Solar Flare/CME Range Limits

Question

The Setting: A binary solar system comprised of a KV-class Orange Dwarf, and an M-Class Red Dwarf which orbits roughly 600AU away. The Orange Dwarf has 4 planets orbiting around it, including one roughly-Earthlike planet in the star's habitable zone. The planet has a magnetosphere, but no ozone layer. Life predominantly exists in the oceans - Cambrian-adjacent levels of biodiversity and advancement.

The Idea: I'm considering ideas for what sort of extinction events might occur on this planet in the near future. I recall that on Earth, the Ordovician/Silurian extinction event is believed to have been caused by radiation from a Gamma-Ray-Burst (at least in theory). The argument for that theory is that the high-energy radiation and particles from the GRB punched a hole in the minimal ozone layer & magnetosphere of Earth at that time, and caused an ice age.

I am wondering if a similar effect could be caused by a stray solar flare or CME from the nearby red dwarf. As others have observed, most if not all red dwarfs are flare stars, which means higher than average periods of high-energy solar radiation. In addition, many sources discuss the threat that CME's pose to our own planet, though our star is much closer to us. Thusly, this concept could, in theory, create a similar effect to a GRB, at the difference of it being a localized phenomena instead of one originating from many light-years away.

The Problem: There are two potential roadblocks to this concept of a CME-induced extinction event: the parent star, and distance. The Orange Dwarf is larger, and the planet orbits much more closely to it than the red dwarf. Thus, it's possible that the solar wind and magnetosphere of the orange star might interfere with or dampen the effect of its sibling's flares within its own sphere.

More concerning to this concept, though, is distance. Though there is much discussion about the energy effects of solar flares and CME's, one thing I do not often see discussed is how far these flares & CME's can travel. GRB's have the advantage (situationally speaking) of being a more condensed burst - the energy does not readily dissipate until long after it has left the stars SOI. Flares and CME's, though, are not condensed, and instead spread outward over an area. With this logic, it's possible that the CME would stretch over such a vast area that by the time it reaches the planet, only a small portion of that energy would reach it - not enough to punch a hole through the ozone or magnetosphere.

The Question: How feasible is this concept? How far do CME's & solar flares travel, and what is the "effective range" of these phenomena? What would need to change about this situatoon to make such an extinction possible, if it even is?

Thanks to anyone who can offer sources to research this particular topic.

Answer 1

We don't have enough information about heliosphere physics for a solid numerical answer, because we have only one example that we can study, but this does not look plausible, for at least these two reasons:

• Red dwarfs can get much brighter when they flare, but they start from a very low base. The brightest red dwarf flare I've found with a bit of digging happened to Proxima Centuri in 2016, and increased its brightness by a factor of about 68. To magnitude 6.8, at only 4.3 light years: its absolute magnitude would have been about 11.2. This is vastly less than a nearby gamma-ray burster,

• With the two stars orbiting each other at about 600AU, they will be outside each other's heliopauses (the Sun's heliopause is about 115AU from the star). So a CME from the red dwarf has to enlarge its heliosphere to 600AU radius, at least in the right direction, and push in the heliosphere of the orange dwarf far enough to reach the planet. That does not seem plausible, because the gas and magnetic fields of the orange star become denser as they are compressed, according to the inverse-cube law, while the CME gets weaker according to the inverse-cube law. When you have two cubed factors operating against you, any scenario gets hard.

To make the scenario more plausible, you need the stars much closer together.

Answer 2

Well, it depends. Mostly on the environmnent, that is shielding or bending the flares. And that is were the crux is, depending on the two stars lining up, the might catch each others flares or do stranger things still, amplify or redirect it.

Imagine a dual solar system, were the green belt goes in between the two stars from time to time and a planet circles through it.. It can be calm waters, but in some years, there is a solar flar from one side. Then there are the hell years, were the solar flares come from both sides, forming a sort of vortex through which the planet sails.