The gruesome fate of every planet when the Sun dies | by Ethan Siegel | Starts With A Bang! | Mar, 2024

When our Sun evolves into a red giant and then dies in a planetary nebula/white dwarf combination, the innermost worlds will be engulfed and swallowed, while the outermost worlds will likely be ejected. The anticipated survivors, which may include Mars, Jupiter, and Saturn, will be stripped of their atmospheres, but may persist beyond the death of the Sun in some form. (Credit: WP/Wikimedia Commons)

For now, our Solar System’s eight planets are all safe, and relatively stable. Billions of years from now, everything will be different.

Today, our Solar System is relatively stable.

The inner Solar System, including the planets, asteroids, gas giants, Kuiper belt, and more, is minuscule in scale when compared to the extent of the Oort Cloud. Sedna, the only large object with a very distant aphelion, may be part of the innermost portion of the inner Oort Cloud, but even that is disputed. On a linear scale, depicting the entire Solar System in a single image is incredibly limiting; to characterize the orbit of a faraway bound object requires years or even centuries of data. (Credit: NASA/JPL-Caltech/R. Hurt)

Eight planets, an asteroid belt, Kuiper belt, and Oort cloud all orbit the Sun.

A logarithmic chart of distances, showing Voyager, our Solar System, the Oort Cloud, and our nearest star: Proxima Centauri. In jumps of factors of 10, we go from Earth’s orbit to Saturn’s orbit to Voyager 1’s distance to the inner Oort cloud to the middle of the Oort cloud to more than a light-year away. Stars and other masses move through the galaxy over time, and routinely pass within the Oort cloud. (Credit: NASA/JPL-Caltech)

However, the Sun is evolving, and won’t live forever.

After its formation some 4.6 billion years ago, the Sun has grown in radius by approximately 14%. It will continue to grow, doubling in size when it becomes a subgiant, but it will increase in size by more than ~100-fold when it becomes a true red giant in another ~7–8 billion years, total, all while growing in brightness by a factor of at least a few hundred. (Credit: ESO/M. Kornmesser)

Over the next 7 billion years, it will heat up and swell, becoming a red giant.

When stars fuse hydrogen to helium in their core, they live along the main sequence: the snaky line that runs from lower-right to upper-left. As their cores run out of hydrogen, they become subgiants: hotter, more luminous, cooler, and larger, before evolving into true red giants that fuse helium in their cores. The red giant phase for a Sun-like star results in a luminosity that’s hundreds or even 1000+ times as bright as the Sun is presently. (Credit: Richard Powell)

Mercury and Venus, the innermost worlds, will quickly be engulfed.

As the Sun becomes a true red giant, the Earth itself may be swallowed or engulfed, but it will definitely be roasted as never before. However, it remains to be seen whether any of the effects of swallowing Mercury, Venus, or even possibly Earth will be noticeable by a distant alien civilization. (Credit: Wikimedia Commons/Fsgregs)

The Earth, although there is a chance it will survive, should be the final devoured planet.

The Sun, when it becomes a red giant, will become similar in size to Arcturus. Antares is more of a supergiant star and is much larger than our Sun (or any Sun-like stars) will ever become. Even though red giants put out far more energy than our Sun, they are cooler and radiate at a lower temperature at their surfaces. Inside their cores, where helium fusion occurs, temperatures can rise into the tens of millions of K. (Credit: Sakurambo/SkateBiker at English Wikipedia)

In the giant phase, the Sun will shine thousands of times as bright as today.

During the main phase of a star’s life, planets can orbit at nearly any distance from it, including very close in. As the star evolves, it becomes a subgiant and eventually a true giant. As the star increases in size, the frictional drag force on the innermost planet increases; eventually, it will come into contact with and be devoured by the parent star, while the increased stellar brightness has severe consequences for planetary atmospheres and ice-rich objects. (Credit: International Gemini Observatory/NOIRLab/NSF/AURA/P. Marenfeld)

The asteroids, Kuiper belt, and inner Oort cloud objects should sublimate away, leaving rock-and-metal cores.

Comet 67P/Churyumov-Gerasimenko was imaged many times by the ESA’s Rosetta mission, where its irregular shape, volatile and outgassing surface, and cometary activity were all observed. In the future, when the Sun heats up and swells into a red giant, objects in the asteroid belt, Kuiper belt, and possibly even the inner Oort cloud will be heated so severely that their volatile ices will be evaporated away. (Credit: ESA/Rosetta/MPS/UPD/LAM/IAA/SSO/INTA/UPM/DASP/IDA)

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