> A piece of extraplanetary mass being brought to Earth only changes the planet's orbit insofar as its orbit on entry to Earth mismatches that of rest of the planet.
No, the Earth’s orbit would also be affected over time by the altered gravitational relationship with other bodies as a result of its increased mass.
Good point. That's a second-order effect I had not considered. However, orbital mechanics being what it is, that would not result in the Earth "sinking into the sun," which is the claim I was responding to.
J6 floated an idea like that above, but a less drastic outcome where the earth takes on some very small fraction of one percent of additional mass, and the shape of its orbit merely changes a tiny bit, is also a possibility.
No, the Earth’s orbit would also be affected over time by the altered gravitational relationship with other bodies as a result of its increased mass.