How the Sun stole Mars’ atmosphere

The solar wind has made Mars a cold desert, and a tougher environment for would-be colonists. Alan Duffy explains the latest research.

 

Four billion years ago, Mars and Earth were like twins. Water flowed on the Martian surface beneath an atmosphere rich in carbon dioxide, oxygen, methane and water vapour. Today the Martian atmosphere is vanishingly thin, just a hundredth the density of Earth’s, and its surface water has disappeared.

Where did it all go? To find out NASA sent MAVEN – the Mars Atmosphere and Volatile Evolution spacecraft – all decked out with sensitive new instruments. It’s been orbiting the planet since last September and this November it finally answered the riddle. The solar wind blew away the Martian atmosphere. This result was the highlight of a landslide of papers published in November using data collected by MAVEN – four inScience and 40 in Geophysical Research Letters.

The first hints water used to flow on Mars came from NASA’s Viking missions in the 1970s. The orbiters beamed back pictures of valleys that looked like they’d been carved by ancient rivers. More recent landers showed fossilised ripples of lakebeds and streams known as mudstone. And just in September, instruments on the Mars Reconnaissance Orbiter detected the signatures of hydrated salts streaking down crater edges. The briny residue showed water may still be found occasionally on the surface of Mars. But it’s a drop in the ocean compared to the bodies of water that resided in the ancient lakes some four billion years ago.

Billions of years ago when the Red Planet was young, it appears to have had a thick atmosphere that was warm enough to support oceans of liquid water – a critical ingredient for life. This animation shows what Mars might have looked like at the time, before transitioning to the dusty red planet we see today.

So where did the water go? Some thought it was locked away in subsurface ice deposits. And as for the atmosphere, carbon dioxide and other gases might have chemically reacted with rocks over hundreds of millions of years, and become locked away inside Mars’ geology – similar to the way carbon dioxide in Earth’s atmosphere can get locked away as limestone.

The other possibility was that both had been lost to space: first the atmosphere, then the water, which in the thin air would simply have evaporated away. If this theory was right, the real question was, why did the atmosphere vanish in the first place? It shouldn’t have: Mars’ gravity, a third of Earth’s, is sufficiently strong to keep its atmosphere.

“Like the theft of a few coins from a cash register every day,

the loss becomes significant over time”

First off, MAVEN established that the Martian atmosphere was indeed vanishing into space. Dipping in and out of the Red Planet’s upper atmosphere, it detected wisps of ionised air escaping at the rate of about 100 grams each second. “Like the theft of a few coins from a cash register every day, the loss becomes significant over time,” says Bruce Jakosky, MAVEN principal investigator at the University of Colorado, Boulder.

MAVEN was also present when a solar storm hit Mars in March 2015.

The rate of atmospheric loss increased up to 20-fold when the storm struck. The storm was the result of a coronal mass ejection by the Sun, which hurled billions of tonnes of superhot material into space. Unlike the constant, steady stream of particles of the solar wind, these events are far more energetic and damaging. With each direct hit, more of the Martian atmosphere is lost.

The Sun had been caught in the act of planetary vandalism. MAVEN’s data showed the long suspected culprit, the solar wind (and its sometime partner in crime, solar storms), was easily capable of removing an atmosphere. While the Sun is still at work shearing away the Martian atmosphere today, four billion years ago a youthful Sun was even more tempestuous with storms that were more frequent and powerful than those of today.

So why was Earth spared this fate? Our planet is blessed with a magnetic shield that deflects the charged solar particles; Mars is not. A magnetic shield is created by a churning liquid iron core, which Earth has. Mars once had a molten core too but around four billion years ago, it cooled and solidified. Just why we have been spared this fate is not entirely understood – perhaps it is simply because Mars is smaller and lost heat more quickly. The same fate undoubtedly awaits Earth too, but not for many millions (if not billions) of years yet.

Without a liquid iron core, Mars’ magnetic field faded away. The solar wind then ripped away most of the atmosphere, leaving the oceans to evaporate into space. But the removal of its atmosphere would have taken place over a few hundred million years, so any life that existed had time to adapt to living underground; the Sun’s ultraviolet radiation would be fatal to life on the surface.

For the first time, NASA’s MAVEN spacecraft has observed the solar winds in action stripping away Mars’ atmosphere. This video shows a simulation of the solar wind striking Mars, then adds a colourful overlay of Mars’ atmosphere being removed (the new measurements taken by MAVEN).

This is good news for scientists hoping to find life on Mars, but bad news for human colonists.

Some had hoped the gases that made up the atmosphere might still be present beneath the surface, awaiting our arrival to unlock all that carbon dioxide, begin to grow plants and terraform the Red Planet. Not so: at least as far as the atmosphere goes, colonisers will need to bring their own.

Source: How the Sun stole Mars’ atmosphere

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How the Sun stole Mars’ atmosphere

#DSCOVR today’s new image of #Earth. What made the Blue Marble so special? #EarthRightNow

It was the first full photo of the Earth, taken on December 7, 1972, by the American crew of the Apollo 17 spacecraft. The original Blue Marble is thought by many to be the most-reproduced image of all time.

What made the Blue Marble so special? Sure, it might have been the first full photo of the Earth that we took, but we’ve taken a bunch more since then.

Like this one.

And this one.

And this one.

So why is the “Blue Marble” a bigger deal than these? Turns out, it’s quite tricky to take a good photo of the entire Earth.

The first challenge is that our planet is big. The only way to view all of it at once is to get much farther away from the Earth than we do for many of our activities in outer space. The International Space Station, for instance, orbits at a height of just 400 kilometers, or about 249 miles away from Earth.

The second problem is a familiar one that plagues many photographers who are Earthbound: lighting. In order to view the Earth as a fully illuminated globe, a person (or camera) must be situated in front of it, with the sun directly at his or her back. Not surprisingly, it can be difficult to arrange this specific lighting scheme for a camera-set up that’s orbiting in space at speeds approaching thousands of miles per hour.

As a result of these challenges, NASA, NOAA, and other science agencies most often rely on composite images to depict our planet. These images stitch together multiple high-resolution snapshots taken by satellites already in orbit to produce one seamless portrait of the Earth. And that’s what the three photos above are: composite images produced by NASA over the past fifteen years (released respectively in 2002, 2007, and 2012).

Composite imaging is an extremely useful tool for helping people understand the Earth — they allow researchers to capture certain features at higher resolution; reduce the obscuring effect of cloud coverage in certain areas; and overlay various data layers to help identify patterns and trends. Composites can result in some truly remarkable images, like this “Black Marble,” which, by stitching together multiple views of the planet, shows a full global view of the Earth’s city lights.

But there’s something remarkable about a single snapshot of the Earth — an intact view of our planet in its entirety, hanging in space.

Apollo 17 astronaut Eugene Cernan explained:

“…you’re looking at the most beautiful star in the heavens — the most beautiful because it’s the one we understand and we know, it’s home, it’s people, family, love, life — and besides that it is beautiful. You can see from pole to pole and across oceans and continents and you can watch it turn and there’s no strings holding it up, and it’s moving in a blackness that is almost beyond conception.”

That’s why today, I am excited to see that NASA has released its new Blue Marble, the first of many more to come later this year.

This Blue Marble is the first fully illuminated snapshot of the Earth captured by the DSCOVR satellite, a joint NASA, NOAA, and U.S. Air Force mission. After launching in February 2015, DSCOVR spent months rocketing away from Earth before reaching its final orbit position in June 2015 at Lagrange point 1 (L1), about one million miles away from Earth. (A Lagrange point, in case you were wondering, is “a position where the gravitational pull of two large masses precisely equals the centripetal force required for a small object to move with them.” For our purposes, that means that a Lagrange point is a spot at which a satellite can maintain a fixed position relative to the Earth.)

DSCOVR just after launch.

The DSCOVR mission serves several important purposes, including providing scientific data on heat and radiation fluxes across the Earth’s atmosphere, and maintaining the nation’s ability to provide timely alerts and forecasts for space weather events, which can disrupt telecommunications capabilities, power grids, GPS applications, and other systems vital to our daily lives and national and local economies.

And with its Earth Polychromatic Imaging Camera (which has an epic acronym. Seriously. It’s EPIC), DSCOVR will capture and transmit full images of the Earth every few hours! The information gathered by EPIC will help us examine a range of Earth properties, such as ozone and aerosol levels, cloud coverage, and vegetation density, supporting a number of climate science applications.

One of the best parts of this mission is that NASA will make all of the data, data products, and images collected by DSCOVR freely available to the public, including the new “Blue Marble” images. Starting soon, you’ll be able to view and download new “Blue Marble” images taken by DSCOVR every day.

In addition to providing useful data to scientists and researchers, these images will remind all of us that we live on a planet, in a solar system, in a universe. And that we are not just Americans, but citizens of Earth.

Source: A New Blue Marble

#DSCOVR today’s new image of #Earth. What made the Blue Marble so special? #EarthRightNow