Would the Earth's core start expanding and release its heat? Would some of the metal(iron-nickel) evaporate due to boiling point temperatures and no pressure anymore? Would it affect the orbits of nearby planets or not. The Earth has some effect on some of the nearby inner planets like Venus and Mars. So what would this core do to those nearby planets? What if the core was placed near Mars?
Ignoring how it would affect Earth's gravitational pull and the tides, I could see two things happening:
1) The Earth would lose its molten core, and this would have devastating consequences on the tectonic plates, meaning no more volcanoes, geysers or earthquakes. While the molten core is cooling over time and will eventually turn into a non-geological planet like Mars, this will not happen for billions of years.
2) No more magnetic fields to protect the Earth from solar radiation.
Earth would collapse without its core that holds up the outer parts. Everything on the surface of Earth would fall hundreds of miles at least. So Earth would face total disaster even if the core was magically teleported into space instead of being ripped out through part of the crust.
As for the gravitational effect of the core on other planets, that depends on the new orbit of the core around the Sun - if the core remains in the solar system instead of going someplace else.
Every particle of matter in the universe, no matter how small, has some gravitational effect on every other particle of matter in the universe, no matter how far apart they are.
But for a planet orbiting the Sun like Venus or Mercury, the gravity of the Sun would be stronger than all the other gravitation forces on it combined. The orbit of a planet is primarily determined by the gravitational effects of the Sun, and the gravitational forces of other planets cause only minor perturbations in the orbit of the planet.
The Earth's core would have less mass than the entire Earth, and thus less powerful gravity.
The escape velocity from Earth, a measure of the strength of Earth's gravitational attraction, is 11.186 kilometers per second at the surface of the Earth. At Earth's distance from the Sun,the Sun's escape velocity is 42.1 kilometers per second.
Anyway, there are computer programs where you could choose a mass for the Earth's core and a trajectory for the Earth's core and run calculations to see how the Earth's core's gravity affects the orbits of other planets.
If so the planet would lose nearly 1/3 of it's mass. it's gravity would decline to such a degree it's atmosphere would probably dissapate. The orbital stability would decline either freezing the planet if it wobbled too far from the sub or burn if it got too close. It's magnetic field would dissipate and the planet would be bathed in radiation equivalent to A millions of nuclear weapons.
The Earth's core was a planetoid of it's own. It lends to the theory of how the moon formed. During the Earth's early history; it's molten state, a small rogue planetary body scientists dubbed "Theia" slammed into the Earth at an oblique angle. This had several side effects.
- Gave the Earth it's signature axial tilt.
- Probably added several hundred quintillion tons to the Earth's core mass, thus permitting it's continous thermal operation to this day.
Would the Earth's core start expanding and release its heat?
Yes. Not much, but it would expand a little bit with the weight of the mantle and crust taken off of it. And without all that insulation, it would indeed start losing heat far more rapidly. It would be glowing white.
Would some of the metal(iron-nickel) evaporate due to boiling point temperatures and no pressure anymore?
Yes. The temperature of the outer core is around 5000°C. The boiling point of iron is 2862°C. So yeah, a large amount of nickel and iron would immediately evaporate to form a metal gas atmosphere, so of which would end up lost to space. (Not very much, though. Iron and nickel are heavy, and the atmosphere would be cooling rapidly.)
After a while, the atmosphere would recondense and you'd have a liquid metal ocean exposed to near vacuum. Since iron and nickel sink when they freeze, that liquid surface will remain until the entire body has frozen through from the inside out. You will end up with a new atmosphere consisting of volatiles outgassed from the liquid metal as it circulates in convection cells--most likely a variety of simple carbon, sulfur, and oxygen compounds, along with nickel and iron carbonyls (which may end up forming lakes once the surface has fully cooled).
Would it affect the orbits of nearby planets or not.
Strictly speaking, yes. Enough to notice? No.
So what would this core do to those nearby planets?
If it remains in Earth's current orbit, nothing significant.
What if the core was placed near Mars?
How near? The core is about 1/3 of the Earth's total mass, and Mars is about 1/10th of Earth's mass... so the core on its own is still a planet more than three times more massive than Mars. It could form a double planet, or Mars could end up as a moon of the new iron world, depending on how far apart they end up. If they are not gravitationally bound, but are nevertheless in close orbits, the best scenario would be to end up in horseshoe co-orbital arrangement like Saturn's moon Janus and Epimetheus, or else in an eccentricity-exchanging co-orbital arrangement. The latter is likely the destabilize the rest of the inner solar system unless arranged very carefully; and in any other scenario, they end up flinging each other around largely unpredictably, which definitely destabilizes the rest of the inner solar system.