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.


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Sci-Fu Black Belt
Guest
Sci-Fu Black Belt
January 31, 2008 5:25 PM

So sad.

I think I’m going to cry.

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

Richard
Guest
Richard
January 31, 2008 5:47 PM

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

N Stone
Guest
N Stone
January 31, 2008 8:10 PM

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

___———-___
Black Hole Sun

Derek C. F. Pegritz
Guest
January 31, 2008 8:45 PM

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.

Johnny Blues
Guest
Johnny Blues
February 1, 2008 5:11 AM

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.

Brian
Guest
Brian
January 31, 2008 10:45 PM

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.

Brian
Guest
Brian
January 31, 2008 10:48 PM

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”?

Greg
Member
Greg
January 31, 2008 11:00 PM

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.

David Madison, Sr.
Guest
David Madison, Sr.
February 1, 2008 6:40 AM

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.

Chuck Lam
Guest
Chuck Lam
February 1, 2008 6:52 AM

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.

Phil
Guest
Phil
February 1, 2008 7:26 AM

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….

Muhammad Azhar
Guest
Muhammad Azhar
February 1, 2008 1:28 AM

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.

sophie
Guest
sophie
February 1, 2008 7:34 AM

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

Andrew
Guest
Andrew
February 1, 2008 8:02 AM

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.

Andrew
Guest
Andrew
February 1, 2008 8:09 AM

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.

Steve
Guest
Steve
February 1, 2008 8:33 AM

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.

John Mendenhall
Member
John Mendenhall
February 1, 2008 8:50 AM

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.

david
Guest
david
February 1, 2008 9:28 AM

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.

Andrew
Guest
Andrew
February 1, 2008 10:01 AM

David,

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.

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