primary atmospheres

just-some-writer  asked:

I have a world in my novel that being investigated for terraformation. It's a large moon (slightly smaller than Earth) orbiting a gas giant. It's tidal-locked to its planet. Would the planet-facing hemisphere have a different climate than the non-planet-facing hemisphere? I currently have it written that the outward-facing side is more temperate, while the other is much warmer. But that just struck me as a fun idea and I don't actually want to use it if it's weird or implausible. Thanks!

Note: the following is for the moon to support life-as-we-know-it (carbon-based, some type of DNA or analogue, etc). Silicon-based life or other exotic life could live in very different environs..

A habitable moon orbiting a gas giant (which we will call the primary) would require both the gas giant primary and the habitable moon to have certain characteristics.

For analysis, lets assume the primary is a Jupiter-sized gas giant. We’d have to move it closer to it’s star than Jupiter is in our system, so there would be enough heat from the star to keep the planet habitable. The additional heat from the primary will help so we don’t have to move it as close to the star as we otherwise might.

This would make your primary a ‘hot Jupiter’ - a gas giant that orbits close to it’s star. We know of a lot of hot Jupiters in nearby systems.

Having an Earth-sized moon isn’t a stretch at all. The second largest moon in our Solar system is Titan, a moon of Saturn. It has a radius of 2575 km, about half the size of the Earth. It also has an atmosphere - one made of nitrogen, methane, and hydrogen. Ick, but this shows that a large moon with an atmosphere is possible.

The biggest danger to your habitable moon is the primary’s magnetosphere. This is the magnetic field generated by the primary. Although this magnetic field will help shield your moon from cosmic rays and radiation from its star, it also traps a lot of radiation particles and keeps them close to the primary - like Earth’s Van Allen Belts but much, much bigger and powerful. On moons close to the primary, that’s enough radiation to kill everything. Jupiter’s inner moons are orbiting inside a giant microwave oven.

To have a life-bearing moon, we need to do one of two things to it - preferably both to be on the safe side: move the moon outside of the radiation belts of the magnetosphere and/or give the moon it’s own magnetic field.

As your moon is about Earth-sized, it probably has a rotating iron core. It’ll have a magnetic field, but lets place it outside the primary’s radiation danger zone just to make sure.

For Jupiter, the safe distance is about 1.5 million km. So, lets put your moon at the orbit of Callisto at 1.8 million km. At this distance, what little radiation your moon gets from the primary’s belts is blocked by the moon’s magnetic field.

Good call on the moon being tidally-locked to its primary. Jupiter’s and Saturn’s largest, closest moons are tidally-locked to their primaries (including Callisto). What this situation will do is make your moon’s day-night cycle quite a bit more interesting than just sunlight and darkness.

As the above mages shows, your moon will have a varying amounts of illumination - a time where only the star is visible (true day), a time where both star and primary is visible (brighter day), a time where the primary only is visible (false day), and a dark time where neither primary nor star is visible (true night). The moon will have a day length equal to the time it takes to orbit it’s primary.

Putting your moon at the same, safe distance as Callisto, it will orbit it’s primary in about 16.5 Earth days, so the moon’s ‘day’ will be just under 400 hours. If your moon orbits in the same plane that the primary’s orbit is in (and it probably does, cause that’s how most orbits work), you’ll have a short eclipse of the star by the primary every day for a couple of hours. Indeed, it’ll happen at local noon.

The tidal-locking of your moon probably wont have much of an effect on the planet’s environment. The side pointing towards the star will get really hot, seeing 200 hours of daylight, but it’ll cool off at night. The heat from the star will have much more impact than the heat form the primary. 

A good atmosphere and oceans (like Earth’s) will do a lot to spread the heat across the planet more evenly. It’ll probably have more extreme days and nights than Earth, but probably not enough to make living there too difficult.

Of course, the view from your moon would be spectacular. The primary will hang in the same spot in the sky looking about nine times the diameter of Earth’s full moon. It’ll be dozens of times brighter than the full moon, as well.

tl;dr:  Your setup is quite plausible and believable, and you’ve got the basics pretty good.. There is nothing known that would make such a setup implausible.

Hey, if it’s good enough for the Rebels…

BNHA - Space (symbolism) Edition

So @saisai-chan and I were talking about awesome space stuff and it bled into talking about BNHA, which led to this - BNHA characters as symbolic celestial *SPACE* objects. We’re just… Really enthusiastic about space…..


All Might - Sun. Center of everything, provides life/energy to the solar system, largest celestial body in solar system. (All Might’s influence.) Also protects the solar system from objects from outside the system. (Again, his influence, symbol of peace, number one hero)

Midoriya Izuku - Earth. Has life on the planet, the only planet bestowed with life thanks to the sun. (KINDA LIKE… ONE FOR ALL)

Bakugou Katsuki - Venus. Zero chill, greenhouse effect, VOLCANOES EVERYWHERE (which contributes to erosion and therefore makes the surface very “new” - lowkey nod to Mama Bakugou’s quirk glycerin, making her eternally youthful), atmosphere that burns up pretty much everything before it can actually hit Venus’ surface (kinda like how Bakugou doesn’t really get close to people that much; they are often repelled/intimidated by his attitude). Secondary Atmosphere is almost entirely CO2 - because its temperatures are so high, water could never condense and bring CO2 to the crust. Venus never underwent the change that Earth and Mars had, remaining as it did with greenhouse effect => high temperatures; it never cooled off. (Bakugou is stubborn, change is very slow, still hot-headed with zero-chill af)

Uraraka Ochako - Saturn. Lots of gravity, really pretty to look at, can float on water (average density is less than water).

Todoroki Shouto - Mars. Cold and Red, Mars had a secondary atmosphere like Earth’s at one point - lost Primary Atmosphere like all the terrestrials, gained a secondary like Earth’s (caused by water condensing and falling to the crust, bringing CO2 with it). Suspected to have been substantially warmer earlier on in its life. As its core continues to cool, the planet itself cools.

Kaminari Denki - Uranus. Only planet that’s tilted on its side (he’s a dork), looks plain and boring but actually isn’t. (Kaminari seems like a joke character at first but hey! He has a personality too, has friends, cares about them, will defend them. He’s more complex than he looks, even though it isn’t much) Also, storm planet. (Electricity, lightning. Fire + wind, Bakugou and Kaminari)

Kirishima Eijirou - Neptune. Water planet, a pair with Uranus. (Kinda like a complimentary opposite of venus - water + lava (from venus) makes land, land = life (Bakugou, Kirishima, and Kaminari), goes from Raging Inferno to HOPE.)

Tokoyami Fumikage - Pluto probably. Because it’s the edgiest celestial body in our solar system, furthest from the sun (darkness aesthetic). Has a giant heart-shaped mark on its surface. (He’s a dork and not nearly as cool and edgy as he thinks.)

Todoroki Enji - Jupiter. Second largest object in the solar system, right behind mars, separated by asteroid belt. Extreme pressure (expectations on others/daunting presence) and multiple natural satellites (his own following, influence in the world). Big Red Spot. Jupiter’s coriolis effect/numerous wind cells (this guy has some inner conflicts and issues, man). Protects the Earth and inner planets but also kinda directs some asteroids towards us.

Todoroki’s Mom - Frost Line. (FROST. ICE QUIRK.) Located in the Asteroid Belt, not an actual object (we’ve only seen her, like, twice? She is Elusive), but a distance from the sun, separation between the terrestrials and Jovians. SEPARATES MARS FROM JUPITER. (she tried to protect Todoroki from Enji before)

Midoriya Inko - Ceres. Dwarf Planet, named after goddess of fertility and motherhood. (kind of out there away from the focal point; a little forgotten sometimes but also not)

Izumi Kouta - Moon. Created literally after a celestial object collided with earth. (“sorry I punched you in the dick”) Controls the tides (Kouta controls water)

Shigaraki Tomura - Mercury. Fully-formed planet before, but as it died, it’s liquid core shrank - causing wrinkles on its surface as the crust collapsed on itself. Dead, metal, and flakey. (His wrinkles. He could have had a bright future, but it died.) BUT ALSO NOT AS DEAD AS WE THOUGHT. Literally a recent finding. (Still has surprises for us, he is still a Mystery)

AfO - Black Hole. (Maybe his brother = a smaller star that turned into a white dwarf, while he = a black hole.) Giant black hole at the center of the Milky Way. (headcanon, but AfO is integrated in society in various ways without the government/hero associations knowing. He is old and influential, is a massive force. Like a black hole at the center of the galaxy)

Villains/League of Villains - Oort Cloud. Cluster of debris that surrounds the solar system; is kept at the far reaches of it. (Villains are the rejects of society, they try to stay as far away from All Might as possible)

Other students in Yuuei - Asteroid Belt.

Yuuei/Japan - Solar System. (has all of this stuff)


EXCERPT FROM CHAT (b/c I think it’s funny):

saisai-chan: YE AH
i imagine the solar system is like either UA or japan specifically
since AFO is the giant black hole at the center of the galaxy

athanatosora: And honestly, AfO at the center - I have seen and have too many headcanons that he is integrated in society in various ways without the heroes knowing. He is too old and influential to not be

saisai-chan: so he has influence all around

athanatosora: YEAH

saisai-chan: YEAH

the ppl who actually think Bernie Sanders has a chance…… read a newspaper.. watch any news channel (like MSNBC or Fox literally any of them)….. learn about electoral history in the US…please don’t believe that he can win based on the number of notes on a tumblr post about him