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, arbiters sent to map its valleys and ridges. They are all asking the same question.
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| The Mars rover, Curiosity |
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.
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| Ancient Mars Source: Ittiz / CC BY-SA |
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 kilometres 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 Venus’ atmosphere 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 life.
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| coronal mass ejections Source: NASA Goddard Space Flight Center / CC BY |
How 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 defence. 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 unevenness 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. A 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?
In March 11, 2015… near the peak of its 11-year magnetic cycle, the Sun emitted a powerful x-class flare. Four days later, on the 15th, it erupted in a coronal mass ejection, or CME. Two days later, the blast raced past Earth, producing some of the most colorful auroras in recent memory. Astronauts aboard the international space station recorded them as they flew over the Indian Ocean. This so-called St. Patrick’s Day storm continued on to the fourth rock from the Sun… Mars. The newly arrived spacecraft, the Mars Atmosphere and Volatile Evolution mission, or MAVEN… was there to record its arrival. On our planet, solar plasma is deflected and channeled by a global magnetic field down toward the poles. There, it interacts with nitrogen and oxygen molecules in the upper atmosphere to produce the light shows of the aurora borealis and aurora Australis. Mars lacks a global magnetic field, so when the St. Patrick’s Day storm washed over the planet, it produced a diffuse aurora that engulfed the planet.
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| Aurora Borealis and Aurora Australis Source: The original uploader was 14jbella at English Wikipedia. / CC BY-SA |
It turned out to be an important data point in Maven’s quest to answer a single question… How did Mars, once lined with the blue tint of flowing water, go so dry?
Maven’s findings take us back to a time over three and a half billion years ago. On Earth, ponds, hot springs, and undersea vents were crawling with microbes. Life was taking hold. Earth back then was steadily evolving into the connected system we know today…. Molten rock wells up from deep below the surface… surface rock and water circulating into the interior. Volcanoes replenishing the atmosphere, Oceans and atmospheric systems circling the globe. Add to these, a long-term carbon cycle for removing the greenhouse gas, carbon dioxide, from the atmosphere and at the center of it all, a vibrant biosphere. For reasons that are not fully understood, the connection between Mar’s interior and surface never evolved. Volcanic activity, concentrated in large structures such as Olympus Mons, came to a halt.
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| Olympus Mons Source: UdeCgmt / CC BY-SA |
The planet became static, with surface water and rock stuck in place. Scientists estimate that Mars had enough water to cover its surface in a layer 140 meters deep. That implies that the planet had a much thicker and denser atmosphere than it does today. The atmosphere began to slowly but surely bleed away, in a process that is visible to this day.
The spacecraft Maven has measured the average erosion rate at 100 grams per second. That works out to over a metric ton of atmosphere lost per Earth year. During the St. Patrick’s storm, that rate jumped by a factor of 10 or 20. This event allowed scientists to model the erosion of Mars’ atmosphere. When solar particles strike the upper atmosphere, most are deflected along a boundary called a bow shock. During a solar storm, this boundary pushes deeper into the atmosphere. When this happens, solar particles accelerate protons and electrons in the atmosphere, sending them flying out into space. The loss is most pronounced in a tail flowing away from the planet’s dark side, and out near the pole. This view compares the simulation with data from the Maven spacecraft. Billions of years ago, when the sun was much younger, powerful flares and CMEs were much more common. With a declining, or absence of a global magnetic field, Mars was at the mercy of the sun. Over time, its atmosphere thinned… its oceans dried up… and any chances of developing a life-supporting climate disappeared. Today, from a planet protected by its own robust global magnetic field… …we reach out across the void to understand the Mars that once was. Did life have enough time to begin… and if so, how far did it get? It may take a geologist, digging and scraping directly into Martian rocks, to answer that question. Ultimately, the parallel stories of Earth and Mars can tell us much about what it takes for a planet to forge life… and how common that really is across a galaxy like ours? research keep going. thank you for reading
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