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  • 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.

  • Theyve 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 Venusupper 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 Venussouthern 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 asweatheringconverts 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 Venussize, 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 Venusfate.

  • 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 Venusatmosphere.

  • 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 beEarth-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

From the fires of a sun’s birth, twin planets emerged.

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Venus: Death of a Planet

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    Wonderful posted on 2013/10/20
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