Is this shattered planet scenario possible?

Question

Suppose there's a planet that has similar characteristics of Earth and can provide life, suddenly shatters in many pieces and scattered over the system. A small but very dense object is attached into the bottom of one planet fragment that has enough mass to provide enough gravity for other side of the planet fragment to have a Earth-like gravity. Throughout all years of orbiting, the fragment builds enough atmosphere (perhaps from terraforming by humans or sucking atmosphere from other planet?) to make it suitable for humans or other living organisms to live. The fragment will have some water carried from old planet where it came from. After the fragment's transformation is complete, it becomes a home for humans. Is it possible?

If you can, explain how different the experience the humans will have when they live on that fragment instead of Earth. The actual borders in the horizon? Different gravity?

Answer 1

Atmospheric escape

The atmosphere and water would be sucked into to the gravity well. You'd end up with no air on top of the platter, and the entire atmosphere in a tight sphere around the dense object.

To prevent this you could use walls around the edge. They would have to be high enough to prevent the air from pouring over the top.

Humans looking out would see right to the edge, and then a huge, impossible wall.

Gravity gradient

A small dense object (like a chunk of neutronium, or a black hole for example) will also generate a significant gravity gradient which would likely be noticeable to anyone living on the surface.

Gravity would be much stronger as you moved closer to the object, possibly lethally strong at the pole, depending on the thickness of the platter.

Gravity would always pull towards the object. Humans near the rim would have thinner air. Walking towards the edge would be like walking uphill. You would weigh less at the rim than at the pole, and would be able to jump higher.

Tendency to a sphere

Objects in space with sufficient mass will tend to become spherical. Rock is brittle. If it becomes unstable it will crack. You will need to account for this.

A note on stability

Ordinary matter would not be dense enough to have sufficient mass to replace the mass of the planet. You would be looking at some type of exotic matter, such as a singularity or neutron star.

At sub-planetary mass, neither of these would be stable, so you'd need some kind of technology to stop them evaporating in a wave of killer radiation. You'd also need some way to prevent the platter from collapsing into the gravity well.

The alternative would be to use some type of alien gravity generator.

A further note on solar radiation shielding

The magnetic core of the earth shields us from high energy solar rays which can strip away a planetary atmosphere. You will need some kind of solar shielding for long term survival. Perhaps your chunk generates a sufficiently powerful magnetic field.

Answer 2

Fragments don't remember where they came from.

A fragment of the original planet doesn't remember that it was once part of a planet.

Let's say you take a section out of a planet, like the part removed from this image. The fragment has one point that used to be at the bottom (in the core of the planet) and one surface that used to be the surface of the planet.

Now it's all by itself, an irregularly-shaped planet of its own. "Down" doesn't mean "towards the old center", it means "towards the center of this fragment".

Let's say there's a city in the middle of the old surface on this fragment. Buildings in that city will still be vertically oriented, because "old down" and "new down" are in the same direction. But a city out near the edge of the old surface will find itself on a steep slope, with buildings falling over and everything tumbling down the slope.

Moving the center of gravity makes it worse.

So you've found some dense material to put on one of the peaks of your new planet. (Remember, the point that used to be in the middle of the old planet is now the top of a peak of the new one.) This has only made things worse.

Now you have a planet that's like a house balancing on the ridge of its roof. Rock isn't that strong. Most of the planet will fall down and land on the core.

Answer 3

Well, it's really, really, really, really unlikely, but I suppose there's a mechanism for it (albeit unlikely). I think you get the picture.

Take your planet. Now take a very dense neutron star. Propel said neutron star through space at a high speed, and have it hit the planet. If the speed is high enough, the collision will most likely break apart the planet. Neutron stars are very dense and hard to break apart; I would think that this neutron star could attract a piece of the planet, imparting it with a strong gravitational field.

After that, the scenario enters its "unlikely" phase. Neutron stars aren't conducive to life. For one thing, they're composed of neutron degenerate matter, and are very dense, imparting an enormous gravitational field. This is going to be very bad for any life that finds its way onto this planet-star-fragment-thing. Second, the neutron star may be a pulsar, in which case there's going to be a lot of radiation, or a magnetar, in which case strong magnetic fields may make any life forms in the nearby area very miserable.

Because of all the neutron degenerate matter, I think it's really unlikely that any life will have more than a whelk's chance in a supernova of developing here.