Can anyone explain to me how the Earth remains in orbit?

Question

The mass of the Earth and the Sun are obviously changing continuously as the Sun gives off energy and we burn natural resourses from within the Earth that cannot be regenerated or replaced. It takes calculations carried out to an extreem degree to put the shuttle in orbit for just a couple weeks. If the Earth is being acted upon by external forces (asteroid impacts and the like), shouldn't the Earth have moved out of its orbit a couple million years ago?

Answer 1

1. The changing mass of the earth has virtually no effect on its orbit. This is sort of the same principle that says that two objects of different mass will both fall at the same speed. If the earth's mass were suddenly cut in half, its acceleration around the sun (i.e. its orbit) would be virtually unchanged (it would make a miniscule difference in how much the sun wobbled; but that would be about all.)

2. Burning natural resources does not change the mass of the earth. The products of combustion have the same mass as the original, and that stays in the atmosphere and/or recombines with the surface material. Almost none of it escapes from the earth's gravitational pull.

3. Asteroid impacts, etc. do change the earth's orbit very slightly; but this is because of the momentum of the impactors; not because of the mass they add to the earth. Over very, very long periods, the combined effects of the impacts would act like a "friction" that would rob the earth of kinetic energy and gradually send it spiraling into the sun. But at the current rate, the sun will turn into a red giant long, long before that happens.

4. The mass of the sun is decreasing due to nuclear fusion which converts its mass directly into energy (this is much different from the ordinary combustion which occurs on earth). The sun's mass is decreasing at a rate of 4.2 billion kg per second. This sounds like a lot, but it is a very miniscule amount compared to the sun's total mass. At that rate, after a MILLION YEARS the sun will have lost about 0.0000066 percent of its mass. This is enough to make the earth's orbital radius increase (after a million years) by about 23,000 miles -- which is nothing compared to the 3 million-mile variation that it already experiences between January and June every year.

Answer 2

The Earth and Sun are losing VERY little mass as compared to their size. Definitely not nearly enough to make a difference in the orbits. The Earth is also not gaining all that much from asteroids as compared to the mass of the Earth. Without a very large collision, the Earth will stay in it's orbit for another 5 billion or so years (and at that point, nothing will matter to the Earth as the Sun engulfs it).

Answer 3

Obviously is is very easy for Earth and all planets to stay in orbit since they have done so for a very long time with no help at all.

The mass of the Earth is not changing because of energy use. Burning resources just changes coal to smoke or whatever without reducing mass. Nuclear reactions do destroy some mass, but such a small amount that it makes no difference at all. The Sun is loosing far more mass in nuclear reaction than Earth, but even it is loosing mass so slowly that the change is far too small to measure even with the best instruments.

And orbits are stable for reasons that seem so obvious to me and so unclear to most people even when I take great pains to explain it that I have all but given up trying to explain it. Suffice it to say that it is a conservation of energy problem. Earth has kinetic energy and potential energy, and when it moves closer to the Sun it looses potential energy but gains kinetic energy in such a way that it wants to move back away from the Sun again, so it just stays in a stable orbit instead.

Answer 4

The sun's mass is huge compared to the planets and the mass lost from energy conversion is small. Despite resources being used on earth this is small and they are only converted to different forms - the mass stays the same. The earth has a velocity in the forward direction and the sun has a force that pulls it toward it. These balance causing a circular orbit. As the earth travels forward and moves away from the sun the sun's gravity pulls it a little closer.

Answer 5

It is an equilibrium between the centripetal force of the sun and the centrifical force of the earth that keeps the earth in orbit with the sun. Remember, most asteroids that strike the earth are very small with respect to the size of the earth and they do not have sufficient force to knock the earth out of orbit. If an asteroid was large enough to knock the earth out of orbit then the earth would eventually find it's equilibrium again with the sun.

Answer 6

Perhaps there is too much mass
involved for these small events to
cause a change.