Snippet: Will the Earth be Safe From Solar Expansion? The Outlook Isn’t Great…

As the Sun runs out of fuel, it will swell… but will it swell enough to swallow the Earth? Image credit: Mark Garlick/HELAS. Source:

In 7 billion years time, the Sun will run out of fuel. As it dies, it will swell so big that many predict that it will reach as far as Earth’s orbit. Naturally, the likelihood of the Earth still harbouring life may be debatable (after all 7 billion years is a long, long time), but should the human race still be around, and evolved into something totally unrecognizable, what will we see?

For starters, we’ll observe an impossibly big red disk, taking up most of the sky. The Sun would now be going through its Red Giant phase, where fusion has stopped in the core, but it continues in a shell around the core. The plasma surrounding will become more and more tenuous and the surface of the Sun will have cooled considerably. But where does that leave the Earth?

Solar radius evolution. Credit: K.-P. Schroder and R.C. Smith

Previous thinking suggests that the Sun will have devoured all the inner planets, including the Earth. But new research by K. Schroder (Universidad de Guanajuato, Mexico) and Robert Connon Smith (University of Sussex, UK) suggests that in this late phase of the Suns life, substantial quantities of mass will have been lost. As a planet orbits the Sun, should the mass of the Sun be reduced by the solar wind and radiation, the planet’s orbit should increase, and in the case of the Earth, saving it from a fiery death.

So, Smith’s team got to work…

Bad news.

The kicker is that the Sun will still swell like a balloon, burning up the Earth before it comes close to being promoted to a higher orbit.

So, the end is nigh… in 7 billion years time…

Saving Earth from the Sun’s expansion –


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