Does the Earth's mass change?

[OLTB]

Morning all - my eight year old asked me yesterday, 'how much does the earth weigh?'. We looked up the answer on Dr Google and discovered the correct term to use was 'mass' rather than 'weight' as mass is the amount of matter contained in a body.

He then asked does the earth get heavier. We thought about it and I couldn't quite work it out - animals/humans grow, as do trees, plants etc. but in order to grow, they consume and burn, which just transfers weight from one source to another. The trees and plants that grow take nutrients from the earth, as well as water, so it seems to be just transferring elements from one place to another.

I was trying to explain that it's not possible for things to just appear, they have to 'grow' from something and that growth means having to use other existing elements which would keep the weight, or mass, constant.

In the end, I told him that I think the earth would slightly get 'heavier' because of meteors that randomly hit the earth every now and then and as they aren't from the earth originally, the result is a slightly heavier planet.

I then said I would check with some Lemon people who are far cleverer than me!

Cheers, OLTB.

[kempiejon]

Well satellites are launched into space how that balances against meteors I do not know. Does the atmosphere count as the earth in this question?

[tea42]

Thought of added mass of meteorites… vs… loss of atmosphere, then checked with Wiki which agreed I think we are losing mass. Doomsday scenario.

[Gengulphus]

Almost all satellites are launched into orbits around the earth and will eventually come down again through orbital decay caused by drag from the very thin traces of atmosphere still remaining at their height (though it may take a very long time if their orbit is quite high and they're not eventually deliberately brought down - which seems likely to become a more common occurrence in future as concerns about 'space junk' grow and the technology for bringing them down is developed). So the long-term net loss to the earth's mass due to satellites is confined to those that are sent to other bodies in the solar system, into orbit around them, or out of the solar system entirely, and those that are sent into earth orbits so high that the remaining atmospheric drag is not the dominant effect in how those orbits will evolve (the main other effects are gravitational ones from other bodies in the solar system).

That will be a very small effect compared with what seem to generally be reckoned to be the main two effects on the earth's mass: falling meteors adding to it (with a very large proportion of it being due to dust rather than sizeable meteors) and atmospheric loss subtracting from it. The latter is basically because gas molecules in the upper parts of the atmosphere are moving with a range of velocities that depends on its temperature and the mass of the molecule (the lighter the molecules, the faster they move on average). For the lightest molecules, there's a significant chance that they're moving faster than earth escape velocity, a roughly 50% chance that they're heading away from the earth rather than towards it, and because they're in the upper atmosphere, a significant chance that they won't collide with another molecule before they escape entirely. So hydrogen and helium in the upper atmosphere have a fair chance of escaping entirely from the earth (and other gases can do the same, though generally at rapidly reducing rates as their molecular masses rise).

And both hydrogen and helium are present in the upper atmosphere - I believe the main sources are that helium is created by radioactive decay within the earth, escapes into the atmosphere by diffusing out through porous rocks or being released by volcanism or human activity, and then diffuses up through the atmosphere, while hydrogen is created by a variety of processes within the earth or at surface level and then also diffuses up through the atmosphere, or by the action of ultraviolet (and more energetic) radiation on water vapour high in the atmosphere.

Each of those two effects seems to be estimated as having hundreds-of-tonnes per day effect on the earth's mass, with atmospheric loss looking likely to be the bigger effect but by no means certain. There are quite a few smaller effects, such as satellites being launched as described above, radioactive decay releasing radiated particles that escape from the earth (neutrinos in particular are almost certain to do so and do have a mass, though a very small one), radiated particles from the sun being absorbed by the earth (for instance, there are huge numbers of neutrinos from the sun, most of which pass straight through the earth, out the other side and on into space, but a very small proportion of them are absorbed), etc. But even all put together, those smaller effects seem unlikely to do more than slightly perturb the net effect of meteors and atmospheric losses.

Gengulphus

[ReformedCharacter]

Every day, Earth is bombarded with more than 100 tons of dust and sand-sized particles.

https://www.nasa.gov/mission_pages/aste ... facts.html

RC

[bungeejumper]

Every day, Earth is bombarded with more than 100 tons of dust and sand-sized particles.

Aha, that explains it. Most of it seems to land on my car.

BJ

[XFool]

Every day, Earth is bombarded with more than 100 tons of dust and sand-sized particles.

Aha, that explains it. Most of it seems to land on my car.

Now you say that... Perhaps it really does.

Long ago, before I used to drive I was occasionally given a lift by other people. One day, the car windscreen was hit by a small piece of grit or small stone (no damage). There didn't seem to be any obvious explanation where it came from, I asked the driver, he said "It's a small stone dropped by a passing bird." I accepted his explanation.

Years later driving my own car, much the same thing happened - I immediately thought: "It's a passing bird...". But then I thought: "But I didn't see any birds and why would they be carrying small stones anyway?"

I got to thinking of alternative explanations and the thought came to mind that the Earth is struck by myriads of small meteors every day. Why shouldn't one, or a remnant, find its way to Earth and happen to hit the windscreen of a passing car?

[bungeejumper]

I got to thinking of alternative explanations and the thought came to mind that the Earth is struck by myriads of small meteors every day. Why shouldn't one, or a remnant, find its way to Earth and happen to hit the windscreen of a passing car?

Dammit, you're right. Why didn't I think of that?

Somewhere up there, in a galaxy far, far away, there's a row of little green men with peashooters, all getting increasingly pissed on their pan-galactic gargleblasters and challenging each other to hit the exact same spot on some poor earthling's car - repeatedly. My bonnet is the intergalactic equivalent of a double top, and it takes a fair bit of beam-bending to counteract the solar wind so that the meteoric speck hits the exact same spot every single time.

The winner of the game is the first one to bore a hole right through the car. And it's getting boring, and it's got to stop, you bastards. Now.

BJ

[XFool]

Somewhere up there, in a galaxy far, far away, there's a row of little green men with peashooters, all getting increasingly pissed on their pan-galactic gargleblasters and challenging each other to hit the exact same spot on some poor earthling's car - repeatedly. My bonnet is the intergalactic equivalent of a double top, and it takes a fair bit of beam-bending to counteract the solar wind so that the meteoric speck hits the exact same spot every single time.

The winner of the game is the first one to bore a hole right through the car. And it's getting boring, and it's got to stop, you bastards. Now.

They've already scored:

USA Today

Only in the US of A...

[didds]

[
Somewhere up there, in a galaxy far, far away, there's a row of little green men with peashooters, all getting increasingly pissed on their pan-galactic gargleblasters and challenging each other to hit the exact same spot on some poor earthling's car - repeatedly. My bonnet is the intergalactic equivalent of a double top, and it takes a fair bit of beam-bending to counteract the solar wind so that the meteoric speck hits the exact same spot every single time.

The winner of the game is the first one to bore a hole right through the car. And it's getting boring, and it's got to stop, you bastards. Now.

CF Rob McKenna !
http://hitchhikers.wikia.com/wiki/Rob_McKenna

didds