
Astronomers Find Planet Hotter Than Most Stars - el_duderino
https://www.jpl.nasa.gov/news/news.php?release=2017-160
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gigatexal
It's also losing 10 million kilograms of mass a second. The universe never
ceases to be mind boggling large.

~~~
dwaltrip
It has a mass of roughly 10^27 kg (per the article, it is very comparable to
Jupiter in mass).

Using a loss of 10 million (or 10^7) kg per second , we can calculate that the
planet is losing 10^7 / 10^27 percent of its mass per second:

10^7 / 10^27 = 10^(-20) % = 0.00000 00000 00000 00001 % of its mass per second

If we change the time interval to one year, then we simply multiply the number
of seconds in year (32 million, roughly), which moves the leading digit 7
places to the left.

The resulting answer is that the planet is losing 3*10^-13 %, or 0.00000 00000
003 %, of its mass per year =)

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flukus
Is it close enough to the star for relativistic effects to make a difference
here?

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greglindahl
Very slight. Mercury is close enough for very very slight.

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twic
> KELT-9b is 2.8 times more massive than Jupiter, but only half as dense.

> Because the planet is tidally locked to its star

What does it mean for a gas giant to be tidally locked?

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greglindahl
It means that if you average together the motion of all of the mass of the
planet, it revolves once per orbit around the star. Which is the same as what
it means for a rocky planet, if you think about it, it's just a little less
obvious.

Another way to think about it is that the gas giant moves such that tidal
friction caused by the gravity of the star is minimized... because that's why
it's moving like that.

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ChuckMcM
Makes me wonder what shape such a planet would take.

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adrianratnapala
Very slightly elongated along the axis between itself and the star. Still
nearly spherical and the deviation would be essentially ellipsoidal (not egg-
shaped).

~~~
greglindahl
It's probably a bit more exciting than that when you include evaporation and
the stellar wind! But yes, an ellipsoid is the basic shape, the tides elongate
the planet both towards and away from the star, same as the tides on the Earth
caused by the moon.

~~~
adrianratnapala
Yep. The original post even speculates the thing might have a comet-tail
because of the evaporation.

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ChuckMcM
I kind of imagine it looking sort of like a Hersey's Kiss shape :-)

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douche
I wonder how broken our astrophysical models will prove to be once we are more
and more effectively able to peer outside our home system. There is a universe
of examples out there, and I would find it slightly depressing if all of that
complexity could be described by the theories of a swiss patent clerk.

~~~
openasocket
Einstein's field equations are a system of extremely nonlinear partial
differential equations. Actually using them to compute something is very
nontrivial. And of course gravity is but one of the many forces at play here.
You still have to account for thermodynamics, chemistry, nuclear physics, and
other complicated effects to understand what's going on here.

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nonbel
Is the sun going to end up being called a "Dwarf Star"?

Also, this means nothing to me: "With a dayside temperature of more than 7,800
degrees Fahrenheit (4,600 Kelvin)"

Where in the atmosphere is this temperature begin measured? The temperature
can vary wildly by altitude, latitude, and time of "day". As far as we can
tell, as the atmosphere of a planet gets thicker the temperature keeps
increasing indefinitely (eg check out fig 1):
[http://faculty.washington.edu/dcatling/Robinson2014_0.1bar_T...](http://faculty.washington.edu/dcatling/Robinson2014_0.1bar_Tropopause.pdf)

~~~
nonbel
Looking closer:

>"Given the high stellar luminosity and close orbit, the planet receives a
large stellar insolation flux (Table 1). As a result, it has an extremely high
equilibrium temperature: calculations, assuming zero albedo and perfect heat
redistribution, give a value of approximately 4,050 K."[1]

That 4,050 K value is reported as the equilibrium temperature, which I
understand to be the output of the Stefan-Boltzmann law:

    
    
      T = (I*(1-alpha)/(epsilon*sigma))^.25
      where,
      I       = Incident Flux
      alpha   = albedo
      epsilon = emissivity
      sigma   = SB constant = 5.670373e-8
    

According to the paper the planet receives 61.1 x10^9 erg/s/cm^2.[1] The solar
constant is ~1360 W/m^2.[2] In the same units the planet gets 6.11 x 10^7
W/m^2, which is about 45 thousand times greater than what the earth receives.
Anyway, plugging into the SB law I get:

    
    
      (6.11e7*(1-0)/(1*5.670373e-8))^.25 = 5729.377 K
    

So I am certain it is I rather than them with the error. Where did I go wrong?

[1]
[http://www.nature.com/nature/journal/vaop/ncurrent/full/natu...](http://www.nature.com/nature/journal/vaop/ncurrent/full/nature22392.html)

[2]
[https://en.wikipedia.org/wiki/Solar_constant](https://en.wikipedia.org/wiki/Solar_constant)

~~~
nonbel
I see now, I was calculating the temperature at the subsolar point, they are
averaging over a uniformly illuminated sphere.

Since the illuminated side is a disc with area pi x R^2 and the sphere has
surface area 4 x pi x R^2 we need to include a factor of 1/4:

    
    
      (6.11e7*(1-0)/(4*1*5.670373e-8))^.25 = 4051.281 K

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rdiddly
I just want to know where it is, jeez. Map of the galaxy please! (Assuming
it's in this galaxy.)

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malydok
Does the article specify the planet's distance from Earth? I can't seem to
find this rather fundamental information.

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dEnigma
Seems like the article indeed forgets to mention the distance. I guess the
nature article[0] has all the information, but since I can't access that one
right now I also found a Washington Post article[1], according to which the
distance from Earth is about 650 light-years.

[0][https://www.nature.com/nature/journal/vaop/ncurrent/full/nat...](https://www.nature.com/nature/journal/vaop/ncurrent/full/nature22392.html)

[1][https://www.washingtonpost.com/news/speaking-of-
science/wp/2...](https://www.washingtonpost.com/news/speaking-of-
science/wp/2017/06/05/the-hottest-planet-ever-discovered-has-an-atmosphere-as-
warm-as-a-stars/)

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peterburkimsher
Planets: so hot right now.

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yawz
_> He worked on this study while on sabbatical at NASA's Jet Propulsion
Laboratory, Pasadena, California._

While on sabbatical? Wow! That's dedication.

~~~
goodcanadian
Ummm . . . I think you misunderstand the meaning of "sabbatical." It doesn't
mean vacation. It means freedom from teaching and administrative duties to
give you time to go to another institution, learn new things, and work on
interesting problems. This is exactly the sort of thing that I expect an
academic on sabbatical to be doing.

~~~
flukus
I wonder why we don't see this in the corporate world more? When we need a
change of pace we have to quit one company and start at another one, you'd
think it would be in the companies best interest to have people go elsewhere
to get their fix and then come back with their old knowledge plus any relevant
new knowledge.

~~~
microtherion
Apple used to have sabbaticals until 1997 or so (6 paid weeks off every 5
years). Anecdotally, I heard that many employees used the leisure time to look
for new jobs, but that may have been due to the turmoils Apple was undergoing
in the 1990s.

~~~
y7
6 paid weeks off is hardly a sabbatical. For many jobs in the EU you get that
many vacation days anyway each year.

