Venus: Death of a Planet

From the fires of a sun’s birth, twin planets
emerged. Venus and Earth. Two roads diverged in our young solar system.
Nature draped one world in the greens and blues of life. While enveloping the other in acid clouds,
high heat, and volcanic flows. Why did Venus take such a disastrous turn? And what light can Earth’s sister planet
shed on the search for other worlds like our own? For as long as we have gazed upon the stars,
they have offered few signs that somewhere out there are worlds as rich and diverse as
our own. Recently, though, astronomers have found ways
to see into the bright lights of nearby stars. They’ve been discovering planets at a rapid
clip, using orbiting observatories like NASA’s Kepler space telescope, and an array of ground-based
instruments. The count is almost a thousand and rising. These alien worlds run the gamut, from great
gas giants many times the size of our Jupiter, to rocky, charred remnants that burned when
their parent star exploded. Some have wild elliptical orbits, swinging
far out into space, then diving into scorching stellar winds. Still others orbit so close to their parent
stars that their surfaces are likely bathed in molten rock. Amid these hostile realms, a few bear tantalizing
hints of water or ice, ingredients needed to nurture life as we know it. The race to find other Earths has raised anew
the ancient question, whether, out in the folds of our galaxy, planets like our own
are abundant, and life commonplace? Or whether Earth is a rare Garden of Eden
in a barren universe? With so little direct evidence of these other
worlds to go on, we have only the stories of planets within our own solar system to
gauge the chances of finding another Earth. Consider, for example, a world that has long
had the look and feel of a life-bearing planet. Except for the moon, there’s no brighter
light in our night skies than the planet Venus, known as both the morning and the evening
star. The ancient Romans named it for their goddess
of beauty and love. In time, the master painters transformed this
classical symbol into an erotic figure, then a courtesan. It was a scientist, Galileo Galilei, who demystified
planet Venus, charting its phases as it moved around the sun, drawing it into the ranks
of the other planets. With a similar size and weight, Venus became
known as Earth’s sister planet. But how Earth-like is it? The Russian scientist Mikkhail Lomonosov caught
a tantalizing hint in 1761. As Venus passed in front of the Sun, he witnessed a hair thin
luminescence on its edge. Venus, he found, has an atmosphere. Later observations revealed a thick layer
of clouds. Astronomers imagined they were made of water vapor, like those on Earth.
Did they obscure stormy, wet conditions below? And did anyone, or anything, live there? The
answer came aboard an unlikely messenger, an asteroid that crashed into Earth. That is, according to the classic sci-fi adventure,
“The First Spaceship on Venus.“ A
mysterious computer disk is found among the rubble. With anticipation rising on Earth, an international
crew sets off to find out who sent it, and why. What they find is a treacherous, toxic world. No wonder the Venusians want to switch planets. It was now time to get serious about exploring
our sister planet. NASA sent Mariner 2 to Venus in 1962, in the
first-ever close planetary encounter. Its instruments showed that Venus is nothing
at all like Earth. Rather, it’s extremely hot, with an atmosphere made up mostly of
carbon dioxide. The data showed that Venus rotates very slowly,
only once every 243 Earth days, and it goes in the opposite direction. American and Soviet scientists found out just
how strange Venus is when they sent a series of landers down to take direct readings. Surface temperatures are almost 900 degrees
Fahrenheit, hot enough to melt lead, with the air pressure 90 times higher than at sea
level on Earth. The air is so thick that it’s not a gas,
but a “supercritical fluid.” Liquid CO2. On our planet, the only naturally occurring
source is in the high-temperature, high-pressure environments of undersea volcanoes. The Soviet Venera landers sent back pictures
showing that Venus is a vast garden of rock, with no water in sight. In fact, if you were to smooth out the surface
of Venus, all the water in the atmosphere would be just 3 centimeters deep. Compare that to Earth, where the oceans would
form a layer 3 kilometers deep. If you could land on Venus, you’d be treated
to tranquil vistas and sunset skies, painted in orange hues. The winds are light, only a few miles per
hour, but the air is so thick that a breeze would knock you over. Look up and you’d see fast-moving clouds,
streaking around the planet at 300 kilometers per hour. These clouds form a dense high-altitude
layer, from 45 to 66 kilometers above the surface. The clouds are so dense and reflective that
Venus absorbs much less solar energy than Earth, even though it’s 30% closer to the
Sun. These clouds curve around into a pair of immense
planetary hurricanes as the air spirals down into the cooler polar regions. Along the equator, they rise in powerful storms,
unleashing bolts of lightning. Just like earth, these storms produce rain,
only it’s acid rain that evaporates before it hits the ground. At higher elevations, a fine mist forms, not
of water but of the rare metal tellurium, and iron pyrites, known as fool’s gold. It can form a metallic frost, like snowflakes
in hell. Scientists have identified around 1700 major
volcanic centers on Venus ranging from lava domes, and strange features called arachnoids
or coronae, to giant volcanic summits. The planet is peppered with volcanoes, perhaps
in the millions, distributed randomly on its surface. Venus is run through with huge cuts
thousands of kilometers long that may well be lava channels. Our sister planet is a volcanic paradise,
in a solar system shaped by volcanism. The largest mountain on Earth, Hawaii’s
Mauna Kea volcano, measures 32,000 feet from sea floor to summit. Rising almost three times higher is the mother
of all volcanoes: Olympus Mons on Mars. Jupiter’s moon Io, is bleeding lava. It’s
produced deep underground by the friction of rock on rock, caused by the gravitational
pull of its mother planet. Then there’s Neptune’s moon Triton, with
crystals of nitrogen ice shooting some 10 kilometers above the surface. Saturn’s moon Titan, with frozen liquid
methane and ammonia oozing into lakes and swamps. On our planet, volcanoes commonly form at
the margins of continents and oceans. Here, the vast slabs of rock that underlie the oceans
push beneath those that bear the continents. Deep underground, magma mixes with water,
and the rising pressure forces it up in explosive eruptions. On Venus, the scene is very different. In
the high-density atmosphere, volcanoes are more likely to ooze and splatter, sending
rivers of lava flowing down onto the lowlands. They resemble volcanoes that form at hot spots
like the Hawaiian islands. There, plumes of magma rise up from deep within the earth,
releasing the pressure in a stream of eruptions. To see a typical large volcano on Venus, go
to Sappas Mons, at 400 kilometers across and 1.5 kilometers high. The mountain was likely built through eruptions
at its summit. But as magma reached up from below, it began to drain out through subsurface
tubes or cracks that formed a web of channels leading onto the surrounding terrain. Is Venus, like Earth, still volcanically active? Finding the answer is a major goal of the
Venus Express mission, launched in 2005 by the European Space Agency. Armed with a new
generation of high-tech sensors, it peered through the clouds. Recording the infrared light given off by
several large mountains, it found that the summits are brighter than the surrounding
basins. That’s probably because they had not been subject to as much weathering in
this corrosive environment. This means that they would have erupted sometime
within the last few hundred thousand years. If these volcanoes are active now, it’s
because they are part of a deeper process that shapes our planet as well. On Earth, the release of heat from radioactive
decay deep in its mantle is what drives the motion of oceanic and continental plates. It’s dependent on erosion and other processes
associated with water. With no water on Venus, the planet’s internal
heat builds to extreme levels, then escapes in outbreaks of volcanism that may be global
in scope. This may explain why fewer than a thousand
impact craters have been found on Venus. Anything older than about 500 million years has literally
been paved over. So why did Venus diverge so radically from
Earth when it was born in same solar system and under similar circumstances? There is growing evidence, still circumstantial,
that Venus may in fact have had a wetter, more Earth-like past. One of the most startling findings of the
early Venus missions was the presence of deuterium, a form of hydrogen, in Venus’ upper atmosphere.
It forms when ultraviolet sunlight breaks apart water molecules. Additional evidence recently came to light.
Venus Express trained its infrared sensors on the planet’s night side, to look at how
the terrain emits the energy captured in the heat of the day. This picture is a composite of over a thousand
individual images of Venus’ southern hemisphere. Higher elevation areas, shown in blue, emit
less heat than the surrounding basins. That supports a hypothesis that these areas
are made not of lava, but of granite. On Earth, granite forms in volcanoes when
magma mixes with water. If there’s granite on Venus, then there may well have been water. If Earth and Venus emerged together as twin
blue marbles, then at some point, the two worlds parted company. Earth developed ways to moderate its climate,
in part by removing carbon dioxide, a greenhouse gas, from its atmos phere. Plants, for one, absorb CO2 and release oxygen
in photosynthesis. One square kilometer of tropical jungle, for example, can take in
several hundred tons of co2 in just a year. That’s nothing compared to the oceans. In
a year’s time, according to one recent study, just one square kilometer of ocean can absorb
41 million tons of CO2. Earth takes in its own share of CO2. When
rainfall interacts with rocks, a chemical reaction known as “weathering” converts
atmospheric CO2 to carbonate compounds. Runoff from the land washes it into rivers and the
seas, where they settle into ocean sediments. With little water and no oceans, Venus has
no good way to remove CO2 from its atmosphere. Instead, with volcanic eruptions adding more
and more CO2 to the atmosphere, it has trapped more and more of the sun’s heat in a runaway
greenhouse effect. Venus is so hot that liquid water simply cannot
survive on the surface. Nor, it seems, can it last in the upper atmosphere. The culprit is the Sun. The outer reaches
of its atmosphere, the corona, is made up of plasma heated to over a million degrees
Celsius. From this region, the sun sends a steady stream of charged particles racing
out into the solar system. The solar wind reaches its peak in the wake
of great looping eruptions on the surface of the Sun, called coronal mass ejections. The blast wave sweeps by Venus, then heads
out toward Earth. Our planet is fortified against the solar
blast. Plumes of hot magma rise and fall in Earth’s
core as it spins, generating a magnetic field that extends far out into space. It acts as a shield, deflecting the solar
wind and causing it to flow past. It’s this protective bubble that Venus lacks. Venus Express found that these solar winds
are steadily stripping off lighter molecules of hydrogen and oxygen. They escape the planet
on the night side, then ride solar breezes on out into space. All this may be due to Venus’ size, 80%
that of Earth. This prevents the formation of a solid iron core, and with it the rising
and falling plumes that generate a strong magnetic field. There may be another reason too, according
to a theory about the planet’s early years. A young planet Venus encountered one or more
planet-sized objects, in violent collisions. The force of these impacts slowed its rotation
to a crawl, and reversed it, reducing the chances that a magnetic field could take hold. This theory may have a surprising bearing
on Earth’s own history. Scientists believe the sun was not always
as hot as it is. In fact, going back several billion years, it was cool enough that Earth
should have been frozen over. Because it was not, this is known as the faint
young sun paradox. Earth’s salvation may well be linked to
Venus’ fate. The idea is that the Earth occupied an orbit
closer to the Sun, allowing it to capture more heat. The gravity of two smaller planets
with unstable orbits would have gradually pushed it out to its present orbit. The pair
would eventually come together, merging to form the Venus we know. As dead as Venus is today, it has brought
surprising dividends in the search for life. On its recent crossing between Earth and the
Sun, astronomers were out in force. In remote locations where the viewing was
optimal, such as the Svalbard islands north of Norway. The data gathered here would be
added to that collected by solar telescopes on the ground and in space. To object for most was to experience a spectacle
that will not occur again till the year 2117. It was also to capture sunlight passing through
Venus’ atmosphere. Today, the Kepler Space Telescope is searching
for planets around distant stars by detecting dips in their light as a planet passes in
front. Telescopes in the future may be able to analyze
the light of the planet itself. If elements such as carbon or oxygen are detected, then
these worlds may well be “Earth-like.” Venus provides a benchmark, and some valuable
perspective. So what can we glean from the evolution of
planet Venus? As we continue to scan the cosmic horizons,
the story of Venus will stand as a stark reminder. It takes more than just the right size, composition,
and distance from the parent star, for a planet to become truly Earth-like. No matter how promising a planet may be, there
are myriad forces out there that can radically alter its course. For here was a world, Venus, poised perhaps
on the brink of a glorious future. But bad luck passed its way. Now, we can only
imagine what might have become of Earth’s sister planet? 8

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