One of the first rules of astronomy is humility. We don’t phrase it that way. Instead, we say there is a cosmological principle, and it says we don’t live in either a special time or a special place, and if you look at a large enough chunk of the universe, everything really is the same everywhere. The thing is that sometimes we take this rule too far, and we assume even our planets are pretty normal.
Folks, I’m starting to believe there is no such thing as normal.
Jupiter. We constantly compare other worlds to Jupiter like it was a normal measure of a planet. There are hot Jupiters, super Jupiters, sub-Jupiters, cold Jupiters. There is a laundry list of adjectives used to describe worlds as they relate to Jupiter as if it were the normal one. It is not normal, not even in our own solar system.
Jupiter is the most dramatically colorful world in our solar system, and these colors come from its rich mixture of elements – elements that include xenon, krypton, argon, and nitrogen. In general, these elements weren’t all that common where Jupiter is today when the planets were forming, and the closer one got to the Sun, the fewer of these gases were around. This strange reality – that Jupiter has these elements, and yet, these elements like it better in the outer solar system – led two different teams in 2019 to speculate that Jupiter may have formed in the outer solar system and spiraled in.
Except we had already built this cool model of Jupiter and Saturn starting closer in and moving out, and do we really want to play yo-yo with planets? Don’t answer that. I know I actually would totally play yo-yo with Jupiter if I could.
Anyway, not wanting to fling Jupiter around more than necessary, another research team has come up with a new idea: what if a pile-up of dust and debris cast a shadow that let Jupiter form where it was both cool and close?
Midway through the asteroid belt was a snow line. Inside that line, water was liquid, and at that line, just like in a winter storm, the phase changed and things got messy. Imagine if, at this line, a broad ring could form that cast a shadow big enough to allow Jupiter to lurk in the shadow, grabbing up weird elements, and preparing for its colorful future. It’s a cool picture, and while we may never know if it’s real, it’s kind of amazing to know that the science is possible.
This work appeared in Astronomy and Astrophysics and was performed by Kazumasa Ohno and Takahiro Ueda.
A shadowy birthplace may explain Jupiter’s strange chemistry (Science News)
“Jupiter’s “cold” formation in the protosolar disk shadow,” Kazumasa Ohno and Takahiro Ueda, 2021 July 1, Astronomy & Astrophysics