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How can I make a colonizable planet/moon that receives intense UV/x-ray radiation on parts of its surface while receiving much less on the rest of it?

The most obvious way of doing this is to have the atmosphere over most of the planet significantly reduce the received radiation, but to have one spot where much more radiation gets through because of atmospheric changes (similar to the fears about ozone depletion.) Specifically, I need enough radiation to cause severe damage to even hardened electronics exposed to sunlight for less than a day, and substantially raise the cancer risk for even sheltered organic life. And no, just having it in a tidally-locked orbit around a white dwarf or neutron star won't do. I need less than a third of the surface to receive this intense radiation.

There are three major components to this question:

1. A star that produces significant amounts of UV and x-ray radiation: The simplest way of doing this would be to make the star massive, since large and bright stars tend to have high-energy emissions. Unfortunately, larger stars die much sooner, and I need a system that can survive long enough to produce mature planets and be able to keep them for at least another 500 million years. An x-ray binary is probably my best option for this, though the supernova necessary to create the neutron star it requires might hurt the chances of the system's planets managing to hold onto enough atmosphere to make this work.

2. An atmosphere that can block most of this radiation: Ozone is great at blocking UV rays, and thick atmospheres excel at blocking intense radiation. Smog and other physical blockers reduce a wide variety of radiation. What other naturally-occurring chemicals/compounds/substances would block radiation? The more efficient the better.

3. An area of the atmosphere that blocks much less radiation than the rest: This is where it starts to get tricky. CFCs can break down ozone, but I'm not sure about the rest of it. The best candidates are ways to either break down the blocking agents or else move them out of the way. Of course, this needs to be kept local so that it doesn't propagate through the entire atmosphere. A couple of possibilities:

  • Volcanic activity could probably disperse smog, and may or may not be able to able to move other blocking agents out of the way. There is also the possibility that it could break some of them down.

  • Clouds on rapidly rotating planets tend to arrange themselves in bands encircling the planet. This might be a good way of channeling smog and other heavy blocking agents to certain latitudes, though I'm not sure whether they would end up concentrated near the equator or near the poles.

Or maybe I'm on the complete wrong track, and there's a way to make only part of a planet receive intense radiation despite having a uniform atmosphere.

Optional requirements for bonus points:

  • Do this with as little radiation as possible (in other words, make the atmosphere as effective at blocking radiation as possible, while making the unprotected area let through as much radiation as possible.)

  • Do this for a planet that would be a terrible candidate for terraforming while still being plausible to colonize with advanced technology.

A follow-up to this question. The basic premise is to make a planet (or moon) that seems completely uninhabitable from a certain point on its surface but is much more hospitable (though not necessarily friendly to organic life) beyond that point. Additional relevant details copied from the original:

There can't be anything that would make mining or research seem to be worth the risk. Obvious signs of abundant rare elements, scientific anomalies, alien civilization, or native life would all be too interesting. I want anyone who discovers that the planet is inhabited to wonder why the inhabitants bothered. Planets with really unusual dangers are cool, but I want explorers to be saying "Wow, this place sucks!" rather than "Wow, I wonder what's up with this place!"

'Colonizable' means the following:

  • Temperatures between -250° and 200° C.

  • Surface pressure ranging from vacuum to 3 atms.

  • Gravity at or below 2.5g.

  • No conditions that would frequently destroy buildings dug into the crust.

  • At least 75% of the time, external conditions wouldn't cripple or kill a human in a hardened space suit.

  • Flooding, tides, or underwater land aren't an issue unless the liquid would be hazardous long-term to a deep-sea submersible.

  • The presence of enough metals and carbon for at least low-scale industry, and enough power options (solar, geothermal, volatiles, fusion, etc.) to support a colony.

Please note: Any answer that would make scientists seriously question whether the conditions on this planet arose naturally and abiotically is not a good fit for this question.

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  • $\begingroup$ Consider irregular magnetic fields like those present in other planets near here $\endgroup$ – Zxyrra Dec 9 '16 at 20:29
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You could have a concoction of uniquely badass magnetosphere, oddly powerful solar wind and highly elevated (perhaps due to an icy plate floating on a deep ocean) northern pole.

Our own magnetosphere channels charged particles flung from the sun, the stars, and other cosmic entities along it's field lines to the northern (and some to the southern, lets not get chargeist) poles. There they interact with the atmosphere and cause pretty pretty lights!

They also ionise the atmosphere, and the channelling effect causes higher levels of cosmic radiation at the poles. The higher up you are, the more likely you are to be exposed to higher doses. If your pole is high enough then you can put yourself in a worrying situation. Bump up the magnetosphere and the solar wind and you'll have a planet with planetwide aurora (aurorae?) and particularly vicious radiation conditions at the North Pole.

Or, if your atmosphere isn't too thick, just a stream of cosmic plasma bombarding the North Pole. Ho Ho Ho.

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There are actually a couple ways to do this even with a star & earth similar to ours such as:

  1. Make the magnetic poles point towards/away from the star (earth's equator equivalent). This would mean that when facing the sun the pole would get bombarded by the radiation with minimal protection while the rest of the planet would be relatively safe. As well, due to this bombardment, the O3 would break down more rapidly here such that it's an actual hole. Due to the magnetic field lines and unless the planet was tidally locked, it'd only be dangerous for x amount of time depending on the planet's rotation.

  2. Either as it's own planetary feature or in conjunction with 1 which would make it worse: Is have an atmospheric circulation that prevents ozone from collecting easily around a point/band of the planet making it dangerous. This is actually part of the reason the Antarctic has an ozone hole in the first place as certain times of year the jet stream circling that continent tightens and prevents ozone created by storms and other atmospheric conditions from distributing there. I can't find the papers, but it's been theorized that our ozone "hole" (not complete yet or likely ever) is actually partially due to this atmospheric feature in conjunction with the CFCs and the natural breakdown due to blocking the high energy radiation.

Thos are just the couple I came up with quickly. There are probably other ways too, but these can both exist in worlds very similar to earth (and plenty of dissimilar worlds too).

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  • $\begingroup$ The magnetic pole facing the start is a good idea. Assuming the star is putting out lots of nasty high energy protons, those would get pulled into the magnetic south pole. So you want the south pole facing the sun. Further, since magnetic poles can move, this can be a wandering radiation hot-spot. $\endgroup$ – kingledion Dec 9 '16 at 18:27
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  1. Have a solar system like ours

  2. Have a nearby x-ray pulsar or some other extremely energetic star located perpendicular to the plane of the solar system, along the axis of orbit of the planets

  3. The northern (or southern) hemisphere of the affected planet would be bathed in life-threatening bad juju rays.

  4. Bonus option. Modify axial tilt control exposure to the x-ray star. If the axial tilt is 90 degrees, for example, the entire star gets heavy radiation and at some point and there is no life. However, in a planet with an earth-like 23.5 axial tilt, the x-ray radiation coming from the northern hemisphere never extends farther south than 23.5 S - the southern Tropic of Capricorn. Now life can develop in the un-radiated part of the world.

  5. Double-bonus option. Modify day length to control time of exposure. Unlike the seasons caused by the earth's rotation around the sun, the exposure to a star above the North pole will be controlled by day length. So in an Earth-like axial tilt situation, everywhere north of the Tropic of Capricorn gets hit with radiation at least once per day. If you make the day length equal to a year, then everything gets hit once a year with radiation.

  6. Modify strength of radiation to control size of no-go zone. If the radiation is relatively weak, then maybe only the areas that are permanantly exposed to it are no-go zones. For example, if we have an earth-like 23.5 degree tilt, then only the areas north of the Tropic of Cancer are permanantly exposed to radiation, while areas in the tropics get some partial exposure, and areas south of the Tropics get none.

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Start with pulsar planet like the ones that formed around the pulsar Lich, but a little further out and tidally locked so that it becomes something like a hot eyeball world:

Hot Eyeball World

Set the planet at just the right distance from a pulsar, which are very hot, but not very bright, and most of their energy is in the form of radiation.

Because of being tidally locked the back side would be cold, and the front would be blasted by radiation, but around the terminator would be a band of clouds and storms that would reflect some of radiation. Air from the front would be heated and pour around the planet toward the the cold back side, where it would cool down and rush back around to the front side bringing moisture with it and causing the storms.

The back side would be colder, but because of the circulation not freeze completely.

As to how life got there in the first place in only 1 billion years, it was seeded by the travelers that left the gates.

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How about a ring system, like Saturn, where the rings keep the sunlight filtered except in a gap? This answer is inspired by this question: By what mechanism could a planet be locked into permanent solar eclipse? This answer explores the idea of a tidally-locked binary pair of planets such that one keeps the other always in shadow. If the inner one is more dense, it would be smaller, allowing it to remain on the inside of the orbit and only allow full sunlight in a ring onto the larger planet. There is some debate in the answer about the orbital mechanics. Seems like it might be worth trying to set up in a simulator.

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How can I make a colonizable planet/moon that receives intense UV/x-ray radiation on parts of its surface while receiving much less on the rest of it?

Up from the below.

UV radiation is tricky, but you can have your world get lots of ionizing radiation in the form of X-rays and gamma rays by having your crust enriched in radioactive elements that emit this type of radiation.

The earth contains elements which emit ionizing radiation; the radioactive decay of these are responsible for heating the deep earth and generating radon gas in the crust. You could have a lot of radioactive elements in one area of your world, including some with shorter half-lives like americium. You could have these elements arrive on your world in meteors from some distant supernova - a few of these breaking up on entry would enrich parts of your world with radioactive isotopes while sparing the rest.

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