Comet Question

[Chesterton]

Do comets lose mass as they orbit near the sun and "blow off steam"? Seems like they would, and if so, would less mass eventually change their orbit? After some millennia, do they eventually fly out of their orbit?

 

[lesliedellow]

Do comets lose mass as they orbit near the sun and "blow off steam"? Seems like they would, and if so, would less mass eventually change their orbit? After some millennia, do they eventually fly out of their orbit?

They lose mass as they blow off steam, but that won't alter their orbit, unless the steam they blow off acts like a mini jet engine, and increases their speed slightly; in which case they will go into a slightly lower orbit.

 

[Chesterton]

But the gravitational pull is based on the mass of the two bodies, so wouldn't the pull lessen over time?

 

[lesliedellow]

But the gravitational pull is based on the mass of the two bodies, so wouldn't the pull lessen over time?

The gravitational pull would lessen, but the centripetal acceleration would remain the same. At the surface of the Earth, different objects fall at the same rate irrespective of their mass.

 

[Chesterton]

Ah yes, I guess I forgot my basic Galileo. Or maybe I don't understand it to begin with. If the planet Jupiter were reduced to, say, 1/10 of its current mass, it would maintain the same orbit it does now?

 

[lesliedellow]

Ah yes, I guess I forgot my basic Galileo. Or maybe I don't understand it to begin with. If the planet Jupiter were reduced to, say, 1/10 of its current mass, it would maintain the same orbit it does now?

Yes it would. The only thing which would cause it to change its orbit would be a different orbital velocity.

 

[essentialsaltes]

But the gravitational pull is based on the mass of the two bodies, so wouldn't the pull lessen over time?

The pull would lessen, but that would not change the orbit. Less pull on less mass will result in the same acceleration, and therefore the same orbit.

This is basically the same concept as 'heavy things and light things fall at the same rate when you drop them' (neglecting air resistance).


I believe the ultimate fate of comets is that all the volatile gases finally escape, leaving behind just some rocks and dust, that slowly drift apart generally along the comet's previous orbit and these are a source of meteor showers, if the previous comet orbit intersects the earth's orbit. In fact, I think some existing meteor showers are associated with particular comets.

 

[Chesterton]

Yes it would. The only thing which would cause it to change its orbit would be a different orbital velocity.

Okay, let me ask about something on a bigger scale. The Milky Way and Andromeda galaxies are falling towards each other. But there was a time in the distant past when neither galaxy had the concentrated mass that they now have, right? So how did they start falling towards each other, and have their velocities been the same since...since before they would have been recognized as galaxies?

I believe the ultimate fate of comets is that all the volatile gases finally escape, leaving behind just some rocks and dust, that slowly drift apart generally along the comet's previous orbit and these are a source of meteor showers, if the previous comet orbit intersects the earth's orbit. In fact, I think some existing meteor showers are associated with particular comets.

How could the rocks and dust drift apart in the vaccum of space? They'd stay together if nothing's acting upon them.

 

[Michael]

Do comets lose mass as they orbit near the sun and "blow off steam"? Seems like they would, and if so, would less mass eventually change their orbit? After some millennia, do they eventually fly out of their orbit?

As others aptly noted, any given comet would have to lose a whole lot of mass for that to happen. Eventually however, maybe. More commonly they simply "break up" and disintegrate over time, and slow down in the atmosphere if they get too close to the sun. Comet Lovejoy was the exception to that rule however.

SOHO's Lasco-C2 and C3 images commonly register various comets slamming themselves into the sun. They usually burn up long before they ever reach the chromosphere.

 

[essentialsaltes]

How could the rocks and dust drift apart in the vaccum of space? They'd stay together if nothing's acting upon them.

The dust and rocks are ejected with the gas as it sublimates and shoots out of the comet, which gives the rocks little pushes that overcome the tiny gravity of the comet, and all these particles slowly separate.

 

[AV1611VET]

The gravitational pull would lessen, but the centripetal acceleration would remain the same. At the surface of the Earth, different objects fall at the same rate irrespective of their mass.

If I drop a 16 lb. bowling ball, and then an 8 lb. bowling ball, which will land first?

 

[Shemjaza]

If I drop a 16 lb. bowling ball, and then an 8 lb. bowling ball, which will land first?

If they are the same size, they would hit at the same time

EDIT: LOL, I just noticed "16 lb. bowling ball, and then an 8 lb. bowling ball".

Almost got me. The 16 lb will hit first.

 

[AV1611VET]

Almost got me. The 16 lb will hit first.

... You guys are too smart!

 

[Justatruthseeker]

Do comets lose mass as they orbit near the sun and "blow off steam"? Seems like they would, and if so, would less mass eventually change their orbit? After some millennia, do they eventually fly out of their orbit?

No, they loose mass as they electrically discharge. And have not been in their present orbits for but a few thousand years, else they would be eroded into nothing. When the electrical stress becomes too great they disintegrate.

https://www.youtube.com/watch?v=34wtt2EUToo&list=PLwOAYhBuU3UfvhvcT1lZA6KbSdh0K2EpH

 

[pgp_protector]

If they are the same size, they would hit at the same time

EDIT: LOL, I just noticed "16 lb. bowling ball, and then an 8 lb. bowling ball".

Almost got me. The 16 lb will hit first.

He also didn't say from what height he's dropping them from, or through what medium.
He might drop the 16lb ball through a vat of molasses, that's 20 feet tall, and the 8 ball from 5 feet in a vacuum.

 

[Chesterton]

Bear with me please, I'm trying to understand. If all objects fall towards the center of the Earth at the same speed, why don't all objects fall towards the Sun at the same speed? Why does Mercury move faster than Neptune?

 

[essentialsaltes]

Bear with me please, I'm trying to understand. If all objects fall towards the center of the Earth at the same speed, why don't all objects fall towards the Sun at the same speed? Why does Mercury move faster than Neptune?

All objects released from the same height will fall with the same acceleration. The force of gravity depends on the inverse square of the distance between the object and the center of the earth (or whatever the attracting body is). For most human applications, you don't notice any difference between dropping something on the top of building versus at ground level, because the height of a building is insignificant compared to the radius of the earth. The additional height doesn't change the acceleration very much.

But if you're at the height of a satellite, you're far enough away from the center of the earth for the gravity of the earth to be substantially weaker. And the moon accelerates even less.

The moon is an important example, since Newton calculated the acceleration it felt in its orbit around the earth, and by comparing that acceleration to the acceleration of, say, an apple at the earth's surface, he was able to deduce the inverse square law.

In short, the closer you are, the greater the acceleration.

Mercury is closer to the sun than Neptune, so it feels a greater acceleration due to the sun's gravity. (For a stable orbit, that requires Mercury to be moving faster in its orbit, otherwise it would fall into the sun, since it's being pulled harder.)

 

[Michael]

Bear with me please, I'm trying to understand. If all objects fall towards the center of the Earth at the same speed, why don't all objects fall towards the Sun at the same speed? Why does Mercury move faster than Neptune?

essentialsaltes did a great job with the verbal explanation, but maybe this will help?

Gravitation Funnel Marble Run - YouTube

 

[Chesterton]

In short, the closer you are, the greater the acceleration.

But according to Newton things don't accelerate at all unless acted upon by an external force, do they?

 

[essentialsaltes]

But according to Newton things don't accelerate at all unless acted upon by an external force, do they?

Correct. Gravity is an external force, one of the few fundamental forces that exists.