Small, Rocky Planets Are Most Likely to Survive the Death of a Star

by Ryan Whitwam

Stars are not forever, although they have lifetimes measured in millions of billions of years. When they finally reach the end of their life, most of the planets that have called a solar system home will be blasted to pieces or ejected into deep space. New research from the University of Warwick points out that some planets may survive and have a greater impact on the solar remnant that remains.

When a “main sequence” star like the sun gets on in years, it exhausts its hydrogen fuel. It will be able to keep up the fusion reaction by creating heavier elements, but eventually, it swells into a red giant. During this phase, many of the planets in a solar system are consumed or pushed out into space. Later, the star blasts off its outer layers and becomes a white dwarf. Larger stars end up as neutron stars, and very large ones can become black holes.

The University of Warwick analysis focused on stars like the sun that will become white dwarfs. The team developed a computer model to simulate what happens to a solid, nearly spherical planet as it experiences the intense tidal forces of a star’s death throes. The team determined that larger solid worlds are more likely to crumble under the pressure and that less monolithic balls of ice and rock will break apart regardless of size. It’s the small, solid planets like Earth that could survive the transformation of a star into a white dwarf.

An artist’s concept of a planet orbiting a white dwarf. Credit: NASA

This is important information for astronomers to have because almost all the exoplanets currently known orbit main sequence stars that will one day become white dwarfs. Many of the white dwarfs in the universe could have the lightly toasted remnants of Earth-like planets in orbit, and they could have an effect on those stellar corpses, even if they’re below the limit for direct detection.

With the large gravitational bodies in a solar system long gone, small rocky planets dominate the currents of space. They can direct asteroid, bits of former planets, and other debris into the atmosphere of the white dwarf. This work could help us look for signs of planets around white dwarfs, and therefore get a glimpse at Earth’s eventual fate. While Earth itself could survive, it won’t be the same planet we know today. Any life still calling Earth home when the sun burns out won’t survive.

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Originally published at on May 16, 2019.