mass/weight related to orbit ?

[Alessandro]

hi all,

is the mass or weight related to the orbit of a planet ?
if the mass or the weight of a planet changes, his orbit around to his star changes ?

[selden]

Yes and yes.

Actually, what matters is the sum of the star's mass and the planet's mass. Usually the star's mass is so much larger than the planet's mass that changes in the planet's mass would have a very small effect on the planet's orbit. Those changes would have a larger effect on the orbits of the planet's moons, since their masses are so much less than the planet's mass.

[Alessandro]

Hi Selden,

thank you for yr answer very speed.

how much have to change for example the mass of earth to really or sensibly impact the moon orbit then?
should be in order of half planet, quarter, or much less is enough?

[selden]

Alessandro,

When you're talking about fractions of the total mass, "much less" would have a big effect over a few centuries. However, don't forget that the mass of the Earth is gigantic -- some 5.9742 ? 10^24 kilograms or about 6,000,000,000,000,000,000,000,000 kg. "Much less" would still be a very large amount of matter.

[Alessandro]

yes but moon is "only" 7.35^22 kg that's 1,2% ca of earth.

and for example phobos is very little compared to mars
1,08^16 vs 6.42^23 that's 0,000001682% of mars

I'm asking my self if the fact to lighten the planet by extracting and destroing underground materials could impact the stability of his moon,
perhaps in centuries of years.

is that possible or is just groundless(italian = infondata) immagination?

ciao

[tony873004]

how much have to change for example the mass of earth to really or sensibly impact the moon orbit then?
should be in order of half planet, quarter, or much less is enough?

Reducing Earth's mass by 10% will cause the Moon to noticably spiral outward.

Reducing it by 10% again will throw it into an Earth-bound chaotic orbit heavily influenced by the solar gravitational tide.

Reducing it by 10% again will allow the Sun to take over and strip the Moon from the Earth.

[Alessandro]

that clears my idea
it represent a lot of material also concerning other inferior mass planets.

thank you Selden thank you tony873004.