An Ultrahot Exoplanet Has Metallic Skies | Hacker News Reader

An Ultrahot Exoplanet Has Metallic Skies

scientificamerican.com

96 pointsyaseen-rob31 comments

Remids me metal based life forms[0] - mind-blowing.

[0] https://www.newscientist.com/article/dn20906-life-like-cells...

I wonder if the first extraterrestrial lifeforms we discover will be anything like we expect.

This reminds me about the Scaly-foot gastropod[1] mollusc which "possesses a trilayered structure comprised of a mineralized iron sulfide–based outer layer (OL) containing greigite..."[2]

[1] https://en.wikipedia.org/wiki/Scaly-foot_gastropod [2] http://www.pnas.org/content/107/3/987

That article is from 2011, I wonder how much of it any continued to be developed?

I'm confused, they say the planet doesn't emit light of its own, but if it's that hot -- hotter than most stars, they say -- shouldn't it be giving off blackbody radiation in the visible spectrum?

Size matters. To be clear, it very much likely gives off BB radiation, but it may not be big enough to be detectable here.

Eh, it's double the radius of Jupiter, which makes it about one fifth that of the sun, right? So the apparent BB area is a 25 times less than a star, which is small but not crazy small. More importantly, the amount of light from the parent star filtering through the planet's atmosphere would seem to be much less than the amount emitted directly by the planet, since the apparent surface of the former is only a thin ring of area around the surface for the latter.

Several things: stars get much cooler than the sun, a factor of five in radius is a factor of 25 in surface area, the heat may be focused on the side pointing at the star (meaning the star masks the light), and light from the star could be overwhelming the light emitted by the planet. Astronomy is filled with orders of magnitude.

You repeated one of my own points back to me and then condescended down to me about not appreciating orders of magnitude. (I'm a physicist myself.) The whole purpose of my comment is that 25 is not that small of a factor on astronomical scales and it suggests the BB radiation of the planet itself would be detectable. As it turns out, this is the case

> As a result, [the planet] has an extremely high equilibrium temperature, assuming zero albedo and perfect heat redistribution, of ∼4050 K. This is as hot as a late K-type star, and thus we expected a large thermal emission signal, which we easily confirmed with our z'-band detection of the secondary eclipse with a depth of ∼ 0.1% (Figure 1). This measurement implies an even hotter day-side temperature of ∼ 4600 ± 150 K, likely indicating poor redistribution of energy to the night side of the planet and a temperature closer to that of a mid-K star.

https://arxiv.org/pdf/1706.06723

Note also that, contra your suggestion that the planet might just be too cold on night side to have significant BB radiation, the night-side temperature is only 15% lower than the mean.

Yeah, that got me too. That's not just "hot enough to emit some light", that's "half again as hot as an incandescent light bulb", enough to emit a warmish white light.

I think the article is simply being imprecise for simplicity sake. The temperature quoted for the article is the day side temperature. The planet is a tidally-locked hot Jupiter. Night side temperatures will be significantly cooler.

It is, see my quote from a paper below.

https://news.ycombinator.com/item?id=17800935

It's super impressive to me how much mileage we've gotten out of the Hubble Space Telescope. The article implies that this finding was made found in old data once the researchers knew what to look for.

Does anyone know how much data from Hubble is sitting there, and whether it's publicly available?

EDIT: I found this: https://hla.stsci.edu/

Impressive! Do you guys are looking for interns?

I call BS. I'm not saying the planet doesn't have iron or titanium, just that I don't think their data shows it.

The researchers supposed that this planet might have iron and titanium in the atmosphere, they have an image of the star with a slight dimming from the passing of the planet across it, and they find the spectral signature of iron and titanium.

The percentage of the light collected that was emitted by iron and titanium, if it existed in the atmosphere, would be so mind-boggling minuscule compared to the light of the star itself, I would think that the iron and titanium signatures would come from elements trapped in or around the star.

I think if they looked hard enough they could find whatever elements they want.

So quick to call BS without knowing what you're talking about. Transit spectroscopy is a well established scientific method. To put it simply... obviously they accounted for that.

I should apologize, I am probably, hopefully wrong. I'm still skeptical but clearly more work has been put into this than I realized and I shouldn't have been so quick to condemn it.

Life is short. It's fun to have opinions if you are willing to be wrong :)

I'm glad this had a happy ending! :D

Sometimes I feel bad piling on a downvote train -- especially considering the psychology research showing that people usually just dig in further in such situations...

To be honest, it would have been better to explain how they do the spectroscopy than to just say "you don't understand" and downvote. I should have raised a question instead of making a statement, the response should have been an explanation, instead of basically "you're an idiot" (which still no one has done as of this time). They are making the same error I did. The article posted didn't explain, the paper costs $9 to read. I wouldn't call this a productive discussion at this point.

Edit: someone just attempted to explain the technology behind it, thanks amluto

Respect for recognizing that you started things off on the wrong foot. Not everyone is willing to take ownership like that.

You are totally right, the best response is a clear, calm explanation. Unfortunately, the time, energy, and expertise to do so is not always available. It's in moments like those where I hesitate between ignoring the comment entirely and downvoting.

As for transit spectroscopy, I'm going off memory/rederivation/speculation here (not sure how much of each), but I believe it works by first taking the spectrum of the parent star by itself, then observing the spectrum of the starlight travelling through the transiting planet's atmosphere, and then diffing the two results to isolate the spectrum of the planet's atmosphere.

It works basically like that. The spectrum of the star will be an absorption spectrum. The star produces a continuous spectrum and then the atoms in its atmosphere absorb specific wavelengths. The light then travels through the planet's atmosphere where other atoms and molecules absorb other wavelengths; the signatures of which are known, telling scientists the makeup of the atmosphere.

Ah yeah, that makes sense. Thanks for clarifying!

Email the authors. There's a 50-50 chance they'll just give you the paper.

Though I wouldn't lead with calling BS ...

Totally agree with you anecdotally. When I am heavily downvoted on any site, I instantly believe my own dogma more, whether it is right or wrong, because now it is "mine" and it's under attack like a poor little defenseless puppy.

Honestly I feel like we shouldn't be down voting opposing opinions. Those should be the ones rising to the top, because that's the best way to cross reference, and get a different perspective.

I think the only things that should sink to the bottom are distasteful or rude comments.

Did you read the paper?

https://www.nature.com/articles/s41586-018-0401-y

The fact that this was doable doesn’t surprise me. A spectrometer essentially outputs an intensity as a function of wavelength. The output is a combination of the signal plus a background from the star plus mostly additive noise. The researchers knew what signal they wanted to find, and standard statistical techniques are very good at this.

The data used in this paper came from an instrument called HARPS North. This is an amazing spectrometer. Forget finding a signature from iron — HARPS North can detect a Doppler shift of a bright spectral line or less than 1 cm/s. This lets it detect planets by measuring the degree to which they wiggle their star.

(For an old classic example, there’s a device called a lock-in amplifier that looks for a specific sine wave modulation of a noisy signal. They are extremely sensitive.)

Compulsory link to save google a search:

https://en.wikipedia.org/wiki/Lock-in_amplifier

The research is fine, but the clickbait title of this article is BS. The Iron and Titanium are not in a metalic state, so - no metalic sky

Tone judgments aside, I think it's okay to be skeptical because spectroscopy is far from an exact science. Reminds me of the sensational "diamond planet"[0] a few years ago that was based on a dubious interpretation of the host star's spectrum.[1]

[0] https://www.forbes.com/sites/petercohan/2012/10/12/diamond-p...

[1] https://uanews.arizona.edu/story/diamond-super-earth-may-not...

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