Artist's impression of a red giant star.
Artist's impression of a red giant star.

Astronomy, Earth, Guide to Space

Will Earth Survive When the Sun Becomes a Red Giant?

31 Jan , 2008 by

Billions of years in the future, when our Sun bloats up into a red giant, it will expand to consume the Earth’s orbit. But wait, you say, the Earth travels the Earth’s orbit… what’s going to happen to our beloved planet? Will it be gobbled up like poor Mercury and Venus?

Astronomers have been puzzling this question for decades. When the sun becomes a red giant, the simple calculation would put its equator out past Mars. All of the inner planets would be consumed.

However, as the Sun reaches this late stage in its stellar evolution, it loses a tremendous amount of mass through powerful stellar winds. As it grows, it loses mass, causing the planets to spiral outwards. So the question is, will the expanding Sun overtake the planets spiraling outwards, or will Earth (and maybe even Venus) escape its grasp.

K.-P Schroder and Robert Cannon Smith are two researchers trying to get to the bottom of this question. They’ve run the calculations with the most current models of stellar evolution, and published a research paper entitled, Distant Future of the Sun and Earth Revisted. It has been accepted for publication in the Monthly Notices of the Royal Astronomical Society.

According to Schroder and Smith, when the Sun becomes a red giant star 7.59 billion years, it will start to lose mass quickly. By the time it reaches its largest radius, 256 times its current size, it will be down to only 67% of its current mass.

When the Sun does begin to bloat up, it will go quickly, sweeping through the inner Solar System in just 5 million years. It will then enter its relatively brief (130 million year) helium-burning phase. It will expand past the orbit of Mercury, and then Venus. By the time it approaches the Earth, it will be losing 4.9 x 1020 tonnes of mass every year (8% the mass of the Earth).

But the habitable zone will be gone much sooner. Astronomers estimate that will expand past the Earth’s orbit in just a billion years. The heating Sun will evaporate the Earth’s oceans away, and then solar radiation will blast away the hydrogen from the water. The Earth will never have oceans again. It will eventually become molten again.

One interesting side benefit for the Solar System. Even though the Earth, at a mere 1.5 astronomical units, will no longer be within the Sun’s habitable zone, much of the Solar System will be. The new habitable zone will stretch from 49.4 AU to 71.4 AU, well into the Kuiper Belt. The formerly icy worlds will melt, and liquid water will be present beyond the orbit of Pluto. Perhaps Eris will be the new homeworld.

Back to the question… will the Earth survive?

According to Schroder and Smith, the answer is no. Even though the Earth could expand to an orbit 50% larger than today’s orbit, it won’t get the chance. The expanding Sun will engulf the Earth just before it reaches the tip of the red giant phase. And the Sun would still have another 0.25 AU and 500,000 years to grow.

Once inside the Sun’s atmosphere, the Earth will collide with particles of gas. Its orbit will decay, and it will spiral inward.

If the Earth were just a little further from the Sun, at 1.15 AU, it would be able to survive the expansion phase. Although it’s science fiction, the authors suggest that future technologies could be used to speed up the Earth’s spiraling outward from the Sun.

I’m not sure why, but thinking about this far future of the Earth gives an insight into human psychology. People are genuinely worried about a future billions of years away. Even though the Earth will be scorched much sooner, its oceans boiled away, and turned into a molten ball of rock, it’s this early destruction by the Sun that feels so sad.

Original Source: Arxiv

By  -          
Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

67 Responses

  1. Sci-Fu Black Belt says:

    So sad.

    I think I’m going to cry.

    Thanks a lot! This is not what I need to hear.

  2. Richard says:

    Thanks a lot but science might change and the might come with new formual

  3. Fraser Cain says:

    Oh it probably will. This is based on the most cutting edge theories for red giant expansion and mass loss. There could be new calculations in the future that bring it around to the Earth’s survival.

  4. N Stone says:

    I think we’ll all be dead before a couple billion years

    Black Hole Sun

  5. This ball of raw materials will have been stripmined for atomic matter to use in building computronium long before the sun’s aging becomes a concern for the biosphere.

  6. Johnny Blues says:

    Oh yeah, push the earth out to a safe distance. Not. Life on earth will end as soon as the asteroid belt is jumbled up and meteors come screaming in from every direction. There won’t be a safe hole in the solar system to hide.

  7. Brian says:

    Shields, anyone?

    Seriously though, who knows what will happen to the human race in a billion years. By that time, we will at least have a greater understanding of what can be done, if anything, to save our planet. Or perhaps we will have evolved, or moved on to another star system. One thing that all of us can do to prepare is buy as many shares in Coppertone as we can.

  8. Brian says:

    One question I did forget to ask, is there a way (theoretical) to stop a sun from becoming a red giant? Correct me if I’m wrong, but doesn’t this happen when the star’s fuel source (ie: hydrogen) runs low? How might we “fill the tank up again”?

  9. Greg says:

    Most likely we will have maneuvered asteroids into new orbits around the Earth such that they will impart orbital energy to the Earth and push its orbit out artifically. The moon would probably be lost, unless some effort is made to save it as well. Of course any miscalculation would likely result in a catastrophic asteroid impact. Also we are assuming that mankind has not already driven itself to extinction and we survive that long.

  10. David Madison, Sr. says:

    Muhammad Azhar had by far the best response. Understand the scale of what he said.

    All solutions proposed so far are futile. Take just one for instance. Using asteroids cannot work because collectively they do not have significant mass.

  11. Chuck Lam says:

    I suspect Schroder and Smith are nearly 100% correct in their projections. The bigger more interesting question is will humans still be around to witness this solar expansion? Probably not unless some heretofore yet undiscovered phenomenon is exploited before the expansion that will allow practical space travel and colonization. Based on current developing propulsion technology, a space vehicle sent to the solar system’s nearest neighboring star will span thousands of generations traveling in space. It is challenging to wrap your mind around the chances of survival for an evacuation effort on the scale needed for human survival. The distances are simply too great and the human too fragile.

  12. Phil says:

    WELL I’VE GOT DIBs ON EUROPA… I’ve always liked the ocean!!!

    Seriously… if there are humans around in 4-5 million years they won’t be anything like we are now (e-v-o-l-u-t-i-o-n!!)….. You guys are talking about BILLIONS of years in the future!!! This is all speculation anyway but I bet there won’t be “humans” (like we know them) around to care….

  13. Muhammad Azhar says:

    Believe me human beings should not be worried about the future far far in billion years because there are lot of other resources to completely destroy our planet within just next 1000 years. Human beings have not been on the planet even for the last million years and we are thinking about billions!! waste of time. The planning of Human beings can work only upto 200 years in advance and after that every thing is upto nature. All the calculations will finally be proven wrong and our future generations will call us fools and ignorant ancients.

  14. sophie says:

    thanx for the information………….
    technology is developing,may be by that time we may have shifted to some other solar system………..
    hope so…….

  15. Andrew says:

    To Phil,

    I don’t believe humans are evolving naturally anymore as there are no selective pressures acting on the population.

    That’s my understanding, but I could be wrong.

  16. Andrew says:

    Unless society crumbles sometime in the future and/or the government starts releasing tigers periodically on the general population.

    Then maybe we could get evolution back in gear.

  17. Steve says:

    I’ll have to agree with Andrew. We’ve nearly done away with natural selection so our evolution won’t continue in the “classic” sense. We as a species may even have lost the ability to adapt to gradual changes in our environment, let alone the rapid changes we’re causing ourselves. So in all likelyhood, humans will be extinct in substantially less than the timescales talked about in the article.

  18. John Mendenhall says:

    Lam “Based on current developing propulsion technology, a space vehicle sent to the solar system’s nearest neighboring star will span thousands of generations traveling in space.”

    I think you are off by several orders of magnitude on the time required. With current technology, 1/10 c is possible for an unmanned no deceleration probe to A. Centauri. Allowing a conservative 1/100c for a generation ship and 33 years per generation, it’s still only 12 generations. Even at 1/1000c, or 186 miles per second, only 120 generations are required. For reference, low Earth orbit satellites move at about 5 miles per second.

  19. david says:

    I disagre with the idea that humans have or will stop evolveing. Instead of adapting to the natural world we will adapt to the artifical one we create. However sence we design our artifical environments to sute how we are now I could, in retrospect, expect a slowdown in evolution.

    But sence tha average lifespan of all previous hominid species is only 250,000 years this may all be a little academic.

  20. Andrew says:


    Evolution is not adaption. It is a change in gene frequency in response to selective pressures, and because human society protects those individuals who would normally be selected out we have essentially stopped our natural evolution. We won’t design artificial enviroments to be selective because that goes against basic human morality. You just don’t design something which selectively kills or makes infertile a certain group of people. It’s just not cool.

    This is not to say that we cant’ change technologically, socially, ethically or even change physically but this will not be an evolutionary change.

    One thing I forgot though is susceptibility to disease, which is still a selective pressure in places that lack proper medication.

  21. Martin Beech says:

    In response to the question by Brian – is there any way of stopping the Sun from becoming a red giant? The answer is yes. It will need to be fully mixed and reduced in mass over time. The Sun starts to become a red giant after consuming only about 1/10th of its total hydrogen supply, so the mixing allows it to convert all of its hydrogen into helium. The mixing also stops the Sun from swelling up into a giant star. The mass loss is needed to reduce the luminosity increase with age.

    With shameless advertising a book on this topic has recently been published by Springer called Rejuvenating the Sun and avoiding other global catastrophies (buy and enjoy).

  22. Gerald McKeegan says:

    Actually, there is considerable evidence that human evolution is proceeding at a faster rate today than it did 10,000 years ago. Because the Earth is now over-populated with humans, the number of minor genetic mutations per time period is substantially higher than it was thousands of years ago. And because of over-population, the opportunities for those mutations to be passed on to new generations are much greater.

  23. Brian says:

    All we need to figure out now is how to mix a star, and reduce its mass.

  24. Chuck Lam says:

    To John M. Your math is interesting. However, take another look at your numbers. Alpha C is over (4) light years from earth. (12) to (120) generations to reach Alpha C. I don’t think so!

  25. RAy mowlam says:

    yea like the human race is goin survive that long…. the dinosaurs were aronud for millions of years and we hav been here for the blink of an eye in astronomical terms and already set about destrying our home… we are already past the point of no return,… Im worried for the future of my children, but they dont seen to care.! RAy

  26. Essel says:

    I think there are serious deficiencies in the article:

    The current age of sun is 4.57 billion years.

    [Sun becomes a red giant star 7.59 billion years]

    [When the Sun does begin to bloat up, it will go quickly, sweeping through the inner Solar System in just 5 million years. It will then enter its relatively brief (130 million year) helium-burning phase]

    The above does not match with: [But the habitable zone will be gone much sooner. Astronomers estimate that will expand past the Earth’s orbit in just a billion years.]

    Can someone explain?

  27. Paul says:


    “Sun becomes a red giant star 7.59 billion years” – that’s in 7.59 billion years from now

    “When the Sun does begin to bloat up, it will go quickly, sweeping through the inner Solar System in just 5 million years. It will then enter its relatively brief (130 million year) helium-burning phase” – these seem consistent with the other figures – millions not billions

    “The above does not match with: [But the habitable zone will be gone much sooner. Astronomers estimate that will expand past the Earth’s orbit in just a billion years.]” – this is about how the habitable zone of the solar system changes while the Sun is still in it’s Main Sequence phase – long before the final Red Giant convulsions. The full article declares that the Sun’s luminosity will increase 10% in the next billion years – making it too hot for us here! Mars might be quite comfortable. The Sun will still be pretty much the same diameter as it is now.

  28. Mal says:

    It is romantic to think our species will be around in some form at that future time, and will have adapted and evolved to a point where we can escape to a safe haven.
    However , we evolved here with the sun as our life force, I think , if we are still here , it is fittng that our evolution comes to an end when the sun reaches its evelutionary end. Isn’t many billions of years (if we are very lucky) more than enough for any species?

  29. MJG says:

    […Brian Says: All we need to figure out now is how to mix a star, and reduce its mass….]

    Y’all can use my blender, but I’ll need it back for margaritas. A Kitchenaid professional mixer might hold up better, though… lolz!

  30. David Madison, Sr. says:

    To put future billions of years in perspective, in less than one tenth that time in the past, our most highly evolved ancestors were one celled microbes. Species normally survive only one or ten million years before going extinct. Man is a species. Our tendency is to assume that we will live longer because . . . and we find a because that suits our emotions.

    As for not evolving any more, somewhere recently I read a magazine article, Time or Discover or some such, that made Gerald McKeegan’s case that the human race is presently evolving 160 times faster now than it was in the past. Yeah, it surprised me too, even though the Darwin Award winners remind me that some people today are hell bent on improving the gene pool.

    Last thought. You cannot extend the life of the sun by adding mass. That would shorten its life because it would then burn its total fuel supply faster.

  31. loveall says:

    Don’t forget Andromeda! Much before the sun bloating up, there could be a galactic collision with our neighbour, which might even throw us out of the Milky way. Everything would be changed. The sun may be orbiting a black-hole or some other supergiant. We need a real megasuper computer to calculate all that. Hence a second revisit!

  32. Peter K says:

    How this affects us humans is a moot point. We most certainly will not be here, either cuz it isn’t us, or because we’ve moved on. It will destroy our history though ): However, that will happen much, much sooner when the sun warms up in some 500 million years. Only a tiny portion of humanity has to survive to keep us genetically viable and allow the species to continue to live and evolve. Think of the ships, giant solar sails flying, heading out on the solar wind from our burgeoning red giant sun. And as for Alpha Centauri, who’s to say IT will still be around? That’s one hell of a long time. Let’s do some quick math…(just in case) A.Centauri at 4 light years…therefore 4 years at light speed, 40 years at 1/10 light speed. Chuck Lam…how fast do you think we’ll be going in half a million years, let alone 7 billion? You scoffed at 120 generations…that’s 2400 years! That’s only 1/600th the speed of light. I tried to work out acceleration of 1 g for 20 years turning around at mid trip and decelerating for the rest but even though it gave me some odd numbers, it did suggest that we could make it to a substantial portion of c and therefore enjoy some time dilation on the way! Like a 40 year mort-gage BUT paid off BI-weekly!

  33. ziiphly says:

    Sun will heat up as it ages during it’s life as a main sequence star, in mere millions (let alone billions) it will be far too hot to survive on this planet. Hopefully by then we will have technology comparable to the forerunner in “Halo” and moving planets around and terraforming, even making new worlds to live on would be trivial; but it’s more likely we’ll kill each other before then, in a matter of centuries, if not decades.

  34. akshaya says:

    thank u so much for this info & i feel so sad for my generations

  35. Cool person says:

    This is really stupid of people, y r we worring about something the human race might not even get a chance to experience, i mean we do have billions of years to evolve.We might turn into something brainless, and by the way i do think that we will kill r selfs before this has a chance to happen.We’ll sooner or later start a nuclear war or maybe global warming will turn everthing into deserts, like wat happened to the creatures before the dinosaurs (everthing turned to deserts, killing 99% of the earths creatures)

  36. Cool person says:

    ohh and one more thing even if we have the tech. to avoid the sun, it will still vaporize every ocean on the planet.And if we hav the tech to avoid it by a long shot then the sun will sooner or later going to die and turn into a black hole and everyone knows we can live without sunlight.The only way we can survive is to find a terastrial planet and try to get to it and live in it.

  37. Jon W. says:

    No!!! We Must survive!!! After all, since all other possible intelligent life out there is supposedly super friendly, the universe needs and intelligent specie to rise to power and make life miserable for them all. The way so many talk, I think it means we are the best candidate to make that happen, right?

    So, we must survive if only to make other aliens miserable!!! Muwhahahah!!!

  38. Mr D says:

    i know i wont proberly live to see the world end be it war, global warming, exploding sun but if i do i would be so glad. Think about it the human race is one hell of an evil race we have mass murded fellow humas for beliving something different we invade countrys for its oil and in the process kill others. These are so small topics in the universe if aliens visted us and we told them we were on the verge of necular war they would proberly laugh at us and why aliens even want to vist us any way were rude, greedy stupid.

  39. Yngve Holmqvist ( Mr ) says:

    Long before our planet goes into the first of many final stages, human technology has created spacecraft for emigration to other planets. An including all the means for developing a biological, that is, real life. I am quite convinced about this. But it is a sad fact to encounter, for all of us: the death of Tellus. The fragile frame of our lives here on earth, the very short time we exist, is a sad fact. Existence is, on the other hand, a wise construction or creation: when we have lived, we go to rest again. This is, for me, a proof of a divine force behind it all. Rest is peaceful sleep forever. Creating love and humane conditions on earth is our timeless task. Never lose your hope. Life is too precious.

  40. louis says:


  41. Iyad Hijazi says:

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    Part 3. Sun Grows Into Red Giant

  42. julie says:

    hey i need to know what impact would be on fuels if there were no sun????/

  43. destiny says:

    i bet the sun is gettin bigger every decade or so. man! i wish the universe didn’t have to go down so bad i wish. to bad i won’t be able to see the earth die or survive. plus it will take a long time to go to a solar system similar to or the milkay way. maybe we can use that theory it’s called, Attackons. it can go way faster than light travel. it would take 100 million years to reach the cloest star ever!!!!!!!!! man those scenitists better act fast so we can live on a planet just like earth. mars!! are u kiddin me! no way hosa i ain’t gonna die because of that sun destroyin those inner planets.

  44. destiny says:

    the fuels will be gone when the sun dies, juile.

  45. destiny says:

    ii swear why did god make us worry about so much hell that’s gonna happen later in life? why god why?

  46. Fatboy slim says:

    Travon,.. why you gotta be a hater. True it is gods plan, but that doesn’t means existence will end. After all, during the beginning of sun’s transformation human beings should adapt to the constantly rising temperatures. Just perhaps we won’t have to leave earth will might just aquire the ability or organs to breathe with no oxygen or possibly survive in the earth’s crust like mole men. Also, I think that deep down inside no nation is crazy or insane enough to launch a nuclear attack. Humans will eventually realize that the idea of wiping out whole nations is an unreasonable and unwanted resolution to win a war or obtain resources.

  47. BenDavis himself says:

    Technology will be modified to deal with these circumstances. I think that once humans realize that their all about to die in a twisted dry death. All nations will unite and an amazing invention will be forged from the minds of top scientists around the planet. Perhaps the Earth will develop their once custom made atmosphere to protect against the heat and provide oxygen. Maybe a giant rocket would be built on earth to launch the earth many billions of light years away to safe haven in another galaxy. Although i am not sure which will happen I have foreseen the earth’s survival in meditation. God’s speed to you all! *BD*

  48. giant ballz says:

    I’m sorry, I will correct myself, the sun is not large enough to eventually turn into a black hole, so erase that part

  49. Aydan says:

    I doubt humans will become extinct, we’ve so far in such a short amount of time, makes you really appreciate the human capacity to advance.

    Human’s might be destructive in nature, but I believe that’s because we’re meant to be, a huge part of our technological advancement has come about through conflict, I’d go so far as to say WE NEED IT. An example I like to use is Velcro:

    War between Soviets and Americans results in practical rocket technology, rocket technology sparks space race resulting in Nasa, Nasa creates Velcro because astronauts are unco.
    War > Nasa > Velcro.

    As for space travel, I think it would be easier if we just turned the Earth into a spaceship and layered it to accommodate for earth’s expanding population.

    I’d be more worried about Earth’s rapid climate change than the sun though :)

  50. Candice says:

    Earth is only about 4.6 billion years, we’re even a little than a half way and human in the future would be different and more intelligence.

  51. Robert says:

    Hmmm.. billions of years from now we will have evolved into a new species.. more intelligent I hope. possibly not even needing a physical body. Yes we are evolving… getting taller, more people with not enough room on their jaw for wisdom teeth.
    We will have either destroyed ourselves, been destroyed by an asteroid or comet impact, or we would have conquered space itself and spread through at least the galaxy if not even to other galaxies in the next few million years. No need to worry about our sun expanding into a Red Giant.

    • Tommy says:

      you are correct sir, which is admirable. we will evolve and stop it before it happens.

  52. karen says:

    Well, I think that no human beings will ever survive the problems today coz after every species of every kind and every drop of water(drinkable water is just .5%!!) is gone, there is NO food, NO water and NO clean air to breath with. How can we be able to survive that? It would be a miracle. I think we wont be able reach that phase of life on Earth.

  53. mload says:

    theater the earth will survive until the moom map of iapeted

  54. JAMES says:

    which contains more ‘SPACE’. a feather, or 1, 000,000 planets…
    both are empty space
    subatomically apeaking….

  55. keke says:

    i think that the earth will take a long time to end

  56. brooke says:

    i dont know much im only ten but if you mind will you stop talking about this im acualy scared now soo plz!?

  57. elizebeth says:

    i am only 12 and i dont know what to do

  58. bobby says:

    this is stupid know one knows

  59. win says:

    im trying to get readers to my blog too and was wondering if i could purchase a link in your blog roll via paypal? let me know – thanks :)

  60. trish says:

    if you guys don’t want to talk about it. then leave this site lol. .freaaaaaaaaaks

  61. trish says:

    yeah!. no one knows when or how will end this. only God knows.

  62. Tommy says:

    the earth will be consumed in billions of years. you have nothing to worry about.nothing gonna happen in your lifetime.

  63. Tommy says:

    the earth will be consumed in billions of years. you have nothing to worry about.nothing gonna happen in your lifetime.

  64. Anonymous says:

    All you people worrying, read it carefully.
    We will all be dead and no one will be alive when this happens, its states that even before the Sun is close to us, the Earth will be inhabitable in the first place, and this is 7.59 billion years away, even more. Because 7.59 billion years is when they estimate it to start. So don’t worry!

  65. Anonymous says:

    All you people worrying, read it carefully.
    We will all be dead and no one will be alive when this happens, its states that even before the Sun is close to us, the Earth will be inhabitable in the first place, and this is 7.59 billion years away, even more. Because 7.59 billion years is when they estimate it to start. So don’t worry!

  66. riey goodieguy says:

    and the doomsday god only knows. not tomorrow or 21.12.12

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