
The Earth-Twin Planet That Nobody Talks About - yummyfajitas
http://blogs.discovermagazine.com/outthere/2015/09/30/twinplanet/#.ViAmMPmqpBc
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gojomo
NASA's latest vision for a Venus visit involves giant dirigibles – and perhaps
someday a 'cloud city' like that of Bespin in Star Wars:

[http://www.space.com/29140-venus-airship-cloud-cities-
incred...](http://www.space.com/29140-venus-airship-cloud-cities-incredible-
technology.html)

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Axsuul
Or if that depicted in Asimov's "The Sultan of the Clouds". Venus' atmosphere
at a specific altitude is actually very similar in composition to that of
Earth's at sea level (21% oxygen, 78% nitrogen).

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twic
What is the deal with Venus's atmosphere? How can it be so much higher
pressure than Earth's when the gravity at the surface is 0.9 g? Is it just
that CO2 is heavier than N2 (44 vs 28 g/mol?)? If we could magically convert
the CO2 to O2, would the pressure be lower? Where is all Venus's nitrogen?

Where does all this sulphuric acid come from? Does Earth have the same amount
of sulphur, just locked up in rocks? If so, why doesn't it react and
precipitate out on Venus?

Okay, time to read the Wikipedia article [1].

So, Venus's atmosphere actually has _four times as much_ nitrogen as Earth's.
But that's overwhelmed by having about a hojillion times more carbon dioxide.
There's more than enough nitrogen for an Earth-like atmosphere, crushed down
into a tiny space.

Plus, the lack of a magnetic field means the solar wind hits the atmosphere
harder than it does at Earth; hard enough to blow water vapour off the planet,
although i don't know if that's in significant quantities.

Apparently at the surface, the CO2 has enough density and pressure that it's
supercritical. So it's not so much an atmosphere, as an ocean. Kind of. We
don't have a word for what it is, but it's atrocious.

As for sulphur, it came from wherever (volcanic eruptions, let's say), but the
reason it stays in the atmosphere is that sulphuric acid never reaches the
ground: if it falls as rain, the heat of the deep atmosphere evaporates it
before it lands. I assume there's still a lot of gas-phase sulphuric acid at
the surface, but perhaps that doesn't allow a fast enough reaction to take it
out of the atmosphere.

And finally, Earth had an atmosphere like Venus's during the Hadean era, from
its formation to four billion years ago [2]. Despite being ludicrously hot,
liquid water oceans were stable due to the high pressure. Those oceans
apparently allow some chemistry that takes most of the CO2 out of the
atmosphere. For some reason, that didn't happen (or stopped happening) on
Venus. Maybe because the water was whipped away by the solar wind? Or because
Venus was just a bit too hot for liquid water? Or because you need not only
oceans but plate tectonics to bury the carbon deep in the crust, and Venus
doesn't have plate tectonics?

Don't ask me why Venus doesn't have plate tectonics. Probably the same reason
it doesn't have a magnetic field, which on Earth is generated by stuff
convecting around in the core.

So, total basket case really.

[1]
[https://en.wikipedia.org/wiki/Atmosphere_of_Venus](https://en.wikipedia.org/wiki/Atmosphere_of_Venus)

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

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personjerry
Could it be that rather than being stuck "four billion years ago", Venus is
actually ahead of Earth in its timeline? Perhaps what we are seeing on Venus
is the eventual result of climate change on Venus, not unlike what we are
experiencing now?

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SFLemonade
This could make for an incredible movie plot. Humans spend all this time
studying climate change and debating about it, only to find out that we were
staring the result of it right in the face the whole time: Venus. We discover
that the origin of man is not Earth. Rather, we were colonized here by our
great ancestors, forgotten in time. Ancestors that came from Venus. They left
after destroying the planet. And now, here we are on Earth, repeating history.

~~~
TeMPOraL
That's actually one of the real reasons we study Venus - because it's an
existing case of runaway global warming, and we want to learn something about
our future from it.

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humble_dev
Lack of effort to explore space always makes me sad - especially that last
picture of Venus surface comes from 1982.

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JabavuAdams
Yeah. I've been watching a lot of Apollo footage recently. Our concerns seem
so mundane, by comparison.

That said, I think the next 50 years will be a new golden age for space
exploration...

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humble_dev
I've been watching Apollo footage recently too ;)

I am not sure about next 50 years, so far It looks like people would spend
more on some selfie sticks than space exploration.

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mhurron
Mercury, Gemini and Apollo were standins for open war with the Soviet Union,
so they got more war-like funding and focus. 'Terrorists' aren't going to be
shown up by space travel and no one believes we're really at war with the
Chinese so no one is willing to throw money at it.

The US has never really funded anything that isn't related directly or
indirectly to war, that includes Space Exploration.

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legulere
I wonder wether earth first looked similar to venus today and was made
habitable by (what we today consider) extremophiles. If most of venus'
atmosphere was captured in solids or fluids it would look way more habitable.

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twic
Close! Earth's atmosphere was much the same as Venus's up to four billion
years ago. But it seems that what made the difference was the carbonate cycle:

[https://en.wikipedia.org/wiki/Carbonate%E2%80%93silicate_cyc...](https://en.wikipedia.org/wiki/Carbonate%E2%80%93silicate_cycle)

That article blames the difference on the temperature. Elsewhere, i've seen
the presence of water oceans being implicated. Either way, i don't think life
was the mechanism at that point. Life didn't really have much of an impact for
another billion years or two:

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

~~~
jerf
Partially in response to your other post as well, I've also seen it
hypothesized that the collision that produced Earth's moon stripped away most
of Earth's atmosphere, the idea being that Venus' atmosphere may actually be
the "normal" atmosphere for an Earth-sized planet.

As usual, the core problem is just that our data set is too darned small. Is
our Solar System mostly normal? Is our Solar System a bizarre, billions-to-one
odds freak case? We don't really _know_.

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jgalt212
Total Clickbait title (could be rephrased as):

Near Clone of Planet Earth Responds to Charges of Plagiarism in Best Way
Possible.

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swasheck
seeing that it's discovermagazine.com, i thought that the clickbait statement
went without saying.

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cosarara97
I wouldn't oppose HN editorializing click-baity titles.

