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As of Monday, we now know that liquid water flows down the walls of Martian craters. Here are some of the other incredible facts about the Red Planet.
OUT OF THIS WORLD | Earth, Space And The Stuff In Between - a daily journey through weather, space and science from meteorologist/science writer Scott Sutherland

Along with flowing water, here's what we know about Mars

Scott Sutherland
Meteorologist/Science Writer

Tuesday, September 29, 2015, 7:53 PM - As of Monday, we now know that liquid water flows down the walls of Martian craters. Here are some of the other incredible facts we know about the Red Planet.

Smaller, weaker, thinner

Although Mars is our solar system next-door neighbor, it is quite different from Earth when it comes to its size, mass and atmosphere.

Credit: NASA/JPL/MSSS/Wikimedia Commons

The planet is a little over half as big as Earth is, and it has just 28 per cent of Earth's surface area - about the equivalent of Earth's total area of dry landmass. 

Despite being around half as big, Mars is only around one-tenth as massive as Earth, due to the planet's lower density. This results in a weaker force of gravity on the surface, the equivalent of 0.376 g, so a person who weighed 200 lbs on Earth would weigh only around 75 lbs on Mars.

Due in part to the weak gravity (along with being locked up in rocks and stripped away by the solar wind), Mars has very little atmosphere (less than 1 per cent) compared to Earth. That means that air pressure at the surface of Mars is about the same as it is 30 kilometres above the surface of Earth - right around the middle of the stratosphere. As a result, winds can get very fast on Mars, up to hurricane speeds as measured here on Earth, but these winds carry very little force with them. They can pick up copious amounts of dust, whip them into global dust storms, however a person might barely feel a Martian gale.

More colourful than it might seem

Look at any image of Mars from afar, or even the image below, and it's not hard to see how the planet earned it's nickname, The Red Planet. However, depending on where you look and even how you look at the planet, it can be surprisingly colourful.

Sand, dust and rocks, as far as the eye can see. This true-colour panorama of Mars was taken by the Opportunity rover in May of 2014, showing "Pillinger Point" on the rim of Endeavour Crater. Credit: NASA/JPL-Caltech/Cornell Univ./Arizona State Univ.

Just from a true colour view, produced by combining red, green and blue (RGB) filtered images from rover or satellite cameras, the scenery shows off subtle shades, from butterscotch to brown, as shown above.

Change how you look at the planet, by reaching a bit further towards the ends of the spectrum of light with your camera, and things get a bit more interesting. Replace red in the RGB image above with near-infrared, and replace blue with violet, and the scene becomes something more like this:

Pillinger Point, using exposures from Opportunity's Pancam through filters that pick up wavelengths of 753 nanometers (near-infrared), 535 nanometers (green) and 432 nanometers (violet). Credit: NASA/JPL-Caltech/Cornell Univ./Arizona State Univ.

While this view of Mars is not one that anyone standing on the surface would see (at least without some kind of special sci-fi optics in their helmet), the purpose of this view is to help scientists here on Earth pick out differences in the local geology, and identify interesting targets for study.

Look at other regions of the planet, and you'll find the whites and cappuccino hues of the polar ice caps, the blue-greys of Martian basaltic rock and sand, and possibly even a greenish tinge from the presence of olivine minerals on the surface.

Right: Mars' north polar ice cap looks like a cappuccino-hued hurricane in this image from the Mars Global Surveyor (Credit: NASA/JPL-Caltech/MSSS). Left: Dust devils reveal the grey/blue colour of Mars' basaltic sand dunes as they sweep up fine-grain red dust in intricate swirling designs (Credit: NASA/JPL-Caltech/Univ. of Arizona).

No planetary magnetic field

Here on Earth, a wide, relatively strong magnetic field protects the planet's surface and atmosphere from being too heavily impacted by the constant stream of matter being put off from the Sun. This field extends far out into space, to about 30,000 km in the direction of the Sun and by over 20 times that distance in the opposite direction. The field is generated by the churning motion of the liquid iron in Earth's outer core, and much of the higher orders of life here were able to develop due to the presence of this magnetic field.

On Mars, however, there is no planetary magnetic field. Instead, many small localized magnetic fields pop up above the surface, due to deposits in Mars' crust. 

Without this source of protection, the atmosphere and surface of Mars are exposed to high-energy charged particles from the Sun, both in the more constant solar wind and from more concentrated coronal mass ejections. This strips away molecules from Mars' upper atmosphere, and allows those high-energy particles to reach the ground. NASA's Curiosity rover showed that the remaining atmosphere does provide enough protection that people could live on Mars without fear of lethal exposure, however, this is still a concern for any future long-term stays on the planet's surface.

Water, water, everywhere...

This latest announcement from NASA was not the first indication that water existed on the surface of Mars.

The very idea that Mars could be inhabited, back from the late 1700s, originated from telescope observations of polar ice caps and wispy clouds above the surface. Further along, Mars orbiters showed us images of rivers carved into the landscape. They detected clays and minerals that regularly form in water here on Earth. On the ground, landers and rovers sent to investigate different parts of the planet revealed evidence of potentially water-formed minerals (Martian "blueberries"), and rock and sediment formations that were consistent with what we see in flowing water here on Earth.

The latest rover, Curiosity, drilled into rocks and sent back data that showed water was trapped in the rock structure - water that had the right properties to have been clean, fresh, drinkable water if it was sitting or flowing on the surface. Another study, using data from the Mars Reconnaissance Orbiter's HiRISE instrument, revealed trillions of tons of glacial water ice locked away under the surface of Mars' mid-latitudes.

There's certainly no lack of water on Mars, but the circumstances of the water continue to get more interesting with each discovery.

"Warm-season flows" on the wall of Newton Crater, as imaged by the Mars Reconnaissance Orbiter. Credit: NASA/JPL-Caltech/Univ. of Arizona

What's significant about this week's announcement is the fact that this isn't water locked away as molecules amid the lattice structure of a rock, or dense ice trapped beneath the surface. This is flowing water - an extremely salty brine containing perchlorate salts, but flowing nonetheless.

The scientists involved in researching the recurring slope lineae shown above - thin dark streaks on the walls of craters, which grow each Martian summer and retreat each autumn - had their suspicions that they were caused by water, but there was no direct evidence to confirm their suspicions until now.

While there may be underground ice pockets or water reservoirs that feed these flows, it is also possible that the brine comes from the perchlorate salts soaking up water directly from the air, in a process known as deliquescence.

According to Dr. Livio Tornabene, a research scientist from the University of Western Ontario who has worked on the MRO HiRISE team, if these flows are forming through deliquescence, that would be an important discovery for life on Mars.

"In the extremes of the Atacama desert, bacterial life takes advantage of deliquescence of salts to survive under the extreme conditions," Tornabene wrote in an email to The Weather Network. Thus, if these recurring slope lineae occur due to this process, he said, it "has significant implications for life."

There IS life on Mars

One moment from Monday's announcement that may have surprised people is when Jim Green, the director of planetary science at NASA Headquarters, said "there is life on Mars." However, it should not be too shocking, as we are the ones who sent it there.

When landers and rovers are sent to Mars, they are cleaned as thoroughly as possible to remove any microbes. The reason for this is very simple and straight forward.

If we are going to have a robot search for life on Mars - life that actually developed there and has survived there over time - we need to eliminate the possibility that we are seeing "contamination" from the robot. The discovery Martian life would be truly incredible, however far less so if it turned out that life simply hitched a ride from Earth.

However, while older spacecraft, like the Viking landers, were cleaned extremely thoroughly, Curiosity did not receive the same treatment before it left Earth. In either case, it is possible that some microbes may have made the journey to Mars.

WATCH BELOW: In a press conference on Monday, September 28, 2015, NASA announces the discovery of liquid water on today's Mars. Fast forward to 39 minutes in to hear Jim Green discuss how we know there is life on Mars today.

Whether these "hitchhikers" survived their arrival on Mars is another question. The surface of Mars is very hostile to life, however just as there are microbes that survive in extremely hostile conditions here on Earth, it's possible that something sent along with these missions could find a niche to live in.

The key to our continued search, though, is finding extant life that is native to Mars. For that, as John Grunsfeld, associate administrator of NASA’s Science Mission Directorate, said on Monday, "we follow the water."

Sources: NASA | NASA Goddard | NASA JPL | NASA

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