oceans turn to vapor and you have a scorching
The dream Venus of our past was irrevocably
steam atmosphere. That, in short, is runaway
gone. But perhaps . . . we should look into
greenhouse effect.
Venus’ own past and see what we find there.
But how quickly did it happen on Venus? The
estimates vary wildly. Kasting’s model led to an
Through the looking glass into the
estimate of six hundred million years, if we dis-
land of models
count the cooling inf luence of clouds. Other
Reconstructing planetary history is a diff i-
models postpone ocean evaporation to over
cult job. We barely know how exactly Earth
two billion years of existence—roughly half the
started out. Yes, we have radiometric dating,
age of the Solar System. Optimistic, isn’t it? If
planetary accretion models, and many proxies
Venus kept its oceans for two billion years, life
throughout our planet’s history—yet we don’t
could have developed there, couldn’t it?
know when and how exactly did Earth’s plate
These models usually take into account the
tectonics start, what was the composition of
cooling effect of clouds, raising the planet’s
early Earth’s atmosphere, whether life could
albedo, and Venus’ slow rotation (a day on
have appeared before the Late Heavy Bom-
Venus takes longer than its year), which
bardment. The further into the past we go,
would allow a temperate climate even under
the more uncertain our picture gets.
higher insolation values, up to some extent—
But to compare Earth’s and Venus’ evolu-
it’s largely an effect of cooling through the
tion, we perhaps must go to the very begin-
planet’s nightside and concentration of cloud
ning. Both planets formed approximately 4.6
cover on the dayside.
billion years ago in the circumstellar disk
But there are also models suggesting that al-
around the young Sun. Both are very similar in
though Venus may have had lots of water in its
size and composition. The most marked dif-
past (we can conjecture that from the hydro-
ference anyone will point out f irst are their
gen/deuterium ratio in Venus’ atmosphere,
different orbits. Earth orbits roughly 150 mil-
pointing at substantial water loss), it was nev-
lion km far from the Sun, or 1 au (astronomi-
er in a liquid state. So far, we cannot com-
cal unit). Venus circles the Sun just a little over
pletely exclude the possibility that Venus
0.7 au away from our star. “Circles” is a
started out with a thick vapor atmosphere and
metaphor not far from reality in this case.
a magma ocean that had quickly outgassed
Venus has the lowest orbital eccentricity of all
more greenhouse gases. Solar irradiation
planets in our system.
broke down water vapor into hydrogen and
Is its proximity to the Sun the sole cause of
oxygen, the hydrogen escaped, oxygen was
its hellishness today? Being closer to our star,
sequestered, and Venus soon gained its thick
Venus has always received much more insola-
carbon dioxide atmosphere.
tion than Earth. But would it alone suffice to
So how can we tell which of these
turn Earth’s sister into Hell—and if so, how
“retellings of Venusian past” rings closest to
quickly?
the truth? Most terrestrial objects have their
62
JULIE NOVAKOVA
JANUARY/FEBRUARY 2018
Simulated view of Venus based on the Magellan radar images.
https://photojournal.jpl.nasa.gov/catalog/PIA00104
history written all over them. We can see the
if anything, of earlier would have survived
cratering, ridges, cracks, fossil outflow chan-
that. But if something had . . . it might provide
nels . . . What about Venus?
evidence of rock-water interaction, past tem-
Starting in 1990, the Magellan probe imaged
peratures, and more. We could also study the
Venus through radar observations and found
isotopic composition of Venus’ atmosphere,
that it sports very few craters, too few even
which can further constrain things such as
when accounting for its thick atmosphere.
outgassing of rock, water loss, water delivery
There were also vast plains, likely of volcanic
by impacts, and so on.
origin, and more volcanic features than you
Sending a mission capable of doing that to
can count. What happened there?
Earth’s “sister planet” would be advisable. But
It seems that roughly a half a billion years
some are proposing other missions goals as
ago, the planet underwent a massive volcanic
well—among them search for life.
event leading to global resurfacing. Very little,
* * *
HELL IS OTHER PLANETS
63
ANALOG
Venus as an abode of life?
bility of the cloud environment. The clouds
It might sound preposterous: life on Venus?!
need gases such as sulphur dioxide to form,
But the notion is not nearly as crazy as it may
and it is produced by volcanic activity. Has
seem. First, let us consider the more optimistic
Venus been constantly volcanically active, or
of Venus’ climate models. If they prove cor-
did it have quiescent periods? If so, did the
rect, then Venus may have had liquid water
clouds persist? And could life adapt to changes
oceans for about half of its history, more than
in the atmospheric pressure and composition?
long enough for life to originate and develop.
On Earth, life adapted to catastrophes such as
But could anything have survived the ocean
the great oxygenation event, which over-
evaporation?
turned the previous atmospheric composition;
On Earth, you can f ind life practically any-
but changes in temperature and pressure had
where you look—be it on the surface, below it
been comparatively small.
in the depths of the ocean or rock . . . or above
Alas, it seems unlikely that Venus today har-
it. It would be exaggerating to say that Earth’s
bors life—but to test the possibility, we should
troposphere—the lower part of the atmo-
go there. As to long-extinct life . . . To those
sphere, essentially where weather happens—
who enjoy big, hard-to-achieve dreams, I sug-
is teeming with life. But it is present there. We
gest looking for Venusian meteorites. Finding a
don’t know of any microorganisms specialized
rock from some epoch of the planet’s history
for life in the tiny water droplets or on dust
could tell us more about its atmosphere and
grains in the air, but we know that many can
survive such an environment for a prolonged
ing very optimistic, it could even yield fossils
period of time, and it’s probably a common
of hypothetical Venusian life. That’s why the
way of transport of microorganism across the
Moon presents a great astrobiological location:
planet. They can’t control how long they’ll stay
it must be laden with meteorites from various
there or where they end up, but there is
epochs on Earth, providing great grounds for
enough water and basic nutrients for them to
fossil hunters. The meteorites would remain
survive. Some can even be lifted by strong cur-
pristine in the Moon’s vacuum. Temperature
rents and electric f ields in storms into the
changes, radiation and particle sputtering
stratosphere.
might erode the tiny ones in time, but there
But could life adapt to living solely in the air?
should still be a lot of work for space paleon-
On Venus, the current conditions seem quite
tologists. Could there also be some meteorites
favorable. Its cloud deck has temperature and
from Venus?
pressure similar to Earth’s surface, and unlike
We know of at least 120 Martian meteorites
in Earth’s atmosphere, the circulation is very
on Earth, and that’s only the recent ones that
stable. With the currents present there, even a
haven’t been destroyed by the active geology
large dust grain could spend months up there
of our planet and that the scientists have
before sinking to the hell below. Dust grains
found. But Mars is smaller and has a lower es-
present there could potentially provide basic
cape velocity. Moreover, it’s outward in the So-
nutrients and shielding against UV irradiation.
lar System, and any ejected debris would more
The water availability isn’t good and acidity is
likely spiral inward—down the gravitational
high, but overall, simple acidophilic algae
well on a slow journey into the Sun. Or Earth,
known from many Earth environments should
if it crashes here. Venus is inward, larger than
be able to survive there.
Mars, and currently has an atmosphere so
There have been findings raising our hopes
dense that only a huge impact might be able to
in this matter, among them especially several
first hit the surface without burning up in the
chemical disequilibria in Venus’ atmosphere. If
atmosphere, and then eject debris with suffi-
two chemical species that react together are
cient velocity. Therefore we can hardly expect
present, generally an equilibrium will estab-
f inding any recent Venusian meteorites any-
lish—unless something is producing or deplet-
where. But what of its past? If it had a thinner
ing one of the reactants. On the other hand,
atmosphere two or three billion years ago,
these disequilibria can be just as easily ex-
could there be something? The odds are
plained by UV-driven chemistry on the grains.
strongly against us, but it’s not impossible.
There is also the question of the long-term sta-
* * *
64
JULIE NOVAKOVA
JANUARY/FEBRUARY 2018
The quest for answers
paper as of now, and likely will for a prolonged
How long, if ever, did Venus harbor liquid
time or forever. Mission selection process is al-
water? Did it ever possess plate tectonics, so
ways difficult and must rely on what the scien-
far known only from Earth, or perhaps an in-
tists want, what the engineers can do, what
trinsic magnetic f ield like Earth or Mercury?
are the launch options, how much finance is at
How and when did it gain its extremely slow
disposal, whether the mission exceeds the cost
rotation? How wild were its “mood swings”
cap or has its resources trimmed, and more.
throughout history? If we can say anything
Venus has the bad luck of not being among the
with certainty about Venus, it’s that we need
top priorities of any space agency as of this
to go there to get the answers to our questions.
time. In Solar System exploration, NASA focus-
We need to scour the clouds with atmospheric
es mostly on Mars, and the “Ocean Worlds” are
probes to try to find the possible, if highly im-
becoming the next great priority. In addition,
probable extant life. We need to measure the
an ice giant orbiter might become the next big
levels of various elements’ isotopes in Venu-
mission (Flagship-class). ESA also has Mars
sian atmosphere to constrain the history of
plans with its ExoMars 2020, it plans to go to
outgassing, atmospheric loss, and more. We
Mercur y in cooperation with JAXA, and
need to land on the surface and analyze the
Jupiter’s icy moons have a green light for the
oldest rocks we can find to learn whether they
JUICE mission. Venus is currently not on the
have been altered by chemical interaction with
menu, despite being much easier to reach than
water, or whether they hold traces of an an-
Mars. Does Venus need better PR in order to
cient magnetic f ield (Venus currently has
spark the interest of established as well as new
none, but that’s not saying it has always been
space agencies, or even private companies?
so), if past temperatures on Venus allowed
Luckily, Earth’s sister planet has a lot of out-
magnetization to persist . . .
spoken advocates. Their arguments don’t cen-
There are detailed concepts on how to do it.
ter just on the planet itself. Venus’ fate is
But none of them is currently slated to actually
increasingly relevant for exoplanet research. If
go to Venus. ESA’s Venus Express provided us
we want to search for “Earth 2.0,” we should
with a good picture of the circulation in Venus’
be able to discern it from “early Venus 2.0.”
atmosphere, exciting hints for ongoing volcan-
Why so? When Venus’ oceans evaporated and
ism, and more, but the mission ended in early
it was rapidly losing its hydrogen, a lot of oxy-
2015 and wasn’t equipped to answer many of
gen could have stayed in its atmosphere for a
the remaining questions. JAXA’s Akatsuki en-
prolonged period of time. Let us imagine we
joyed miraculous success in its second attempt
find a planet near the inner edge of the “habit-
to enter Venus’ orbit and is currently observing
able zone,” with the right size and mass, and
the planet, but it too wasn’t built for measur-
with oxygen spectral signature in its atmo-
ing isotopic composition or search for poten-
sphere. Is it a reason fo
r celebration, for we
tial biosignatures. NASA had two Venus
have found alien life?
missions in its latest Discovery-class mission se-
Not quite. Without other biosignatures or
lection, DAVINCI and VERITAS—both focused
good temperature measurements, it’s possible
on the second planet’s atmosphere and poten-
that we’ve found a second Venus. Moreover,
tially able to provide some of the answers
learning more about Venus’ history enables us
we’re waiting for. But neither was selected for
to form a better picture of Earth’s future. As
implementation.
the Sun’s luminosity increases, Earth is in for a
Missions focused on surface geochemistry
drastic if slow and distant-future change. Will
would be much more demanding. But many
its oceans evaporate soon enough and leave
such concepts exist, such as VISE, Venus Mo-
behind a potentially habitable if quite hot
bile Explorer, VITL . . . Apart from those, JPL
desert planet? Or will it suffer the same fate as
scientist and well-known SF writer Geoffrey
Venus and turn into a pressurized hellscape?
Landis is the author of an intriguing proposal
We must hope that some Venus missions will
of a Venus landsailing rover. The rover is con-
be selected in the foreseeable future. Only that
ceived to be low-energy, sturdy, as heat-resis-
will enable us to learn more.
tant as possible and yet capable of achieving
For now, Venus remains shrouded in her veil
impressive science results. But it remains on
of mystery. ■
HELL IS OTHER PLANETS
65
Illustrated by Tomislav Tikulin
The
Journeyman:
Through
Madness
Gap
Michael F. Flynn
66
MICHAEL F. FLYNN
JANUARY/FEBRUARY 2018
Teodorq and Sammi previously appeared in the pages of Analog in “The Journeyman: In the Great North Wood” (June 2016), “The Journeyman: Against the Green (July/August 2014), “The Journeyman: In the Stone House” (June 2014), and “The Journeyman: On the Short-Grass Prairie” (October 2012).
Like one that on a lonesome road
But in the doorway of the bedroom stood a
Doth walk in fear and dread
broad-shouldered, elegantly dressed man with
—Coleridge
a pointed beard. In his hand was an elegantly
held and equally pointed rapier. Teo reasoned
A bird in the hand
that this was Lar Haddafahm, and he smiled
Analog Science Fiction and Fact Page 18