tidderred t1_je1vi30 wrote on March 28, 2023 at 8:23 PM

Reply to comment by Paaaaap in Is NaCl relatively common in the galaxy/universe? by PHealthy

(Have read through the first few chapters of Stars and Their Spectra by James Kaler, so most of what I will say is explained in more detail there.)

On the topic of chemical composition of stars, only cool stars, like M dwarfs or L and T type ultra-cool brown dwarfs can have complex molecules survive in their cores. If the star is any hotter (which is the result of a lot of other variables) only pure elements or hardy molecules with strong bonds can survive that chaotic environment without being ripped apart. For example L-T stars can be identified if their chronosphere contains TiO, which is a) a molecule and b) has titanium, which is heavier than sodium or chloride, so somewhere out there NaCl should exist.

But as far as we know L-T stars along with white dwarves and type 0 stars make up about 5% of stars in the universe, so not a lot of NaCl should exist in stars both in quantity and spatial spread.

Like you said, detecting chemicals on exoplanets is much more challenging, where NaCl can exist in greater quantities, without being disturbed by immense heat and pressure stellar cores have. We just cannot know for sure, but it is fun to think about! (Which is a very non-sciency way of saying we should be looking into this.)

EDIT: After an experienced scientist chimed in I realized my answer didn't take into account the fact that the molecule itself needs to radiate some energy for us to detect it, or it should absorb some energy from the envelope to create noticeable dips in the spectrum. In either case, it will heat up, not so much to break the molecule, but not as cold as L-T stars would require (about a few hundred kelvin at most). I also didn't base my speculation on any real detection, just wanted to chime in since what I learned about seemed to coincide with this topic. Still leaving this up in case anyone wants to take this info and go on their own rabbit hole. Also, just saw JWST detected some silicate dust in a what looks to be a hot jupiter (VHS 1256 b), so exoplanets being challenging to study might already be changing with JWST's observations.

adamginsburg t1_je29j3x wrote on March 28, 2023 at 9:53 PM

I think you're on the right track that L/T/Y dwarves (brown dwarves) should have cool enough atmospheres to have NaCl in them. I don't know what references to go to say for sure, though.

One of the problems isn't just that the salt molecules need to be warm to emit (that's true), but that the wavelengths at which we see their radiation are tough to observe in stars and planets. The detection we reported was in a disk - which is very, very big compared to a star or planet, and so we could see it at radio/millimeter wavelengths. We generally can only detect stars themselves at optical and infrared wavelengths, and it turns out that NaCl and KCl don't have many transitions at wavelengths we usually observe (e.g., https://ui.adsabs.harvard.edu/abs/2014MNRAS.442.1821B/abstract). Most of their strong emission/absorption lines are at >=26 microns, which is just at the edge of what JWST is capable of observing with its MIRI instrument. No other telescope has observed at these wavelengths with enough sensitivity to pick up salt molecules. I think there's some possibility JWST will detect salts in either hot jupiters or brown dwarves, though; there are weaker salt lines covering JWST's whole range. The trick is, there are lots of other molecules that could obscure the salts in an atmosphere - I'm not sure whether we'll be able to identify the molecules cleanly. It's a much easier job at radio wavelengths.