aliens observing the solar system: [untranscribable telescope name]-59172 has 2 planets. It's a pair of relatively small, cold gas planets, called [untranscribable telescope name]-59172b and c. [untranscribable telescope name]-59172c was discovered only a few years ago. Systems with multiple cold gas planets are rather uncommon, so this is pretty exciting
theyre probably not gonna know earth is third for some time, since mercury is a very small planet at a fairly medium distance. The moon, too, obviously.
Long before that happens though, these aliens discover [UTN]-59172d and [UTN]-59172e and determine d is uninhabitable and e is *probably* uninhabitable (because their idea of the habitable zone is slightly different and earth, already at the inner edge in our conception, happens to fall just slightly on the wrong side of the line they've drawn)
artist's impression
I wonder what they'd think of Uranus and Neptune if they spotted them. The REALLY cold and small gas bodies.
our models at least predict neptune-like planets, that is, ice giants, are probably more common than saturn-like small gas giants, although they're much harder to detect
when planets cross a certain mass threshold while gas is still plentiful, they tend to grow very rapidly, and form large gas giants, usually larger than jupiter. if they only reach that mass after the gas has mostly dissipated, they may become ice giants or smaller gas-rich icy superearths. but producing a light gas giant like saturn requires the planet to reach the mass threshold at a very specific time
This is really interesting to me, where could I read more about our models for what typical planetary systems look like?
this is a paper simulating the evolution of planetary systems around sunlike stars. the 50 and 100 embryo simulations likely reflect reality
https://www.aanda.org/articles/aa/full_html/2021/12/aa38863-20/aa38863-20.html
I came across the “Grand Tack Hypothesis” recently, which focuses on the orbital relationship between Jupiter and Saturn. According to the hypothesis, Jupiter formed 3.5 AU from the sun, then its mass brought it in towards the sun, at around 1.5 AU, before its dance with Saturn brought it back out to its current 5.2 AU resting place. This interrupted the rocky planets’ formations, Jupiter likely sucked up a lot of the material and water that would otherwise have become Mars, but it also cleared the orbital paths for the inner planets, contributing to the relative calmness in the system that reduced interruptions of life developing on our watery rock. A lot of the basis for the hypothesis comes from observations of other star systems, which shows gas giants tending to inhabit the inner orbits of their parent star, indicating that Sol’s inner-rocky-planet/outer-gas-planet arrangement is a rarity, not how star systems tend to form.
