Expert: Jayendra Upadhye - 4/15/2004

Question
Hi,

Does earth's orbit around sun a stable one or does it change ?. I have read in physics books that gravitational pull between objects depend on
the mass of the objects.With Sun continuously losing mass due to Nuclear fission/Fusion how does it maintain its gravity grip on earth ?

Thanks
Sriram


Answer
Hi Sriram,
As I always say..I am weak with figures..I dont remember the solar mass attrition rate, but could you please look up a few questions before yours on this site where i answered with exact figure and the link to the site for that figure?
Now coming to your main question..the answer is simple.
You are right! But the spiralling "outwards" of the earth due to loss of solar mass (lost in fusion related mass defect based conversion and subsequent radiation as energy..) is so insignificant that over a few billion years it would be a couple of km at the worst!
by that time, the expanding sun's surface would have caught up with it already! so loose no sweat on that count!
[The sun will in due course enter the red giant stage and its surface will extend upto mars!]
While on the topic of spiralling orbits, have you thought of how the moon is spiralling away from earth at about 3.8 cm per year owing to the laws of conservation of angular momentum and tidal interactions with earth?
If not look it all up on the www! It is called lunar recession rate. look it up at
http://www.irishscientist.ie/2000/contents.asp?contentxml=190as.xml&contentxsl=i...
Jayen