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  • There is a region on Mars, roughly the size of Australia, that rises high above the surface

  • of the planet. Three of the largest volcanoes in the solar system line up to guard its western

  • flank.

  • To the East, a vast canyon, six to seven times deeper than the Grand Canyon, cuts into the

  • barren Martian plain. This strange region, once so baffling to scientists, recalls the

  • planet's violent past, a time long ago when the planet's core erupted, pushing molten

  • rock to the surface.

  • It's part of a larger story, a planetary tragedy, in which Mars began its descent into the cold,

  • dry, and lifeless state that we see today. We are now scouring its surprisingly complex

  • surface for clues to the events that long ago doomed the Red Planet, Mars.

  • Since the early 1960s, we've tried 46 times to send spacecraft to Mars across the 55 million

  • kilometers of its closest approach to Earth.

  • Over half failed at launch or upon arrival. The rest flew around the planet, snapping

  • pictures, recording data. Or they landed to test its soil and rocks, and crawl around

  • its canyons and craters.

  • These probes may one day pave the way for human explorers, who will dig deeper still,

  • in search of answers to our most pressing question:

  • Did Mars, at some point long ago develop far enough for life to arise? If so, does anything

  • still live within Mars' dusty plains, beneath its ice caps, or somewhere underground?

  • Mars does not give up its secrets easily. Over the years, that has led observers on

  • this planet to jump to all sorts of conclusions.

  • In the year 1877, the Italian astronomer Giovanni Schiaparelli noted markings on Mars' surface,

  • a latticework of lines. He called them "canali" in Italian, meaning "channels" in English.

  • A careful and thorough observer, Schiaparelli began to sketch them and name them, connecting

  • them in a vast global network.

  • Over a 15-year period, beginning in 1894, the American astronomer, Percival Lowell,

  • closely examined these features. He saw a remarkable drama unfolding on our neighboring

  • planet.

  • In his view, Schiaparelli's channels were artificial canals, designed perhaps to carry

  • melting snow from the poles to the dry interior. After all, on Earth, the Suez Canal had been

  • open since 1869. Construction on the Panama Canal had just gotten underway.

  • The Martian canals, Lowell surmised, had been built by a sophisticated society confronting

  • an environmental catastrophe on the grandest of scales. Its inhabitants faced an urgent

  • choice: move water across vast arid regions, or perish on an increasingly dry planet.

  • In a series of three best-selling books, Lowell took his case to the public. The public responded

  • with some ideas of their own.

  • With the means to remake an entire planet, perhaps these Martians were more advanced

  • than humans. Some of us began offering schemes for making contact. Giant mirrors to flash

  • greetings. Light beams. Mental telepathy.

  • Lowell vision fell by the wayside in 1964. The Mariner Four spacecraft flew by Mars and

  • got a good look. What it saw looked more like the Moon than the Earth. Three more Mariners

  • followed, culminating in the arrival of Mariner Nine in 1971, the first spacecraft to go into

  • orbit around Mars.

  • These missions documented a heavily cratered landscape, pocked with huge dormant volcanoes...

  • and cut with the deepest and longest canyon in the solar system. They saw no traces of

  • life, present or past.

  • Then, in the mid-1970's, two lander-orbiter robot teams, named Viking, went in for an

  • even closer look. The landers tested the soil for the chemical residues of life. All the

  • evidence from Viking told us: Mars is dead. And extremely harsh.

  • The mission recorded Martian surface temperatures from -17 degrees Celsius down to -107. We

  • now know it can get even colder than that at the poles. The atmosphere is 95% carbon

  • dioxide, with only traces of oxygen. And it's extremely thin, with less than one percent

  • the surface pressure of Earth's atmosphere.

  • And it's bone dry. In fact, the Sahara Desert is a rainforest compared to Mars, where water

  • vapor is a trace gas in the atmosphere. On Earth, impact craters erode over time from

  • wind and water... and even volcanic activity. On Mars, they can linger for billions of years.

  • Earth's surface is shaped and reshaped by the horizontal movement of plates that make

  • up its crust driven by heat welling up from the planet's hot interior. At half the width

  • and only 11% the mass of Earth, Mars doesn't generate enough heat to support wide-scale

  • plate tectonics.

  • Nor does it have the gravity to hold a thick atmosphere needed to store enough heat at

  • the surface to allow liquid water to flow. Nonetheless, some areas that looked to Viking-era

  • scientists like craters and volcanic areas, were later shown to be riverbeds, lake bottoms,

  • and ocean shorelines.

  • If water once flowed on Mars' surface, where did it all go?

  • This was the scene at NASA's Jet Propulsion Lab in 2004. The twin rovers Spirit and Opportunity

  • had just bounced down on the Red Planet. When the excitement died down, the rovers were

  • set off on one of the most remarkable journeys in the history of planetary exploration.

  • Opportunity had come to rest in a small crater near the equator, at a spot called Meridiani

  • Planum. Here, in plain view, on a nearby crater wall, its camera revealed exposed bedrock,

  • the first ever seen on Mars. Not far away, the rover found layered rocks on the face

  • of a cliff. On Earth, they typically form as sedimentary layers at the bottom of oceans.

  • And at every turn, Opportunity rolled across tiny, smooth, round pellets. They became known

  • as "blueberries" because they appeared purplish-brown against Mars' rust-colored surface. Initially

  • thought to be volcanic in origin, they turned out to be iron-rich spherules of the type

  • that form within cavities in the mud at the bottom of an ocean.

  • Drilling into rocks, the rover inserted a spectrometer to read the mineral content.

  • The readings showed significant amounts of sulfate salt, a tracer for standing water.

  • That wasn't all. Spirit's broken wheel, dragging behind it, exposed soils saturated in salt.

  • Clearly there once was water on Mars' surface, but how long ago? And, if there is anything

  • left, where would you find it? One possible answer: the North Pole. From orbit, this region

  • seemed to be covered in frozen CO2 - what we call dry ice. But was there water ice below

  • the surface?

  • Enter Phoenix, a lander that touched down near the North Pole in early 2008. Radar readings

  • from orbit, taken by the Mars Express mission, hinted at the presence of ice just below the

  • surface.

  • The Phoenix lander's descent thrusters blew away the top layer of soil, allowing its camera

  • to snap pictures of what looked like ice. Scientists instructed the robot to conduct

  • a simple experiment: reach out and dig a trench, then watch what happens.

  • As expected, clumps of white stuff appeared. A couple of days later, it was gone. Vaporized.

  • That means it can't be salt or frozen CO2, which is stable in the cold dry temperatures

  • of the Martian pole. So it had to be water, the first ever directly seen on Mars.

  • There are indications that the North Pole was actually warm enough in the recent past

  • for water ice to become liquid. The Mars Reconaissance Orbiter, or MRO, used radar pulses to peer

  • beneath the surface of the ice cap. These data reveal that the ice, just over a mile

  • thick, formed in a succession of layers as the climate alternated between warm and cold.

  • Our planet avoids mood swings like this in part because its spin is stabilized by a massive

  • moon. Mars' spin is not, so it can really wobble, with the pole tilting toward the sun

  • for long periods. New observations by the MRO spacecraft show that these wobbles can

  • lead to dramatic releases of CO2, and warming periods due to an increase in the greenhouse

  • effect.

  • The ice now detected below Mar's surface is a remnant of a much earlier time. The thinking

  • is that not long after its birth, the planet's molten interior would have spewed out enough

  • gas to form an atmosphere.

  • Carbon dioxide and water vapor began to trap heat from sunlight. Temperatures rose high enough to allow liquid

  • water to flow on the surface, creating myriad rivers, ponds, lakes and oceans.

  • Evidence of this thicker atmosphere landed, literally, in Opportunity's backyard. The

  • rover spied a strange bluish rock, a nickel iron meteorite named Block Island. Streaking

  • through a thin atmosphere, this massive chunk of metal should have been obliterated on contact.

  • Instead, its fall was likely slowed, and its impact softened, by a much thicker atmosphere.

  • What then caused the atmosphere, and the water, to disappear, and the planet to grow cold

  • and dry? The answer comes from data recorded by the Mars Global Surveyor just after it

  • went into orbit in 1997.

  • Its instruments detected the presence of a weak magnetic field emanating from the planet,

  • a reading that scientists eagerly compared to that of Earth. Our planet's magnetic field

  • is generated by molten rock deep in its core that rises and falls into a vast region below

  • the outer crust, called the mantle.

  • It has turned Earth into an electric dynamo. The rising and sinking motion within, combined

  • with the spinning motion of the planet, generates a strong magnetic field. You can trace this

  • field back to Earth's early years, when large amounts of heavy elements such as iron sank

  • into its core. Radioactive decay began to generate heat and the planet's mass is large

  • enough to hold it in.

  • Earth's magnetic field extends far enough out into space to deflect the wind of high-energy

  • solar particles. Without a similar electromagnetic "deflector shield" on Mars, solar radiation

  • lashed the planet, gradually stripping it of its atmosphere. What water Mars had would

  • have vaporized into space or frozen underground.

  • However, there is evidence that at one time Mars did have a robust magnetic field. Rocks

  • in some of the older craters bear a strong imprint of this field, while newer craters

  • indicate a much weaker field.

  • What happened to it? The answer lies deep in Mars' past, in events so powerful they

  • are still written on the landscape. This is a simple elevation map of Mars' surface, from data gathered by the Mars Odyssey spacecraft.

  • The South Pole, colored in red and orange, is piled high with ice.

  • Moving off these southern highlands, we make our way north. The landscape is pocked with

  • craters. The largest and oldest ones have faded, their edges softened by windblown dust.

  • Moving up along the equator, we pass into a region called Tharsis, based on a biblical

  • name for the western edge of the known world.

  • On the edge of this vast high altitude plateau is a series of enormous volcanoes: Ascraeus

  • Mons: 18 kilometers high. Pavonis Mons: 14 kilometers. Arsia Mons: 16 kilometers. Just

  • beyond, is the largest volcano in our solar system, Olympus Mons, 25 kilometers in elevation.

  • The thinking is that the Tharsis region bulged out when a giant dome of magma pushed up from

  • the planet's core. The volcanoes grew large because Mars lacks the constant shifting of

  • crustal plates that, on Earth, leads to chains of smaller volcanoes like the Hawaiian Islands.

  • Just to the East is the great Valles Marineris - named for the Mariner Nine mission that

  • found this vast gash in the Martian landscape. It's about 4000 kilometers long and up to

  • 200 kilometers wide. On Earth, Valles Marineris would stretch from Los Angeles all the way

  • to the Atlantic coast.

  • If you went to Valles Marineris, you'd see dust devils sweeping along the plains above

  • it and dust blowing up the canyon walls. Here's a realistic rendering of data captured by

  • spacecraft. Giant landslides have caused the walls to slump off and pile onto the valley

  • floor.

  • Feeding into the valley: a maze of side channels. Scientists think these and other tributary

  • features were formed when underground water flowed into the main basin, and the land above

  • collapsed. Wider parts of the canyon are regarded as possible landing sites for a manned mission.

  • They offer flat surfaces and possible access to liquid water that may remain below the

  • surface.

  • The theory is that Valles Marineris formed when the planet began to cool. Its sides were

  • pulled apart as the Tharsis plateau, just to the west, began to rise up. That chain

  • of events is now being linked to a much larger planetary event, what one scientist called

  • "the" defining moment in Mars' history.

  • Travel north, down the slopes of Mars's great volcanoes. The elevation drops as we move

  • across what appears to be an immense ocean, colored here in blue. With this so-called

  • Borealis Basin in the north, and the high elevations of the South, Mars is a lopsided

  • planet. In fact, there is a difference of about 30 kilometers in the thickness of the

  • crust in these two regions.

  • Here's the reason:

  • Early on, when the Solar System was young, Mars was hit by at least 15 large asteroids.

  • Scientists have linked these events to a time around 3.9 billion years ago, known as the

  • late heavy bombardment, when rock samples from the Apollo landings show that our own

  • moon was seriously pummeled.

  • One theory holds that these impacts heated the outer subsurface layer of the planet,

  • Mars' "mantle." That prevented molten rock in its core from rising up... and caused the

  • crust to thicken. This had the effect of shutting off Mars' magnetic field, exposing the planet

  • to damaging solar winds, and over time, turning it into a wasteland.

  • One model says that as the newly formed giant gas planets, Jupiter and Saturn, moved in

  • their orbits, they hurled a rain of asteroids and comets at the inner solar system. There

  • are other theories that explain the disappearance of Mars magnetic field and its atmosphere.

  • What's certain is that at some point early in its history, the Red Planet grew increasingly

  • desolate.

  • The Martian landscape we see today is replete with coded signals from those early times,

  • ancient riverbeds and lake bottoms, flood plains, and volcanic cones, as well as the

  • battering it received from impacts.

  • But is Mars a dead world? Maybe. Maybe not. An infrared telescope on Hawaii's Mauna Kea

  • volcano was trained on Mars over several years. Astronomers used a spectrometer to split the

  • light into its individual wavelengths... to identify chemical fingerprints in the atmosphere.

  • They found the signature of methane gas, in amounts that change from place to place. Because

  • methane should disappear quickly in Mars' atmosphere, there must be some source that

  • constantly replenishes it.

  • That source could amount to nothing more than the chemical reactions in Mars' crust. Or

  • it could be biological in nature, perhaps microbes alive and well in heated pools underground.

  • So far, neither the satellites flying over Mars, nor the robots on the ground, have turned

  • up anything close to clear proof of life. It may take the searching eyes, flexible minds,

  • and nimble fingers of human explorers to find that buried treasure, if it exists.

  • In the meantime, we are finding that even if Mars is dead, it's certainly not dull.

  • Mars has nowhere near the dynamism of Earth, with its oceans, atmosphere, volcanism, and

  • shifting continents. But it does do some fascinating things:

  • If you take an atmosphere, however tenuous, add heat from the sun. You get the renowned

  • dust devils of Mars. With no trees to hold the soil down, landslides are common.

  • The Mars Reconnaissance Orbiter has returned images showing that Mars is actively remaking

  • its surface, not in canals built by the Martian engineers of Percival Lowell's imagination,

  • but in sand dunes shaped by the wind, and in landscapes molded by a gradually changing

  • climate. Some scientists have even turned up hints of low-level plate tectonics.

  • Whether or not we ever find life-forms on Mars, we can still marvel at the beauty of

  • our neighboring planet, its surface subtly sculpted over eons of time, on a world that

  • never was.

  • 7

There is a region on Mars, roughly the size of Australia, that rises high above the surface

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Mars: World That Never Was

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    Wonderful posted on 2013/10/20
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