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Starts With A Bang

The science of how Earth will meet its ultimate end

The past ~4 billion years have been an incredibly successful, unbroken run for life on Earth. The future won't be nearly so bright.
When lower-mass, sun-like stars run out of fuel, they blow off their outer layers in a planetary nebula, but the center contracts down to form a white dwarf, which takes a very long time to fade to darkness. Over time, any remaining planets will lose gravitational radiation, where they’ll eventually merge with our sun’s stellar remnant. (Credit: Mark Garlick/University of Warwick)
Key Takeaways
  • Life on Earth has been surviving and thriving for over 4 billion years, but that's all going to change.

  • The sun will heat up, boiling Earth's oceans, and eventually become a red giant.

  • Many more catastrophic events will ensue, but Earth's ultimate end — falling into the sun's corpse — might not happen for 10^26 years.

For over 4 billion years, terrestrial life has survived and thrived.

This aerial view of Grand Prismatic Spring in Yellowstone National Park is one of the most iconic hydrothermal features on land in the world. The colors are due to the various organisms living under these extreme conditions, and depend on the amount of sunlight that reaches the various parts of the springs. Hydrothermal fields like this are some of the best candidate locations for life to have arisen on Earth. (Credit: Jim Peaco/National Parks Service)

But as time passes, future catastrophes will afflict planet Earth.

This cutaway showcases the various regions of the surface and interior of the sun, including the core, which is where nuclear fusion occurs. As time goes on, the region of the core where nuclear fusion takes place expands, causing the sun’s energy output to increase. (Credit: Wikimedia Commons/KelvinSong)

As the sun ages, its core expands and heats up, increasing the rate of nuclear fusion.

If all else fails, we can be certain that the evolution of the sun will cause the death of all life on Earth. Long before we reach the red giant stage, stellar evolution will cause the sun’s luminosity to increase significantly enough to boil Earth’s oceans, which will surely eradicate humanity, if not all life on Earth. The exact rate of increase of the sun’s size, as well as the details about its mass loss in stages, are still not perfectly known. (Credit: Wikimedia Commons/OliverBeatson)

After another 1 or 2 billion years, its energy output will boil Earth’s oceans away.

Today on Earth, ocean water only boils, typically, when lava or some other superheated material enters it. But in the far future, the sun’s energy will be enough to do it, and on a global scale. (Credit: Jennifer Williams via Flickr)

Subsequently, gravitational interactions among the inner planets perturbs their orbits.

The planets move in the orbits that they do, stably, because of the conservation of angular momentum. With no way to gain or lose angular momentum, they remain in their elliptical orbits arbitrarily far into the future. However, if they exert mutual forces on each other and the sun takes up a finite volume, the gravitational and tidal forces exerted could lead to evolutionary scenarios so chaotic that one or more of these planets may eventually get ejected. (Credit: NASA/JPL/J. Giorgini)

There’s a small probability that each rocky planet, including Earth, gets ejected.

When a planetary body gets gravitationally perturbed by a great enough amount, its orbit can become unstable, leading to a catastrophe like ejection or getting hurled into the sun, as illustrated here for HD 189733b, a planet getting devoured by its parent star. (Credit: NASA/GSFC)

After 4 billion years, the inevitable Andromeda-Milky Way merger occurs.

A series of stills showing the Milky Way-Andromeda merger, and how the sky will appear different from Earth as it happens. This merger will occur roughly 4 billion years in the future, with a huge burst of star formation leading to a red-and-dead, gas-free elliptical galaxy: Milkdromeda. A single, large elliptical is the eventual fate of the entire local group. Despite the enormous scales and numbers of stars involved, only approximately 1-in-100 billion stars will collide or merge during this event. (Credit: NASA; Z. Levay and R. van der Marel, STScI; T. Hallas; A. Mellinger)

Despite new star formation, supernovae, and stellar collisions, Earth likely remains unaffected.

After approximately five to seven billion years from now, the sun will exhaust the hydrogen in its core. The interior will contract, heat up, and eventually helium fusion will begin. At this point, the sun will swell, vaporize Earth’s atmosphere, and char whatever’s left of our surface. But even when that catastrophic event occurs, Earth may not be swallowed, remaining a planet, albeit a very different one from the world we know today. (Credit: ESO / L. Calçada)

A few billion years later, the sun becomes a red giant.

As the sun becomes a true red giant, the Earth itself may be swallowed or engulfed, but will definitely be roasted as never before. Venus and Merucry won’t be so lucky, as the sun’s red giant radius will handily encompass both of our Solar System’s innermost worlds, but it’s estimated that Earth will be safe by approximately 10-to-20 million miles. (Credit: Wikimedia Commons/Fsgregs)

Destined to engulf Mercury and Venus, Earth’s fate remains in doubt.

When the sun has completely run out of its nuclear fuel, it will blow off its outer layers into a planetary nebula, while the center contracts into a hot, compact white dwarf star. It is uncertain whether this process will push Earth far enough away so that it avoids being drawn into the central stellar remnant, or whether our planet will meet our demise during this process. (Credit: V. Peris, J. L. Lamadrid, J. Harvey, S. Mazlin, A. Guijarro)

Stellar mass loss pushes Earth’s orbit outward; we may yet survive.

After the sun exits its red giant phase, its blown-off outer layers dissipate, and only a white dwarf remains, numerous planets, including, potentially, Earth, will remain. If this event doesn’t destroy our planet, we’ll likely survive for another ~10^26 years or so. (Credit: David A. Aguilar / CfA)

If so, we’ll orbit our remnant white dwarf for aeons to come.

When a large number of gravitational interactions between star systems occur, one star can receive a large enough kick to be ejected from whatever structure of which it is part. We observe runaway stars in the Milky Way even today; once they’re gone, they’ll never return. This is estimated to occur for our sun at some point between 10^17 to 10^19 years from now, with the latter option more likely. However, most scenarios involve the Earth-moon system remaining bound to the sun when this occurs. (Credit: J. Walsh and Z. Levay, ESA/NASA)

After ~1019 years, massive interactions eject most stars and solar systems.

Particular configurations over time, or singular gravitational interactions with passing large masses, can result in the disruption and ejection of large bodies from solar and planetary systems. In the early stages of a solar system, many masses are ejected just from the gravitational interactions arising between protoplanets, but in the late stages, it’s only random encounters that cause planetary ejections, and those are rarer than the ones that will eject entire solar systems. (Credit: S. Basu, E. I. Vorobyov, and A. L. DeSouza; arXiv:1208.3713)

Earth, however, remains orbiting our stellar remnant, with gravitational radiation causing an inspiral.

The effects of our planet moving and accelerating through the curved spacetime induced by the central mass anchoring our solar system will cause Earth’s orbit to eventually decay. This loss of energy due to gravitational radiation is slow but steady, and will cause the actual demise of our planet after ~10^26 years. (Credit: American Physical Society)

After ~1026 years, tides will fatally rip the planet apart.

When a single, massive body gets too close to a larger mass, the tidal forces become significant enough to overcome the gravitational binding energy, ripping the object apart and stretching it out into a ring, before it rains down and settles on the surface of the more massive body. The sun’s remnant may do this to the Earth in ~10^26 years. (Credit: NASA/JPL-Caltech)

The sun’s black dwarf corpse will finally devour Earth’s remnant ashes: our ultimate end.

After the sun becomes a black dwarf, if nothing ejects or collides with the remnants of Earth, eventually gravitational radiation will cause us to spiral in, be torn apart, and eventually swallowed by the remnant of our sun. (Credit: Jeff Bryant/Vistapro)

Only the rare, isolated, ejected planets will remain intact for longer.

Rogue planets may have a variety of exotic origins, such as arising from shredded stars or other material, or from ejected planets from solar systems, but the majority should arise from star-forming nebula, as simply gravitational clumps that never made it to star-sized objects. When a microlensing event occurs, we can use the light to reconstruct the intervening planet’s mass. (Credit: C. Pulliam, D. Aguilar/CfA)

Mostly Mute Monday tells an astronomical story in images, visuals, and no more than 200 words. Talk less; smile more.

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