AMU Content Type* Editor's Pick Opinion Original Space

What Would Happen if Earth Was Flung Out of the Solar System?

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By Wes O’Donnell
Managing Editor, AMU Edge

Author’s note: This article is pure speculation. Some facts were obtained from astronomers and scientists, who warn the reader to take this article with a grain of salt.

It’s not often that I experience existential dread. In fact, it’s downright rare. As the clock wound down to midnight on December 31, I was doing what most 40-somethings do on New Year’s Eve — lie in bed and flip through TV stations to find something to doze off to.

It was then that a thought entered my mind unbidden: What if an errant star or large rogue planet made a close pass of our solar system? What disruptions might that cause to our daily lives?

I’m not a scientist, merely a science writer. But I know enough about physics to know that a large interstellar traveler, of which there are many, wouldn’t have to collide with anything to cause Earth to have a real bad day. Its gravitational influence would be more than enough.

I sat upright in bed, my hands suddenly cold and clammy. I may not be outright nihilistic, but I am usually quite blasé about civilization-ending events. After all, they are rare. But for some unknown reason, this thought galvanized my imagination.

70,000 Years Ago, a Red Dwarf Star Came Close to Our Solar System

It turns out that 70,000 years ago, when humans were first leaving Africa, a red dwarf known as Scholz’s star passed through the Oort comet cloud that insulates our solar system, approaching to within 0.6 light-years of Earth.

The Oort cloud has never been observed, but is believed to have at least 1012 icy objects located between 3,000 astronomical units (AU) and 100,000 AU in a spherical distribution around the Sun. Illustration courtesy NASA/JPL

The main issue with the disruption of the Oort cloud is that it could send tens of thousands of disturbed comets toward our inner solar system, an event which would result in a planetary bombardment that would certainly make life on Earth exciting. The sky could be filled with comets and asteroids raining down on Earth in an apocalypse that would rival the chaos of the early solar system.

Fortunately, it’s estimated that the comets from the Oort cloud would require roughly two million years to get to our inner solar system. We haven’t yet experienced the effects of Scholz’s star flyby, but our antecedents may have to contend with it.

What Would Happen If a Rogue Star Entered the Inner Solar System and Flung Earth Away from the Sun?

But what would happen if a rogue star entered the inner solar system? Buckle up — this is where things get interesting.

The chance of another star colliding directly with our sun is astronomical, but that’s not what kept me up on New Year’s Eve. If another star were to pass as close as Earth is to the Sun (93 million miles), its gravitational influence could eject Earth right out of the solar system.

Much like Voyager 2’s gravity assist, an object with more gravity passing close by Earth could fling us right out of the solar system or have the opposite effect — slow down our orbit enough that we simply fall into the Sun. Maybe it’s time to buy some SPF 6,000,000 sunblock. Pictured: Animation of Voyager 2’s trajectory from 20 August 1977 to 31 December 2000. Phoenix7777 CC BY-SA 4.0.

The odds of such an event are about 1 in 100,000 in the next 5 billion years: implausible, but not impossible.

As the hypothetical red dwarf star entered our solar system, we would see a reddish dot appear in our night sky that would grow bigger and bigger over the next several months. After time, it would be visible during the day and be much brighter than a full moon. The night sky would be filled with a strange orange glow.

After a few more months, the star would start shrinking again, but so would our sun as we began our journey out of the solar system.

By the time we reach the orbit of Mars, our global temperature will have dropped by 59 degrees Fahrenheit.

The chances of us hitting another planet on our way out are extremely low, due to the sheer size of the solar system, but we might catch one or two rocks as we pass through the asteroid belt located roughly between the orbits of the planets Jupiter and Mars. Then again, those asteroids are spaced out pretty far.

After a few years, the sun will continue to shrink smaller as we move away, and Earth will descend into perpetual night. Once we reach the orbit of Jupiter, nearly all plant life will be dead, resulting in mass extinction all across the planet.

Without plants to renew our oxygen supply, we’re left with only the gases that currently have in our atmosphere. By one year, the temperature will have dropped to a frosty -103 degrees Fahrenheit. At this point, Earth’s oceans will be covered in several meters of ice.

Any humans left living on the surface would be living on borrowed time. They may huddle together indoors, burning what they can for warmth, but finding food at this point would be a real issue.

Without the energy from sunlight to evaporate water, clouds don’t form and the water cycle grinds to a halt. Eventually, the polar ice caps will meet at the equator, forming what geologists call “Snowball Earth.”

Due to the increasing thickness of ice over the oceans, the concentration of salt in the ocean would increase and kill most sea animals who have survived up to this point.

By the time we reach the orbit of Pluto, the temperature will be only tens of degrees above absolute zero, enough to freeze the gases in the atmosphere. This would cause a peculiar snow of nitrogen and oxygen as our once life-sustaining atmosphere gently falls to the ground.

As Earth finally exited the solar system, it would then become a rogue planet, traveling the interstellar void in darkness and solitude.

But Would All Human Life Be Lost?

Would humanity face total extinction in such a scenario? Not quite.

Humans wouldn’t be surprised by such an event; if we’re lucky, we might have years of warning of the approaching star. Most of humanity would certainly die, but a few million could survive by preparing large, airtight shelters that are powered by geothermal or nuclear energy.

Humanity may be able to survive in this way for tens of thousands of years. Future generations would listen to stories about how we used to have our own star and be awed that our ancestors used to walk the surface with nothing but a thin layer of clothing.

Fortunately, such an event is unlikely in the extreme. But such thought experiments make us realize how lucky we are to be positioned so close to a stable, life-sustaining main sequence star. Our ancient ancestors used to worship the Sun as a god and for good reason — our Sun empowers life.

Wes O’Donnell is an Army and Air Force veteran and writer covering military and tech topics. As a sought-after professional speaker, Wes has presented at U.S. Air Force Academy, Fortune 500 companies, and TEDx, covering trending topics from data visualization to leadership and veterans’ advocacy. As a filmmaker, he directed the award-winning short film, “Memorial Day.”

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