, http://www.windows.ucar.edu/tour/link=/mercury/Mag netosphere/magsphere_overview.html&edu=high [ucar.edu]

Re:Good news for us I guess...

[MillionthMonkey]

Tidal forces should have little effect on Mercury since it's already tidally locked. The same side always faces the sun. The locking occurred because Mercury was once rotating, and tidal forces mostly affect rotating planets. They stretch the planet out like an egg pointing at the sun and Mercury is probably a little egg-shaped.

When the planet is rotating, the tidal force axis swings around all longitudes during the day and it's as if the sun were rolling the planet between its fingers. It gets squashed and stretched every day. Eventually the interior of the planet absorbs all of the rotational energy as heat through this mechanism. The same thing is happening on Jupiter's innermost moon Io, which is not yet tidally locked. Io is covered with volcanoes because its rotational energy is still being converted into internal energy by tidal forces from Jupiter, and there is no hydrosphere to absorb the energy.

If there are no oceans then the solar torque gets applied directly to rock with no cushion in the way. If the planet has oceans, they absorb almost all of it since they give more easily than rock and the sun will apply its torque to the planet via the water, so that the energy loss mechanism occurs at the surface. Either waves crash onto beaches, or if there are no continents, a standing wave circles the planet every day and heats up the water a little bit, so the heat mostly radiates away.

I don't know offhand whether Mercury got its molten interior from its ancient rotational energy or just from radioactivity.

Re:Good news for us I guess...

[Josh Booth]

Don't listen to this guy. Mercury is not tidally locked with the sun, but rotates very slowly at about 3 rotations for every 2 revolutions around the sun. And even more, an ocean does not act as any sort of a buffer against gravitational forces from the sun. There's just not a significant enough amount of water even on Earth to do so.

Corrected Wikipedia link

[sho222]

The corrected link to the Wikipedia article: the Mariner 10 probe [wikipedia.org]

Re:Good news for us I guess...

[MillionthMonkey]

Mercury is not tidally locked with the sun, but rotates very slowly at about 3 rotations for every 2 revolutions around the sun.

I forgot my Mercury trivia; they used to think it was locked [nature.com] before they found the 3/2 resonance. Since the resonance is stable, rotational energy is not being affected anymore. But then that means tidal forces are still heating Mercury over a 1400 hour cycle. The heat loss from friction is probably coming out of the orbital energy making the orbit unstable.

And even more, an ocean does not act as any sort of a buffer against gravitational forces from the sun. There's just not a significant enough amount of water even on Earth to do so.

OK, so the water transmits zero torque until there's how much of it then?

Most of the torque being applied to slow the earth down is transmitted at two hydrosphere/lithosphere boundaries: the one between the inner and outer core, and the one between the crust and the oceans. This is because unlike solid rock, fluids are free to slosh around horizontally. The outer core has more mass but the moment arm and surface area are both bigger for the oceanic boundary.