When the Sun Dies, Earth’s Magnetosphere won’t Provide Protection any More

The Earth’s magnetic field is an underappreciated wonder of the natural world.  It protects our atmosphere, provides some of the most breathtaking scenery when it creates auroras, and allows people to navigate from one side of the world to the other.  Unfortunately, it won’t be able to save us from the death of the Sun though.  At least that’s the finding of some new research by Dr. Dimitri Veras of the University of Warwick and Dr. Aline Vidotto of Trinity College Dublin.

The Sun’s expected life cycle is pretty well mapped out by scientists. After it’s current main sequence phase is over, it will run out of the hydrogen fuel source that powers the nuclear fusion in its core.  Without the pushing force of the fusion, the Sun itself will contract and then heat up.  That additional heat will push its outer atmosphere to many multiples of its size today, potentially even swallowing up Earth, but definitely consuming Venus and Mercury.  

During its red giant phase, the sun will also create a powerful, fluctuating solar wind.  Usually our magnetic field is able to stop the particles of the solar wind from stripping away Earth’s atmosphere.  However, with the increased amount of particles caused by the red giant constantly bombarding it, the magnetic field has little chance of protecting its atmosphere.  As it is stripped away, the probability of life surviving on the planet slowly diminishes, despite the fact that the Earth will likely be pulling farther away from the Sun due to the decrease in gravity associated with the star’s lower mass.

The habitable zone around red giants is much farther out than main sequence yellow stars – putting it out past the orbit of Neptune.  The slow orbital path Earth will be taking won’t get us there in time before all life on the planet’s surface is cooked.  So we can be sure that a dying sun would likely be able to kill us in more than one way.

After its red giant phase, though, a white dwarf emerges, which is much more stable and doesn’t emit any solar wind at all.  But in order for life to survive to this point, its planet’s magnetic sphere has to be approximately 100 times the strength of Jupiter’s, and it has to be able to move quickly between the habitable zones of three different star types.

At least that is the needed characteristics of a planet that is able to continue to support life through these phases according to the models by Drs. Veras and Vidotto.  They ran simulations for the winds of 11 different stars with different masses.  Any planet resembling Earth’s place in the solar system and with its current magnetic field is a lost cause.

Luckily, all this will happen billions of years from now, so humanity has plenty of time to come up with a technological defense strategy.  Currently, though, there are implications of this model for a the number of the exoplanets other astronomers are busy finding.

Some have been found around white dwarfs already, including a few Jupiter sized ones in the habitable zone of these ultra-stable stars.  While the death throes that are required to create a white dwarf would likely have eliminated any previously evolved life, white dwarves themselves are stable for billions of years, giving plenty of time for life to evolve again in a much more benign environment.

For now, our own solar system is a relatively benign environment as well, despite occasional outbursts that could take down humanity’s entire electric grid.  As long as that doesn’t happen, our magnetic field will provide us plenty of time to study other white dwarfs, and watch their exoplanets for the tell-tale signs of any life after their sun’s death.

Learn More:
RAS – Planetary Shields Will Buckle Under Stellar Winds From Their Dying Stars
RAS Monthly Notices – Planetary magnetosphere evolution around post-main-sequence stars
LiveScience – No life will survive the death of the sun — but new life could be born after, new research suggests
California News Times – No life will survive the death of the sun — but new life could be born after, new research suggests

Lead Image:
Artist’s illustration of ejecta from the Sun being blocked by Earth’s magnetosphere.
Credit – MSFC / NASA