What Will Happen To Our Sun In 7 Billion Years [Video]

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8 min readNov 15, 2019

It’s common knowledge nowadays that Earth’s sun won’t last forever. Our sun is burning along merrily as a middle-aged star, but in 5 billion years, as the sun ages, it’ll swell to become a red giant.

What’ll happen to Earth when our sun is some 100 times bigger than it is today?

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An international team of astronomers says they’ve found an analog to the future Earth/ sun system in the distant star L2 Puppis.

Five billion years ago, this star was very similar to our sun as we know it today.

Now L2 Puppis a red giant. What’s more, the team has found an object orbiting the red giant at a distance not terribly different from Earth’s orbit around our sun.

These astronomers’ work was published online December 8, 2016 in the peer-reviewed journal Astronomy & Astrophysics.

Leen Decin from the KU Leuven Institute of Astronomy was a member of the research team. She commented:

… the fate of the Earth is still uncertain. We already know that our sun will be bigger and brighter, so that it will probably destroy any form of life on our planet.

Five billion years from now, the sun will have grown into a red giant star, more than 100 times larger than its current size.

It will also experience an intense mass loss through a very strong stellar wind.

The end product of its evolution, 7 billion years from now, will be a tiny white dwarf star.

This will be about the size of the Earth, but much heavier: one teaspoon of white dwarf material weighs about 5 tons.

During our sun’s metamorphosis from ordinary star to red giant to white dwarf, both Mercury and Venus — worlds inside Earth’s orbit — will be engulfed and destroyed.

What Will Happen To Our Sun In 7 Billion Years [Video]

Earth won’t be engulfed. What will happen to it?

Composite view of L2 Puppis in visible light Image via P. Kervella et al / kuleuven.

Composite view of L2 Puppis and its planet candidate in visible light Image via P. Kervella et al / Kuleuven.

Astronomers are looking to L2 Puppis for answers.

This star is visible to the eye but very faint, located in our sky between the bright stars Canopus and Sirius. It’s 208 light-years away.

The newly found object orbiting L2 Puppis lies about 200 million miles (300 million km) from its star.

That’s in contrast to 93 million miles (150 million km) between our Earth and sun.

So the system is not an exact twin to ours, but these astronomers say it’s similar and:

… offers a unique preview of our Earth 5 billion years from now.

A deeper understanding of the interactions between L2 Puppis and its planet will yield valuable information on the final evolution of the sun and its impact on the planets in our solar system.

Whether the Earth will eventually survive the sun or be destroyed is still uncertain, these scientists say.

They think L2 Puppis may be the key to answering this question.

Meanwhile, how else can we think about the ultimate fate of Earth when our sun swells to its red giant phase?

What about what astronomer Leen Decin said above, about all life on Earth being destroyed?

Is that for certain?

The guys at ASAPScience don’t think so.

They created the video below to give you another answer to the question, involving moving the Earth!

Bottom line: Astronomers have found an object orbiting the red giant star L2 Puppis, which they say can provide insights into our Earth/ sun system as it ages.

Stars are born, they live, and they die.

The sun is no different, and when it goes, the Earth goes with it.

But our planet won’t go quietly into the night.

Rather, when the sun expands into a red giant during the throes of death, it will vaporize the Earth.

Perhaps not the story you were hoping for, but there’s no need to start buying star-death insurance yet.

The time scale is long — 7 billion or 8 billion years from now, at least. Humans have been around only about 40-thousandth that amount of time; if the age of the Earth were compressed into a 24-hour day, humans would occupy only the last second, at most.

What Will Happen To Our Sun In 7 Billion Years [Video]

If contemplating stellar lifetimes does nothing else, it should underscore the existential insignificance of our lives. [What If Earth Were Twice as Big?]

So what happens when the sun goes out?

The answer has to do with how the sun shines.

Stars begin their lives as big agglomerations of gas, mostly hydrogen with a dash of helium and other elements.

Gas has mass, so if you put a lot of it in one place, it collapses in on itself under its own weight.

That creates pressure on the interior of the proto-star, which heats up the gas until it gets so hot that the electrons get stripped off the atoms and the gas becomes charged, or ionized (a state called a plasma).

The hydrogen atoms, each containing a single proton, fuse with other hydrogen atoms to become helium, which has two protons and two neutrons.

The fusion releases energy in the form of light and heat, which creates outward pressure, and stops the gas from collapsing any further.

A star is born (with apologies to Barbra Streisand).

There’s enough hydrogen to keep this process going for billions of years. But eventually, almost all of the hydrogen in the sun’s core will have fused into helium.

At that point, the sun won’t be able to generate as much energy, and will start to collapse under its own weight.

That weight can’t generate enough pressure to fuse the helium as it did with the hydrogen at the beginning of the star’s life.

But what hydrogen is left on the core’s surface will fuse, generating a little additional energy and allowing the sun to keep shining.

That helium core, though, will start to collapse in on itself. When it does, it releases energy, though not through fusion.

Instead it just heats up because of increased pressure (compressing any gas increases its temperature).

That release of energy results in more light and heat, making the sun even brighter.

On a darker note, however, the energy also causes the sun to bloat into a red giant.

Red giants are red because their surface temperatures are lower than stars like the sun.

Even so, they are much bigger than their hotter counterparts.

In this artist conception, an expanding red giant prepares to swallow a too-close gas giant planet.

In the solar system, when the sun becomes a bloated red giant, it will engulf Mercury and Venus, and may devour Earth.

In this artist’s conception, an expanding red giant prepares to swallow a too-close gas giant planet.

In the solar system, when the sun becomes a bloated red giant, it will engulf Mercury and Venus, and may devour Earth.

A 2008 study by astronomers Klaus-Peter Schröder and Robert Connon Smith estimated that the sun will get so large that its outermost surface layers will reach about 108 million miles (about 170 million kilometers) out, absorbing the planets Mercury, Venus and Earth.

What Will Happen To Our Sun In 7 Billion Years [Video]

The whole process of turning into a red giant will take about 5 million years, a relative blip in the sun’s lifetime. [Interesting Facts About Earth]

On the bright side, the sun’s luminosity is increasing by a factor of about 10 percent every billion years.

The habitable zone, where liquid water can exist on a planet’s surface, right now is between about 0.95 and 1.37 times the radius of the Earth’s orbit (otherwise known as astronomical units, or AU).

That zone will continue to move outward. By the time the sun gets ready to become a red giant, Mars will have been inside the zone for quite some time.

Meanwhile, Earth will be baking and turning into a steam bath of a planet, with its oceans evaporating and breaking down into hydrogen and oxygen.

As the water gets broken down, the hydrogen will escape to space and the oxygen will react with surface rocks.

Nitrogen and carbon dioxide will probably become the major components of the atmosphere — rather like Venus is today, though it’s far from clear whether the Earth’s atmosphere will ever get so thick.

Some of that answer depends on how much volcanism is still going on and how fast plate tectonics winds down.

Our descendants will, one hopes, have opted to go to Mars by then — or even farther out in the solar system.

[What If Every Volcano on Earth Erupted at Once?]

But even Mars won’t last as a habitable planet. Once the sun becomes a giant, the habitable zone will move out to between 49 and 70 astronomical units.

Neptune in its current orbit would probably become too hot for life; the place to live would be Pluto and the other dwarf planets, comets and ice-rich asteroids in the Kuiper Belt.

One effect Schröder and Smith note is that stars like the sun lose mass over time, primarily via the solar wind. Planets’ orbits around the sun will slowly expand.

It won’t happen fast enough to save the Earth, but if Neptune edges far enough out it could become a home for humans, with some terraforming.

The death throes of this star have resulted in a gorgeous planetary nebula called NGC 6565.

The death throes of this star have resulted in a gorgeous planetary nebula called NGC 6565.

Eventually, though, the hydrogen in the sun’s outer core will get depleted, and the sun will start to collapse once again, triggering another cycle of fusion.

For about 2 billion years the sun will fuse helium into carbon and some oxygen, but there’s less energy in those reactions.

Once the last bits of helium turn into heavier elements, there’s no more radiant energy to keep the sun puffed up against it’s own weight.

The core will shrink into a white dwarf.

The distended sun’s outer layers are only weakly bound to the core because they are so far away from it, so when the core collapses it will leave the outer layers of its atmosphere behind.

The result is a planetary nebula.

Since white dwarfs are heated by compression rather than fusion, initially they are quite hot — surface temperatures can reach 50,000 degrees Fahrenheit (nearly 28,000 degrees Celsius) — and they illuminate the slowly expanding gas in the nebula.

So any alien astronomers billions of years in the future might see something like the Ring Nebula in Lyra where the sun once shone.

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