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Question 5

If extraterrestrial life did exist, the most likely place scientists would point to would be Mars. Comparatively, even though Mars with a core radius of 1700 Km compared to 3485 Km,1 is smaller than Earth, it is the closest planet to Earth in terms of size and proximity to the sun. Also in common, are its surface topology of volcanoes, valleys, deserts and polar ice caps, and its rotational tilt and the existence of seasonal cycles. However, the present environment on Mars is unfriendly and the planet, unlike Earth, has not evolved to support life.

Today, the Martian environment is one that is extreme. With dry and cold conditions, what life would survive on a planet where the surface rarely exceeds above freezing point and the average temperature is -63ºC?1 Its atmosphere consists of 95.3% carbon dioxide, 2.7% nitrogen, 1.6% argon, 0.13% oxygen and 0.08% carbon monoxide.1 Loss of its magnetosphere leaves the Martian atmosphere unprotected from solar winds which erodes it surface.2 Consequently, this thin atmosphere does not trap any heat radiated from the sun to warm the planet, and its lack of ozone offers little protection from cosmic radiation. With little atmosphere to separate between the surface and space, there is a lack of atmospheric pressure, which sophisticated life forms need.1 As a result, water cannot exist in a liquid state. The surface gravity on Mars is 3.7 m s-2 compared to 9.8 m s-2 on Earth, and the solar irradiance is 589 W m-2 compared to 1,367 W m-2, respectively.Any previously abundant surface water has disappeared to form water ice below the surfaces of the northern and southern polar ice caps, leaving the terrain dry.3 Water ice as much as 1.8 Km wide and 3.5 Km deep has been detected below the surface of the northern and southern ice caps, respectively, by pulse radio waves from the Mars Advanced Radar for Subsurface and Ionosphere Sounding.3 It has been predicted that if these polar ice caps were to melt they would cover the whole surface of the planet in a layer of water up to 10 meters deep.3

If chemical evolution had occurred, it would have had more chance lower under the surface of the planet, where temperatures would have been higher and protection from ultra violet radiation would have been offered. Volcanic activity, which was widespread in the past, would have caused the recycling of elements between the surface and core of the planet. However, NASA's Viking mission reported no findings of traces of organic matter beneath the surface and suggested that, if present, it would be oxidised into carbon dioxide by the highly oxidising minerals on the surface.2 This may explain the high percentage of carbon dioxide in the atmosphere. Volcanoes are now dormant and the absence of any tectonic activity removes the opportunity for the terrestrial recycling of carbon dioxide, which is paramount in the Earth's atmosphere. While these conditions prevail on Mars, it is unlikely that chemical evolution, as hypothesized today would be occurring

The environmental conditions on Mars are extreme and would be hostile to the life we know on Earth. The planet has evolved to lack in the elements, which are essential for life on Earth. Although there are life forms on Earth, which can survive a harsh environment, if life did emerge on Mars, it would certainly have been much challenged and may be different from that we already know.

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