I've come up with a couple of exoplanets for a story, and have reached the limits of my knowledge. I've googled around, and I had a space enthusiast friend look at them, but he freely admits that he's just guessing for most of this, especially the atmospheric makeup.
The other planet is here
This terrestrial moon orbits a 21 earth-mass ice giant that orbits a somewhat unstable main-sequence white star at a distance of 4.5 to 6.3 AU. Iyutha's mass is 0.064 earths and its radius is 0.6 earths, with a surface gravity of 0.178g. Surface temperatures range from -130 to -35 C. Its relatively thick atmosphere has a surface pressure of 1.31 atms, and is primarily helium, nitrogen, and carbon, with moderate quantities of hydrogen and trace amounts of fluorine, chlorine, and sulfur. It has large quantities of hydrocarbons, many of which involve the trace elements. Its planet's atmosphere is typical for an ice giant, though with significantly more hydrocarbons and fluorine, giving it a moderate bluish-green color, with storms being darker. The ice giant has 42 other moons, ranging in size from 0.06 earths to 0.8 earths, many of which have accreted moderate-to-thick atmospheres.
Atmospheric and magnetospheric interactions with interstellar hydrogen and helium, as well as solar wind cause frequent auroras that cover large portions of the moon. This applies to many other moons, and even the planet itself, often filling the sky with coruscating colors. Iyutha has moderate volcanic activity, which works with dimly-understood processes in the mantle to free fluorine and chlorine from molecular bonds, periodically releasing it in great plumes rich in hydrogen fluoride and hydrogen chloride that roil through the atmosphere, reacting with everything around them. The surface abounds in intricate geological formations caused by millenia of these plumes and the volcanic activity. Pockets of radioactive minerals are also sometimes freed by these eruptions.
Its planetary system is quite young; it has not yet finished forming terrestrial planets. It coalesced from the remains of several supernovas, which had remarkably high quantities of fluorine and chlorine. All bodies in the system possess notable levels of both of these elements. The recent formation of a pulsar in a neighboring system irradiated much of the system, as well as sending a super-Jupiter hurtling at it. The super-Jupiter collided with the system's largest gas giant on its way out of the system, spreading much of its victim's mass across the system and disturbing the orbits of most of the planets and protoplanets.
More details on the system are here.
How plausible is it that this moon could have developed naturally? If it's implausible, what changes would make it more realistic?
A few specific concerns I had:
- I had to do a bit of a cop-out in order to get the release of acids. I obviously can't provide scientific support for the freeing of fluorine and chlorine, but is it completely implausible for something like this to occur?
My general goal is to create an interesting exoplanet planet that is thoroughly intimidating to biological life but could reasonably be permanently colonized by a robotic civilization with technology that functions best in the -200 - 200 C range, that has access to smart materials, self-repairing buildings, and nanofabrication. Their ideal gravity range is 0g - 2g, but they can function in up to 4g. Colonization would likely be underground.
The important unique aspects of this planet are that it is a planet with a near-constant radioactive aurora with quantities of liquid and gaseous acids that are far above the norm. Any suggestions for changes to any other aspects that would make the core aspects more plausible are greatly appreciated.
EDIT: Thucydides's post made me realize that my original version is unworkable. I've replaced it with a modified version.