Vox
- Brian Resnick
900 degrees Fahrenheit, crushing pressure, and acid clouds. Venus, what the
hell happened?
|
Courtesy of NASA/JPL
|
“Hellscape” is the most appropriate word to describe the surface of Venus,
the second planet from the sun. At 900 degrees Fahrenheit, it’s the hottest
planet in the solar system, thanks to an atmosphere that’s almost entirely
made up of carbon dioxide.
Clouds made of highly corrosive
sulfuric acid are draped over a volcanic landscape of razor-sharp lava flows.
Most crushingly, the pressure on the surface of Venus is about 92 times the
pressure you’d feel at sea level on Earth.
“It’s really almost entertainingly, comically horrible, like
some sort of cosmic deity had a really, really grumpy day and just went ‘Nope,
I’m gonna ruin this planet,’”
Robin George Andrews, a science journalist and volcanologist, says.
Andrews compares it
to being in a pressure cooker a mile underwater. “If you stood on the surface,
you would be pancaked and you would melt,” he says. Your eyes would explode due
to the pressure — “which would be gross,” he adds.
Yet as Andrews relays in his new book,
Super Volcanoes: What They Reveal about Earth and the Worlds Beyond, some scientists suspect Venus was once much like Earth, with a liquid water
ocean like the ones that support life on our planet.
For Andrews,
the question of what happened to ruin Venus is captivating and even existential.
“Venus and Earth are planetary siblings,” he says. “They were made at the same
time and made of the same stuff, yet Venus is apocalyptic and awful in every
possible way. Earth is a paradise. So why do we have a paradise next to a
paradise lost?”
Scientists know
something on Venus triggered truly
catastrophic levels of climate change, causing surface temperatures to shoot up
hundreds of degrees. But they don’t know exactly what.
I spoke to
Andrews for an episode of
Unexplainable, Vox’s science podcast about unanswered questions, about what could have
triggered Venus’s apocalypse and why we should care about it.
Our
conversation has been edited for length and clarity.
The podcast episode also features a discussion with Sara Seager, an MIT
planetary scientist and an expert on exoplanets, or planets outside our solar
system,
who raises the tantalizing question: What if, despite the cataclysm, something is still alive on Venus?
The origins of Venus could tell us a lot about our place in the
universe
|
On the left, Venus as it is today. On the right, an artist’s
interpretation of where oceans could have lain on the surface in the
past.
NASA/Jet Propulsion Laboratory-Caltech (left) and NASA (right)
|
Brian Resnick: You say the question of “what killed Venus” is existential.
What makes it so?
Robin George Andrews:
It really is a question about why are we here. Answering it will help us
answer the question: How lonely are we? Are there other Venuses or Earths out
there?
If Earth is the odd one out, how lucky are we to exist? If Venus is
the odd one out, then maybe we’re not so special after all.
Brian Resnick: So Earth and Venus started off as similar planets, and then
went down different paths. You want to know what path is more common out there
in the cosmos?
Robin George Andrews:
When you hear in the news that scientists have discovered an Earth-like
exoplanet, they might as well be saying, we found a Venus-like exoplanet. We
don’t know if this is like a habitable world by our human, surface-dwelling
standards, or if it’s gone through this sort of apocalyptic climate change
like Venus.
A good way to work out what may be more common in the
cosmos is to study Earth and Venus, because they are siblings.
We don’t know how often it is that volcanoes decide to trash the
planets they’re on
Brian Resnick: How do scientists know, or suspect, Venus used to be more
pleasant, habitable even?
Robin George Andrews:
So even though Venus today looks and is apocalyptic in every meaning of the
word, probes have looked at its atmosphere and
found
there’s a lot of “heavy water” in the atmosphere. Heavy water is exactly what
it sounds like.
The water we’re used to, this classic H2O, which
is found commonly everywhere on Earth, is a more common type of water
throughout the cosmos. Heavy water just kind of switches out that hydrogen for
something called deuterium, which is like a heavier version of hydrogen.
Brian Resnick: What does finding heavy water mean?
Robin George Andrews:
If you measure how much heavy water exists somewhere, you can make a
reasonable guess as to how much classic water there is or was on that planet.
It suggests that there once was a lot of classic water on Venus, at least an
ocean’s worth of water on Venus.
If that water existed in liquid
form, what are the odds that Venus was habitable at some point? It’s not
unlikely, even though today it looks impossible.
Brian Resnick: How long ago must this have been, this habitable Venus?
Robin George Andrews:
I think there is a possibility that water was always steam, and it might have
never been liquid water. But if it was, then it could have been habitable for
billions of years. Maybe right up until the last billion years.
Brian Resnick: So that’s what we’re talking about when we say Venus used to
be “alive.” What do we mean by “killed”?
Robin George Andrews:
Death, in this case, is runaway climate change. Absolutely irreversible,
world-ending climate change. The average temperature of the planet shot up by
something like several hundred degrees Fahrenheit. It really sort of cooked
itself to death.
Suspect No. 1 for the death of Venus: The sun
|
Plasma spewing out of the surface of the sun.
NASA/Solar Dynamics Observatory
|
Brian Resnick: So the question, I imagine, is how Venus cooked
itself.
Robin George Andrews:
There’s kind of two leading theories as to what killed Venus. Option No. 1 is
the sun. From what we know of our sun and other stars, when they’re kind of in
their teenage years, they get hyper-excitable, and they get hotter and brighter
quite quickly.
If the sun actually gets brighter and hotter
too quickly, even though you might have that water sitting on the
surface, the sun can boil it off. And that is a fate that lots of exoplanets, or
planets outside our galaxy, are presumed to have gone through.
Brian Resnick: And once Venus’s water gets vaporized...
Robin George Andrews:
That steam is a greenhouse gas that would have kicked up the greenhouse gas
effect. And then the carbon dioxide coming out of Venus’s embryonic volcanoes
would have just sealed the deal. That could explain why we see Venus as it is
today.
Brian Resnick: If this young, very excitable sun is what killed Venus, the
Earth would have been fine, right?
Robin George Andrews:
Yeah, the Earth would have been fine. It seems that Earth was spared the worst
of it.
Suspect No. 2 for the death of Venus: Tectonic plate-breaking volcanoes
|
An artist’s depiction of a volcanically active Venus.
NASA/JPL-Caltech/Peter Rubin
|
Brian Resnick: So that’s one suspect in our whodunit. What is the other
suspect?
Robin George Andrews:
The other suspect just happens to be my favorite thing: volcanoes.
Brian Resnick: How could your fave, volcanoes, kill a planet?
Robin George Andrews:
Two hundred and fifty-two million years ago, Earth experienced its worst mass
extinction, something called the
Great Dying. At least 90 percent of all life was wiped out, and the primary suspects were
these volcanic fissures that opened up in Siberia. It produced a continent-sized
flood of lava that took about 2 million years to erupt.
So it causes giant explosions and also unleashed all these greenhouse gases into
the atmosphere, and it created a global warming effect that raised the
temperature
by a dozen degrees
[Celsius]. That caused 90 percent of all the life on Earth to die. Earth had to
kind of reset itself. And the idea is, well, what if that happened on Venus, but
worse?
Brian Resnick: That could kill the planet?
Robin George Andrews:
If you just have one [Great Dying-scale] eruption, it might be okay, because
Venus had plate tectonics. Plate tectonics is essentially
a planet’s thermostat.
Brian Resnick: Plate tectonics — that’s how continents kind of float around
and smoosh into each other. How do those act like a thermostat?
Robin George Andrews:
Carbon dioxide can get soaked up in the ocean, and that filters down to these
tectonic plates. If tectonic plates dive down beneath each other, then you’re
burying carbon [and slowing the greenhouse effect].
Brian Resnick: Okay, but how do you break this carbon-burying system?
Robin George Andrews:
You have
two of these epic, Great Dying-like eruptions at the same time.
That will immediately trigger quite an intense period of global warming. And the
oceans will just start to boil off.
Now, plate tectonics could bury carbon for a while. But if you boil off your
oceans, that carbon dioxide has nothing to dissolve into. And if you get rid of
that water, plate tectonics itself shuts down.
If you dehydrate
[tectonic plates], you make them brittle — they can’t bury the carbon anymore.
That’s essentially game over. If you break plate tectonics you’ve broken the
world.
The scientific jury is still out
|
Venus’s clouds captured in infared.
JAXA/ISAS/DARTS/Damia Bouic
|
Brian Resnick: So we have our two suspects here. We have the sun and we have
massive eruptions on Venus that broke Venus. Which one should we sentence
here?
Robin George Andrews:
The volcanoes seem more likely because we can see how that’s happened on Earth —
just to a slightly lesser extent. But if this was put into a court of law, they
would both be presumed not guilty, just because there isn’t a telltale bit of
evidence yet.
Brian Resnick: So how do we solve this mystery?
Robin George Andrews:
There’s basically a fleet of missions that is going to unravel the geologic
makeup of Venus today. If it looks bone-dry and it was always bone-dry, then
maybe the sun did it, because it’s been dehydrated for a long time.
But if it looks like there’s still some dehydration going on, that means you
still have water somewhere. If Venus was still kind of soggy on the inside, and
it’s still kind of belching water out, the volcanoes probably killed Venus.
Brian Resnick: Could the Earth pull a Venus one day?
Robin George Andrews:
[Laughs.] Yeah, it could. Let’s not panic — I mean, these sorts of eruptions are
like millions of years in timescales. So it’s not like no one would see this
coming and we’d instantly be doomed. But it could happen. And the question is:
Is it normal for a planet to have just
one of these really epic,
game-changer eruptions at one time? Or is it just a fluke?
The fact that no one knows the answer to this is weirdly, perversely exciting to
me. We don’t know how often it is that volcanoes decide to trash the planets
they’re on.
Brian Resnick: People sometimes bring up Venus in the context of climate
change. It’s an example of how bad a planet can become when greenhouse gases
start to accumulate in an atmosphere. Could we humans potentially be the
volcano?
Robin George Andrews:
The pace at which we’re putting carbon dioxide into the sky is worse than what
was happening during the Great Dying, in terms of the amount of carbon per year.
Brian Resnick: But we would need to keep this up for millions of years to
match, right?
Robin George Andrews:
Right.
Brian Resnick: This is weirdly reassuring that humans are unlikely to break
the Earth completely.
Robin George Andrews:
Yeah. I think it would be a terrible idea to pay homage to what happened to
Venus.
Links
