if the sun is fusing hydrogen into helium and there is mass lost, what happens to the earth orbit?

Answer 1

I think you already have that figured out.

The mass loss so far in the life of our solar system has been negligible - not enough to affect the orbits of the planets.
But give it another 3 billion years or so, and the sun will expand to a red giant (and puff off more mass in the process). Over the following several millions of years it will pulsate and continue to expand, puffing off more mass (and an increased solar wind will contribute to major mass loss).
By about 4 billion years from now, the sun will have lost a third of its current mass, and the planets will have started to spiral outward a bit due to the decrease in gravity.
The Earth will end up around 1.61 AU from the sun's centre (instead of the 1.0 AU of today).

Answer 2

As the sun's mass diminishes, it grows larger and larger, our orbit gets further from it, because it is losing mass. It grows, is redder and redder, until it takes up most of the sky . By that time, we won't be here. It's just as well. The sun will eventually expand and trap the closest planets in their doom, then shrink as more of its gasses escape. Eventually, the sun will become a tiny ball of dense matter which could eventually turn into a black hole.
At that point, nearby objects are already being sucked in at fantastic rates. The twenty or so asteroids between the sun and Venus would be swallowed first, then the planets and the rest of the asteroids, and gravitational fields having been disrupted, stars would begin falling in to fill the gap, loosing a chain reaction with galactic disaster as the result, after billions and billions of years.

Never fear for the universe, however. Our own sun Sol is at least a second-generation star, and, perhaps, a third generation.

Life goes on.

Answer 3

The mass loss due to fusion is minuscule, amounting to about 0.07% of the sun's mass during its time (~10 billion years) on the main sequence. The effect on earth's orbital period is 2x 0.07%, or about a half-day per year. Since the sun will get gradually more luminous toward the end, we will be glad to be a little bit further away.

After that, the sun turns into a red giant and will shed a fair percentage of its mass into space. Earth's orbit will change a lot when this happens, but the planet will be too scorched to support life anyhow.

Answer 4

Eventually, the loss of mass will reduce the Sun's gravitational attraction and the orbit of each planet, including Earth, will gradually grow wider and wider.

Realistically, the Sun is 2.0 x 10³⁰ kilograms. You could subtract 1,000,000 kg per second from that for 1,000,000 years and still not notice the difference. So the Earth's orbit won't change much in our lifetime. Nor our children's lifetimes.

Answer 5

I guess I don't get the question. It is my understanding that in the evolution of most stars, they burn from hydrogen to helium and then from helium to carbon when they become red giants and will devour their solar systems. After the red giant stage, they generally explode and start the evolution again or implode and become black holes.