<p>Earth does not lose mass to the moon's orbit. However, there are a few ways it can lose energy to gravitational effects. One way it can lose energy is to gravitational slingshotting, from satellites, asteroids or comets. In the case of a gravitational slingshot, Earth doesn't lose mass, it simply slows down. But since Earth is so massive in comparison that slowdown is extremely slight.</p>
<p>The Earth also loses some rotational energy to tidal forces from the moon. In this case, the Earth simply turns very slightly more slowly. Still, no mass is lost.</p>

CC BY-SA 4.0
2023-03-09T15:38:29.493Z
How could we still be losing rotational energy to the moon when the earth and moon are already tidally locked?
Cruncher
CC BY-SA 4.0
2023-03-09T15:45:46.047Z
@Cruncher The moon is tidally locked to the earth, but the earth is not locked to the moon. That's why we have tides that move around the earth. The land also has tides, although much, much less noticeable. These tides ultimately convert Earth's kinetic energy to heat. Those earth-tides are also hoisting the moon into a higher orbit, so the earth does work on the moon, drawing from its kinetic energy.
erickson
CC BY-SA 4.0
2023-03-08T19:05:02.963Z
2023-03-08T19:05:02.963Z
Dolgubon
<p>No energy is needed for the moon to keep going straight ahead in space that is curved by earth's gravity. Which makes &quot;straight ahead&quot; being orbital around the earth.</p>

CC BY-SA 4.0
2023-03-09T14:15:32.513Z
Yes, gravity curves spacetime, but the spatial curvature of the Moon's orbit is much greater than the spacetime curvature of its worldline. Please see https://physics.stackexchange.com/q/586835/123208
PM 2Ring
CC BY-SA 4.0
2023-03-09T21:07:46.433Z
This answer seems correct according to the theory of general relativity. Gravity isn't a force.
An object in motion stays in motion, and because spacetime is curved around the earth, the moon will continue to 'keep going straight' in curved spacetime around the earth. When something keeps going straight there's no energy lost because it doesn't accelerate in any direction. The moon isn't changing directions and no force is acting upon it. Where there is no force, no energy is used.
Nick Bonilla
CC BY-SA 4.0
2023-03-09T22:54:36.220Z
https://www.youtube.com/watch?v=MTY1Kje0yLg
Kjetil S.
CC BY-SA 4.0
2023-03-11T01:00:25.590Z
@Nick Yes, the Moon's worldline is a timelike geodesic, but Kjetil's answer implies that the Moon's trajectory in space is straight, and that's not correct.
PM 2Ring
CC BY-SA 4.0
2023-03-09T13:30:22.357Z
2023-03-09T17:10:55.797Z
2023-03-09T17:10:55.797Z
Kjetil S.
<p>Apart from the mainly correct replies so far, and just considering the mass of the planet in terms of mass lost to space, or gained from outside, we keep losing some mass from our atmosphere, both from molecules blasted away by solar wind etc, and from the fact that molecules much lighter than N2 (eg water) have typical speeds exceeding Earth's escape velocity.</p>
<p>However, we also are constantly gaining mass from space dust and meteoroids that collide with the planet, thereby becoming meteorites; and I suspect (but have no data) that our input from solar wind plus cosmic &quot;rays&quot; (largely matter particles, such as protons and electrons in terms of mass) exceed our constant leakage into space.</p>
<p>If I am right, then you could say that we still are in a state of accretion as we were early in the history of the solar system, but by now in a very late stage.</p>
<p>In some more billions of years (I have seen various figures) we should find ourselves inside the outskirts of the sun's atmosphere, and accordingly piling in lots more mass, mainly light elements of course. I suspect that when the sun shrinks back to red dwarf status after a few more millions of years, our planet still will be in orbit, and significantly more massive than before, and I would love to see the outcome, but in spite of all my kicking and screaming and writing to congressmen and lawyers, it seems to be very difficult to get ringside tickets.</p>

CC BY-SA 4.0
2023-03-15T10:15:35.813Z
Do you have any numbers to assert your notion that we are gaining net mass? Also the sun will never become a red dwarf. And while Earth, by the time the sun expands to 100-200 solar radii, might accrete some of the solar wind, it will have had most of its atmosphere blasted away by the enormous luminosity of the star.
AtmosphericPrisonEscape
CC BY-SA 4.0
2023-03-15T10:22:55.400Z
@AtmosphericPrisonEscape Earth's mass influx due to meteorites is around 50000t/yr: https://www.lpi.usra.edu/books/MESSII/9021.pdf (end of §3.4)
planetmaker
CC BY-SA 4.0
2023-03-15T10:31:26.087Z
Other authors arrive at a factor of 10 less (a few 1000t/yr): https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JE006241
planetmaker
CC BY-SA 4.0
2023-03-15T10:34:16.597Z
So if we take your upper number, that translates to ~1500 g/s, compared to an estimated 500 g/s and 800 g/s atmospheric loss from H and O escape (Gunell+2018). Seems like it could be a close race..
AtmosphericPrisonEscape
CC BY-SA 4.0
2023-03-15T12:36:59.143Z
@Jon not sure I'd agree to call todays influx from meteorites and zodiacal dust as 'accretion'. Accretion is usually understood as a phase of significant mass gain. We are talking here of a fraction of around 10^-18 .. 10^-17 earth masses per year while the actual planetformation takes place inless than ~10 million years, so accretion rates of 10^-7 earth masses per year. Thus whatever hasn't grown till then, will most likely not grow much more. Today we simply have a mass exchange with the interplanetary medium.
planetmaker
CC BY-SA 4.0
2023-03-15T14:20:45.783Z
https://physics.stackexchange.com/q/297622/123208 suggests that we're probably losing more mass than we're gaining, but the error bars are pretty large.
PM 2Ring
CC BY-SA 4.0
2023-03-16T11:42:25.293Z
Thanks folks, though none of what I said was insincere (ignoring spelling "white dwarf" "red dwarf" sorrryyyy!) I meant no more than expansion of the concept of planetary  mass change and stimulating some exchanges. That worked rather well, and I was very pleased with their standard.
Jon
CC BY-SA 4.0
2023-03-15T09:14:10.617Z
2023-03-15T09:14:10.617Z
Jon
<p>You are wrong that &quot;to keep any object in circular motion requires energy&quot;</p>
<p>In a circular orbit, the force of gravity is always perpendicular to the motion of the moon, so no work is done by gravity, and no energy is required.</p>
<p>This is analogous to the string in a pendulum, which also <a href="https://physics.stackexchange.com/questions/754174/why-is-the-work-done-by-the-tension-in-a-pendulum-string-0">does no work</a>.</p>
<p>In an elliptical orbit, energy is constantly converted between potential and kinetic energy, but the total energy is constant, and over the full orbit, no work is done.</p>
<p>So, no, the gravity doesn't run out, and Earth doesn't lose mass.</p>
<p>In a three-body interaction (for example with a comet, the Earth and the sun) the perturbing effect of the sun can cause the Earth to transfer a bit of its kinetic energy to the comet. In this case the Earth can lose (or gain) some energy. The amount of energy lost is minuscule in comparison to the total amount of energy stored in the motion of the Earth. The mass (by E=mc²) is very very small.  This process of a three body interaction causing the Earth to do work on a comet is called a &quot;gravitational slingshot&quot;.  Again the amount of energy lost in these interaction is very very small, and there is not a snowball's chance that the Earth will ever run out of energy.  </p>
<p>(Earth does lose a little mass in other ways: a little bit of air is always escaping into space, but there is plenty left, and we won't ever run out.)</p>

CC BY-SA 4.0
2023-03-08T08:28:30.357Z
So let's imagine a comet passed by earth's orbit and earth was located behind the comet (when viewed from sun), the earth slows down the comet as comet is moving in the opposite direction of gravity. So does earth loose energy at that time?
Prajwal D M
CC BY-SA 4.0
2023-03-08T15:57:26.400Z
Earth also constantly gains mass from meteor impacts -- I believe at a higher rate than atmosphere loss, but I'm not sure.
Russell Borogove
CC BY-SA 4.0
2023-03-08T18:16:20.877Z
Technically every spacecraft we've ever sent beyond our orbit (Voyager/Pioneer probes, Cassini, Mars/Venus landers, etc.) would also count as mass loss, but obviously very negligible in the long run.  Satellites (and anything we left on the Moon) would *not* count since their mass is still part of the overall Earth system.
Darrel Hoffman
CC BY-SA 4.0
2023-03-08T18:56:00.917Z
@PrajwalDM Both the comet and Earth will exert a gravitational force on each other, and both of their orbits will be changed. (Earth's only fractionally so, because it's much larger; a comet's orbit can be dramatically changed by an encounter with a planet because of its lower mass.) Earth's orbit might either gain or lose energy depending on the exact movement involved, but that energy doesn't come from Earth, it comes from (or goes to) the comet's orbit.
Cadence
CC BY-SA 4.0
2023-03-08T21:21:34.243Z
Doesn't the orbiting of the Earth-Moon system radiate energy as gravitation waves? Not much, but enough to keep OP from being wrong?
DavePhD
CC BY-SA 4.0
2023-03-08T21:30:43.267Z
If I recall, the earth loses about 2 trillionths of a gram every second to gravitational waves. Can't remember where I heard it.  Essentially the OP is wrong.  Orbitors don't require a constant input of energ.
James K
CC BY-SA 4.0
2023-03-08T22:55:34.160Z
I'd take issue with conflating energy and mass. Unless you're talking about *relativistic mass* ([which has largely fallen out of favor as a useful concept](https://physics.stackexchange.com/a/133395/180843)), the Earth's mass doesn't change when objects perturb its orbit or when it radiates gravitational waves.
Sten
CC BY-SA 4.0
2023-03-09T02:50:52.363Z
From https://physics.stackexchange.com/a/412990/123208 the Earth-Sun system radiates ~196 watts as gravitational waves, which is equivalent to ~2.18 picograms per second (just under 69 micrograms per Julian year). But that doesn't affect the rest mass of the Earth or Sun, it just decreases their gravitational potential energy. I suppose you can say it reduces the rest mass of the Sun-Earth system, which is less than the sum of the rest masses of the Sun & Earth, the deficit being equal to their [gravitational binding energy](https://en.wikipedia.org/wiki/Gravitational_binding_energy).
PM 2Ring
CC BY-SA 4.0
2023-03-09T02:51:07.100Z
(cont) Of course, it's a bit silly to treat the Sun & Earth as an isolated two body system. ;)
PM 2Ring
CC BY-SA 4.0
2023-03-09T03:10:54.180Z
+1 for *snowballs chance*
A. I. Breveleri
CC BY-SA 4.0
2023-03-09T07:34:08.707Z
And of course that loss of mass through diffusion of the atmosphere and the little bit we shoot up in the form of rockets is at least in part compensated for by asteroids and other objects being captured by the earth's gravitational field and being pulled in.
jwenting
CC BY-SA 4.0
2023-03-09T14:53:08.383Z
@JamesK, 2 trillionths of a gram _every second_ adds up to well over half a milligram per century.  Yes, I think we can call that small, relative to Earth's total mass.  ;-)
Toby Speight
CC BY-SA 4.0
2023-03-09T15:34:53.473Z
@DekoRevinio-leaningaway- Any processes on earth that create gasses, are not creating gasses out of nothing. They're being converted from another form of mass, and mass is conserved. Short of nuclear fusion and fission, the only mass change to the earth occurs through things leaving or entering through the atmosphere
Cruncher
CC BY-SA 4.0
2023-03-10T18:41:45.743Z
"In this case the Earth can lose (...) some energy." Wouldn't that be expressed as slowed rotation?
RonJohn
CC BY-SA 4.0
2023-03-08T06:38:12.597Z
2023-03-09T17:07:57.177Z
2023-03-09T17:07:57.177Z
James K
<p>The Moon is orbiting the Earth in a circular motion. To keep any object in a circular motion we need energy. Hence, does the Earth lose energy by pulling the Moon? In that case, does the Earth's gravity reduce constantly? If it does, then as gravity is proportional to mass, does the Earth lose mass as well?</p>

CC BY-SA 4.0
2023-03-08T06:40:58.707Z
See: https://astronomy.stackexchange.com/a/32553/35206
Nilay Ghosh
CC BY-SA 4.0
2023-03-08T15:24:01.760Z
related in Earth Science SE: [Is Earth getting heavier or lighter?](https://earthscience.stackexchange.com/q/16688/6031) and links below it to questions in other sites.
uhoh
CC BY-SA 4.0
2023-03-08T23:51:52.533Z
What's wrong with the energy contributed by gravity, please?
Robbie Goodwin
CC BY-SA 4.0
2023-03-09T16:43:23.377Z
The actual, dominating mass-loss from Earth is via loosing atmosphere, around 500-1000g/s both in H and O atoms (see review numbers given in https://ui.adsabs.harvard.edu/abs/2018A%26A...614L...3G/abstract )
AtmosphericPrisonEscape
CC BY-SA 4.0
2023-03-10T12:58:48.303Z
Prajawl.  The very simple answer to the question the way you're thinking about it is just NO.  Say you are in deep space, and there is absolutely no friction.  Say an object (spaceship, whatever) is "moving" at 100 mph.  **It will just keep moving at 100 mph forever**  It's that simple. That's all your asking.  Similarly, if an object is spinning, it will just keep spinning forever. (The "earth-moon" is simply an object spinning.)  Objects keep moving, spinning, forever if there is no friction.
Fattie
CC BY-SA 4.0
2023-03-10T12:59:45.750Z
Gravity and the other forces that keep things together don't "use" energy. It's like a rod connecting them.
Fattie
<orbit><the-moon><gravity><mass>
Does the Earth constantly lose mass?
Prajwal D M
# Does the Earth constantly lose mass?

(Asked by: username_0 on 2023-03-08)

The Moon is orbiting the Earth in a circular motion. To keep any object in a circular motion we need energy. Hence, does the Earth lose energy by pulling the Moon? In that case, does the Earth's gravity reduce constantly? If it does, then as gravity is proportional to mass, does the Earth lose mass as well?

**Tags:** orbit, the-moon, gravity, mass

> **Comments:**
> **username_1**: See: https://astronomy.stackexchange.com/a/32553/35206  
> **username_2**: related in Earth Science SE: [Is Earth getting heavier or lighter?](https://earthscience.stackexchange.com/q/16688/6031) and links below it to questions in other sites.  
> **username_3**: What's wrong with the energy contributed by gravity, please?  
> **username_4**: The actual, dominating mass-loss from Earth is via loosing atmosphere, around 500-1000g/s both in H and O atoms (see review numbers given in https://ui.adsabs.harvard.edu/abs/2018A%26A...614L...3G/abstract )  
> **username_5**: Prajawl.  The very simple answer to the question the way you're thinking about it is just NO.  Say you are in deep space, and there is absolutely no friction.  Say an object (spaceship, whatever) is "moving" at 100 mph.  **It will just keep moving at 100 mph forever**  It's that simple. That's all your asking.  Similarly, if an object is spinning, it will just keep spinning forever. (The "earth-moon" is simply an object spinning.)  Objects keep moving, spinning, forever if there is no friction.  
> **username_5**: Gravity and the other forces that keep things together don't "use" energy. It's like a rod connecting them.  

---

## 4 answers

### Answer by username_14 on 2023-03-08. Score: 44 | Accepted answer

You are wrong that "to keep any object in circular motion requires energy"

In a circular orbit, the force of gravity is always perpendicular to the motion of the moon, so no work is done by gravity, and no energy is required.

This is analogous to the string in a pendulum, which also [does no work](https://physics.stackexchange.com/questions/754174/why-is-the-work-done-by-the-tension-in-a-pendulum-string-0).

In an elliptical orbit, energy is constantly converted between potential and kinetic energy, but the total energy is constant, and over the full orbit, no work is done.

So, no, the gravity doesn't run out, and Earth doesn't lose mass.

In a three-body interaction (for example with a comet, the Earth and the sun) the perturbing effect of the sun can cause the Earth to transfer a bit of its kinetic energy to the comet. In this case the Earth can lose (or gain) some energy. The amount of energy lost is minuscule in comparison to the total amount of energy stored in the motion of the Earth. The mass (by E=mc²) is very very small. This process of a three body interaction causing the Earth to do work on a comet is called a "gravitational slingshot". Again the amount of energy lost in these interaction is very very small, and there is not a snowball's chance that the Earth will ever run out of energy.

(Earth does lose a little mass in other ways: a little bit of air is always escaping into space, but there is plenty left, and we won't ever run out.)

> **Comments:**
> **username_0**: So let's imagine a comet passed by earth's orbit and earth was located behind the comet (when viewed from sun), the earth slows down the comet as comet is moving in the opposite direction of gravity. So does earth loose energy at that time?  
> **username_15**: Earth also constantly gains mass from meteor impacts -- I believe at a higher rate than atmosphere loss, but I'm not sure.  
> **username_16**: Technically every spacecraft we've ever sent beyond our orbit (Voyager/Pioneer probes, Cassini, Mars/Venus landers, etc.) would also count as mass loss, but obviously very negligible in the long run.  Satellites (and anything we left on the Moon) would *not* count since their mass is still part of the overall Earth system.  
> **username_17**: @username_0 Both the comet and Earth will exert a gravitational force on each other, and both of their orbits will be changed. (Earth's only fractionally so, because it's much larger; a comet's orbit can be dramatically changed by an encounter with a planet because of its lower mass.) Earth's orbit might either gain or lose energy depending on the exact movement involved, but that energy doesn't come from Earth, it comes from (or goes to) the comet's orbit.  
> **username_18**: Doesn't the orbiting of the Earth-Moon system radiate energy as gravitation waves? Not much, but enough to keep OP from being wrong?  
> **username_14**: If I recall, the earth loses about 2 trillionths of a gram every second to gravitational waves. Can't remember where I heard it.  Essentially the OP is wrong.  Orbitors don't require a constant input of energ.  
> **username_19**: I'd take issue with conflating energy and mass. Unless you're talking about *relativistic mass* ([which has largely fallen out of favor as a useful concept](https://physics.stackexchange.com/a/133395/180843)), the Earth's mass doesn't change when objects perturb its orbit or when it radiates gravitational waves.  
> **username_10**: From https://physics.stackexchange.com/a/412990/123208 the Earth-Sun system radiates ~196 watts as gravitational waves, which is equivalent to ~2.18 picograms per second (just under 69 micrograms per Julian year). But that doesn't affect the rest mass of the Earth or Sun, it just decreases their gravitational potential energy. I suppose you can say it reduces the rest mass of the Sun-Earth system, which is less than the sum of the rest masses of the Sun & Earth, the deficit being equal to their [gravitational binding energy](https://en.wikipedia.org/wiki/Gravitational_binding_energy).  
> **username_10**: (cont) Of course, it's a bit silly to treat the Sun & Earth as an isolated two body system. ;)  
> **username_20**: +1 for *snowballs chance*  
> **username_21**: And of course that loss of mass through diffusion of the atmosphere and the little bit we shoot up in the form of rockets is at least in part compensated for by asteroids and other objects being captured by the earth's gravitational field and being pulled in.  
> **username_22**: @username_14, 2 trillionths of a gram _every second_ adds up to well over half a milligram per century.  Yes, I think we can call that small, relative to Earth's total mass.  ;-)  
> **username_7**: @DekoRevinio-leaningaway- Any processes on earth that create gasses, are not creating gasses out of nothing. They're being converted from another form of mass, and mass is conserved. Short of nuclear fusion and fission, the only mass change to the earth occurs through things leaving or entering through the atmosphere  
> **username_23**: "In this case the Earth can lose (...) some energy." Wouldn't that be expressed as slowed rotation?  

---

### Answer by username_6 on 2023-03-08. Score: 7

Earth does not lose mass to the moon's orbit. However, there are a few ways it can lose energy to gravitational effects. One way it can lose energy is to gravitational slingshotting, from satellites, asteroids or comets. In the case of a gravitational slingshot, Earth doesn't lose mass, it simply slows down. But since Earth is so massive in comparison that slowdown is extremely slight.

The Earth also loses some rotational energy to tidal forces from the moon. In this case, the Earth simply turns very slightly more slowly. Still, no mass is lost.

> **Comments:**
> **username_7**: How could we still be losing rotational energy to the moon when the earth and moon are already tidally locked?  
> **username_8**: @username_7 The moon is tidally locked to the earth, but the earth is not locked to the moon. That's why we have tides that move around the earth. The land also has tides, although much, much less noticeable. These tides ultimately convert Earth's kinetic energy to heat. Those earth-tides are also hoisting the moon into a higher orbit, so the earth does work on the moon, drawing from its kinetic energy.  

---

### Answer by username_9 on 2023-03-09. Score: 2

No energy is needed for the moon to keep going straight ahead in space that is curved by earth's gravity. Which makes "straight ahead" being orbital around the earth.

> **Comments:**
> **username_10**: Yes, gravity curves spacetime, but the spatial curvature of the Moon's orbit is much greater than the spacetime curvature of its worldline. Please see https://physics.stackexchange.com/q/586835/123208  
> **username_11**: This answer seems correct according to the theory of general relativity. Gravity isn't a force. An object in motion stays in motion, and because spacetime is curved around the earth, the moon will continue to 'keep going straight' in curved spacetime around the earth. When something keeps going straight there's no energy lost because it doesn't accelerate in any direction. The moon isn't changing directions and no force is acting upon it. Where there is no force, no energy is used.  
> **username_9**: https://www.youtube.com/watch?v=MTY1Kje0yLg  
> **username_10**: @username_11 Yes, the Moon's worldline is a timelike geodesic, but username_9's answer implies that the Moon's trajectory in space is straight, and that's not correct.  

---

### Answer by username_12 on 2023-03-15. Score: 0

Apart from the mainly correct replies so far, and just considering the mass of the planet in terms of mass lost to space, or gained from outside, we keep losing some mass from our atmosphere, both from molecules blasted away by solar wind etc, and from the fact that molecules much lighter than N2 (eg water) have typical speeds exceeding Earth's escape velocity.

However, we also are constantly gaining mass from space dust and meteoroids that collide with the planet, thereby becoming meteorites; and I suspect (but have no data) that our input from solar wind plus cosmic "rays" (largely matter particles, such as protons and electrons in terms of mass) exceed our constant leakage into space.

If I am right, then you could say that we still are in a state of accretion as we were early in the history of the solar system, but by now in a very late stage.

In some more billions of years (I have seen various figures) we should find ourselves inside the outskirts of the sun's atmosphere, and accordingly piling in lots more mass, mainly light elements of course. I suspect that when the sun shrinks back to red dwarf status after a few more millions of years, our planet still will be in orbit, and significantly more massive than before, and I would love to see the outcome, but in spite of all my kicking and screaming and writing to congressmen and lawyers, it seems to be very difficult to get ringside tickets.

> **Comments:**
> **username_4**: Do you have any numbers to assert your notion that we are gaining net mass? Also the sun will never become a red dwarf. And while Earth, by the time the sun expands to 100-200 solar radii, might accrete some of the solar wind, it will have had most of its atmosphere blasted away by the enormous luminosity of the star.  
> **username_13**: @username_4 Earth's mass influx due to meteorites is around 50000t/yr: https://www.lpi.usra.edu/books/MESSII/9021.pdf (end of §3.4)  
> **username_13**: Other authors arrive at a factor of 10 less (a few 1000t/yr): https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019JE006241  
> **username_4**: So if we take your upper number, that translates to ~1500 g/s, compared to an estimated 500 g/s and 800 g/s atmospheric loss from H and O escape (Gunell+2018). Seems like it could be a close race..  
> **username_13**: @username_12 not sure I'd agree to call todays influx from meteorites and zodiacal dust as 'accretion'. Accretion is usually understood as a phase of significant mass gain. We are talking here of a fraction of around 10^-18 .. 10^-17 earth masses per year while the actual planetformation takes place inless than ~10 million years, so accretion rates of 10^-7 earth masses per year. Thus whatever hasn't grown till then, will most likely not grow much more. Today we simply have a mass exchange with the interplanetary medium.  
> **username_10**: https://physics.stackexchange.com/q/297622/123208 suggests that we're probably losing more mass than we're gaining, but the error bars are pretty large.  
> **username_12**: Thanks folks, though none of what I said was insincere (ignoring spelling "white dwarf" "red dwarf" sorrryyyy!) I meant no more than expansion of the concept of planetary  mass change and stimulating some exchanges. That worked rather well, and I was very pleased with their standard.  

---

