Dense Neptune-sized exoplanet discovered with TESS | Hacker News Reader

Dense Neptune-sized exoplanet discovered with TESS

phys.org

29 pointswglb6 comments

> TOI-332 b has a radius of about 3.2 Earth radii and an unusually large mass of 57.2 Earth masses, what yields a very high density—at a level of 9.6 g/cm3. The newfound planet orbits its host every 18.65 hours, at a distance of 0.016 AU from it. The equilibrium temperature of TOI-332 b was calculated to be around 1,871 K.

Wow, the headline wasn't kidding.

Assuming these measurements are accurate, I wonder what it's made of? Bismuth, lead, mercury? Probably a very interesting mix of heavy and possibly radioactive metals.

Surface gravity must be pretty intense.

Yeah, "dense" kind of under-sells it. Given the distance to its host star, I would guess that this must be a gas giant core that had its outer envelope blown away? Otherwise this seems hard to fit into our typical models of planet formation

> I would guess that this must be a gas giant core that had its outer envelope blown away

Well yeah? From what I read, this is a larger star than average, as well as a really close orbit.

I am failing to understand why this is surprising to the experts because the description sounds to me like the sort of exoplanet that there is/was a heavy bias towards from the beginning.

Yeah, I was thinking that sounds like a good candidate to chthonian planet ( https://en.wikipedia.org/wiki/Chthonian_planet )

>Bismuth, lead, mercury

It appears (I didn't previously know this) that iron, while less than 8 g/cm3 at our "normal" environment conditions, is thought to be closer to 13 g/cm3 (or more) at Earth's core.

So while 9.6 g/cm3 is dense, it's probably not dense enough that it implies a significant percentage of elements heavier than iron.

And I think that it's elements heavier than iron that would be truly shocking because I was taught that stellar fusion stops at iron, apart from supernovas.

"For iron, and for all of the heavier elements, nuclear fusion consumes energy"

https://en.wikipedia.org/wiki/Iron_peak

That makes sense. My napkin math says 3.2x larger radius would mean ~33x larger volume, so it's less than twice as dense as earth and pressures at the core would be much higher (57x?) so it seems feasible that it wouldn't have to be made of anything particularly unique at all.

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