Concerning the orbit of planets while adding mass

[posskb]

The Earth and Sun add mass continually from infalling debris from space. When their mass increase so does their gravitational attraction. The increasing gravitational attraction would seemingly pull the earth into a closer orbit to the sun which would again increase the pull of gravity and so on and so on. So why haven’t the planets been pulled into the sun?

[posskb]

After searching a little I found that changing mass results in changing orbital speeds which balances out. But this is hard for me to infer. I guess the orbit will maintain regardless of how much the mass increases or are there limits?

[Stranger_On_A_Train]

See Kepler’s Laws of Planetary Motion. As long as M[sub]Sun[/sub] >> m[sub]Earth[/sub] (or any other celestial body orbiting the Sun) the amount of mass is essentially irrelevent; the orbit is essentially the same regardless. Now, when you get systems where M[sub]1[/sub] ~ M[sub]2[/sub], then funny things start happening. If, for instance, the Moon–which already exerts a substantial influence on the Earth–were to increase in mass by about an order of magnitude, the resulting orbit around the Sun would be distinctly chaotic and probably unstable. However, that is extremely unlikely.

Stranger

[posskb]

Thanks for the help Stranger. Astronomy/physics are facinating subjects for me. I’ll read up on the link you provided.

[ZenBeam]

The Sun is actually losing mass, due to both radiation

@Wikipedia

The Sun is about halfway through its main-sequence evolution, during which nuclear fusion reactions in its core fuse hydrogen into helium. Each second, more than 4 million tonnes of matter are converted into energy within the Sun’s core, producing neutrinos and solar radiation; at this rate, the Sun will have so far converted around 100 Earth-masses of matter into energy.

and also the solar wind

Earth’s fate is not clear. As a red giant, the Sun will have a maximum radius beyond the Earth’s current orbit, 1 AU (1.5×10[sup]11[/sup] m), 250 times the present radius of the Sun. However, by the time it is an asymptotic giant branch star, the Sun will have lost roughly 30% of its present mass due to a stellar wind, so the orbits of the planets will move outward. If it were only for this, Earth would probably be spared, but new research suggests that Earth will be swallowed by the Sun due to tidal interactions. Even if Earth escapes incineration in the Sun, its water will be boiled away and most of its atmosphere would escape into space. In fact, even during its life in the main sequence, the Sun is gradually becoming more luminous, and its surface temperature is slowly rising. The increase in solar temperatures is such that in about a billion years, the surface of the Earth will become too hot for liquid water to exist, ending life as we know it.