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Earth scorched by red giant Sun

Will Earth Survive When the Sun Becomes a Red Giant?

9 May , 2016

by

Since the beginning of human history, people have understood that the Sun is a central part of life as we know it. It’s importance to countless mythological and cosmological systems across the globe is a testament to this. But as our understand of it matured, we came to learn that the Sun was here long before us, and will be here long after we’re gone. Having formed roughly 4.6 bullion years ago, our Sun began its life roughly 40 million years before our Earth had formed.

Since then, the Sun has been in what is known as its Main Sequence, where nuclear fusion in its core causes it to emit energy and light, keeping us here on Earth nourished. This will last for another 4.5 – 5.5 billion years, at which point it will deplete its supply of hydrogen and helium and go through some serious changes. Assuming humanity is still alive and calls Earth home at this time, we may want to consider getting out the way!

The Birth of Our Sun:

The predominant theory on how our Sun and Solar System formed is known as Nebular Theory, which states that the Sun and all the planets began billions of years ago as a giant cloud of molecular gas and dust. Then, approximately 4.57 billion years ago, this cloud experienced gravitational collapse at its center, where anything from a passing star to a shock wave caused by a supernova triggered the process that led to our Sun’s birth.

Basically, this took place after pockets of dust and gas began to collect into denser regions. As these regions pulled in more and more matter, conservation of momentum caused them to begin rotating, while increasing pressure caused them to heat up. Most of the material ended up in a ball at the center while the rest of the matter was flattened out into a large disk that circled around it.

Young stars have a disk of gas and dust around them called a protoplanetary disk. Out of this disk planets are formed, and the presence of water ice in the disc affects where different types of planets form. Credit: NASA/JPL-Caltech

Young stars have a disk of gas and dust around them called a protoplanetary disk. Out of this disk planets are formed, and the presence of water ice in the disc affects where different types of planets form. Credit: NASA/JPL-Caltech

The ball at the center would eventually form the Sun, while the disk of material would form the planets. The Sun then spent the next 100,000 years as a collapsing protostar before temperature and pressures in the interior ignited fusion at its core. The Sun started as a T Tauri star – a wildly active star that blasted out an intense solar wind. And just a few million years later, it settled down into its current form.

Main Sequence:

For the past 4.57 billion years (give or take a day or two), the Sun has been in the Main Sequence of its life. This is characterized by the process where hydrogen fuel, under tremendous pressure and temperatures in its core, is converted into helium. In addition to changing the properties of its constituent matter, this process also produces a tremendous amount of energy. All told, every second, 600 million tons of matter are converted into neutrinos, solar radiation, and roughly 4 x 1027 Watts of energy.

Naturally, this process cannot last forever since it is dependent on the presence of matter which is being regularly consumed. As time goes on and more hydrogen is converted into helium, the core will continue to shrink, allowing the outer layers of the Sun to move closer to the center and experience a stronger gravitational force.

This will place more pressure on the core, which is resisted by a resulting increase in the rate at which fusion occurs. Basically, this means that as the Sun continues to expend hydrogen in its core, the fusion process speeds up and the output of the Sun increases. At present, this is leading to a 1% increase in luminosity every 100 million years, and a 30% increase over the course of the last 4.5 billion years.

The life cycle of a Sun-like star, from its birth on the left side of the frame to its evolution into a red giant on the right after billions of years. Credit: ESO/M. Kornmesser

The life cycle of a Sun-like star, from its birth on the left side of the frame to its evolution into a red giant on the right after billions of years. Credit: ESO/M. Kornmesser

Approximately 1.1 billion years from now, the Sun will be 10% brighter than it is today. This increase in luminosity will also mean an increase in heat energy, one which the Earth’s atmosphere will absorb. This will trigger a runaway greenhouse effect that is similar to what turned Venus into the terrible hothouse it is today.

In 3.5 billion years, the Sun will be 40% brighter than it is right now, which will cause the oceans to boil, the ice caps to permanently melt, and all water vapor in the atmosphere to be lost to space. Under these conditions, life as we know it will be unable to survive anywhere on the surface, and planet Earth will be fully transformed into another hot, dry world, just like Venus.

Red Giant Phase:

In 5.4 billion years from now, the Sun will enter what is known as the Red Giant phase of its evolution. This will begin once all hydrogen is exhausted in the core and the inert helium ash that has built up there becomes unstable and collapses under its own weight. This will cause the core to heat up and get denser, causing the Sun to grow in size.

It is calculated that the expanding Sun will grow large enough to encompass the orbit’s of Mercury, Venus, and maybe even Earth. Even if the Earth were to survive being consumed, its new proximity to the the intense heat of this red sun would scorch our planet and make it completely impossible for life to survive. However, astronomers have noted that as the Sun expands, the orbit of the planet’s is likely to change as well.

When the Sun reaches this late stage in its stellar evolution, it will lose a tremendous amount of mass through powerful stellar winds. Basically, 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 who have addressed this very question. In a research paper entitled “Distant Future of the Sun and Earth Revisted” which appeared in the Monthly Notices of the Royal Astronomical Society, they ran the calculations with the most current models of stellar evolution.

According to Schroder and Smith, when the Sun becomes a red giant star in 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 expand, it will do so 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, at which point, 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 Will Earth Survive?:

Now this is where things become a bit of a “good news/bad news” situation. The bad news, according to Schroder and Smith, is that the Earth will NOT survive the Sun’s expansion. Even though the Earth could expand to an orbit 50% more distant than where it is today (1.5 AUs), 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.

Red giant. Credit:NASA/ Walt Feimer

Artist’s impression of a Red giant star. Credit:NASA/ Walt Feimer

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 right now, at 1.15 AU, it would be able to survive the expansion phase. If we could push our planet out to this distance, we’d also be in business. However, such talk is entirely speculative and in the realm of science fiction at the moment.

And now for the good news. Long before our Sun enters it’s Red Giant phase, its habitable zone (as we know it) will be gone. Astronomers estimate that this zone will expand past the Earth’s orbit in about 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, and it will eventually become molten.

Yeah, that’s the good news… sort of. But the upside to this is that we can say with confidence that humanity will be compelled to leave the nest long before it is engulfed by the Sun. And given the fact that we are dealing with timelines that are far beyond anything we can truly deal with, we can’t even be sure that some other cataclysmic event won’t claim us sooner, or that we wont have moved far past our current evolutionary phase.

An interesting side benefit will be how the changing boundaries of our Sun’s habitable zone will change the Solar System as well. While Earth, at a mere 1.5 AUs, will no longer be within the Sun’s habitable zone, much of the outer Solar System will be. This new habitable zone will stretch from 49.4 AU to 71.4 AU – well into the Kuiper Belt – which means the formerly icy worlds will melt, and liquid water will be present beyond the orbit of Pluto.

Perhaps Eris will be our new homeworld, the dwarf planet of Pluto will be the new Venus, and Haumeau, Makemake, and the rest will be the outer “Solar System”. But what is perhaps most fascinating about all of this is how humans are even tempted to ask “will it still be here in the future” in the first place, especially when that future is billions of years from now.

Somehow, the subjects of what came before us, and what will be here when we’re gone, continue to fascinate us. And when dealing with things like our Sun, the Earth, and the known Universe, it becomes downright necessary. Our existence thus far has been a flash in the pan compared to the cosmos, and how long we will endure remains an open question.

We have written many interesting articles on the Sun here at Universe Today. Here’s What Color Is The Sun?, What Kind of Star is the Sun?, How Does The Sun Produce Energy?, and Could We Terraform the Sun?

Astronomy Cast also has some interesting episodes on the subject. Check them out- Episode 30: The Sun, Spots and AllEpisode 108: The Life of the Sun, Episode 238: Solar Activity.

For more information, check out NASA’s Solar System Guide.

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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

Fraser Cain
Admin
January 31, 2008 6:36 PM

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.

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

harrison maguila
Guest
May 9, 2016 11:22 PM

yes probably!

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.

harrison maguila
Guest
May 9, 2016 11:25 PM

yes is very probably this one aha, or other here in the earth but If not the asteroids will take care of us, ejejjejejejeje we all will die. other rock more in the space, that’s it! sad neutral

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.

harrison maguila
Guest
May 9, 2016 11:28 PM

I am not sure of that but the earth don’t have the sufficient energy to go so far in the space also the space is very hostil place, but may be that could pass too, but I am not so sure this will be event will happen? ?

Ellen
Guest
Ellen
May 10, 2016 10:46 AM

it is said that the earth will be pulled towards a less massive sun when ours is expanding, but uman and animal life will be different and im 14 yrs old and i study this if u have questions email me

Mr Whizard
Member
Mr Whizard
May 10, 2016 1:36 PM

I’m glad you have a mind that is interested in these sort of things. You a little mistaken on the effects of gravity, and Relativity, but that OK, There’s plenty of time to learn more. You might want to read up on Issac Newton’s Laws of Motion and Gravity, as well as Albert Einsteins Theories of General and Special Relativity. It’s pretty heady stuff to be reading though, even for those with an understanding of it. Not for the faint of heart, but I encourage you to learn more.

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”?

Dark Gnat
Member
Dark Gnat
May 10, 2016 8:34 AM

We can’t. It’s a done deal.

Ellen
Guest
Ellen
May 10, 2016 10:48 AM

no its not actually it is said that the earth will be pulled towards a less massive sun wen our sun is expanding, but life on earth will be different so will animal life but thi sis 90% possible this is from scientist

Mr Whizard
Member
Mr Whizard
May 10, 2016 1:56 PM
n binary systems this can happen in some rare occasions. A white dwarf can strip the matter from a companion giant until it achieves sufficient mass to re-initiate it’s core fusion process. This has been observed already. @Ellen. Gravity is what holds all the planets in place. Not just the Sun’s gravity, but all the individual planets, and well as their individual and collective gravitational effect(s). The Sun’s gravity pulls the Earth towards it. The Earth’s gravity tries to pull back. At some point. The two gravitational effects will cancel out in a “Lagrangian Point” (look it up), and the two objects will fall into a nice orbit around each other. Locked in a long orbital dance that… Read more »
Mr Whizard
Member
Mr Whizard
May 10, 2016 1:54 PM
In binary systems this can happen in some rare occasions. A white dwarf can strip the matter from a companion giant until it achieves sufficient mass to re-initiate it’s core fusion process. This has been observed already. @Ellen. Gravity is what holds all the planets in place. Not just the Sun’s gravity, but all the individual planets, and well as their individual and collective gravitational effect(s). The Sun’s gravity pulls the Earth towards it. The Earth’s gravity tries to pull back. At some point. The two gravitational effects will cancel out in a “Lagrangian Point” (look it up), and the two objects will fall into a nice orbit around each other. Locked in a long orbital dance that… Read more »
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.

Qev
Member
Qev
May 10, 2016 3:41 PM

Mass isn’t really an issue with using asteroids to adjust Earth’s orbit, given that one can use each asteroid multiple times. The real limiting factor is time, and we have a fair bit of that.

In the interim we can mitigate the effects of the warming Sun in several ways. Perhaps the simplest would be to construct Saturn-like rings around the Earth to reduce insolation.

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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