Mars today is a cold, desert planet with red sands of Iron oxide and planet-wide dust storms along with ice caps on the poles. But geological and geochemical evidences from the planet suggest a totally difference past – a surface which had flowing liquid water, maybe with a huge ocean covering the northern hemisphere, precipitation, active volcanos and much more – feels very much like Earth. So what lead to this dramatic change from a paradise to the current dystopian look? 

Mars currently has a very thin atmosphere – about 1% as dense as Earth’s atmosphere. No large standing body of liquid water exists now because the atmospheric pressure on the Red planet averages just 600 pascals, a figure slightly below the vapour pressure of water at its melting point. Under average Martian conditions, pure water on the Martian surface would freeze or, if heated to above the melting point, would sublime to vapor. 

Mars today is a cold, desert planet with red sands of Iron oxide and planet-wide dust storms along with ice caps on the poles. But geological and geochemical evidences from the planet suggest a totally difference past – a surface which had flowing liquid water, maybe with a huge ocean covering the northern hemisphere, precipitation, active volcanos and much more – feels very much like Earth. So what lead to this dramatic change from a paradise to the current dystopian look? 

Mars currently has a very thin atmosphere – about 1% as dense as Earth’s atmosphere. No large standing body of liquid water exists now because the atmospheric pressure on the Red planet averages just 600 pascals, a figure slightly below the vapour pressure of water at its melting point. Under average Martian conditions, pure water on the Martian surface would freeze or, if heated to above the melting point, would sublime to vapor. 

In the final section of this article, I would like to mention briefly about the four major methods by which gas is lost from an atmosphere –

• Jeans escape – Individual particles of a gas collide with each other. Some of them attain speeds higher than the escape velocity of the planet, leading to loss of gas. This is the slowest mode of loss of gas.

• Hydrodynamic escape – In this case, a large amount of thermal energy, usually through extreme ultraviolet radiation, is absorbed by the atmosphere. As molecules are heated, they expand upwards and are further accelerated until they reach escape velocity.

• Photochemical escape – In the upper atmosphere, high energy UV Photons can react more readily with molecules. Photodissociation can break a molecule into smaller components and provide enough energy for those components to escape.

• Sputtering – First, ultraviolet photons knock electrons out of atmospheric atoms and molecules in the upper Martian atmosphere, forming electrically charged ions. These ions are picked up by the solar wind, which is infused with the Sun’s magnetic field. As the field-carrying solar wind moves by, it drags these ions with it. Some of these ions are flung back into the upper atmosphere at high velocity. There, they collide with neutral atoms and molecules and knock them every which way, like the cue ball scatters balls in a break shot in pool. Some of the atoms are knocked upward with enough velocity to escape Mars — in other words, they’re “sputtered.” This process leads to very high rates of atmospheric loss and is the reason behind the huge loss of the Martian atmosphere.