Barnard's necropolis

So last year, and the year before that, we were talking Proxima Ophiuchi aka Barnard. It has four planets, all with minimum masses double-to-triple Mars'. Xander Byrne and crew are pondering What It All Means.

Besides irradiated Marslikes. We already knew their sunsides were too baked. Also the UV on any of them would be too low for "abiogenesis" even for inner "d" which is the most-roasted. The latter doesn't account for seeding from any other systems this ancient star had passed-through; but if I'm a spore-shooting alien fungus, I'd not bother with Barnard.

The star is ancient, so doesn't flare much, which helps in telling that these planets were for real in the first place (this had been a problem). It is enriched in magnesium by contrast with silicon and thorium. Byrne's paper extrapolates that the planets should be ferropericlase. I don't frankly know what that mineral is, but Petrov says that this doesn't hold water well.

The four are resonant like Trappist-1... and the Jovian system. The inner planets d,b,c might be in a 4:3 MMR chain but since we have less data than what we have for - say - Trappist-1; the paper whiffs on this one.

The paper is able to use the resonance to impose upper mass limits - which is great. Even if the planets aren't great; they're all subEarths. Given the resonance they likely formed about where we see 'em. That is (well) within the soot line let alone the snow line.

So these are all low-mass. And: with more space than Jupiter's moons have. So they don't pull on each other as much. Add to that, their internal radioactive elements (which are halflived well beyond Earth's): they are internally "cool". And the outermost planet e is tidally locked which people aren't anymore saying about Trappist-1.

Knock-on effects are that the planets won't have seeped out volatiles after initial formation. Barnard is quiet... now; but these stars - M dwarf - tend to be flare stars when younger.

The paper also brings "gap complexity". Barnard's four are simple, 0.131. The paper argues that this implies no giant outer planets, but we must counterargue that our system has a lower 0.126 inward of 1.5 AU and... we have four giant outers. Of course we've been looking at this one since van de Kamp so... yea, we ain't seen nuffin'.