MESA, a piece of software referenced in this article, is a pretty incredible system. (Even referring to it as software underplays the extent of its community and impact.)

Many people are involved in MESA and Bill Paxton was always quick to point out the many new folks that worked on it, but this article does a great job of celebrating his impact:

https://www.kitp.ucsb.edu/news/an-accidental-astrophysicist

It's amazing to me that he went from being the voice on the other end of the Mother Of All Demos to having such a major impact on stellar astrophysics during his "retirement." He passed away in 2025.

This might just be me, but I find metaphors like ''Fingerprints' inside the Sun' harder to read than the title of the original paper, which is probably what should be linked here per HN submission guidelines:

> Planetary engulfment as a solution to solar-model discrepancies and its implications for planetary systems https://doi.org/10.1093/mnras/stag1527

For the press release, something like The Real Sun and Its Simulations Disagree. A Planet That Fell In Early Might Explain It. might be easier to follow.

> Their results favour a scenario in which the young Sun engulfed a super-Earth around 5–10 times the mass of Earth

Given the state of the early solar system, it would be surprising if the Sun didn't swallow a lot of metallic and carbonaceous rocks and pebbles. But it seems unclear to me how the researchers would distinguish between one super-Earth and >10^10 smaller rocks? Chemically I feel the two would be largely the same.

That's easy, they'll check whether there's one big fingerprint vs >10^10 little tiny fingerprints and conclude accordingly \j

Funny, but it's roughly how it works. You look at refractory-to-volatile ratios, the same trick used on solar twins. Pebbles accreting steadily wash out into the baseline, while one big engulfment leaves a bump. Gotcha is the convective envelope mixes everything, so you have to model the interior.

>But it seems unclear to me how the researchers would distinguish between one super-Earth and >10^10 smaller rocks?

I have a similar feeling when life on earth is suggested to be "alien", arriving via debris in the solar system as the earth formed. Isn't everything in the solar system coalesced from the same debris?

I don't fully follow (not being an astrophysicist), but it seems like the depth of the metallic material within the star matters a lot for their model. A planet can "bury" it (their word) a lot deeper than small rocks by physically sinking in before it gets destroyed. Sections 4.2 and 4.5 (among others I assume) in the actual paper linked above talk about this stuff.

Rough intuition: small rocks vaporize high up in the envelope, and convection mixes them around until the signal's diluted to nothing. A 5-10 Earth mass planet is dense enough to plunge much deeper before it breaks up, so the metals stay buried where mixing can't wash them out.

This, but how do they rule out the extra stuff landing in the sun much earlier - when the solar system was still a pre-solar nebula, and which bits would end up where (sun vs. planets vs. whatever) was far from settled?

> Researchers also found that such a world could survive its passage through the Sun's outer layers while losing very little mass, which suggests that planets may leave detectable fingerprints inside their host stars long after they have disappeared.

So I guess the large size would have permitted it to smuggle stuff into the core that would have just vaporised in the corona if carried by many smaller objects?

Chemistry isn't the signal, timing is. Pebbles dribbling in early get stirred through a fully convective young Sun and diluted to nothing. One big late hit, after the envelope shrank, leaves a lopsided signature. Same as spotting a single spike versus noise in a time series. Whether the model's right is another matter.

That’s it Apollo! Spit it out, what’s in your mouth, spit it out now!

Has someone got a quick explainer for why adding a planet would result in less lithium? Is it just that a super-earth would be big enough and have so little lithium that it would measurably water down the other elements?

Neither an astrophysics. I skimmed the paper. IIUC the collision with the planet mixed internal layers of the Sun and a lot of the Lithium went to the core and got fussed with Hydrogen.

PS: The paper says that that actual A(Li)=1.1 instead of the expected A(Li)=3.3. I needed a lot of search to understand it until Gemini kindly liked this page. https://astronomy.stackexchange.com/questions/61814/what-do-...

A(Li)=1.1 means the Li/H ratio is 10^(-10.9) = 10^(-8.9)%

A(Li)=3.3 means the Li/H ratio is 10^(-9.7) = 10^(-7.7)%

Not an astrophysicist, but since they mentioned the lithium is depleted, I wonder if that implies the collision of a planetary body with a sun would consume or react with the solar lithium.

You have to get nearly halfway from the surface of the sun (photospere) to its core before the density of the sun’s material is equivalent to that of the earth.

About that artist's impression with the blue spiral: wouldn't any planet or other object do one of these things:

- approach and hit directly, without spiraling

- approach, make a close fly-by and fly off into deep space again

- be in a steady, eliptical orbit

My knowledge is basically that of a Kerbal.

Small nitpick: the first two only apply to something coming in from outside. A planet that formed here is already bound, so it's stuck in an orbit that slowly decays. IIRC tides and drag from the thin outer atmosphere bleed off energy, so the spiral is roughly right, just painfully slow.

There are obviously many things KSP's patched conics approximation can't account for, like lagrange points or how orbits often get twisted around over time, or how the small effects from all the other solar bodies add up to be significant over time.

The simplest thing that comes to mind here is that KSP simulates a mature solar system, where space is mostly empty. This event happens in an early solar system, where there's lots of stuff everywhere. Running into stuff can steal some of the planet's momentum, causing it to fall deeper, causing it to run into more stuff

But planetary migration can be a lot more complicated than that. [1] has an overview. You might also enjoy the Grand Tack hypothesis [2] which involves early Jupiter spiraling into the inner solar system until around the orbit of current-day Mars, before eventually reversing course and getting to its current orbit further out

1: https://en.wikipedia.org/wiki/Planetary_migration

2: https://en.wikipedia.org/wiki/Grand_tack_hypothesis

I find it endlessly fascinating that information cannot be destroyed and we keep finding more and more ways to read the universe at every scale!

Did stellar abundance fits in grad school, getting the Teff systematics out took months.

On a similar note, the Large low-shear-velocity provinces (LLSVPs) are structures in Earth's lower mantle that are hyothized to be remnants of Theia (the planetary-scale body that collied with, resulting in the formation of the Moon):

https://www.nature.com/articles/s41586-023-06589-1

That sentence is kind of scary.

Imagine being a civilization on a planet that knows it's going to be swallowed by their sun.. (during the lifetime of the living members)

The book Seveneves is about civilization confronting impending doom from the moon exploding. I never finished the book because I felt it was depressingly realistic.

how hysterical would it be if the Sun decided to pull the earth into it.

Discussions on X, Reddit and HN titled "Is this it" or "Heat death is medically comfortable".

Crazy stuff.

Nominative determinism- first author's name "Mutlu Yıldız" means "happy star"

Clearly wasn’t a “planet” — failed catastrophically at clearing its neighborhood. The Royal Astronomical Society should be ashamed for publishing something so un-scientific. /s

and how exactly are we going to put our fingers into the sun?

I once ate a peanut too.

When I saw the word 'Fingerprints', I thought it was a brilliant expression.

Worth separating what's measured from what's modeled here. The lithium and refractory abundances are observed; the engulfment scenario is what the stellar models need to reproduce them. As far as I know, that makes it a good fit rather than a detection, and other explanations of the solar lithium deficit remain open.