9
$\begingroup$

My project concerns a world "A", that is a moon of a gas giant "Jovi", in a solar system with no other planets to speak of and a host star much like our own.

"A" is Earth-sized, has no magnetic field of its own, and keeps an atmosphere that is Earth-like in composition and density. It is tidally locked to "Jovi".

"Jovi" has few decided properties apart from being a gas giant roughly the size of our Jupiter.

Now, for "A" I would like its 'antijovian' hemisphere (the hemisphere facing away from "Jovi") to be habitable for humans, while its 'subjovian' hemisphere (the hemisphere facing toward "Jovi") to be uninhabitable, and far too deadly to even cross unprotected on foot - all because of some type of radiation or other effect emanating from planet "Jovi". Problem is, I can't think of the right set of circumstances that would produce this specific division. What comes closest to what I want is Jupiter's moon Io, that is bombarded with radiation from Jupiter's radiation belts on its trailing hemisphere, in contrast to very different 'wheather' on its leading hemisphere. But I want a division specifically subjovian/antijovian AND specifically deadly/habitable respectively.

Could someone please come up with any kind of scientifically plausible properties of this planetary system, particularly properties of the gas giant "Jovi", that would result in the type of division of moon "A" between habitable and unhabitable hemispheres as I described?

Cheers

PS: I thought leaving "A" without its own magnetic field, and instead have it rely on Jovi's magnetic field, would make it easier to think of a way to have part of it be prone to deadly radiation

$\endgroup$
3
  • $\begingroup$ maybe it could be a asteroid thing? $\endgroup$
    – Topcode
    Apr 4, 2020 at 18:22
  • 1
    $\begingroup$ maybe instead of a gas giant it could orbit a en.wikipedia.org/wiki/Brown_dwarf which could give off radiation that would kill things on that side but it could still be orbiting a star too. $\endgroup$
    – Topcode
    Apr 4, 2020 at 18:29
  • $\begingroup$ @Topcode then you would have to deal with the fact that it is tidally locked, and thus the dark side would probably be uninhabitable... with a moon that is tidally locked it would still get enough sun on both sides, as evidenced by our own moon's cycle... $\endgroup$
    – fartgeek
    Jan 3, 2021 at 16:31

6 Answers 6

7
$\begingroup$

Thermonuclear storms

https://en.wikipedia.org/wiki/Stellification

Stellification is a theoretical process by which a brown dwarf star or Jovian-class planet is turned into a star, or by which the luminosity of dim stars is greatly magnified.

For your scenario I pick the 3d of three scenarios offered: sputtering deuterium fusion.

Thermonuclear ignition. It is well established that Jovian-class planets consist mostly of hydrogen and helium.[2] It is theorised that concentrations of hydrogen and helium isotopes at certain depths of a gas-giant planet may be sufficient to support a fusion chain reaction, if sufficient energy can be delivered to ignite the reaction. If a gas giant has a layer with a large concentration of deuterium (>0.3%), ultra-high-speed (2×10⁷ m/s collision of a sufficiently large asteroid (diameter > 100 m) could ignite a thermonuclear reaction.[3]

Your giant with stellar aspirations sometimes undergoes extensive thermonuclear reactions in the deuterium level of its atmosphere. Maybe triggered by asteroids? Maybe by endogenous lightning, or events taking place farther down. They are atomic storms, propagating in spreading circles across the gas giant surface. The reaction and consequent heat expands the atmosphere and then the lights go out. But while the storm is going on, tremendous amounts of radiation, ionizing and otherwise, shine from the planet as it tries to become a star. You want to be on the shady side of the moon when that happens.

Sometimes a couple of days go by between thermonuclear storms. Maybe you can get out on the bright side and back before one comes? Shake a leg!

$\endgroup$
2
$\begingroup$

I am not sure that the following can be really a science based answer, or rather a sciency one.

  • The radiation belt produced by Jovi induces a lot of charges into the upper atmosphere of A
  • The ground of A has a high piezoelectric capability
  • The gravity pull from Jovi triggers other charges on the ground
  • As a result of the increased charges on the ground and in the high atmosphere, there is an humongous shower of lightnings on the Jovi side.

As a practical result, it's very likely for anything to be thunderstruck within seconds, with easily imaginable results.

$\endgroup$
1
  • $\begingroup$ I like it, but I'm worried that since this relies on Jovi's radiation belt, it would affect only the trailing, or the leading hemisphere of A (not sure which), rather than only the subjovian side, since that is how Io is affected by Jupiter. The idea of the piezoelectricity combined with tidal forces is interesting, but again, would this affect only the subjovian side? $\endgroup$
    – N. Bleac
    Apr 4, 2020 at 18:02
2
$\begingroup$

Just shadow - and cold.

A orbits close to Jovi, when compared to Jovi's size, and A and Jovi's orbits are in the same plane. Therefore, nearly half of time A is in Jovi's shade. That's not a problem for the outward side of A, because it's facing the sun when it's not in Jovi's shadow, producing a reasonable day-night cycle.

However, the Jovi facing hemisphere of A alternates between being on Jovi's shadow and facing away of the sun. In other words, that face has a sun eclipse lasting most of the day, while the outward facing hemisphere the eclipses happen at night and can't even be seen.

Additionally, Jovi is very dark - pitch black if you want - , so its albedo doesn't compensate much for the lack of sunlight, and it doesn't have enough internal heat to produce significant radiation.

The result will be that the Jovi facing hemisphere will be a lot colder than the outward facing one - way colder than Earth's poles. Going there may be possible with modern technology, but surely it is not somewhere you may want to live.

$\endgroup$
2
  • 1
    $\begingroup$ Jovi won't be very different in temperature than the "outward" face of A. Even if it has no internal heat left, it's still warmed by the star just as much as A, and the Jovi-facing side of A will get a little direct sunlight on top of that even if it's in very close orbit. If at equilibrium with external heat sources, the side facing Jovi would probably have the mildest temperature swings. $\endgroup$ Jan 3, 2021 at 15:57
  • $\begingroup$ @ChristopherJamesHuff: You have a point here and that makes it less clear than in my answer. $\endgroup$
    – Pere
    Jan 3, 2021 at 16:06
1
$\begingroup$

If we get rid of "tidally locked", then:

spores

As "A" rotates, at some point at or soon after "Jovi"-rise, all the native plants give of a large quantity of spores. These function as a cross between pollen and seeds. Unfortunately, they find human (and most Terran) lungs be an ideal growth condition. If you get the spores in your lungs, you are dead within days.

Fortunately, the spores don't last too long. They tend to be dead by "Jovi"-set. This may be a result of radiations, and lack of "Jovi"-light, or maybe they just don't stay viable that long.

The spores are also easily filtered, allowing simple masks and filters on buildings. Decontamination of someone coming inside is harder, but not impossible.

As a twist, the spore release may be conditional on weather, making spore conditions an important part of the weather report.

and if it is tidally locked

Well, spores could still work, but would only be found on "jovi"-side vegetation, and might not use a concurrent release system.

on "tidally locked"

If "A" is tidally locked, you just occupy one hemisphere, and the deadly side is not a significant factor in peoples lives.

$\endgroup$
0
$\begingroup$

The Jupiter-facing sides of its nearby moons are already uninhabitable (for human-like life) due to the high ionizing radiation spewing out from Jupiter. There are probably some simple and hardy bacteria and microorganisms which can survive this, but it's a perfectly plausible reason to not have anything more complicated.

$\endgroup$
1
  • 1
    $\begingroup$ Jupiter doesn't "spew out" ionizing radiation, it traps it in its magnetosphere. There is an asymmetry due to the Io plasma torus rotating with Jupiter's magnetic field, but there is no "shadowed" side that is protected from radiation. $\endgroup$ Jan 4, 2021 at 2:57
0
$\begingroup$

The only kind of radiation a gas giant would emit that could cause this kind of effect would be heat. Large gas giants could be hot enough to glow dull red, heated by radioactive decay and gravitational contraction...a giant radiant heater in the sky, adding its effect to that of the local star.

The effect wouldn't be sharply defined, but it's plausible that liquid water would be unable to exist where the gas giant is high in the sky, while the far side would be Earthlike. Weather conditions might make permanent inhabitation of the boundary impossible, with the hot spot being completely unsurvivable without protective equipment.

$\endgroup$
2
  • $\begingroup$ Not exactly. Jupiter has a very strong magnetic field, which rips charged particles from its ionosphere (and the top of Io's atmosphere) and accelerates them to high speeds. This is strong enough to kill off humans on jupiters moons surfaces within a short time (hours to days) $\endgroup$
    – Innovine
    Jan 3, 2021 at 22:46
  • 1
    $\begingroup$ @Innovine yes, exactly. The ionizing radiation you describe would not be limited to one hemisphere and leave the other inhabitable. It also probably wouldn't even penetrate a breathable atmosphere...though it may well destroy such an atmosphere by ionizing and heating the upper layers and dissociating water vapor. $\endgroup$ Jan 3, 2021 at 22:51

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .