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  • The Mars rover, Curiosity, is the latest in a long line of missions to Mars

  • Landers sent to scoop its soil and study its rocks, orbiters sent to map its valleys and

  • ridges.

  • They are all asking the same question.

  • Did liquid water once flow on this dry and dusty world? Did it support life in any form?

  • And are there remnants left to find?

  • The science that comes out of these missions may help answer a much larger, more philosophical

  • question

  • Is our planet Earth the norm, in a galaxy run through with life-bearing planets?

  • Or is Earth a rare gem, with a unique make-up and history that allowed it to give rise to

  • living things?

  • On Mars, Curiosity has spotted pebbles and other rocks commonly associated with flowing

  • water.

  • It found them down stream on what appears to be an ancient river fan, where water flowed

  • down into Gale Crater.

  • This shows that at some point in the past, Mars had an atmosphere, cloudy skies, and

  • liquid water flowing.

  • So what could have turned it into the desolate world we know today?

  • One process that very likely played a role goes by the unscientific name, “sputtering.”

  • Like the other planets in our solar system, Mars is lashed by high-energy photons from

  • the Sun.

  • When one of these photons enters the atmosphere of a planet, it can crash into a molecule,

  • knocking loose an electron and turning it into an ion.

  • The solar wind brings something else: a giant magnetic field.

  • When part of the field grazes the planet, it can attract ions and launch them out into

  • space.

  • Another part might fling ions right into the atmosphere at up to a thousand kilometers

  • per second.

  • The ions crash into other molecules, sending them in all directions like balls in a game

  • of pool.

  • Over billions of years, this process could have literally stripped Mars of its atmosphere,

  • especially in the early life of the solar system when the solar wind was more intense

  • than it is today.

  • Sputtering has actually been spotted directly on another dead planet, Venus.

  • The Venus Express mission found that 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.

  • This process has left Venus with an atmosphere dominated by carbon dioxide gas, a heat trapping

  • compound that has helped send surface temperatures up to around 400 degrees Celsius.

  • The loss of Venusatmosphere likely took place over millions of years, especially during

  • solar outbursts known as coronal mass ejections.

  • If these massive blast waves stripped Venus and Mars of an atmosphere capable of supporting

  • lifehow did Earth avoid the same grim fate?

  • We can see the answer as the solar storm approaches earth.

  •   Our planet has what Mars and Venus lack - a

  • powerful magnetic field generated deep within its core.

  •   This protective shield deflects many of the

  • high-energy particles launched by the Sun.

  • In fact, that’s just our first line of defense.  

  • Much of the solar energy that gets through is reflected back to space by clouds, ice,

  • and snow.

  • The energy that earth absorbs is just enough to power a remarkable planetary engine: the

  • climate.  

  • It’s set in motion by the uneveness of solar heating, due in part to the cycles of day

  • and night, and the seasons. That causes warm, tropical winds to blow toward the poles, and

  • cold polar air toward the equator.  

  • Wind currents drive surface ocean currents.  

  • This computer simulation shows the Gulf Stream winding its way along the coast of North America.

  • This great ocean river carries enough heat energy to power the industrial world a hundred

  • times over.  

  • It breaks down in massive whirlpools that spread warm tropical waters over northern

  • seas. Below the surface, they mix with cold deep currents that swirl around undersea ledges

  • and mountains.  

  • Earth’s climate engine has countless moving parts: tides and terrain, cross winds and

  • currents -- all working to equalize temperatures around the globe.

  • Over time, earth developed a carbon cycle and an effective means of regulating green

  • house gases.

  • In our galaxy, are still-born worlds like Mars the norm?

  • Or in Earth, has Nature crafted a prototype for its greatest experiment: Life?

The Mars rover, Curiosity, is the latest in a long line of missions to Mars

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火星はなぜ死に、地球は生きたのか (Why Mars Died, and Earth Lived)

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    黃駿祐 に公開 2021 年 01 月 14 日
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