
An Ultrahot Exoplanet Has Metallic Skies - yaseen-rob
https://www.scientificamerican.com/article/this-ultrahot-exoplanet-has-metallic-skies/
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imhoguy
Remids me metal based life forms[0] - mind-blowing.

[0] [https://www.newscientist.com/article/dn20906-life-like-
cells...](https://www.newscientist.com/article/dn20906-life-like-cells-are-
made-of-metal/)

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

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Sniffnoy
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?

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grigjd3
Size matters. To be clear, it very much likely gives off BB radiation, but it
may not be big enough to be detectable here.

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jessriedel
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.

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grigjd3
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.

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jessriedel
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](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.

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ereyes01
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/](https://hla.stsci.edu/)

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andrescoin
Impressive! Do you guys are looking for interns?

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phyller
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.

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solipsism
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.

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phyller
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.

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anoncoward111
Life is short. It's fun to have opinions if you are willing to be wrong :)

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dwaltrip
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...

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phyller
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

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dwaltrip
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.

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cgriswald
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.

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dwaltrip
Ah yeah, that makes sense. Thanks for clarifying!

