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...

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).

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

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

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?

My understanding is that we know from rocks that conditions on Earth up to four billion years ago were very like those on Venus now. So, we know that the arrow of time runs from Venus-like to Earth-like, at least on Earth. Which doesn't, of course, rule out the possibility that it also runs from Earth-like to Venus-like here as well.

Sadly, I don't think even that would get us to change our ways to prevent it this time around.

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.

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.

All this has happened before, and all this will happen again.

- Six, Battlestar Galactica

A great part of the CO2 on earth is "captured" in Limestone (CaCO3). All this CO2 is released in Venus atmosphere and this explain a great part of the difference in pressure.

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

Landing probes on Venus has been a low priority because it really offers poor value to send something all that way only for it to die within a few hours of landing in the acidic pressure-cooking hell that is Venus' atmosphere. Venera 13 and 14 lasted 127 and 57 minutes respectively. That sounds awful, but the design goal was just 32 minutes! Perhaps our inability to have any kind of presence on Venus' surface has reduced interest in orbital missions too, which is a shame.

You wouldn't have to land. The Soviets sent a couple of balloons:

https://en.wikipedia.org/wiki/Vega_program

And Geoffrey Landis proposed sending a solar-powered drone:

http://media.cleveland.com/science_impact/other/Landis%20Ven...

Until we can get close to self sustaining infrastructure sending people into space seems really pointless. If we could even get something like Biosphere 2 to actually work that seems like a solid first step.

BIOS-3 seemed to work, but Dried meat was imported into the facility, and urine and feces were generally dried and stored, rather than being recycled.

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...

Because with limited resources for space exploration, it makes sense to actually explore someplace where humans could actually land in the near future and maybe has life. Any serious exploration of Venus would be pretty demanding.

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.

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.

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.

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...

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

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.

One thing Venus is lacking that Earth has, which almost surely wasn't created by biological life, is a magnetic field to protect against some of the Sun's radiation.

Total Clickbait title (could be rephrased as):

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

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

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