
Nearby "Super Earth" May Have Oceans, Thick Atmosphere - mattjaynes
http://news.nationalgeographic.com/news/2009/12/091216-new-super-earth-oceans-atmosphere.html
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luchak
"Based on its density, scientists think GJ 1214b is made up of about three-
quarters liquid water with a solid core of iron and nickel and an atmosphere
of hydrogen and helium—not unlike Earth."

what

This is either terrible writing or terrible science (on the author's part, not
the scientists', I would imagine). About 70% of the Earth's _surface_ is
water, but only a fraction of a percent of Earth's mass is water.
(<http://bit.ly/7Gfk8V>, total water volume from
<http://en.wikipedia.org/wiki/Water#Water_on_Earth>). And the Earth's
atmosphere is definitely not primarily hydrogen and helium.

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bioweek
How do they know what it's made of? How do they even know the density?

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boredguy8
The gist: spectrum analysis of light that passes through the planet's
atmosphere from the system's sun compared to light that doesn't pass through
the planet's atmosphere. They look at what light bands the planet's atmosphere
absorbed. (IANA astrophysicist, learn more at
<http://en.wikipedia.org/wiki/Absorption_spectrum> )

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bioweek
I thought the article said they looked at how the stars light was dimmed by
the planet. They also managed to do a spectrum analysis?

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hugh_
No, they didn't -- getting the absorption spectrum of a transiting exoplanet
is an order of magnitude or two beyond the capabilities of present-day
instruments. They just measured the density.

From the density, though, you can get a pretty good idea of what it looks
like. There are three basic ingredients which go into making planets: rock
(including pure metals), "ice" (a catch-all term which includes all phases of
water along with methane and ammonia) and hydrogen/helium mixture. Everything
else is too rare to worry about. Knowing (basically) the density of each of
these components, plus knowing the fact that H/He mixture won't accrete to a
body until its mass goes beyond a certain point, you can put pretty good
constraints on what the composition of a planet of a certain mass and radius
should be.

Of course we could be wrong -- it could equally well be a ball of pure argon
or something; however it's hard to imagine how any such thing would form.

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tocomment
So how do they know the mass?

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hugh_
This can be obtained by looking at the red/blue-shift of the star as it
wobbles back and forth due to the planet's motion. Combine this with the mass
of the star, and you can figure out the mass of the planet.

I forget how you get the mass of the star, but I think it can be pretty well
established from its brightness.

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robobenjie
Using Gmm/r^2 we find that it should have almost exactly the same gavitaional
pull as earth at the surface (89% g). That's neat. Means we could have a boat
with a sealed cabin at the right pressure and sail around the ocean with
basically normal gravity.

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delano
We could walk too!

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ryanwaggoner
OT, but can we send a damn probe to Europa already? I want to know if there's
liquid oceans there, and if so, do they harbor life? It's in our freaking
solar system, for crying out loud!

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rms
Sounds like it will get there eventually. [http://www.washingtonpost.com/wp-
dyn/content/article/2009/02...](http://www.washingtonpost.com/wp-
dyn/content/article/2009/02/18/AR2009021802497.html)

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lutorm
That article is weird. They _already_ sent a probe to Titan:
<http://en.wikipedia.org/wiki/Huygens_probe>

Maybe it doesn't count if NASA doesn't build it?

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hugh_
They did already send a probe to Titan, but the Europa probe project was in
direct competition with a project to send another probe to Titan:

<http://en.wikipedia.org/wiki/Titan_Saturn_System_Mission>

This one would have included a lake lander and a balloon, and would have been
generally neat-o, however I agree with NASA that Europa should be a higher
priority for now.

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jcruz
Link to original article in Nature: <http://dx.doi.org/10.1038/nature08679>
(for those who have access)

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nkassis
$32? Really? For 1 article? I guess they really want you to subscribe at $199
a year. Ridiculous pricing.

