[notum]

Rays hit our planet regardless of Sun, if anything it might block a few. They are caused by ultra-energetic cosmic events, such as star collisions, black hole feeding cycles.

Cosmic rays are just very potent photons, capable of knocking out electrons from an atom (meaning they are ionizing) causing havoc in precision electronics and, well, our DNA.

[andy_ppp]

What is the tolerance for cosmic rays for a human... I ask because on the journey to Mars you’ll get quite a few I guess and also on the planet’s surface after you’re there with such a thin atmosphere?

[tinco]

This is actually a thing people are criticizing Musk for, he is being accused of sending people to Mars with insufficient shielding against cosmic rays.

In my opinion it's a bit silly argument, as there's a whole bunch of other risks and quality of life sacrifices made by the persons who are going to undertake that journey. Some raised chance of cancer is probably the least of their worries.

[mlindner]

He can't send people to Mars yet so how are people accusing him of sending people to mars with insufficient shielding? There are limits to criticism of Musk one would think.

[typon]

Humans going to Mars should expect to never come back

[andi999]

But at least they should reasonably expect to arrive.

[bostonsre]

Anyone know what expectations Columbus or other expeditions had about survival/risk?

[iso1631]

For a normal NASA flight

"NASA told Business Insider it estimates there’s a 1-in-276 chance the flight could be fatal and a 1-in-60 chance that some problem would cause the mission to fail (but not kill the crew)"

That's fairly low - feels like the age of sail would be far higher -- Columbus's second voyage alone had about 25 deaths just from scurvy. His first voyage was only about 90 crew.

But remember that life wasn't exactly easy on land either.

[njarboe]

The Magellan Expedition left with 5 ships and ~270 men and returned with 1 ship and 18 men. People knew that going on long, overseas expeditions was very dangerous, but so was life in general in 1500. I imagine worrying about 50% increase in cancer risk by taking a voyage to fricking Mars, would seem very silly to those explorers.

[tinco]

A lot less than an astronaut has when going to Mars for sure. We at least know how far away Mars is exactly, and what obstacles lie in the way, and what inhabitants it has. They just got on a boat, and pray for fair wind and good weather so they might reach india, and thank god there was a whole other continent in between.

[Sanzig]

That's actually a fascinating question! It turns out we don't know enough to answer one way or another.

The model commonly used in radiation protection to assess cancer risk with respect to radiation dose is called the Linear No-Threshold (LNT) model [1]. The model critically assumes that (1) total radiation dose is the only predictor of cancer risk, and (2) any radiation exposure results in an increased cancer risk.

This model works at high absorbed doses, however, its applicability is highly controversial when used with low abosorbed doses or with relatively high absorbed doses that occur over a long period of time (ie: low dose rate).

The thing is, the human body has built-in defense mechanisms against cancer such as DNA repair. There is a good body of evidence that small doses and low-rate exposures do not result in cancer risk (ie: there is a threshold absorbed dose and probably also a threshold dose rate), but the model does not account for this.

This is particularly problematic when trying to assess excess mortality from things such as radiological accidents: when you multiply the small LNT-predicted risk for a low dose times a very large population, you end up with a lot of cancers. This is one of the reasons you'll see estimates for deaths from the Chernobyl accident vary by orders of magnitude.

It's also problematic when assessing something like a Mars mission: yes, the astronauts would get large cumulative doses, but the dose rate is pretty low over most of the mission (other than during high dose rate solar events where they would need radiation shielding). How much of an elevated cancer risk is it actually? Nobody is quite sure.

[1] https://en.wikipedia.org/wiki/Linear_no-threshold_model

[andi999]

I remember vaguely that if there would have been a sun eruption at the lunar mission the team might have died. I tried a while ago to find a good source on that though. If this were true, forget Mars.

[btkramer9]

As far as cancer rates go I've heard it's about as bad as taking up smoking cigarettes. Which is not great but doesn't seem like a show stopper

[MauranKilom]

According to https://xkcd.com/radiation/, you get about 4x the normal daily background radiation from a transamerican flight.

[moftz]

Cosmic rays can also be high energy ions. Most of the photons come from the sun and the ions can come from outside the universe and the sun.