Question: I am writing a story that involves the colonization of an exoplanet with very similar properties to Earth. This exoplanet would be orbiting a red dwarf, but due to certain factors (it's atmosphere and the presence of one or several moons) it is NOT tidally locked. Upon arrival from humans, to their surprise this planet already harbors complex life. It has a large ocean, continents, fauna and flora much like our own earth.

My question is: despite all the similarities, would it be plausible for this planet to be radioactively hostile towards humans? What I mean by this is, despite the similarities, could the fauna and flora have adapted to thrive in an environment which would be ultimately too harsh for our own bodies in the long run?

To provide some more context as to why i'm asking this: The plot i'm working on makes it so that when humans arrive, they can breathe without their suits, and at first it seems like the planet is just like earth, but soon after they realize that prolongued exposure to the radiation within the planet leads to early offset of cancer and thus humans can't really afford to live in this planet as it is without applying some form of alteration to the atmosphere (that's a wholenother subject i'll leave for another post haha), which would lead to harmful consequences towards the native life that has evolved to thrive within this specific environment.

Love this forum, it's been super helpful, to anyone taking time out of their day to answer: Thank you!

Answer: 
**Radiation belts.**

<https://astronomy.com/magazine/ask-astro/2020/02/what-is-the-source-of-jupiters-radiation>

> 
> Any charged particles in the space around Jupiter will experience the
> planet’s strong magnetic field and get accelerated to high energies.
> These negatively charged electrons and positively charged ions of
> hydrogen (i.e., protons), oxygen, and sulfur form Jupiter’s radiation
> belts... The dominant particle source, however, is the volcanic moon
> Io, which dumps a ton per second of sulfur dioxide gas into space
> where the molecules are broken up and ionized. These processes around
> the moon drive million-amp currents between Io and Jupiter’s
> ionosphere, where they excite intense aurorae on the planet.
> 
> 
> The highest fluxes of energetic particles are found closest to the
> planet, where they form a doughnut-shaped belt around the equator
> (which causes radio emission that astronomers have measured from Earth
> since the 1960s)...
> 
> 
> It is Jupiter’s combination of a strong magnetic field, Io’s
> prodigious source, and the magnetic coupling of charged particles to
> the planet’s rapid (10-hour) spin that drives the intense radiation.
> Earth’s radiation belts (named after James Van Allen, who discovered
> them with the U.S.’s first satellite in 1958) are much weaker.
> 
> 
> 

Your planet has a very strong magnetic field and one of its moons plays the role of Io, dumping particles that are accelerated to high speeds. Fast moving particles are the equivalent of electromagnetic radiation as regards biological damage.

Your people do not realize that these belts exist and dip down to and below the planet surface because the belt is not homogenous - it moves with the moons, with high and low tides. In addition a detection method tuned to short wavelength radiation like Xrays and gamma rays might completely overlook fast moving large ions of sulfur and iron.

As regards the prospect of life not affected by particulate radiation, why not? One could imagine Earth life durable to this sort of thing. A simple method: if radiation makes random changes in a genome you could have multiple copies of the genome and check them against each other frequently, correcting according to consensus for a given gene.
Ramsar, Mazandaran
------------------

[![Lovely Ramsar (Wikipedia)](https://i.stack.imgur.com/fXdX7.jpg)](https://i.stack.imgur.com/fXdX7.jpg)

is a city in Iran known for levels of background radiation 80 times the acceptable level from artificial sources. There is radium in the ground water and radon gas coming up into the air. Yet there is a mystery because reports keep coming in that the cancer rate is *not* elevated. See [Wikipedia](https://en.wikipedia.org/wiki/Ramsar,_Mazandaran) for some description. A leading explanation is a crack-pot theory\* called "radiation hormesis", essentially that you can get an internal suntan from being in radiation. Note this conflicts violently with [government advice from the U.S.](https://www.dep.pa.gov/Business/RadiationProtection/RadonDivision/Pages/Radon-in-the-home.aspx), though that hardly guarantees it's wrong. A [2019 paper in an Iranian journal](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6709356/) even suggested that the residents should be considered as good Mars colonists. There is [a limited amount of ongoing research](https://pubmed.ncbi.nlm.nih.gov/?term=ramsar+radiation&sort=date) but it doesn't seem very enlightening.

Sometimes - often - biology just digs in like a mule and rejects all entreaties to logic and reason.

* *This term of endearment confused some readers. Please note that "crack-pot theories" turn out to be true more often than expected in biology. Why, just the other day we found out [humans carry an HIV-like polymerase to convert RNA to DNA](https://advances.sciencemag.org/content/7/24/eabf1771), which is to say, Lamarckism may be back on the menu. You never know!*