Based on the answers from this question: Would the solar wind from an antimatter star be any different from a non-antimatter star?, it seems that an antimatter Sol type star would conduct fusion exactly the same as a normal matter star, despite the charges being flipped....

The output would also apparently be the same materials and same spectral emissions, except again, the charge would be flipped.

As a thought experiment, what would the atomic and chemical effects be of a Sol type antimatter star's emissions and "solar wind" upon a normal matter planet placed in orbit around it (Terran type)?

  • $\begingroup$ The solar wind would consist of anti-particles, which would generate some interesting auroras when it hits the planet's atmosphere $\endgroup$
    – hdhondt
    Commented Nov 5, 2019 at 5:00

2 Answers 2


The solar wind has a density of about 6 atoms per cubic centimeter at Earth orbit. If we say it moves at 500 km/s at Earth orbit that means that a naked surface will be hit by 30 billion antiprotons per second. That is about 9 watt of annihilation energy per square meter - three orders of magnitude below the energy in sunlight, but in the form of gamma rays. During solar eruptions this may increase by a factor of 100 or 1000 for a day or so.

Over 4.5 billion years it would annihilate 7.1 kg surface material per square meter - not enough to remove small asteroids and moons, but definitely reshape their surface chemistry and texture.

It would also tend to activate nuclei by changing them to isotopes with one less proton (or just blowing up nuclei), making surface materials in space radioactive. Lots of carbon 14 (from nitrogen 14) and tritium (from helium 4). Meteors would bring the more long-lived isotopes to the ground.

Even if Earth is somewhat protected by the magnetic field, auroras would involve annihilation reactions beside high energy collisions.

Overall, this would be a pretty radioactive environment. Not sure what the general radiation level would be, but about 54 tons of newly activated meteor surface material would be arriving each day.


As in my answer here the electron positron annihilation lines would be very evident in the solar wind - earth atmosphere overlap. It is the reason we know the sun is made of matter.

If the sun were antimatter, there would be a lot more cosmic rays coming from annihilations of antiprotons on protons, the effect on the satellites would be very large etc.

Of course it would not be possible to explain how the matter planets evolved from an antimatter sun.

  • $\begingroup$ Concerning formation, I suppose it may be just about possible that a large antimatter star caught a smaller matter star with planets and annihilated it, and somehow a matter planet survived the process and ended up in orbit around what remained of the antimatter star, or possibly there could be wandering lumps of matter detached from a star after a supernova and one got caught into orbit around an antimatter star (if there are any, which seems highly unlikely of course). $\endgroup$ Commented Nov 5, 2019 at 10:41
  • $\begingroup$ Since this is a thought experiment, I'm not concerned with formation, only the effects. I'm pretty sure Einstein wasn't worried about how one might accelerate his ladder to light speed. 。.:☆*:・'(⌒―⌒))) $\endgroup$
    – nijineko
    Commented Nov 6, 2019 at 2:08

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