Travel the universe with Dr. Ethan Siegel as he answers the biggest questions of all
Beyond the oceans boiling and the death of our Sun, Earth’s ultimate fate won’t be determined until far in the distant future.
It took the Universe 13.8 billion years to create planet Earth as we know it, but we won’t last forever.
When two bodies crash into one another in space, the resulting collision can be catastrophic for one or both of them. Even though Earth has been struck before and will likely be struck again many times in the future, the odds of such a collision occurring with enough power to destroy our planet entirely is extraordinarily low, even on astronomical timescales. Our planet will meet its demise in another way.(NASA / JPL)
Many catastrophic events await our world in the future, but Earth will survive most of them.
The largest human-made explosion to ever occur on Earth was the Soviet Union’s Tsar Bomba, detonated in 1961. Nuclear war, and the subsequent damage to the environment, is one potential way that humanity could come to an end. However, even if all the nuclear weapons on Earth were detonated at once, the planet itself would remain intact. (1961 TSAR BOMBA EXPLOSION; FLICKR / ANDY ZEIGERT)
Nothing humanity can do, from triggering global climate catastrophes to thermonuclear war, will truly destroy the planet.
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. (JENNIFER WILLIAMS / FLICKR)
After 2 billion years, increased energy output from the Sun will boil Earth’s oceans, but the planet itself will survive.
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. (NASA; Z. LEVAY AND R. VAN DER MAREL, STSCI; T. HALLAS; AND A. MELLINGER)
In about 4 billion years, Andromeda and the Milky Way will merge, but gravitational ejection and stellar collisions affecting us are disfavored.
After approximately five to seven billion additional years pass, 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 will remain a planet, albeit a very different one from the world we know today. (ESO / LUÍS CALÇADA)
After another ~6 billion years, the Sun will swell, devouring Mercury and Venus, but Earth will persist.
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. (WIKIMEDIA COMMONS/FSGREGS)
Our red giant will die after ~9.5 billion years, with Earth continuing to orbit the Sun’s corpse indefinitely.
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. The planetary nebula our Sun will generate should fade away completely, with only the white dwarf and our remnant planets left, after approximately 9.5 billion years. On occasion, objects will be tidally torn apart, adding dusty rings to what remains of our Solar System, but they will be transient. (MARK GARLICK / UNIVERSITY OF WARWICK)
After 10¹⁵ years, our white dwarf will cool completely, yet Earth will remain undisturbed.
An accurate size/color comparison of a white dwarf (L), Earth reflecting our Sun’s light (middle), and a black dwarf (R). When white dwarfs finally radiate the last of their energy away, they will all eventually become black dwarfs. The degeneracy pressure between the electrons within the white/black dwarf, however, will always be great enough, so long as it doesn’t accrue too much mass, to prevent it from collapsing further. This is the fate of our Sun after an estimated 1⁰¹⁵ years. (BBC / GCSE (L) / SUNFLOWERCOSMOS (R))
10¹⁹ years from now, gravitational interactions between galactic masses will likely eject the remnant Solar System.
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 it’s a part of. 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 1⁰¹⁷ to 1⁰¹⁹ 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. (J. WALSH AND Z. LEVAY, ESA/NASA)
Random mergers, collisions, or gravitational ejections are all possible, but represent unlikely outcomes.
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. (SHANTANU BASU, EDUARD I. VOROBYOV, AND ALEXANDER L. DESOUZA; ARXIV.ORG/ABS/1208.3713)
Instead, Earth’s eventual demise occurs when our orbit decays via gravitational waves.
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 and be swallowed by the remnant of our Sun. (IMAGE COURTESY OF JEFF BRYANT)
When objects get too close in orbit around another mass, such as a white dwarf (or black dwarf, in the far future), gravitational waves will cause them to inspiral at progressively faster rates, while tidal forces will tear the object apart into a ring and/or debris disk. This will be the ultimate fate that brings our planet to its demise. (NASA/JPL-CALTECH)
Mostly Mute Monday tells the scientific story of an object or phenomenon in this Universe in images, visuals, and no more than 200 words. Talk less; smile more.
