Re: If Jupiter became a star, would life on Earth still evolve?

This question is difficult to answer – we can only put forth theoretical possibilities. Going purely on data available today, I would say that life could still have evolved on Earth for the following reasons:

Jupiter has a mass of approximately 1.899*10^27 kilograms (1899 followed by 24 zeros!), and the sun has a mass of 1.99*10^30 kilograms. According to one source, Jupiter would need to be at least 80 times more massive to become a star, which means it would then have a mass of 1.52*10^29 kilograms.

A star with a mass of 1.52*10^29 kilograms, or about one-tenth the mass of the sun would have a lifetime of thousands of billions of years. This means that it would put out relatively little energy per unit time. So any energy this “Jupiter Star” would radiate into space would be small compared to the energy put out by the sun.

In addition, Jupiter is 5.2 times more distant from the sun than the Earth is. This means that Jupiter is also much farther away from the Earth than the Earth is from the sun. Only a tiny amount of the energy put out by Jupiter would reach Earth, and what little would fall upon the Earth is small in comparison to what the Earth receives from the sun. So we don't have to worry about the Earth turning into an oven (which would make it impossible for life as we know to exist).

But these small changes, when looked at over a long period of time are large enough to change the course of evolution. Life forms present today might look or behave different from what we know. For example, animals might have different sleeping patterns due to light coming from Jupiter.

[Moderator's note: A star about one tenth the mass of the Sun would be about 0.001 times as luminous. If it were orbitting in Jupiter's orbit, this would make it about 0.00006 times as bright as the Sun, even at its closest to the Earth. This isn't much brighter than the Full Moon. - Jim O'Donnell, jim@penfold0.demon.co.uk]