Can planets survive their star's death?

The future of any planet depends on how long its sun lasts; if that dies, game over. Or is it really?

 Can planets survive their star's death?

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• The story: When the sun enters its death throes in about 5 billion years, it will incinerate planet Earth and then dramatically collapse into a dead ember known as a white dwarf. But the fate of more distant planets, such as Jupiter or Saturn, is less clear to science.
• A unique planet: Astronomers recently reported observing a tantalising preview of our solar system’s afterlife: a Jupiter-size planet orbiting a white dwarf some 6,500 light years from here. After searching for years for its host star with the Keck II telescope in Hawaii, the study team concluded it was orbiting a white dwarf that is too faint to directly observe.

1. Known as MOA-2010-BLG-477Lb, the planet occupies a comparable orbit to Jupiter. The discovery not only offers a glimpse into our cosmic future, it raises the possibility that any life on “survivor” worlds may endure the deaths of their stars.
2. There is quite a lot of evidence of rocky planetary debris orbiting around white dwarfs, but intact planets are not known.
3. The fate of our own solar system is likely to be similar to MOA-2010-BLG-477Lb, when the sun will become a white dwarf, the inner planets will be engulfed, and the wider-orbit planets like Jupiter and Saturn will survive.

• Technical details: Astronomers using a different method last year reported spotting another intact Jupiter-like planet, known as WD 1856 b, closely orbiting a white dwarf. But MOA-2010-BLG-477Lb circles its hidden stellar husk at nearly 3 times the distance between Earth and the sun, making it the first known planet to occupy a Jupiter-like orbit around a white dwarf. WD 1856 b, by contrast, orbits its white dwarf every 1.4 days, suggesting that it migrated into its current position after the death of its star, though the exact mechanics of that journey are still being hashed out.

1. Some scientists have noted that planets with wide orbits around white dwarfs are probably more abundant than those in tight orbits, but that the latter group are simpler to detect.
2. Dying stars spew out harmful radiation as they grow into a phase called red giants and introduce turbulence in their systems that could obliterate life. But there are some speculative scenarios that might preserve the habitability of white dwarf systems.
3. A planet distant from a red giant star that then moves inward after the star becomes a white dwarf and retains “enough water to potentially be a nice place to live” when the star turns into a white dwarf, is possible.

• White dwarfs: Because white dwarfs are small and dim, such a planet would have to be in a very close orbit for liquid water to exist. However, if life were to emerge on a world like Jupiter’s moon Europa, which might contain a subsurface ocean warmed by Jupiter’s tidal forces, it could potentially survive at a greater distance from the star. So if humanity is somehow still around in 5 billion years, it would probably have a better chance of surviving the sun’s red giant phase on a moon of Jupiter than on Earth.
• EXAM QUESTIONS: (1) Explain the various possible outcomes when a star begins to die. (2) What is the possible future of humanity, 10000 years from now? Speculate.

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