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A Circumplanetary Disk Around PDS70 C [pdf] (eso.org)
72 points by leephillips 31 days ago | hide | past | favorite | 15 comments

Would someone who has knowledge in this domain be willing to explain the significance of this? To me, it just describes 2 protoplanets in a dust disk, but I'm sure it has some importance to astronomers in order to hit front page of HN

Many circumstellar disks have been detected, but this is the first unambiguous detection of a circumplanetary disk. This is believed to be material swirling around a protoplanet, accreting on to it, and perhaps, forming moons. The actual processes of how planets form out of protoplanetary disks are still not well understood, so observations like this will help narrow things down. Quite impressive that they were able to resolve it with ALMA.

No expertise in the matter, but I assume the question is how our solar system formed with gas giants in the outer orbits and rocky planets in the habitable zone and how common this might be around other stars. The final paragraph of the conclusion has some hints.

I am particularly interested in why we are on a planet that is so rich in phosphorus and the final phrase about "delivery of chemically enriched material to planetary atmospheres" is a real tease.

The Bae et al paper linked in that paragraph (https://iopscience.iop.org/article/10.3847/2041-8213/ab46b0) (note Bae is cited second on OP paper) actually has quite a bit more to do with the way planets settle into orbits, based on study of this same system. As a fellow layman I haven't read it in detail but it looks fascinating, will check it out later.

These are really interesting papers and full of pics and diagrams, although the math is beyond me.

From a layperson's perspective (I am not an astronomer at all), it sounds like they found 2 Saturn-like planets in the making. They're still forming from their dust disks. That in itself is cool.

According to Wikipedia, "For the first time, we can conclusively see the tell-tale signs of a circumplanetary disk, which helps to support many of the current theories of planet formation."

I'm confused though... doesn't our own Saturn have a circumplanetary disk?

Do not read Wikipedia.

What is new here is the clear observation of a circumplanetary disk around an exoplanet. Such disks are where moons are formed, so this is the first observation of a moon-forming process outside of our solar system.

> so this is the first observation of a moon-forming process outside of our solar system

Is that really true? We've never seen moons forming elsewhere in the universe?

Correct. The ability to infer this from observational data was only possible with the technique pioneered in this paper.

Remember that we cannot even see exo-planets visually (with one or two very nearby exceptions).

According to Wikipedia, there are not even any confirmed exomoons yet. So it's interesting that a disk was observed first, although given size/brightness that's probably not a surprising result.

My hardwired brain: an old disk from the 70's with an obscure c compiler was found!

It should be rewritten in Rust.

I thought it was an (artificial) orbital ring.

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